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Objective: To study the changes in dynamic compliance (C dyn ), ventilation/perfusion (V˙/ Q˙) mismatch and haemodynamic variables in hypoxaemic anaesthetized horses whose PaO 2 increased following salbutamol inhalation., Study Design: Retrospective, clinical, cohort study., Animals: A group of 73 client-owned horses treated with salbutamol when PaO 2 <100 mmHg (13.3 kPa) during anaesthesia., Methods: Horses were divided into two groups: responders (R), where PaO 2 after salbutamol ≥1.2 PaO 2 before treatment (i.e. ≥20% increase), and non-responders (NR), where PaO 2 after salbutamol <1.2 PaO 2 before treatment. Demographic data and intraoperative variables before treatment were compared between R and NR. C dyn , arterial to end-tidal carbon dioxide difference [P(a-E´)CO 2 ], estimated ratio of dead space to tidal volume (est.V D /V T ), estimated shunt fraction (F-shunt), heart rate, systolic, mean and diastolic arterial pressure and dobutamine requirements were compared before and after treatment within R and NR. For each variable, the difference (Δ) between values pre- and posttreatment was calculated and compared between groups R and NR. Numerical data were compared using univariate or bivariate analysis and categorical data were compared using chi-square test; p < 0.05., Results: Of the 73 horses 50 were classified as R while 23 horses were classified as NR. There was no statistical difference between R and NR for demographic data or initial intraoperative variables except for body weight [R: 531 (170-715) kg, NR: 540 (420-914) kg]. While salbutamol did not alter C dyn in either group, it significantly decreased P(a-E´)CO 2 , est.V D /V T and F-shunt in R only. ΔP(a-E´)CO 2 , Δest.V D /V T and ΔF-shunt were significantly greater in R (-17.8%, -19.0% and -24.1%, respectively) than in NR (11.5%, 6.6% and -0.3%, respectively)., Conclusions and Clinical Relevance: In hypoxaemic anaesthetized horses responding to inhaled salbutamol by a ≥1.2 increase in PaO 2 no change in C dyn was detected, but indicators of V˙/ Q˙ mismatch improved., (Copyright © 2024 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To compare static compliance of the respiratory system (C stRS ) and the ratio of partial pressure of end-tidal to arterial carbon dioxide (Pe'CO 2 /PaCO 2 ), in healthy dogs using two approaches for tidal volume (V T ) selection during volume-controlled ventilation: body mass based and driving pressure (ΔPaw) guided., Study Design: Randomized, nonblinded, crossover, clinical trial., Animals: A total of 19 client-owned dogs anesthetized for castration and ovariohysterectomy., Methods: After a stable 10 minute baseline, each dog was mechanically ventilated with a V T selection strategy, randomized to a constant V T of 15 mL kg -1 of actual body mass (V TBW ) or ΔPaw-guided V T (V TΔP ) of 7-8 cmH 2 O. Both strategies used an inspiratory time of 1 second, 20% end-inspiratory pause, 4 cmH 2 O positive end-expiratory pressure and fraction of inspired oxygen of 0.4. Respiratory frequency was adjusted to maintain Pe'CO 2 between 35 and 40 mmHg. Respiratory mechanics, arterial blood gases and Pe'CO 2 /PaCO 2 were assessed. Continuous variables are presented as mean ± SD or median (interquartile range; quartiles 1-3), depending on distribution, and compared with Wilcoxon signed-rank tests., Results: The V T was significantly higher in dogs ventilated with V TΔP than with V TBW strategy (17.20 ± 4.04 versus 15.03 ± 0.60 mL kg -1 , p = 0.036). C stRS was significantly higher with V TΔP than with V TBW strategy [2.47 (1.86-2.86) versus 2.25 (1.79-2.58) mL cmH 2 O -1 kg -1 , p = 0.011]. There were no differences in Pe'CO 2 /PaCO 2 between V TΔP and V TBW strategies (0.94 ± 0.06 versus 0.92 ± 0.06, p = 0.094). No discernible difference in ΔPaw was noted between the strategies., Conclusions and Clinical Relevance: While no apparent difference was observed in the Pe'CO 2 /PaCO 2 between the V T selection strategies employed, C stRS significantly increased during the V TΔP approach. A future trial should explore if V TΔP improves perioperative gas exchange and prevents lung damage., (Copyright © 2024 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To evaluate the effect of increased respiratory system resistance (R RS ) on dynamic compliance (C dyn ) assessed by the NM3 monitor (C dyn(NM3) ) and the E-CAiOV module (C dyn(ECAiOV) )., Study Design: Prospective laboratory study., Methods: A training test lung (TTL) simulated the mechanical ventilation of a mammal with 50 and 300 mL tidal volumes in three conditions of R RS [normal (R BL ), moderately increased (R 1 ) and severely increased (R 2 )] and a wide range of clinically relevant C dyn . Simulations at increased R RS were paired with simulations at R BL with the same static compliance for comparisons. Pearson's correlation coefficient and concordance correlation coefficient between the measurements at R BL with the ones with increased R RS were calculated. Bland-Altman plots were also used to evaluate the agreement of C dyn(ECAiOV) and C dyn(NM3) at R BL (control values) with their paired values at R 1 and R 2 . Relative bias and limits of agreement (LOAs) were calculated and LOAs larger than 30% were considered unacceptable. Trending ability of C dyn(NM3) and C dyn(ECAiOV) were evaluated by polar plots. Values of p < 0.05 were considered significant., Results: The effect of increased R RS was more pronounced for C dyn(ECAiOV) than for C dyn(NM3) . Unacceptable agreement was only observed in C dyn(NM3) at R 2 in the 300 mL simulation (bias = -18.3% and lower LOA = -45%). For C dyn(ECAiOV) , agreement was unacceptable for all tested R RS in both simulations, being the worst at R 2 in the 300 mL simulation (bias = -54.7% and lower LOA = -100.2%). Both levels of increased R RS caused poor trending ability for C dyn(ECAiOV) , whereas the same effect was only observed for C dyn(NM3) at R 2 ., Conclusions and Clinical Relevance: In the presence of increased R RS , C dyn estimated by the NM3 monitor presented better capability to distinguish between changes in R RS from changes in respiratory system compliance., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Objective: To compare respiratory system compliance (C RS ), expressed per kilogram of bodyweight (C RS BW), calculated without end-inspiratory pause (EIP) and after three EIP times (0.2, 0.5 and 1 seconds) with that after 3 second EIP (considered the reference EIP for static C RS ) and to determine the EIP times that provided C RS BW values in acceptable agreement with static C RS BW during controlled mechanical ventilation (CMV) in anaesthetized dogs., Study Design: Prospective, randomized, nonblinded, crossover clinical study., Animals: A group of 24 client-owned dogs with healthy lungs undergoing surgery in lateral recumbency., Methods: During CMV in dogs undergoing general anaesthesia, five EIPs [0 (no EIP), 0.2, 0.5, 1 and 3 seconds] were consecutively applied in random order. Tidal volume (Vt) was set at 10 mL kg -1 and positive end-expiratory pressure (PEEP) was not applied. Respiratory rate and inspiratory time were established according to each EIP time, setting EIP between 0 and 50% of the inspiratory time. The C RS BW was calculated as [expired Vt/(plateau pressure - PEEP)]/bodyweight and recorded every 15 seconds for 2 minutes after a 5 minute equilibration period with each EIP. One-way anova for repeated measures and the Bland-Altman analysis were used to compare C RS BW and evaluate agreement between EIP times, respectively., Results: The C RS BW was significantly greater as the EIP time increased up to 1 second (p < 0.05). In the Bland-Altman analysis, none of the tested EIPs (0, 0.2, 0.5 and 1 seconds) provided 95% confidence intervals for limits of agreement within the maximum allowed difference considered for acceptable agreement with 3 second EIP., Conclusions: and clinical relevance An EIP ≤ to 1 second does not provide a C RS BW value in acceptable agreement with static C RS BW in healthy dogs. Besides, the application of an EIP ≤ to 0.5 seconds underestimates the static C RS BW to an increasing extent as the EIP time decreases., (Copyright © 2024 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

In premature births, deficiency and/or inactivation of surfactant and incomplete development of lung occur, leading to pulmonary complications and greater need for ventilatory interventions. Prenatal corticosteroid therapy is used to improve neonatal lung function and, thus, may reduce mortality and lower incidence and severity of lung injury. Therefore, this study aimed to assess the need for ventilatory support in preterm lambs subjected or not to prenatal betamethasone treatment, and to evaluate the effectiveness on neonatal survival. Lambing was induced and 13 premature lambs were assigned to Corticosteroid Group (n = 8; lambs from ewes subjected previously to 0.5 mg/kg betamethasone, IM, at 133 days of pregnancy) and Control Group (n = 5; non-treated lambs). Lambs were evaluated for vitality, neurologic reflexes, vital functions and birth weight. Three ventilatory modalities were preconized for critical lambs, according to specific criteria: mask oxygen therapy, self-inflating bag with tracheal tube and mechanical ventilation. Non-treated lambs had lower vitality score, muscle tonus and respiratory rate compared to Corticosteroid Group. Ventilatory support was needed for 3 Control lambs and only 1 Corticosteroid neonate. Corticosteroid lamb required significant less time-frame between birth and onset of ventilatory assistance and remained under ventilation for a shorter time. Percentage of ventilated non-treated lambs correlated negatively with birth weight, muscle tone, heart and respiratory rate. In conclusion, antenatal betamethasone treatment reduces the need for ventilatory assistance in premature lambs. Additionally, mortality is low when a protocol for inducing pulmonary maturity (maternal corticosteroid therapy) and/or ventilatory interventions are employed, ensuring the survival of premature lambs., Competing Interests: Declaration of competing interest The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Objective: To investigate the effects of FLow-controlled EXpiration (FLEX) ventilation expiration time and speed on respiratory and pulmonary mechanics in anesthetized horses in dorsal recumbency., Animals: 6 healthy adult research horses., Methods: In this randomized crossover experimental study, horses were anesthetized 3 times and were ventilated each time for 60 minutes using conventional volume-controlled ventilation (VCV), linear emptying of the lung over 50% of the expiratory time (FLEX50), or linear emptying of the lung over 100% of the expiratory time (FLEX100) in a randomized order. The primary outcome variables were dynamic compliance (Cdyn), hysteresis, and alveolar dead space. The data was analyzed using two-factor ANOVA. Significance was set to P < .05., Results: Horses ventilated using FLEX50 and FLEX100 showed significantly higher Cdyn and significantly lower hysteresis values compared to horses ventilated using VCV. Horses ventilated using FLEX50 had significantly lower alveolar dead space compared to horses ventilated using FLEX100 or VCV. Horses ventilated using FLEX100 had significantly lower alveolar dead space compared to VCV horses., Clinical Relevance: Our results demonstrate improved Cdyn, hysteresis, and alveolar dead space in horses ventilated with either FLEX50 or FLEX100 relative to traditional VCV. The use of FLEX with a faster exhalation speed (FLEX50) offers additional respiratory advantages.

Pulse oximetry (SpO 2 ) identifies a decrease in the partial pressure of oxygen (PaO 2 ) when it falls below 80 mmHg, while oxygen reserve index (ORi), a dimensionless index ranging from 0 to 1, detects PaO 2 changes between 100 and 200 mmHg. This study investigates the usefulness of ORi in detecting impending deoxygenation before traditional SpO 2 . Fifty-one dogs undergoing anesthesia were mechanically ventilated maintaining a fraction of inspired oxygen of 0.50 and an ORi of 1. Animals were classified according to their body condition score (BCS) as normal-fit (BCS 4-5/9), overweight (BCS 6-7/9), or obese (BCS 8-9/9). At the end of the procedure, dogs were placed in sternal recumbency, and after 10 min disconnected from the ventilator and maintained in apnea. ORi added warning time was determined at various ORi values as the time difference in reaching SpO 2 of 95% from ORi of 0.9 and 0.5, compared to the SpO 2 warning time from SpO 2 of 98%. During apnea, ORi decreased before noticeable SpO 2 changes. An ORi of 0.9 anticipated an SpO 2 of 95% in normal-fit dogs by 87 (33-212) [median (range)] seconds or in those with a BCS ≥ 6/9 by 49 (7-161) seconds. Regardless of the BCS class, the median time from ORi of 0.5 to SpO 2 of 95% was 30-35 s. ORi declined from 0.9 to 0.0 in 68 compared to 33 s between normal-fit and obese dogs (p < 0.05). In dogs, ORi added warning time could facilitate timely intervention, particularly in obese patients., Competing Interests: Declaration of competing interest This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. None of the authors has any financial or personal relationships that could inappropriately influence or bias the content of the paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Background: Human records describe pulmonary edema as a life-threatening complication of electric shock. Successful management requires prompt recognition and intensive care. However, in companion animals, electrocutions are rarely reported, even though domestic environments are full of electrical devices and there is always the possibility of accidental injury. Therefore, it is important for veterinarians to know more about this condition in order to achieve successful patient outcomes., Case Presentation: A 3-month-old male Labrador Retriever was presented with a history of transient loss of consciousness after chewing on a household electrical cord. On admission, the puppy showed an orthopneic position with moderate respiratory distress. Supplemental oxygen via nasal catheter was provided, but the patient showed marked worsening of respiratory status. Point-of-care ultrasound exams suggested neurogenic pulmonary edema due to electrical shock close to the central nervous system and increased B-lines without evidence of cardiac abnormalities. Mechanical ventilation of the patient was initiated using volume-controlled mode with a tidal volume of 9 to 15 ml/kg until reaching an end-tidal carbon dioxide ≤ 40 mm Hg, followed by a stepwise lung-recruitment maneuver in pressure-controlled mode with increases of the peak inspiratory pressure (15 to 20 cm H 2 O) and positive end-expiratory pressure (3 to 10 cm H 2 O) for 30 min, and return to volume-controlled mode with a tidal volume of 15 ml/kg until reaching a peripheral oxygen saturation ≥ 96%. Weaning from the ventilator was achieved in six hours, and the patient was discharged two days after admission without neurological or respiratory deficits., Conclusions: We present a rather unusual case of a neurogenic pulmonary edema subsequent to accidental electrocution in a dog. Timely diagnosis by ultrasound and mechanical ventilation settings are described. Our case highlights that pulmonary edema should be considered a potentially life-threatening complication of electrical shock in small animal emergency and critical care medicine., (© 2024. The Author(s).)

Parenteral nutrition (PN) is commonly used in intensive care units (ICUs) and is associated with earlier hospital outcome. However, there is scarcity of information about the metabolic effects of PN caloric distribution for dogs. Considering the high tolerance of dogs to lipids and, also, that hospitalized animals usually present insulin resistance, PN formulation with high fat instead high glucose can provide metabolic benefits in this specie. This study evaluated two PN protocols, based on high lipid or high carbohydrate in 12 healthy dogs under sedation/ventilation during 24 h. For baseline data, blood samples were collected 24 h before the study beginning. After fasting, the dogs were anesthetized and put under mechanical ventilation without energy support for 12 h to obtain: daily energy expenditure (DEE), respiratory quotient (RQ), oxygen consumption (VO 2 ), carbon dioxide production (VCO 2 ), lactate, glucose, cholesterol, and triglycerides concentrations. After, the dogs were allocated into two groups: lipid-based energy group (LEG) and carbohydrate-based energy group (CEG). Both groups received the PN infusions at a rate of 3 mL/kg/h for 12 h. Blood tests were performed 12, 24, and 48 h after infusion's completion. VO 2 increased after PN in LEG, increasing energy expenditure compared to CEG. RQ remained close to 1 in CEG, indicating carbohydrate preferential consumption. Triglycerides increased in both groups after propofol infusion, remaining higher in LEG until the end of the evaluation. Glycaemia increased in CEG compared to baseline. In conclusion, both PN protocols can be used in healthy animals undergoing prolonged sedation protocols. However, high lipid PN had higher VO 2 and DEE, and resulted in higher triglycerides concentrations and lower glycaemia indexes than carbohydrate, making high carbohydrate PN preferable to high lipid PN. Therefore, for use in critically ill patients, the data obtained in this study should be extrapolated, taking into consideration the specificity of each case., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Objective: To describe seizure activity in juvenile dogs successfully weaned from long-term mechanical ventilation., Case Series Summary: Three juvenile dogs (all approximately 3 months old) underwent long-term mechanical ventilation with IV anesthesia for suspected noncardiogenic pulmonary edema. Within 24 hours of extubation and within 10 hours of discontinuing midazolam continuous infusions, all dogs experienced seizures, which is 1 sign of iatrogenic withdrawal syndrome. Each dog was treated with an anticonvulsant protocol, and none experienced seizures after being discharged., New or Unique Information Provided: Each dog received IV anesthesia, including fentanyl, dexmedetomidine, midazolam, and propofol, during mechanical ventilation and subsequently experienced seizures after successful weaning from mechanical ventilation. Juvenile dogs may be at risk for seizures after weaning from mechanical ventilation and IV anesthesia. Neurological monitoring and further research into an appropriate weaning protocol may prove beneficial in juvenile dogs requiring prolonged anesthesia., (© Veterinary Emergency and Critical Care Society 2024.)

Objectives: This study compared the effectiveness of a new supraglottic airway device (SGAD) in cats undergoing anaesthesia using two types of mechanical ventilation: volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV)., Methods: A total of 13 healthy cats (five male, eight female; median age 2 years [range 1-3]) were randomly allocated to either VCV or PCV. Five tidal volumes (6, 8, 10, 12 and 14 ml/kg) and five peak inspiratory pressures (4, 5, 6, 7 and 8 cmH 2 O) were randomly applied with a minute ventilation of 100 ml/kg/min. Various parameters, such as blood pressure, gas leakage, end-tidal CO 2 (ETCO 2 ) and work of breathing (WOB), were measured while using VCV or PCV., Results: The occurrence of hypotension (mean arterial blood pressure <60 mmHg) was slightly less frequent with VCV (38 events, 65 ventilating sessions) than with PCV (40 events, 65 ventilating sessions), but this difference did not reach statistical significance ( P  = 0.429). The number of leakages did not differ between the VCV group (3 events, 65 ventilating sessions) and the PCV group (3 events, 65 ventilating sessions) ( P  = 1.000). Hypercapnia was identified when using VCV (10 events, 65 ventilating sessions) less frequently than when using PCV (17 events, 65 ventilating sessions), but this difference did not reach statistical significance ( P  = 0.194). The study found a significantly higher WOB in the PCV group compared with the VCV group ( P <0.034)., Conclusions and Relevance: The present results suggested that both VCV and PCV can be used with an SGAD during anaesthesia, with VCV preferred for prolonged mechanical ventilation due to its lower workload. Adjusting tidal volume or inspiratory pressure corrects hypercapnia., Competing Interests: Conflict of interestThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Mechanical ventilation can be used in mice to support high-risk anesthesia or to create clinically relevant, intensive care models. However, the choice of anesthetic and inspired oxygen concentration for prolonged procedures may affect basic physiology and lung inflammation. To characterize the effects of anesthetics and oxygen concentration in mice experiencing mechanical ventilation, mice were anesthetized with either isoflurane or pentobarbital for tracheostomy followed by mechanical ventilation with either 100% or 21% oxygen. Body temperature, oxygen saturation, and pulse rate were monitored continuously. After 6 h, mice were euthanized for collection of blood and bronchoalveolar lavage fluid for evaluation of biomarkers of inflammation and lung injury, including cell counts and cytokine levels. Overall, both isoflurane and pentobarbital provided suitable anesthesia for 6 h of mechanical ventilation with either 21% or 100% oxygen. We found no differences in lung inflammation biomarkers attributable to either oxygen concentration or the anesthetic. However, the combination of pentobarbital and 100% oxygen resulted in a significantly higher concentration of a biomarker for lung epithelial cell injury. This study demonstrates that the combination of anesthetic agent, mechanical ventilation, and inspired oxygen concentrations can alter vital signs and lung injury biomarkers during prolonged procedures. Their combined impact may influence model development and the interpretation of research results, warranting the need for preliminary evaluation to establish the baseline effects.

Objective: To evaluate the agreement between the Tafonius large animal ventilator-integrated volumetric capnography (vCap) software and the Respironics NICO noninvasive cardiac output monitor reference system., Animals: Data were collected from 56 healthy adult horses undergoing general anesthesia., Methods: Animals were placed under general anesthesia and connected to the Tafonius large animal ventilator circle system. A flow partitioning device with CO2 and flow sensors was utilized to couple the endotracheal tube to the NICO monitor. Tafonius CO2 and flow sensors are incorporated into the Y-piece of the breathing circuit. Arterial blood samples were collected to determine the partial pressure of arterial carbon dioxide (PaCO2) immediately before data collection. The PaCO2 was input into the Tafonius and NICO monitor, and dead space ventilation (%Vd), end-tidal CO2 partial pressure (ETco2), mixed-expired CO2 partial pressure (Peco2), and expired tidal volume (Vt) were calculated over a single breath. Multiple measurements were completed for each patient, with a total of 200 paired data points collected for analysis. Data were assessed for normality, and Bland-Altman analysis was performed. Bias and 95% limits of agreement were calculated., Results: The limits of agreement for %Vd of the ventilator-derived measurements fell within ± 10% of the NICO monitor reference method., Clinical Relevance: Our results indicate that, when compared to the NICO monitor method, the Tafonius-integrated vCap software provides clinically acceptable values of Peco2, Vt, and %Vd in healthy adult horses.

Objective: To evaluate the impact of a 30% end-inspiratory pause (EIP) on alveolar tidal volume (V Talv ), airway (V Daw ) and physiological (V Dphys ) dead spaces in mechanically ventilated horses using volumetric capnography, and to evaluate the effect of EIP on carbon dioxide (CO 2 ) elimination per breath (Vco 2 br -1 ), PaCO 2, and the ratio of PaO 2 -to-fractional inspired oxygen (PaO 2 :FiO 2 )., Study Design: Prospective research study., Animals: A group of eight healthy research horses undergoing laparotomy., Methods: Anesthetized horses were mechanically ventilated as follows: 6 breaths minute -1 , tidal volume (V T ) 13 mL kg -1 , inspiratory-to-expiratory time ratio 1:2, positive end-expiratory pressure 5 cmH 2 O and EIP 0%. Vco 2 br -1 and expired tidal volume (V TE ) of 10 consecutive breaths were recorded 30 minutes after induction, after adding 30% EIP and upon EIP removal to construct volumetric capnograms. A stabilization period of 15 minutes was allowed between phases. Data were analyzed using a mixed-effect linear model. Significance was set at p < 0.05., Results: The EIP decreased V Daw from 6.6 (6.1-6.7) to 5.5 (5.3-6.1) mL kg -1 (p < 0.001) and increased V Talv from 7.7 ± 0.7 to 8.6 ± 0.6 mL kg -1 (p = 0.002) without changing the V TE . The V Dphys to V TE ratio decreased from 51.0% to 45.5% (p < 0.001) with EIP. The EIP also increased PaO 2 :FiO 2 from 393.3 ± 160.7 to 450.5 ± 182.5 mmHg (52.5 ± 21.4 to 60.0 ± 24.3 kPa; p < 0.001) and Vco 2 br -1 from 0.49 (0.45-0.50) to 0.59 (0.45-0.61) mL kg -1 (p = 0.008) without reducing PaCO 2 ., Conclusions and Clinical Relevance: The EIP improved oxygenation and reduced V Daw and V Dphys , without reductions in PaCO 2 . Future studies should evaluate the impact of different EIP in healthy and pathological equine populations under anesthesia., (Copyright © 2023 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To compare PaO 2 and PaCO 2 in horses recovering from general anesthesia maintained with either apneustic anesthesia ventilation (AAV) or conventional mechanical ventilation (CMV)., Study Design: Randomized, crossover design., Animals: A total of 10 healthy adult horses from a university-owned herd., Methods: Dorsally recumbent horses were anesthetized with isoflurane in oxygen [inspired oxygen fraction = 0.3 initially, with subsequent titration to maintain PaO 2 ≥ 85 mmHg (11.3 kPa)] and ventilated with AAV or CMV according to predefined criteria [10 mL kg -1 tidal volume, PaCO 2 40-45 mmHg (5.3-6.0 kPa) during CMV and < 60 mmHg (8.0 kPa) during AAV]. Horses were weaned from ventilation using a predefined protocol and transferred to a stall for unassisted recovery. Arterial blood samples were collected and analyzed at predefined time points. Tracheal oxygen insufflation at 15 L minute -1 was provided if PaO 2 < 60 mmHg (8.0 kPa) on any analysis. Time to oxygen insufflation, first movement, sternal recumbency and standing were recorded. Data were analyzed using repeated measures anova, paired t tests and Fisher's exact test with significance defined as p < 0.05., Results: Data from 10 horses were analyzed. Between modes, PaO 2 was significantly higher immediately after weaning from ventilation and lower at sternal recumbency for AAV than for CMV. No PaCO 2 differences were noted between ventilation modes. All horses ventilated with CMV required supplemental oxygen, whereas three horses ventilated with AAV did not. Time to first movement was shorter with AAV. Time to oxygen insufflation was not different between ventilation modes., Conclusions: Although horses ventilated with AAV entered the recovery period with higher PaO 2 , this advantage was not sustained during recovery. Whereas fewer horses required supplemental oxygen after AAV, the use of AAV does not preclude the need for routine supplemental oxygen administration in horses recovering from general anesthesia., (Copyright © 2023 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To measure changes in regional lung perfusion using CT angiography in mechanically ventilated, anesthetized ponies administered pulsed inhaled nitric oxide (PiNO) during hypotension and normotension., Animals: 6 ponies for anesthetic 1 and 5 ponies for anesthetic 2., Procedures: Ponies were anesthetized on 2 separate occasions, mechanically ventilated, and placed in dorsal recumbency within the CT gantry. Pulmonary arterial, right atrial, and facial arterial catheters were placed. During both anesthetics, PiNO was delivered for 60 minutes and then discontinued. Anesthetic 1: hypotension (mean arterial pressure < 70 mmHg) was treated using dobutamine after 30 minutes of PiNO delivery. Following the discontinuation of PiNO, dobutamine administration was discontinued in 3 ponies and was continued in 3 ponies. The lung was imaged at 30, 60, and 105 minutes. Anesthetic 2: hypotension persisted throughout anesthesia. The lung was imaged at 30, 60, and 90 minutes. At all time points, arterial and mixed venous blood samples were analyzed and cardiac output (Q˙t) was measured. Pulmonary perfusion was calculated from CT image analysis., Results: During PiNO delivery, perfusion to well-ventilated lungs increased if ponies were normotensive, leading to increased arterial oxygenation, reduced alveolar dead space, and reduced alveolar to arterial oxygen tension gradient. When PiNO was stopped and dobutamine administration continued, alveolar dead space and venous admixture increased, in contrast to when dobutamine and PiNO were both discontinued., Clinical Relevance: If PiNO is administered to mechanically ventilated, anesthetized ponies with concurrent hypotension and low Q˙t, this must be supported to achieve favorable redistribution of pulmonary perfusion to improve pulmonary gas exchange.

Objective: To evaluate the effects of providing 100% O2, compared with the provision of 21% O2 (equivalent to room air), in mechanically ventilated, sevoflurane-anesthetized green sea turtles (Chelonia mydas)., Animals: Eleven juvenile green sea turtles., Procedures: In a randomized, blinded, cross-over study (1-week interval between treatments), turtles were anesthetized with propofol (5 mg/kg, IV), orotracheally intubated, mechanically ventilated with 3.5% sevoflurane diluted in 100% O2 or 21% O2 for 90 minutes. Sevoflurane delivery immediately ceased and animals remained under mechanical ventilation with the assigned fraction of inspired oxygen until extubation. Recovery times, cardiorespiratory variables, venous blood gases, and lactate values were evaluated., Results: Cloacal temperature, heart rate, end-tidal partial pressure of carbon dioxide, and blood gases were unremarkable between treatments. The SpO2 was higher with the provision of 100% O2 than 21% O2 during both anesthesia and recovery (P < .01). Time to bite the bite block was longer in 100% O2 (51 [39-58] minutes) than in 21% O2 (44 [31-53] minutes; P = .03), while time to first muscle movement, attempt to extubate, and extubation were comparable between treatments., Clinical Relevance: Blood oxygenation appears to be lower during sevoflurane anesthesia in room air than in 100% O2, though both fractions of inspired oxygen were able to supply the aerobic metabolism of turtles based on acid-base profiles. In relation to room air, the provision of 100% O2 did not produce meaningful effects on the time to recovery in mechanically ventilated green turtles submitted to sevoflurane anesthesia.

Objective: To evaluate the use of the caudal vena cava collapsibility index (CVCCI) and the inspiratory/minimum and expiratory/maximum diameters of the vena cava to predict fluid responsiveness in hospitalized, critically ill cats with hemodynamic and tissue perfusion abnormalities., Design: Diagnostic test study in a prospective cohort of hospitalized cats., Setting: Private practice referral hospital., Animals: Twenty-four hospitalized cats with spontaneous breathing and compromised hemodynamics and tissue hypoperfusion., Interventions: Ultrasonographic examination before and after fluid expansion with 10 ml/kg of lactated Ringer's solution., Measurements and Main Results: Fluid responsiveness was evaluated using the velocity-time integral (VTI) of the subaortic blood flow, by measuring it before and after a fluid load of 10 ml/kg of lactated Ringer's solution. The CVCCI was calculated using the following formula: (maximum diameter - minimum diameter / maximum diameter) × 100. Ten cats were fluid responders (42 %) and 14 were nonresponders (58 %). The area under the receiver operating characteristic curve (AUROC) with their 95% confidence interval for the predictors and the best cutoff values were as follows: CVCCI, AUROC = 0.83 (0.66-1.00) and cutoff = 31%; inspiratory/minimum diameter, AUROC = 0.86 (0.70-1.00) and cutoff = 0.24 cm; expiratory/maximum diameter, AUROC = 0.88 (0.74-1.00) and cutoff = 0.22 cm. A significant lineal correlation was observed between the percentage of increase in VTI after expansion and CVCCI (r s  = 0.68, P < 0.001), expiratory/maximum diameter (r s  = -0.72, P < 0.001), and inspiratory/minimum diameter (r s  = -0.71, P < 0.001). The intraobserver and interobserver variability was low for VTI, and the expiratory/maximum diameter and inspiratory/minimum diameter were high for CVCCI., Conclusions: Caudal vena cava measurements could be useful to predict the response to fluids in hospitalized cats with hemodynamic and tissue perfusion alterations. Additional studies are required to draw definitive conclusions about the role of these variables to guide fluid administration in cats., (© Veterinary Emergency and Critical Care Society 2022.)

Objective: To describe the transportation and clinical outcome of 9 dogs transported to a referral hospital on mechanical ventilation (MV)., Design: Retrospective case series (2015-2020)., Setting: University teaching hospital., Animals: Nine dogs transported to a referral center on MV., Interventions: All dogs underwent MV during vehicular transport., Measurement and Main Results: The medical records of 9 dogs transported on a MV to a university teaching hospital were reviewed. Data collected included signalment, reason for MV, ventilator settings, sedation protocol, monitoring in transit, distance traveled, complications, clinical outcome, and cost. All dogs transported survived transport to the referral hospital and 8 of 9 were successfully weaned from the ventilator and discharged home., Conclusions: MV during transport in this setting was practical and safe. Dogs in this study had a high survival rate compared to previous studies of dogs undergoing MV, likely due to selection of cases assessed to have a correctable underlying disease., (© Veterinary Emergency and Critical Care Society 2022.)

Objective: To compare cardiopulmonary variables and blood gas analytes in guinea pigs (Cavia porcellus) during anesthesia with and without abdominal carbon dioxide (CO 2 ) insufflation at intra-abdominal pressures (IAPs) 4 and 6 mmHg, with and without endotracheal intubation., Study Design: Prospective experimental trial., Animals: A total of six intact female Hartley guinea pigs., Methods: A crossover study with sequence randomization for IAP and intubation status was used. The animals were sedated with intramuscular midazolam (1.5 mg kg -1 ) and buprenorphine (0.2 mg kg -1 ) and anesthetized with isoflurane, and an abdominal catheter was inserted for CO 2 insufflation. Animals with endotracheal intubation were mechanically ventilated and animals maintained using a facemask breathed spontaneously. After 15 minutes of insufflation, the following variables were obtained at each IAP: pulse rate, respiratory rate, rectal temperature, oxygen saturation, end-tidal CO 2 (intubated only), peak inspiratory pressure (intubated only), noninvasive blood pressure and blood gas and electrolyte values, with a rest period of 5 minutes between consecutive IAPs. After 4 weeks, the procedure was repeated with the guinea pigs assigned the opposite intubation status., Results: Intubated guinea pigs had significantly higher pH and lower partial pressure of CO 2 in cranial vena cava blood (PvCO 2 ) than nonintubated guinea pigs. An IAP of 6 mmHg resulted in a significantly higher PvCO 2 (65.9 ± 19.0 mmHg; 8.8 ± 2.5 kPa) than at 0 (53.2 ± 17.2 mmHg; 7.1 ± 2.3 kPa) and 4 mmHg (52.6 ± 10.8 mmHg; 7.01 ± 1.4 kPa), mean ± standard deviation, with intubated and nonintubated animals combined., Conclusions and Clinical Relevance: Although the oral anatomy of guinea pigs makes endotracheal intubation difficult, capnoperitoneum during anesthesia induces marked hypercapnia in the absence of mechanical ventilation. An IAP of 4 mmHg should be further evaluated for laparoscopic procedures in guinea pigs because hypercapnia may be less severe than with 6 mmHg., (Copyright © 2022 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To evaluate the accuracy of selected echocardiographic variables used to predict fluid responsiveness in hospitalized dogs with compromised hemodynamics and tissue hypoperfusion., Design: Diagnostic test study in a prospective cohort of hospitalized dogs., Setting: Veterinary referral clinics., Animals: Forty-four hospitalized dogs with compromised hemodynamics and tissue hypoperfusion were utilized in this study., Interventions: Echocardiographic examination before and after fluid replacement with 30 ml/kg of lactated Ringer's solution., Measurements and Main Results: Pre-fluid replacement measurements of velocity of transmitral E wave (E-peak), the left ventricular end-diastolic internal diameter normalized to body weight (LVIDdN), and the left ventricular end-systolic internal diameter normalized to body weight (LVIDsN) were significantly lower in fluid-responsive patients compared with nonresponders (P < 0.001). The area under the receiver operating characteristic curve (AUROC) with its 95% confidence interval (CI) for each significant predictor was as follows: E-peak 0.907 (0.776-1.000, P < 0.001) and LVIDdN 0.919 (0.801-1.000, P < 0.001). The predictive capacity of LVIDsN was not significantly better than chance (AUROC, 0.753; 95% CI, 0.472-1.000, P = 0.078). A significant negative linear correlation was observed between the percentage of increase in velocity-time integral after expansion and the echocardiographic variables LVIDdN (r s  = -0.452, P = 0.023) and E-peak (r s  = -0.396, P = 0.008) pre-fluid replacement. The intraobserver and interobserver variability was very low (<5 %) for all measurements., Conclusions: In this study using critically ill dogs with compromised hemodynamics and tissue hypoperfusion, pre-fluid replacement measurements of LVIDdN and E-peak adequately predict fluid responsiveness. Because a small number of fluid nonresponders were involved in the present study (11.4%), further studies that include larger numbers of fluid-nonresponsive animals are required., (© Veterinary Emergency and Critical Care Society 2022.)

Objectives: To determine if the tidal volume (V T ) delivered (V TDEL ) to canine patients being mechanically ventilated by a volume-controlled ventilator differed from the volume set on the ventilator (V TSET ) at three fresh gas flow (FGF) rates. To determine if V TDEL could be accurately predicted by an FGF-based mathematical model., Study Design: Prospective proof-of-concept study., Animals: A total of 23 adult client-owned dogs undergoing elective orthopedic surgery., Methods: Dogs were anesthetized and ventilated with a volume-controlled mechanical ventilator with constant respiratory rate (f R ) of 10 breaths minute -1 , inspiratory-to-expiratory ratio of 1:2 [fraction of inspiratory time (T I ) in one respiratory cycle (T tot ) 1:3], and V TSET as body weight (kg) × 15 (mL kg -1 ). V TDEL was measured in 20 dogs at three FGF (500, 1000 and 4000 mL minute -1 ). A mathematical model was used to calculate predicted volume (V TPRED ) for each animal at each FGF: V TSET  + {FGF × [(T I /T tot )/f R ]}. Linear repeated measures models were fit comparing V TDEL to V TSET and to V TPRED by FGF., Results: V TDEL was significantly higher than V TSET at every FGF (p < 0.05), and differences were larger at higher FGF (p < 0.001). There were no statistically significant differences between V TDEL and V TPRED at FGF rates of 500 and 4000 mL minute -1 and, although the mean V TDEL was statistically significantly higher than V TPRED at FGF 1000 mL minute -1 (p = 0.017), the mean difference of 9 mL was not clinically significant., Conclusions and Clinical Relevance: Dogs on volume-controlled ventilators may be ventilated at a higher V TDEL than intended depending on the FGF settings. Ventilation of small animals at high FGF could inadvertently induce pulmonary damage. A mathematical equation can be used to achieve a desired V TDEL by adjusting V TSET values based on FGF, f R and T I /T tot ., (Copyright © 2022 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To evaluate agreement between end-tidal carbon dioxide (Pe'CO 2 ) and PaCO 2 with sidestream and mainstream capnometers in mechanically ventilated anesthetized rabbits, with two ventilatory strategies., Study Design: Prospective experimental study., Animals: A total of 10 New Zealand White rabbits weighing 3.6 ± 0.3 kg (mean ± standard deviation)., Methods: Rabbits anesthetized with sevoflurane were intubated with an uncuffed endotracheal tube (3.0 mm internal diameter) and adequate seal. For Pe'CO 2 , the sidestream capnometer sampling adapter or the mainstream capnometer was placed between the endotracheal tube and Bain breathing system (1.5 L minute -1 oxygen). PaCO 2 was obtained from arterial blood collected every 5 minutes. A time-cycled ventilator delivered an inspiratory time of 1 second and 12 or 20 breaths minute -1 . Peak inspiratory pressure was initially set to achieve Pe'CO 2 normocapnia of 35-45 mmHg (4.6-6.0 kPa). A total of five paired Pe'CO 2 and PaCO 2 measurements were obtained with each ventilation mode for each capnometer. Anesthetic episodes were separated by 7 days. Agreement was assessed using Bland-Altman analysis and linear mixed models; p < 0.05., Results: There were 90 and 83 pairs for the mainstream and sidestream capnometers, respectively. The mainstream capnometer underestimated PaCO 2 by 12.6 ± 2.9 mmHg (proportional bias 0.44 ± 0.06 mmHg per 1 mmHg PaCO 2 increase). With the sidestream capnometer, ventilation mode had a significant effect on Pe'CO 2 . At 12 breaths minute -1 , Pe'CO 2 underestimated PaCO 2 by 23.9 ± 8.2 mmHg (proportional bias: 0.81 ± 0.18 mmHg per 1 mmHg PaCO 2 increase). At 20 breaths minute -1 , Pe'CO 2 underestimated PaCO 2 by 38.8 ± 5.0 mmHg (proportional bias 1.13 ± 0.10 mmHg per 1 mmHg PaCO 2 increase)., Conclusions and Clinical Relevance: Both capnometers underestimated PaCO 2 . The sidestream capnometer underestimated PaCO 2 more than the mainstream capnometer, and was affected by ventilation mode., (Copyright © 2022 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Background: The possibility of accurately and continuously measuring arterial oxygen partial pressure (PaO 2 ) in horses may facilitate the management of hypoxaemia during general anaesthesia., Objectives: The aim of this study was to evaluate the ability of a novel fibreoptic sensor to measure PaO 2 (PaO 2Sensor ) continuously and in real time in horses undergoing ventilatory manoeuvres during general anaesthesia., Study Design: In vivo experimental study., Methods: Six adult healthy horses were anaesthetised and mechanically ventilated in dorsal recumbency. A fibreoptic sensor was placed in one of the facial arteries through a catheter to continuously measure and record PaO 2Sensor . After an alveolar recruitment manoeuvre, a decremental positive end-expiratory pressure (PEEP) titration using 20-minute steps of 5 cm H 2 O from 20 to 0 cm H 2 O was performed. An arterial blood sample was collected at 15 minutes of ventilation at each PEEP level for PaO 2 measurement using an automated blood gas machine (PaO 2Ref ). The agreement between PaO 2Sensor and PaO 2Ref was assessed by Pearson's correlation, Bland-Altman plot and four-quadrant plot analysis. In the last minute of ventilation at each PEEP level, a slow tidal inflation/deflation manoeuvre was performed., Results: The mean relative bias between PaO 2Sensor and PaO 2Ref was 4% with limits of agreement between -17% and 29%. The correlation coefficient between PaO 2Sensor and PaO 2Ref was 0.98 (P < .001). The PaO 2Sensor and PaO 2Ref concordance rate for changes was 95%. Measurements of PaO 2Sensor during the slow inflation/deflation manoeuvre at PEEP 15 and 10 cm H 2 O were not possible because of significant noise on the PaO 2 signal generated by a small blood clot., Main Limitations: Small sample size., Conclusion: The tested fibreoptic probe was able to accurately and continuously measure PaO 2Sensor in anaesthetised horses undergoing ventilatory manoeuvres. A heparinised system in the catheter used by the fibreoptic sensor should be used to avoid blood clots and artefacts in the PaO 2 measurements., (© 2021 EVJ Ltd.)

Objective: To describe new onset of generalized seizures in 3 young dogs following cessation of a benzodiazepine-containing sedation protocol to facilitate mechanical ventilation (MV) for hypoxemia., Series Summary: Three dogs under 5 months of age underwent MV due to severe hypoxemia. All 3 dogs were sedated with a constant rate infusion of benzodiazepines as part of their sedation protocol to facilitate MV. All 3 dogs had an acute onset of generalized seizures within 36 hours of sedation cessation and weaning from MV. All 3 dogs' seizures were successfully managed with a slow, tapering course of benzodiazepines. One dog was additionally treated with levetiracetam at the time of initial seizure activity, which was discontinued 1 year following discharge and absence of ongoing seizure activity. All 3 dogs were discharged successfully with no reports of ongoing seizures or neurologic deficits after discharge., New or Unique Information Provided: Young dogs managed with benzodiazepines to facilitate MV may have acute onset of generalized seizures following cessation, which can be successfully managed with short-term benzodiazepine therapy. The 3 cases in this series demonstrated a positive outcome and were successfully managed following acute onset of generalized seizure activity post-MV., (© 2022 The Authors. Journal of Veterinary Emergency and Critical Care published by Wiley Periodicals LLC on behalf of Veterinary Emergency and Critical Care Society.)

Objective: To compare the effects of three recruitment airway pressures (RP aw ) on lung aeration and volumes in mechanically ventilated dogs during propofol anesthesia., Study Design: Prospective, crossover randomized experimental study., Animals: A total of eight healthy anesthetized experimental Beagle dogs in dorsal recumbency., Methods: Dogs were mechanically ventilated with a tidal volume of 15 mL kg -1 and zero positive end-expiratory pressure and 100% oxygen. Three maneuvers consisting of a 30 second inspiration at RP aw s of 15 (RP aw 15), 25 (RP aw 25) and 35 (RP aw 35) cmH 2 O were performed randomly, 15 minutes apart. Changes in lung aeration and lung deformation were compared with end-expiratory baseline (before the application of each RP aw ) and between-RP aw s using computed tomography scans and calculations of global lung strain. Between-group comparisons were performed with one-way anova for repeated measures followed by Tukey test for multiple comparisons. A p value < 0.05 was considered significant., Results: The amount of nonaeration was minimal (<1%) at baseline and not different with the application of the RP aw s. The amount of hypoaeration and normoaeration during baseline decreased with all RP aw s (p < 0.001). There was no difference between RP aw s regarding hypoaeration (all p > 0.999), whereas normoaeration was higher at RP aw 15 than RP aw 25 and RP aw 35 (p < 0.009). Compared with baseline, the fraction of hyperaerated alveoli increased with each RP aw (p < 0.001) and was lower during RP aw 15 than RP aw 25 and RP aw 35 (both p ≤ 0.007). Global lung strain was lower during RP aw 15 than at higher RP aw (p < 0.001)., Conclusions and Clinical Relevance: A RP aw of 15 cmH 2 O for 30 seconds was the recommended RP aw because it was as effective at reversing hypoaeration as RP aw s of 25 and 35 cmH 2 O but with less hyperaeration and potential for overdistension of the lungs in this particular population of dogs with negligible atelectasis., (Copyright © 2022 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To evaluate the effects of combining one-lung ventilation and carbon dioxide insufflation (OLV-CDI) on intrathoracic working space (determined by means of CT) during thoracoscopy in dogs and investigate conditions that could safely improve working space compared with OLV alone., Animals: 6 healthy Beagles., Procedures: Dogs were anesthetized, and right- or left-sided (n = 3/side) OLV was instituted. On the blocked side, a laparoscopic trocar sleeve was placed in the ninth intercostal space for CDI. CT was performed under 3 conditions: with OLV alone, with OLV-CDI at an intrapleural pressure (IPP) of 3 mm Hg, and with OLV-CDI at an IPP of 5 mm Hg. Working space volume (WSV), ventilation space volume (VSV), and thoracic cavity volume (TCV) were determined from CT images., Results: With OLV-CDI at an IPP of 3 or 5 mm Hg, WSV and TCV were significantly increased, compared with values obtained during OLV alone. With OLV-CDI at an IPP of 5 mm Hg, VSV and Spo2 were significantly decreased, compared with values obtained during OLV alone. Additionally, contralateral pneumothorax was observed in 4 dogs at an IPP of 5 mm Hg., Clinical Relevance: Combining OLV and CDI could provide a larger working space than OLV alone, even with an IPP of 3 mm Hg, in dogs of limited size. However, an evaluation of the effects on oxygenation and cardiovascular variables is needed before clinical use.

Objective: To compare the cardiopulmonary effects of apneustic anesthesia ventilation (AAV) and conventional mechanical ventilation (CMV) in dorsally recumbent anesthetized horses., Study Design: Randomized, crossover design., Animals: A total of 10 healthy adult horses from a university-owned herd., Methods: Following xylazine, midazolam and ketamine administration, horses were orotracheally intubated and positioned in dorsal recumbency. Anesthesia was maintained with isoflurane in oxygen [inspired oxygen fraction (FiO 2 ) = 0.3 initially, with subsequent titration to maintain PaO 2 ≥ 85 mmHg (11.3 kPa)]. Horses were instrumented and ventilated with AAV or CMV for 1 hour according to predefined criteria [10 mL kg -1 tidal volume (V T ), PaCO 2 of 40-45 mmHg (5.3-6.0 kPa) during CMV and <60 mmHg (8.0 kPa) during AAV]. Dobutamine was administered to maintain mean arterial pressure (MAP) >65 mmHg. Cardiopulmonary data were collected at baseline, 30 and 60 minutes. The effects of ventilation mode and time were analyzed using repeated-measures anova with significance defined as p < 0.05., Results: Data from nine horses were analyzed. A significant effect of mode at one or more time points was found for respiratory rate, arterial and end-tidal CO 2 tensions, arterial pH, mean airway pressure (P aw ), respiratory system dynamic compliance index (C rs I), venous admixture (Q˙ s /Q˙ t ), mean pulmonary artery pressure and systemic vascular resistance. No significant differences between modes were found for V T , FiO 2 , PaO 2 , arterial hemoglobin saturation, alveolar dead space, heart rate, MAP, cardiac index, stroke volume index, oxygen delivery index, oxygen extraction ratio and dobutamine administration., Conclusions and Clinical Relevance: In dorsally recumbent anesthetized horses, both ventilation modes supported adequate oxygenation with minimal supplemental oxygen. Compared with CMV, AAV resulted in higher C rs I and lower Q˙ s /Q˙ t . Despite higher mean P aw with AAV, the cardiovascular effects of each mode were not different. Further trials of AAV in anesthetized horses are warranted., (Copyright © 2022 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. All rights reserved.)

The use of transthoracic echocardiography (TTE) and esophageal Doppler (ED) for the measurement of hemodynamic variables in anesthetized dogs was studied. Fourteen mixed-breed dogs, without cardiac disease, undergoing general anesthesia for diagnostic or therapeutic procedures were included in this prospective preliminary study. Dogs were premedicated with dexmedetomidine (3 μg/kg) and methadone (0.3 mg/kg), intramuscularly. General anesthesia was induced with propofol intravenously titrated to effect and maintained with isoflurane in oxygen. Animals were positioned in dorsal recumbency. Transthoracic echocardiography was performed using a 5-2 MHz cardiac ultrasound probe placed in the subcostal window, whereas esophageal Doppler was performed using a CardioQ probe (MP50; Deltex Medical, Chichester, UK). Once an appropriate view of the aortic flow was obtained, the variables peak velocity (PV) and velocity-time integral (VTI) were measured. Agreement between methods was evaluated using the Bland-Altman method with single observation per individual. The bias and the limits of agreement (LOA) between the two methods were determined. Mean (± SD) PV was 99.46 cm/s (± 42.73 cm/s) and 110.29 cm/s (± 35.86 cm/s), and VTI was 13.24 cm (± 4.33 cm) and 13.05 cm (± 4.47 cm), for TTE and ED, respectively. Mean differences and LOA were 10.83 cm/s (range: -20.50 to 42.16 cm/s) and -0.19 cm (range: -3.32 to 2.95 cm) for PV and VTI, respectively. No statistically significant differences were determined in the variables measured between TTE and ED in anesthetized dogs without cardiac disease, positioned in dorsal recumbency. This could be of clinical relevance when an evaluation of the intraoperative hemodynamic status of anesthetized dogs is desired., (Copyright and/or publishing rights held by the Canadian Veterinary Medical Association.)

Objectives: To determine the complications associated with positive-pressure ventilation (PPV) in dogs and cats., Design: Retrospective study from October 2009 to September 2013., Setting: University Teaching Hospital., Animals: Fifty-eight dogs and 9 cats., Measurements and Main Results: Medical records were retrospectively reviewed; signalment, complications associated with PPV, duration of PPV, and outcome were recorded. Complications most commonly recorded during PPV included hypothermia 41/67 (61%), hypotension 39/67 (58%), cardiac arrhythmias 33/67 (49%), a positive fluid balance 31/67 (46%), oral lesions 25/67 (37%), and corneal ulcerations 24/67 (36%). A definition of ventilator-associated events (VAE) extrapolated from the Center of Disease Control's criteria was applied to 21 cases that received PPV for at least 4 days in this study. Ventilator-associated conditions occurred in 5 of 21 (24%) of cases with infection-related ventilator-associated conditions and ventilator-associated pneumonia identified in 3 of 21 (14%) cases., Conclusions: Complications are common and diverse in dogs and cats receiving long-term PPV and emphasizes the importance of intensive, continuous patient monitoring and appropriate nursing care protocols. Many of the complications identified could be serious without intervention and suggests that appropriate equipment alarms could improve patient safety. Development of veterinary specific surveillance tools such as the VAE criteria would aid future investigations and allow for effective multicenter studies., (© Veterinary Emergency and Critical Care Society 2022.)

Objectives: To determine the indications and outcomes of positive-pressure ventilation (PPV) and identify factors associated with successful weaning., Design: Retrospective study from October 2009 to September 2013., Setting: University teaching hospital., Animals: One hundred and eleven dogs and 16 cats., Measurements and Main Results: Medical records were retrospectively reviewed; signalment, indication for PPV, patient characteristics, blood gas, and ventilator variables during PPV, duration of PPV, and outcome were recorded. Dogs were most commonly ventilated for pneumonia (36/111; 32%) and cats for multiple pulmonary diseases (8/16; 50%). The median duration of PPV for all animals was 25.7 h (range, 0.1-957 h). Long-term PPV (≥24 h) was performed in 53% of cases. No differences were noted in successful weaning rates between cases ventilated for pulmonary etiologies (23/99; 23%) versus nonpulmonary etiologies (9/28; 32%). Overall, 32 of 127 (25%; 30 dogs, 2 cats) animals were successfully weaned from PPV and 28 of 127 (22%; 26 dogs, 2 cats) survived to hospital discharge. Long-term ventilation had a higher likelihood of successful weaning (26/67 [39%] vs 6/60 [10%], P = 0.0002) and higher rates of survival to discharge (23/67 [34%] vs 5/60 [8%], P = 0.0005) than short-term ventilation. Animals with higher Pao 2 /Fio 2 and Spo 2 /Fio 2 and lower APPLE and SOFA scores on day 1 of PPV were more likely to be weaned (P < 0.03)., Conclusions: The outcome of PPV appears to be most heavily determined by the underlying disease process and no clear improvement in outcome could be demonstrated in this study, despite advances in veterinary critical care and ventilator management strategies since previous studies. Dogs and cats receiving PPV for more than 24 h in this study had a higher likelihood of a positive outcome. Several indices of oxygenation and illness severity at the onset of PPV were predictive of outcome and maybe useful when considering prognosis of these cases., (© Veterinary Emergency and Critical Care Society 2022.)

High-flow nasal oxygen therapy (HFNT) and positive pressure ventilation (PPV) are interventions used in the management of animals with respiratory failure. The indications for the use of these modalities, clinical application, prognosis, and a review of the current veterinary evidence are provided., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The aim of this study was to evaluate the validity of the SpO 2 /FiO 2 diagram in estimating gas exchange in horses under general anaesthesia. In this prospective, controlled clinical study were included 10 horses under general anaesthesia. FiO 2 was progressively reduced with the following steps: 0.6, 0.4, 0.3 and 0.21; SpO 2 was recorded at each step. An arterial blood sample was collected at the steps of 1.0 and 0.21, to calculate intrapulmonary shunt with the Fshunt formula. The Fshunt value calculated at 0.21 FiO 2 was defined as "Fshunt 0.21", the one calculated at 1.0 FiO 2 as "Fshunt 1.0". The FiO 2 vs SpO 2 data points were analyzed using a computer algorithm which uses the haemoglobin and a fixed value for arterial-venous oxygen difference of 3.5 mL/dL. The algorithm estimates a shunt value fitting the obtained data with an ideal SpO 2 /FiO 2 curve. The value of shunt (Sshunt) was considered for the study. Correlation between "Fshunt 1.0", "Fshunt0.21" and SShunt was determined using the Spearman Rank Correlation Coefficient test, the analysis of the regression curve and the coefficient of determination (r 2 ). Values of P < .05 were considered statistically significant. A significant and strong correlation (P = .0069; r = 0.839; r 2 =0.6194) and a significant and moderate correlation (P = .0443; r = 0.644; r 2 =0.2336) was found between Sshunt and "Fshunt 1.0" and between Sshunt and "Fshunt 0.21", respectively. The SpO 2 /FiO 2 diagram proved to be a useful and non-invasive tool to characterize gas exchange in horses under general anaesthesia and mechanical ventilation., Competing Interests: Conflict of Interest All authors have no financial and personal relationship with other people or organization that could inappropriately influenced their work in this study., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Objective: Mechanical ventilation is usually achieved by active lung inflation during inspiration and passive lung emptying during expiration. By contrast, flow-controlled expiration (FLEX) ventilation actively reduces the rate of lung emptying by causing linear gas flow throughout the expiratory phase. Our aim was to evaluate the effects of FLEX on lung compliance and gas exchange in anesthetized horses in dorsal recumbency., Animals: 8 healthy horses., Procedures: All animals were anesthetized twice and either ventilated beginning with FLEX or conventional volume-controlled ventilation in a randomized, crossover design. Total anesthesia time was 3 hours, with the ventilatory mode being changed after 1.5 hours. During anesthesia, cardiac output (thermodilution), mean arterial blood pressures, central venous pressure, and pulmonary arterial pressure were recorded. Further, peak, plateau, and mean airway pressures and dynamic lung compliance (Cdyn) were measured. Arterial blood gases were analyzed every 15 minutes. Data were analyzed using ANOVA (P < 0.05)., Results: FLEX ventilation resulted in significantly higher arterial oxygen partial pressures (521 vs 227 mm Hg) and Cdyn (564 vs 431 mL/cm H2O) values compared to volume-controlled ventilation. The peak and plateau airway pressure were lower, but mean airway pressure was significantly higher (4.8 vs 9.2 cm H2O) in FLEX ventilated horses. No difference for cardiovascular parameters were detected., Clinical Relevance: The results of this study showed a significant improvement of the Pao2 and Cdyn without compromising the cardiovascular system when horses were ventilated by use of FLEX compared to conventional ventilation.

Objective: To measure changes in pulmonary perfusion during pulsed inhaled nitric oxide (PiNO) delivery in anesthetized, spontaneously breathing and mechanically ventilated ponies positioned in dorsal recumbency., Animals: 6 adult ponies., Procedures: Ponies were anesthetized, positioned in dorsal recumbency in a CT gantry, and allowed to breathe spontaneously. Pulmonary artery, right atrial, and facial artery catheters were placed. Analysis time points were baseline, after 30 minutes of PiNO, and 30 minutes after discontinuation of PiNO. At each time point, iodinated contrast medium was injected, and CT angiography was used to measure pulmonary perfusion. Thermodilution was used to measure cardiac output, and arterial and mixed venous blood samples were collected simultaneously and analyzed. Analyses were repeated while ponies were mechanically ventilated., Results: During PiNO delivery, perfusion to aerated lung regions increased, perfusion to atelectatic lung regions decreased, arterial partial pressure of oxygen increased, and venous admixture and the alveolar-arterial difference in partial pressure of oxygen decreased. Changes in regional perfusion during PiNO delivery were more pronounced when ponies were spontaneously breathing than when they were mechanically ventilated., Clinical Relevance: In anesthetized, dorsally recumbent ponies, PiNO delivery resulted in redistribution of pulmonary perfusion from dependent, atelectatic lung regions to nondependent aerated lung regions, leading to improvements in oxygenation. PiNO may offer a treatment option for impaired oxygenation induced by recumbency.

Background: Brachycephalic dogs (BCD) are increasingly popular companion animals and widely recognized to suffer from respiratory compromise based upon their conformation; however, the actual percentages of BCD in veterinary ICUs are unknown. This study aimed to evaluate a canine ICU census, as well as the presence, development, and severity of respiratory compromise in BCD using syndromic surveillance., Key Findings: Ten institutions provided surveillance data twice weekly over an 11-week study period. The total canine ICU census was 1254 dogs hospitalized during the days and times of the study period; of this population, 125 (10%) were BCD. Fifty-six (45%) BCD were hospitalized in ICUs because they were perceived to be at risk of respiratory complications while recovering from general anesthesia or had a nonrespiratory condition requiring ICU admission, with the remaining 69 dogs (55%) being treated for respiratory disease. Twenty dogs (16%) developed respiratory complications requiring ICU admission after initially being hospitalized for another condition. Four percent of dogs were supported with mechanical ventilation., Clinical Significance: Syndromic surveillance was a useful method for evaluating the number of BCD in a veterinary ICU. Almost 1 in 5 BCD developed respiratory compromise after initial evaluation for an unrelated problem. Ongoing evaluation of the medical issues associated with brachycephaly is warranted., (© Veterinary Emergency and Critical Care Society 2021.)

Objective: To determine the effect of fraction of inspired oxygen (FiO 2 ) on intrapulmonary shunt fraction as measured by F-shunt in ponies during isoflurane anaesthesia., Study Design: Prospective, randomized clinical study., Animals: A group of 23 adult Shetland ponies undergoing a total of 32 anaesthetic procedures., Methods: Ponies were premedicated intravenously (IV) with detomidine (0.01 mg kg -1 ) and either morphine (0.1 mg kg -1 ) or butorphanol (0.02 mg kg -1 ). Anaesthesia was induced with ketamine (2.2 mg kg -1 ) and midazolam (0.07 mg kg -1 ) administered IV. Ponies were randomly allocated to maintenance of anaesthesia with isoflurane in oxygen (group TH; FiO 2  = 0.95) or a mixture of oxygen and medical air (group TL; FiO 2  = 0.65); all ponies were given a constant rate of infusion of detomidine. Animals were mechanically ventilated to maintain PaCO 2 between 40 and 50 mmHg. Arterial blood gas analysis was performed every 30 minutes. The F-shunt equation was calculated for each time point T0, T30, T60 and T90. Data were analysed using linear mixed model analysis and presented as mean ± standard deviation (p < 0.05)., Results: PaO 2 was greater in group TH than in group TL (TH: 406 ± 90, 438 ± 83, 441 ± 69 and 464 ± 53 mmHg versus TL: 202 ± 90, 186 ± 84, 172 ± 85 and 191 ± 98 mmHg at T0, T30, T60 and T90, respectively; p < 0.0001). In TH, F-shunt was < TL. Significant differences were found at T60 (TH: 13.2% ± 4.3 versus TL: 19.4% ± 8.3; p = 0.016) and T90 (TH: 11.7% ± 3.5 versus TL: 18.6% ± 9.5; p = 0.036)., Conclusions and Clinical Relevance: Our findings do not support a beneficial effect of using a reduced FiO 2 to improve oxygenation in anaesthetized and mechanically ventilated Shetland ponies., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The medical records of 59 puppies from 6 hospitals undergoing mechanical ventilation (MV) between 2006 and 2020 were reviewed to describe the signalment, underlying disease, duration of ventilation, and outcome. The most common underlying diseases were pneumonia ( n = 18), non-cardiogenic pulmonary edema ( n = 16), and trauma ( n = 8). Twenty-six (44%) puppies were weaned from the ventilator. The overall survival rate was 39% (23/59) including 19 non-brachycephalic dogs and 4 brachycephalics. Median duration of mechanical ventilation was 27 hours (range: 4 to 144 hours). Brachycephalic dogs were less likely to survive than nonbrachycephalic dogs ( P = 0.032). English bulldogs were over-represented with pneumonia. No association between age and survival to discharge ( P = 0.716) or outcome ( P = 0.579) was detected. The survival rate, and underlying disease process and severity for mechanically ventilated puppies was similar to previous studies in adult dogs., (Copyright and/or publishing rights held by the Canadian Veterinary Medical Association.)

Objective: To compare pulse pressure variation (PPV) and systolic pressure variation (SPV) measured from a peripheral artery to predict fluid responsiveness in anesthetized healthy dogs., Study Design: Prospective study., Animals: A total of 39 dogs (13.8-26.8 kg) anesthetized with isoflurane for elective ovariohysterectomy., Methods: Ventilation was controlled (tidal volume 12 mL kg -1 ; 40% inspiratory pause). PPV and SPV were recorded from a dorsal pedal artery catheter using an automated algorithm. A fluid challenge (FC) with lactated Ringer's solution (20 mL kg -1 over 15 minutes) was administered once (21 animals) or twice (18 animals) before surgery. Increases in transpulmonary thermodilution stroke volume index > 15% from values recorded before each FC defined responders to volume expansion. Final fluid responsiveness status was based on the response to single FC or second FC. Predictive ability of PPV and SPV was compared by receiver operating characteristic (ROC) curve analysis and by the range of cut-off values associated with uncertain results (gray zone)., Results: All animals after the single FC were responders; all animals administered two FCs were nonresponders after the second FC. The area under the ROC curve (AUROC) of PPV (0.968) did not differ from that of SPV (0.937) (p = 0.45). Best cut-off thresholds to discriminate responders from nonresponders were >11.7% (PPV) and >7.4 mmHg (SPV). The gray zone of PPV and SPV was 8.2-14.6% and 7.0-7.4 mmHg, respectively. The percentage of animals with PPV and SPV values within the gray zone was less for SPV (10.2%) than for PPV (30.8%)., Conclusions and Clinical Relevance: PPV and SPV obtained from the dorsal pedal artery are useful predictors of fluid responsiveness in dogs. Using an automated algorithm, SPV may more accurately predict fluid responsiveness than PPV, with responders identifiable by PPV > 14.6% and SPV > 7.4 mmHg., (Copyright © 2021. Published by Elsevier Ltd.)

Hypoxaemia is a common complication in anaesthetised or immobilised elephants. It is presumably because of hypoventilation and ventilation-perfusion mismatch. To prevent hypoxaemia, orotracheal intubation and positive pressure ventilation are recommended. This case report describes a hypoxaemic period despite positive pressure ventilation in a 46-year-old female Asian elephant (Elephas maximus) anaesthetised with azaperone-etorphine, medetomidine and an etorphine constant rate infusion in lateral recumbency for a dental procedure. The hypoxaemia was corrected utilising positive end-expiratory pressure (PEEP) of 5 cm - 10 cm H2O, a technique that has not previously been reported in the management of anaesthetised elephants. PEEP decreases atelectasis, shunt fraction, and increases lung compliance. Positive end-expiratory pressure was achieved by partial occlusion of the tailpiece of a manually triggered demand valve ventilator during expiration. This is a simple effective method of generating PEEP and correcting hypoxaemia without the need for any additional specialised equipment. However, PEEP decreased arterial blood pressure and should be implemented with caution if arterial blood pressure is not monitored.

Objectives: To compare pulmonary gas exchange, tissue oxygenation and cardiovascular effects of four levels of end-expiratory pressure: no positive end-expiratory pressure (ZEEP), positive end-expiratory pressure (PEEP) of maximal respiratory system compliance (PEEPmaxC rs ), PEEPmaxC rs  + 2 cmH 2 O (PEEPmaxC rs+2 ), PEEPmaxC rs  + 4 cmH 2 O (PEEPmaxC rs+4 ), in isoflurane-anesthetized dogs., Study Design: Prospective randomized crossover study., Animals: A total of seven healthy male Beagle dogs, aged 1 year and weighing 10.2 ± 0.7 kg (mean ± standard deviation)., Methods: The dogs were administered acepromazine and anesthesia was induced with propofol and maintained with isoflurane. Ventilation was controlled for 4 hours with ZEEP, PEEPmaxC rs , PEEPmaxC rs+2 or PEEPmaxC rs+4 . Cardiovascular, pulmonary gas exchange and tissue oxygenation data were evaluated at 5, 60, 120, 180 and 240 minutes of ventilation and compared using a mixed-model anova followed by Bonferroni test. p < 0.05 was considered significant., Results: Cardiac index (CI) and mean arterial pressure (MAP) were lower in all PEEP treatments at 5 minutes when compared with ZEEP. CI persisted lower throughout the 4 hours only in PEEPmaxC rs+4 with the lowest CI at 5 minutes (2.15 ± 0.70 versus 3.45 ± 0.94 L minute -1 m -2 ). At 180 and 240 minutes, MAP was lower in PEEPmaxC rs+4 than in PEEPmaxC rs , with the lowest value at 180 minutes (58 ± 7 versus 67 ± 7 mmHg). Oxygen delivery index (DO 2 I) was lower in PEEPmaxC rs+4 than in ZEEP at 5, 60, 120 and 180 minutes. Venous admixture was not different among treatments., Conclusion and Clinical Relevance: The use of PEEP caused a transient decrease in MAP and CI in lung-healthy dogs anesthetized with isoflurane, which improved after 60 minutes of ventilation in all levels of PEEP except PEEPmaxC rs+4 . A clinically significant improvement in arterial oxygenation and DO 2 I was not observed with PEEPmaxC rs and PEEPmaxC rs+2 in comparison with ZEEP, whereas PEEPmaxC rs+4 decreased DO 2 I., (Copyright © 2021 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objectives: To evaluate the use of enteral and parenteral nutrition in a population of mechanically ventilated cats and dogs, identify factors associated with implementation of nutrition, and assess the frequency of nutritional support within 72 hours of absent caloric intake., Design: Retrospective, single-center audit from June 2013 to June 2016., Setting: ICU of a veterinary university teaching hospital., Animals: Fifty-eight animals (50 dogs, 8 cats) that underwent mechanical ventilation for ≥6 hours with complete medical records., Interventions: None., Measurements and Main Results: Data collected included nutritional provision, time to initiation of nutrition, period of absent caloric intake, percentage of caloric intake obtained, and possible factors contributing to the delay or failure to implement nutrition. Thirty-one percent of patients (dogs 16/50, 32%; cats 2/8, 25%) received nutritional support during mechanical ventilation with all but 2 dogs receiving parenteral nutrition. Of those patients that did not receive nutrition (dogs 34/50, 68%; cats 6/8, 75%), documented contraindications or notations within the medical record for its omission were present in 16 of 34 dogs (47%) and 4 of 6 cats (66.7%). Thirteen animals (11 dogs, 2 cats) had >72 hours of absent caloric intake with only a small number of these receiving nutrition (dogs 4/11, 36.4%; cats 0/2, 0%)., Conclusions: Only 18 of 58 (31%) mechanically ventilated dogs and cats at our institution received nutritional support, and the majority of these were fed parenterally (16/18, 88.9%). For animals that did not receive nutrition, there was no clear reason for its absence in many cases. Animals with absent caloric intake >72 hours had poor implementation of nutritional support in contrast to current guidelines. A repeat audit after implementing changes to institutional protocols for nutritional provision is warranted to assess the impact on morbidity and mortality., (© 2021 The Authors. Journal of Veterinary Emergency and Critical Care published by Wiley Periodicals LLC on behalf of Veterinary Emergency and Critical Care Society.)

The aim of this study was to determine whether use of a commercially available fish tank air pump (FTAP) could predictably lower the fraction of inspired oxygen (FiO 2 ) within an anesthetic circuit below the level of risk for O 2 toxicity (FiO 2 < 0.6). Three different anesthesia machines and an anesthesia ventilator were each outfitted with an FTAP. The FiO 2 was measured at 4 different tidal volumes and 3 O 2 flow rates at a set respiratory rate of 15 breaths per minute, and mean FiO 2 was calculated. For each O 2 flow rate and tidal volume combination, the FiO 2 was reduced (FiO 2 < 1). The FiO 2 was more reliably decreased at lower O 2 flow rates. A significant limitation of the study was the makeshift construction, leading to measurable leaks within the circuit. This technique could represent an economical and practical approach to providing ventilatory support in a resource limited setting., (Copyright and/or publishing rights held by the Canadian Veterinary Medical Association.)

Low arterial oxygen is a common complication in anesthetized horses and placing the animal in reverse Trendelenburg (RT) position may treat hypoxemia. The objective of this study was to assess the arterial partial pressure of oxygen (PaO 2 ) in horses placed in a 5-degree RT compared to horizontal (H) position. Client-owned healthy horses (n = 60) undergoing elective surgeries were enrolled in a randomized controlled clinical study. Horses were sedated with butorphanol, an α 2 -adrenoceptor agonist, ± acepromazine and induced with ketamine combined with a benzodiazepine, propofol, or guaifenesin. Anesthesia was maintained with isoflurane in oxygen with mechanical ventilation. Each group (RT and H) included 30 horses, 10 in each recumbency (dorsal, right and left lateral). Arterial blood gas analyses (aBG) were performed following arterial catheter placement then hourly. Time first-to-last aBG, changes in PaO 2 , dynamic compliance (C dyn ), estimated pulmonary shunt fraction (F-shunt), and alveolar dead space to tidal volume ratio (V D /V T ) were evaluated with a 2-way analysis of variance. Statistical significance was set at p < .05. Overall, PaO 2 increased in all groups; however no significant difference was found between recumbencies (dorsal, right and left lateral) and RT versus H in changes over time for PaO 2 (p = .064 and p = .070, respectively), C dyn (p = .721 and p = .672, respectively), F-shunt (p = .055 and p = .054, respectively), or V D /V T (p = .616 and p = .064, respectively). In healthy anesthetized horses, 5-degree RT did not affect changes in PaO 2 as compared to H position., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Objective: To evaluate the ability of transthoracic echocardiographic aortic flow measurements to discriminate response to a fluid challenge (FC) in healthy anesthetized dogs., Study Design: Prospective experimental study., Animals: A total of 48 isoflurane-anesthetized dogs (14.2-35.0 kg) undergoing elective surgery., Methods: Fluid responsiveness was evaluated before surgery by FC (lactated Ringer's 10 mL kg -1 intravenously over 5 minutes). Percentage increases in transpulmonary thermodilution stroke volume (ΔSV TPTD ) >15% from values recorded before FC defined responders to volume expansion. A group of 24 animals were assigned as nonresponders (ΔSV TPTD ≤15%). When ΔSV TPTD was >15% after the first FC, additional FC were administered until ΔSV TPTD was ≤15%. Final fluid responsiveness status was based on the response to the last FC. Percentage increases after FC in aortic flow indexes [velocity time integral (ΔVTI FC ) and maximum acceleration (ΔVmax FC )] and in mean arterial pressure (ΔMAP FC ) were compared with ΔSV TPTD ., Results: After one FC, 24 animals were responders. For nonresponders, ΔSV TPTD was ≤15% after one, two and three FCs in eight/24, 15/24 and one/24 animals, respectively. The FC that defined responsiveness increased ΔSV TPTD by 29 (18-53)% in responders and by 8 (-3 to 15)% in nonresponders [mean (range)]. The area under the receiver operating characteristics curve (AUROC) of ΔVTI FC (0.901) was larger than the AUROCs of ΔVmax FC (0.774, p = 0.041) and ΔMAP FC (0.519, p < 0.0001). ΔMAP FC did not predict responsiveness (p = 0.826). Best cut-off thresholds for discriminating responders, with respective zones of diagnostic uncertainty (gray zones) were >14.7 (10.8-17.6)% for ΔVTI FC and >8.6 (-0.3 to 14.7)% for ΔVmax FC . Animals within the gray zone were 17% (ΔVTI FC ) and 50% (ΔVmax FC )., Conclusions and Clinical Relevance: Changes in VTI induced by FC can determine responsiveness with reasonable accuracy in dogs and could play an important role in goal-directed fluid therapy., (Copyright © 2021 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To evaluate the influence of reservoir bag types, volumes and previous use on the peak pressures (Pmax) and the times to develop 30 cmH 2 O pressure (P30) within a nonrebreathing system with a closed adjustable pressure-limiting (APL) valve., Study Design: In vitro study using three-way factorial design with repeated measure on one factor., Subjects: A total of 75 new anesthesia reservoir bags (five types, three volumes, five bags from each type × volume). The bag types were reusable latex (RL), disposable latex (DL) and three disposable neoprene (DN-1, DN-2 and DN-3)., Methods: Each bag was tested three times (treatments): new, after prestretching and 1 week later. The bags were attached to a Bain system and anesthesia machine with closed APL valve and patient port with O 2 flow 2 L minute -1 until Pmax was reached. The Pmax and time to reach P30 values were determined from recorded pressure traces. General linear mixed model analysis was used to examine the effects of bag type, volume and treatment. One-sided 95% upper prediction limits of Pmax were calculated to test the null hypothesis that predicted Pmax of new bags would be ≥ 50 cmH 2 O for each factor combination., Results: RL bags were the least and DN-3 bags were the most compliant. Prestretching increased compliance in all bag types. Smaller bags of RL, DL and DN-1 were less compliant than larger ones. The predicted Pmax values were < 50 cmH 2 O only for DN-3 bags after prestretching. The time to reach P30 was critically low when using 0.5 L bags (median 17 seconds)., Conclusions and Clinical Relevance: To minimize the risk of barotrauma, highly compliant reservoir bags (e.g. DN-3) are recommended and reusable bags should be avoided. Bags should be prestretched before first use, 0.5 L bags should be avoided and fresh gas flow minimized., (Copyright © 2020 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)