Search

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 the efficacy of inhaled salbutamol with salmeterol for the treatment of arterial hypoxaemia in anaesthetized horses., Study Design: Prospective, randomized, clinical study., Animals: A total of 108 client-owned horses (American Society of Anesthesiologists status I-V) anaesthetized for elective and emergency procedures., Methods: Horses were premedicated with acepromazine [intramuscularly 0.1 mg kg -1 or intravenously (IV) 0.05 mg kg -1 ] and xylazine (0.6 mg kg -1 IV). Midazolam (0.06 mg kg -1 IV) and ketamine (2.2 mg kg -1 IV) were combined to induce anaesthesia, and isoflurane in oxygen/air mixture (inspired oxygen fraction 0.7) was used for maintenance of anaesthesia. Mechanical ventilation was initiated without delay using the following ventilator settings: tidal volume 10 mL kg -1 , respiratory rate 8 breaths minute -1 , inspiratory-to-expiratory time ratio 1:2, no positive end-expiratory pressure. If arterial blood gas analysis revealed PaO 2 < 100 mmHg (13.3 kPa), the administration of either inhaled salbutamol (2 μg kg -1 ) or salmeterol (0.5 μg kg -1 ) was randomly assigned Blood gas analysis was repeated 15 and 30 minutes after treatment. The intervention was considered successful when PaO 2 after treatment ≥ 1.2 × PaO 2 before treatment (i.e. ≥20% increase). PaO 2 at 15 and 30 minutes was compared between groups using Mann-Whitney U test; p < 0.05 was considered significant., Results: Of the 108 horses, 60 were administered salbutamol, 65% and 60% responded successfully at 15 and 30 minutes, increasing their initial PaO 2 by 38% and 44%, respectively. The other 48 horses were administered salmeterol, 35% responded successfully at 15 and 30 minutes, increasing their initial PaO 2 by 3% and 4%, respectively. PaO 2 was significantly higher after salbutamol than after salmeterol at 15 and 30 minutes., Conclusions and Clinical Relevance: Using the described protocol, inhaled salbutamol was more effective than salmeterol in improving PaO 2 in anaesthetized horses with value < 100 mmHg (13.3 kPa)., (Copyright © 2024 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To investigate the effect of hypoxaemia, hypotension and hypercapnia, among others, on quality of recovery from general anaesthesia in horses., Study Design: Retrospective, single-centre study., Animals: A sample of 1226 horses that underwent general anaesthesia between June 2017 and June 2021., Methods: Horses and ponies weighing > 200 kg, aged > 6 months, anaesthetized using a xylazine- or medetomidine-isoflurane balanced anaesthesia protocol and presenting a complete anaesthetic record were included. Data were extracted from the clinic record system and from the original anaesthesia records. Recoveries were divided into 'good' and 'bad' based on the available recovery scores. Influence of hypoxaemia [PaO 2 < 60 mmHg (7.99 kPa)], hypotension (mean arterial pressure < 70 mmHg for at least 15 minutes) and hypercapnia [PaCO 2 > 60 mmHg (7.99 kPa)], anaesthesia protocol, body weight, age, breed, sex, American Society of Anesthesiologists status, type of procedure, emergency or nonemergency, duration of anaesthesia, positioning, times spent in lateral and sternal recumbency during recovery, time until standing and nonassisted or assisted recovery on the assigned recovery score (good/bad) were investigated using generalized linear regression analysis (p < 0.05)., Results: Hypoxaemia and prolonged duration of anaesthesia were significantly associated with a bad recovery score. No other factors had a significant influence on recovery quality., Conclusion and Clinical Relevance: Hypoxaemia and prolonged anaesthesia duration have a negative effect on quality of anaesthetic recovery in horses. Clinically, this highlights the importance of keeping anaesthetic time as short as possible and to monitor oxygenation and treat hypoxaemia as soon as possible., (Copyright © 2023 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To investigate the statistical association of severe intraoperative hypoxemia in thoracic surgery with mortality, postoperative hospitalization times and cost of care., Study Design: Retrospective study., Animals: Dogs that underwent thoracic surgery in three veterinary hospitals between October 1, 2018 and October 1, 2020., Methods: Anesthesia and hospitalization records from 112 dogs were reviewed and 94 cases met inclusion criteria. Recorded data included signalment, disease etiology, pulmonary or extrapulmonary nature of disease, surgical procedure performed, episodes of severe intraoperative hypoxemia defined as a pulse oximetry reading (SpO 2 ) <90% of 5 minutes or longer duration, survival to discharge, time from extubation to hospital discharge and total invoice cost for clinical visit. Dogs were divided into two groups, those that experienced severe hypoxemia (group A) and those in which SpO 2 reading <90% was not observed throughout the procedure (group B)., Results: Group A had a greater risk of mortality (odds ratio 10.6, 95% confidence interval 1.9-106.7; p = 0.002), prolonged hospitalization (median 62 hours versus 46 hours; p = 0.035) and more expensive cost of care (median US$10,287 versus $8506; p = 0.056) than group B. No significant difference was found for the type of surgical procedure or pulmonary versus extrapulmonary nature of disease., Conclusions and Clinical Relevance: Severe intraoperative hypoxemia was statistically associated with an increased risk of mortality and longer postoperative hospitalization times. Although not achieving statistical significance, there was a trend toward increased costs to the client for animals with intraoperative hypoxemia., (Copyright © 2023 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To investigate the sedative and cardiorespiratory effects of intranasal atomization (INA) of alfaxalone using a mucosal atomization device in Japanese White rabbits., Study Design: Randomized, prospective, crossover study., Animals: A total of eight healthy female rabbits, weighing 3.6-4.3 kg and aged 12-24 months., Methods: Each rabbit was randomly assigned to four INA treatments administered 7 days apart: Control treatment, 0.15 mL 0.9% saline in both nostrils; treatment INA0.3, 0.15 mL 4% alfaxalone in both nostrils; treatment INA0.6, 0.3 mL 4% alfaxalone in both nostrils; treatment INA0.9, 0.3 mL 4% alfaxalone in left, then right, then left nostril. Sedation was scored 0-13 using a composite measure scoring system for rabbits. Simultaneously, pulse rate (PR), respiratory rate (f R ), noninvasive mean arterial pressure (MAP), peripheral hemoglobin oxygen saturation (SpO 2 ) and arterial blood gases were measured until 120 minutes. The rabbits breathed room air during the experiment and were administered flow-by oxygen when hypoxemia (SpO 2 <90% or PaO 2 <60 mmHg; 8.0 kPa) developed. Data were analyzed using the Fisher's exact test and the Friedman test (p < 0.05)., Results: No rabbit was sedated in treatments Control and INA0.3. All rabbits in treatment INA0.9 developed loss of righting reflex for 15 (10-20) minutes [median (25th-75th percentile)]. Sedation score significantly increased from 5 to 30 minutes in treatments INA0.6 and INA0.9 with maximum scores of 2 (1-4) and 9 (9-9), respectively. f R decreased in an alfaxalone dose-dependent manner and one rabbit developed hypoxemia in treatment INA0.9. No significant changes were observed in PR and MAP., Conclusions and Clinical Relevance: INA alfaxalone resulted in dose-dependent sedation and respiratory depression in Japanese White rabbits to values considered not clinically relevant. Further investigation of INA alfaxalone in combination with other drugs is warranted., (Copyright © 2023 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To evaluate arterial oxygenation during the first 4 postoperative hours in dogs administered different fractions of inspired oxygen (FiO 2 ) during general anesthesia with mechanical ventilation., Study Design: Prospective, randomized clinical trial., Animals: A total of 20 healthy female dogs, weighing >15 kg and body condition scores 3-7/9, admitted for ovariohysterectomy., Methods: Dogs were randomized to breathe an FiO 2 >0.9 or 0.4 during isoflurane anesthesia with intermittent positive pressure ventilation. The intraoperative PaO 2 :FiO 2 ratio was recorded during closure of the linea alba. Arterial blood was obtained 5, 60 and 240 minutes after extubation for measurement of PaO 2 and PaCO 2 (FiO 2  = 0.21). Demographic characteristics, duration of anesthesia, PaO 2 :FiO 2 ratio and anesthetic agents were compared between groups with Wilcoxon tests. The postoperative PaO 2 , PaCO 2 , rectal temperature, a visual sedation score and events of hypoxemia (PaO 2 < 80 mmHg) were compared between groups with mixed-effects models or generalized linear mixed models., Results: Groups were indistinguishable by demographic characteristics, duration of anesthesia, anesthetic agents administered and intraoperative PaO 2 :FiO 2 ratio (all p > 0.08). Postoperative PaO 2 , PaCO 2 , rectal temperature or sedation score were not different between groups (all p > 0.07). During the first 4 postoperative hours, hypoxemia occurred in three and seven dogs that breathed FiO 2 >0.9 or 0.4 during anesthesia, respectively (p = 0.04)., Conclusions and Clinical Relevance: The results identified no advantage to decreasing FiO 2 to 0.4 during anesthesia with mechanical ventilation with respect to postoperative oxygenation. Moreover, the incidence of hypoxemia in the first 4 hours after anesthesia was higher in these dogs than in dogs breathing FiO 2 >0.9., (Copyright © 2020 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: Evaluation of the reliability of pulse oximetry at four different attachment sites compared to haemoglobin oxygen saturation measured by a co-oximeter and calculated by a blood gas analyser in immobilized impala., Study Design: Randomized crossover study., Animals: A total of 16 female impala., Methods: Impala were immobilized with etorphine or thiafentanil alone, or etorphine in combination with a novel drug. Once immobilized, arterial blood samples were collected at 5 minute intervals for 30 minutes. Then oxygen was insufflated (5 L minute -1 ) intranasally at 40 minutes and additional samples were collected. A blood gas analyser was used to measure the arterial partial pressure of oxygen and calculate the oxygen haemoglobin saturation (cSaO 2 ); a co-oximeter was used to measure the oxygen haemoglobin saturation (SaO 2 ) in arterial blood. Pulse oximeter probes were attached: under the tail, to the pinna (ear) and buccal mucosa (cheek) and inside the rectum. Pulse oximeter readings [peripheral oxygen haemoglobin saturation (SpO 2 ) and pulse quality] were recorded at each site and compared with SaO 2 and cSaO 2 using Bland-Altman and accuracy of the area root mean squares (A rms ) methods to determine the efficacy. P value < 0.05 was considered significant., Results: Pulse quality was 'good' at each attachment site. SpO 2 measured under the tail was accurate and precise but only when SaO 2 values were above 90% (bias = 3, precision = 3, A rms  = 4). The ear, cheek and rectal probes failed to give accurate or precise readings (ear: bias = -4, precision = 14, A rms  = 15; cheek: bias = 12, precision = 11, A rms  = 16; and rectum: bias = 5, precision = 12, A rms  = 13)., Conclusions and Clinical Relevance: In order to obtain accurate and precise pulse oximetry readings in immobilized impala, probes must be placed under the tail and SaO 2 must be above 90%. Since SaO 2 values are usually low in immobilized impala, pulse oximeter readings should be interpreted with caution., (Copyright © 2020 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To compare immobilization efficacy of a nonpotent opioid drug combination, ketamine-butorphanol-medetomidine (KBM) to the preferred etorphine-azaperone (EA) combination in zebras., Study Design: Randomized crossover trial., Animals: A group of ten adult zebra (six females and four male)., Methods: KBM and EA were administered once to the zebras in random order by dart, 3 weeks apart. Once a zebra was recumbent and instrumented, physiological parameters were measured and recorded at 5-minute intervals until 20 minutes. Antagonist drugs were administered at 25 minutes. KBM was antagonised using atipamezole (7.5 mg mg -1 medetomidine dose) and naltrexone (2 mg mg -1 butorphanol dose). EA was antagonized using naltrexone (20 mg mg -1 etorphine dose). Induction and recovery (following antagonist administration) times were recorded. Physiological parameters, including invasive blood pressure and blood gas analysis, were compared between combinations using a general linear mixed model. Data are reported as mean ± standard deviation or median (interquartile range)., Results: The doses of KBM and EA administered were 3.30 ± 0.18, 0.40 ± 0.02 and 0.16 ± 0.01 mg kg -1 ; and 0.02 ± 0.001 and 0.20 ± 0.01 mg kg -1 , respectively. KBM and EA induction times were 420 (282-564) and 240 (204-294) seconds, respectively (p = 0.03). Zebras remained recumbent throughout the study procedures. Systolic blood pressure (226 ± 42 and 167 ± 42 mmHg) and oxygen partial pressure (64 ± 12 and 47 ± 13 mmHg) were higher for KBM compared to EA (p < 0.01). Recovery time, after administering antagonists, was 92 (34-1337) and 26 (22-32) seconds for KBM and EA, respectively (p = 0.03)., Conclusions and Clinical Relevance: Compared to EA, KBM also immobilized zebras effectively. Systemic hypertension and moderate hypoxaemia are clinical concerns of KBM and severe hypoxaemia is a concern of EA. This occurrence of hypoxaemia highlights the importance of oxygen administration during immobilization., (Copyright © 2019 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To evaluate clinical and physiological responses in moose to thiafentanil administration for immobilization., Study Design: Cross-sectional clinical study., Animals: Eleven (six males and five females) free-ranging adult moose (Alces alces)., Methods: Each moose was darted from a helicopter with 7.5 mg thiafentanil during March 2014 in northern Sweden. Physiological evaluation included vital signs and blood gases. Arterial blood was collected after induction and again after 10 minutes of intranasal oxygen administration and analyzed immediately with an i-STAT analyzer. A total of 10 mg naltrexone per milligram of thiafentanil was administered to all animals for reversal. Data were analyzed using descriptive statistics., Results: All moose were sufficiently immobilized with a single dart injection. Induction occurred within 3 minutes in 10 of 11 moose. One individual became recumbent while crossing a river and naltrexone was immediately administered. Animals maintained sternal recumbency with their head raised and vital signs were stable. Nine of 10 moose were hypoxemic before oxygen administration, with seven becoming markedly hypoxemic [partial pressure of arterial oxygen (PaO 2 ) between 40 and 59 mmHg (5.3-7.9 kPa)]. The PaO 2 increased significantly between samples, but six moose remained hypoxemic despite therapy. Hypercapnia was seen in all moose, with eight having marked hypercapnia [partial pressure of arterial carbon dioxide (PaCO 2 ) > 60 mmHg (>8.0 kPa)]. All moose were acidemic, with nine showing marked acidemia (pH < 7.20). The pH increased significantly with time and lactate decreased. Recoveries were rapid and uneventful, and all moose were living 6 months after capture., Conclusions: Thiafentanil provided rapid and sufficient immobilization of moose and its effects were rapidly reversed with naltrexone. As with other opioids, moose showed hypoxemia and varying degrees of respiratory and metabolic acidosis. Arterial oxygenation of moose improved following intranasal oxygen, but hypoxemia was not fully resolved despite therapy., Clinical Relevance: Thiafentanil (7.5 mg per adult) is effective for immobilization of free-ranging moose. Supplemental oxygen may be of benefit when using this regimen; however, further investigation is required to confirm these results., (Copyright © 2018 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 pulsed inhaled nitric oxide (INO) on arterial oxygenation in horses during abdominal surgery., Study Design: Prospective, randomized, clinical trial., Animals: Thirty horses that underwent abdominal surgery at the University Animal Hospital in Uppsala, Sweden., Methods: Anaesthesia was induced according to a standard protocol - romifidine, butorphanol, diazepam and ketamine and maintained with isoflurane in oxygen. Fifteen horses were administered pulsed INO and 15 served as controls. After baseline data collection, pulsed INO delivery commenced. Arterial and venous blood were collected and analysed. Cardiorespiratory parameters were measured, and oxygen content and F-shunt were calculated., Results: Arterial oxygen tension (PaO 2 ) and arterial oxygen saturation (SaO 2 ) increased from 10.9±5.7 kPa (82±43 mmHg) and 93±6% to 17.3±6.9 kPa (134±52 mmHg) (p<0.0001) and 98±2% (p<0.0001), respectively, in horses administered pulsed INO. In the control group, PaO 2 and SaO 2 decreased from 13.9±9.1 kPa (104±68 mmHg) and 93±7% to 12.1±8.6 kPa (91±65 mmHg) (p=0.0413) and 91±8% (p=0.0256), respectively. At the end of anaesthesia, the oxygen content was significantly higher in horses administered pulsed INO compared to controls (p=0.0126). The calculated F-shunt decreased from 39±10% to 27±6% (p<0.0001) in horses administered pulsed INO, and remained unchanged in controls, 40±12% to 44±12%. Blood lactate concentration decreased (-17±21%) in horses administered pulsed INO (p=0.0119), whereas no difference was measured in controls (2±31%)., Conclusions and Clinical Relevance: The present study showed that it is possible to effectively reduce the F-shunt and improve arterial oxygenation in horses during abdominal surgery by continuous delivery of pulsed INO., (Copyright © 2017 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To determine the anti-inflammatory efficacy of choline in vivo and in vitro and to investigate the anti-inflammatory mechanisms of choline., Study Design: Randomized, controlled studies., Animals: In vivo trials used 16 Romney sheep. In vitro experiments utilized RAW 264.7 mouse macrophage cells., Methods: Hypoxaemia induced in 16 sheep by intravenous (IV) injection of 50 μg kg -1 xylazine, an α-2 agonist, was measured in sheep at 0, 1 and 4 minutes using arterial blood gas analysis with and without 50 mg kg -1 IV choline chloride premedication. Cell culture studies used enzyme-linked immunosorbent assay to measure the release of tumour necrosis factor (TNF-α) from lipopolysaccharide (LPS) stimulated macrophages with and without choline chloride premedication. TNF-α release was compared to thalidomide suppressed and untreated cells., Results: Choline premedication in sheep mitigated a reduction in arterial partial pressure of oxygen (PaO 2 ) but did not prevent development of clinically significant hypoxaemia. Decrease in mean PaO 2 of choline treated sheep was 6.36 kPa (47.7 mmHg) compared to 9.81 kPa (73.6 mmHg) in control sheep. In vitro studies demonstrate that choline administered concurrent with LPS activation did not significantly suppress TNF-α expression but that treatment of cells with choline 10 minutes prior to LPS activation did significantly suppress TNF-α expression. Choline pretreated cells expressed 23.99 ± 4.52 ng mg -1 TNF-α while LPS only control cells expressed 33.83 ± 3.20 ng mg -1 ., Conclusions: Choline is able to prevent macrophage activation in vitro when administered prior to LPS activation and may reduce hypoxaemia in sheep developing pulmonary oedema after xylazine administration. This effect requires premedication with choline., Clinical Relevance: Pharmacological manipulation of autonomic inflammatory responses holds promise for the treatment of inflammation. However, the complex cellular mechanisms involved in this reflex means that an adequate therapy should approach multiple pathways and mechanisms of the inflammatory response., (Copyright © 2017 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To discuss how hypoxaemia might be harmful and why horses are particularly predisposed to developing it, to review the strategies that are used to manage hypoxaemia in anaesthetized horses, and to describe how successful these strategies are and the adverse effects associated with them., Databases Used: Google Scholar and PubMed, using the search terms horse, pony, exercise, anaesthesia, hypoxaemia, oxygen, mortality, morbidity and ventilation perfusion mismatch., Conclusions: Although there is no evidence that hypoxaemia is associated with increased morbidity and mortality in anaesthetized horses, most anaesthetists would agree that it is important to recognise and prevent or treat it. Favourable anatomical and physiological adaptations of a horse for exercise adversely affect gas exchange once the animal is recumbent. Hypoxaemia is recognised more frequently in horses than in other domestic species during general anaesthesia, although its incidence in healthy horses remains unreported. Management of hypoxaemia in anaesthetized horses is challenging and often unsuccessful. Positive pressure ventilation strategies to address alveolar atelectasis in humans have been modified for implementation in recumbent anaesthetized horses, but are often accompanied by unpredictable and unacceptable cardiopulmonary adverse effects, and some strategies are difficult or impossible to achieve in adult horses. Furthermore, anticipated beneficial effects of these techniques are inconsistent. Increasing the inspired fraction of oxygen during anaesthesia is often unsuccessful since much of the impairment in gas exchange is a direct result of shunt. Alternative approaches to the problem involve manipulation of pulmonary blood away from atelectatic regions of the lung to better ventilated areas. However, further work is essential, with particular focus on survival associated with general anaesthesia in horses, before any technique can be accepted into widespread clinical use., (Copyright © 2017 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To determine physiologic responses to apnea-induced severe hypoxemia in anesthetized horses., Study Design: Prospective experimental study., Animals: Six university-owned horses with a median (range) body weight of 500 (220-510) kg and aged 13.5 (0.8-24.0) years scheduled for euthanasia., Methods: Xylazine-midazolam-ketamine-anesthetized horses breathing room air spontaneously were instrumented with a facial artery catheter for pressure measurement and blood sampling, and were made apneic with atlanto-occipital intrathecal lidocaine (4 mg kg -1 ). Cardiopulmonary, biochemical and hematologic variables were recorded before (baseline) and every minute for 10 minutes after lidocaine injection., Results: PaO 2 values were: baseline, 55 mmHg (7.3 kPa); 1 minute, 28 mmHg (3.8 kPa); 2 minutes, 18 mmHg (2.4 kPa); 3 minutes, 15 mmHg (2.0 kPa), and 4-10 minutes, (8-11 mmHg (1.1-1.5 kPa). PaCO 2 values were: baseline, 50 mmHg (6.7 kPa); 1 minute, 61 mmHg (8.1 kPa), and 2-10 minutes, 64-66 mmHg (8.5-8.8 kPa). Base excess values at baseline, 1 minute and 2-10 minutes were 5.3 mmol L -1 , 6.5 mmol L -1 and 7.0-8.1 mmol L -1 , respectively. Pulse rates at baseline, 1 minute and 2-7 minutes were 36, 53 and 54-85 beats minute -1 , respectively. Asystole occurred at 8 minutes. Pulse pressures were 50 mmHg at baseline and 1 minute, and 39 mmHg, 31 mmHg, 22 mmHg, 17 mmHg and 1-9 mmHg at 2, 3, 4, 5 and 6-10 minutes, respectively. Lactate was 0.9 mmol L -1 at baseline, progressively increasing to 1.7-2.4 mmol L -1 at 7-10 minutes. Packed cell volume increased after 7 minutes of apnea. There were no other major changes., Conclusions and Clinical Relevance: Apnea immediately exacerbated hypoxemia and hypercapnia and rapidly caused hemodynamic instability. Apnea in hypoxemic anesthetized horses is associated with a serious risk for progress to cardiovascular collapse., (© 2016 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia.)

Objective: To determine the relationship between tissue oxygen saturation (StO2) and oxygen delivery (D˙O2) during hypoxemia and hyperoxemia., Study Design: Prospective, randomized study., Animals: Eight purpose-bred Beagle dogs., Methods: Dogs were anesthetized with isoflurane, ventilated to eucapnia, and instrumented for thermodilution cardiac output, invasive mean arterial pressure (MAP), sartorius muscle StO2 and airway gas monitoring. Dogs were administered rocuronium to facilitate mechanical ventilation and esmolol to minimize anesthetic effects on cardiac output. Instrumentation and baseline data collection were at 0.21 fractional inspired oxygen (FIO2). Dogs were evaluated at high (0.40 then 0.95) and low (0.15 then 0.10) FIO2 sequences in random order with a 60 minute rest period at FIO2 0.21 between sequences. Target FIO2 was achieved by manipulating nitrogen and oxygen flow rates. Data collected at each FIO2, after a 10 minute period of stabilization, included heart rate (HR), MAP, cardiac index (CI) and StO2. Arterial oxygen content (CaO2) and oxygen delivery index (D˙O2I) were calculated at each FIO2. Data analysis included Pearson's correlation analysis and mixed-model anova (p < 0.05)., Results: There were no significant differences in HR, MAP or CI across all FIO2 values. Significant decreases occurred in mean ± standard deviation StO2 (90 ± 4% to 69 ± 18%; p = 0.0001), D˙O2I (458 ± 70 to 281 ± 100 mL minute(-1) m(-2); p = 0.0008) and CaO2 (13.2 ± 1.53 to 8.4 ± 2.05 mL dL(-1); p = 0.0001) from FIO2 0.21 to 0.10, but not at remaining FIO2 values. The correlation between StO2 and D˙O2I across all FIO2 values was strong (r = 0.97; p = 0.0013) and linear., Conclusions and Clinical Relevance: In this model of hypoxemia and hyperoxemia, the strong correlation between StO2 and D˙O2I suggests that StO2 can be used to estimate D˙O2., (© 2015 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia.)

Objective: Hypoxemia is common during equine field anesthesia. Our hypothesis was that oxygen therapy from a portable oxygen concentrator would increase PaO2 during field anesthesia compared with the breathing of ambient air., Study Design: Prospective clinical study., Animals: Fifteen yearling (250 - 400 kg) horses during field castration., Methods: Horses were maintained in dorsal recumbency during anesthesia with an intravenous infusion of 2000 mg ketamine and 500 mg xylazine in 1 L of 5% guaifenesin. Arterial samples for blood gas analysis were collected immediately post-induction (PI), and at 15 and 30 minutes PI. The control group (n = 6) breathed ambient air. The treatment group (n = 9) were administered pulsed-flow oxygen (192 mL per bolus) by nasal insufflation during inspiration for 15 minutes PI, then breathed ambient air. The study was performed at 1300 m above sea level. One-way and two-way repeated-measures anova with post-hoc Bonferroni tests were used for within and between-group comparisons, respectively. Significance was set at p ≤ 0.05., Results: Mean ± SD PaO2 in controls at 0, 15 and 30 minutes PI were 46 ± 7 mmHg (6.1 ± 0.9 kPa), 42 ± 9 mmHg (5.6 ± 1.1 kPa), and 48 ± 7 mmHg (6.4 ± 0.1 kPa), respectively (p = 0.4). In treatment animals, oxygen administration significantly increased PaO2 at 15 minutes PI to 60 ± 13 mmHg (8.0 ± 1.7 kPa), compared with baseline values of 46 ± 8 mmHg (6.1 ± 1 kPa) (p = 0.007), and 30 minute PI values of 48 ± 7 mmHg (6.5 ± 0.9 kPa) (p = 0.003)., Conclusions: These data show that a pulsed-flow delivery of oxygen can increase PaO2 in dorsally recumbent horses during field anesthesia with ketamine-xylazine-guaifenesin., Clinical Relevance: The portable oxygen concentrator may help combat hypoxemia during field anesthesia in horses., (© 2015 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia.)

Objective: The study aimed to investigate the effect of varying pulse lengths of inhaled nitric oxide (iNO), and 2.5 hours of continuous pulse-delivered iNO on pulmonary gas exchange in anaesthetized horses., Study Design: Experimental study., Animals: Six Standardbred horses., Methods: Horses received acepromazine, detomidine, guaifenesin, thiopentone and isoflurane in oxygen, were positioned in dorsal recumbency and were breathing spontaneously. iNO was on average pulsed during the first 20, 30, 43 or 73% of the inspiration in 15 minute steps. The pulse length that corresponded to the highest (peak) partial pressure of arterial oxygen (PaO(2) ) in the individual horses was determined and delivered for a further 1.5 hours. Data measured or calculated included arterial and mixed venous partial pressures of O(2) and CO(2) , heart rate, respiratory rate, expired minute ventilation, pulmonary and systemic arterial mean pressures, cardiac output and venous admixture. Data (mean ± SD) was analysed using anova with p < 0.05 considered significant., Results: Although the pulse length of iNO that corresponded to peak PaO(2) varied between horses, administration of all pulse lengths of iNO increased PaO(2) compared to baseline. The shortest pulse lengths that resulted in the peak PaO(2) were 30 and 43% of the inspiration. Administration of iNO increased PaO(2) (12.6 ± 4.1 kPa [95 ± 31 mmHg] at baseline to a range of 23.0 ± 8.4 to 25.3 ± 9.0 kPa [173 to 190 mmHg]) and PaCO(2) (8.5 ± 1.2 kPa [64 ± 9 mmHg] to 9.8 ± 1.5 kPa [73 ± 11 mmHg]) and decreased venous admixture from 32 ± 6% to 25 ± 6%. The increase in PaO(2) and decrease in venous admixture was sustained for the entire 2.5 hours of iNO delivery., Conclusions: The improvement in arterial oxygenation during pulsed delivery of iNO was significant and sustained throughout 2.5 hours of anaesthesia., Clinical Relevance: Pulsed iNO potentially could be used clinically to counteract hypoxemia in anaesthetized horses., (© 2012 The Authors. Veterinary Anaesthesia and Analgesia. © 2012 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists.)

Objective: To evaluate the cardiorespiratory effects and plasma concentrations of medetomidine-midazolam-ketamine (MMK) combinations administered by intramuscular (IM) or subcutaneous (SC) injection in sable ferrets (Mustela putorius furo)., Study Design: Prospective randomized experimental study., Animals: Eighteen adult ferrets: weight median 1.19 (range 0.81-1.60) kg., Methods: Animals were allocated to one of three groups: group IM07 received 20 μg kg(-1) medetomidine, 0.5 mg kg(-1) midazolam and 7 mg kg(-1) ketamine IM; group IM10 20 μg kg(-1) medetomidine, 0.5 mg kg(-1) midazolam and 10 mg kg(-1) ketamine IM; and group SC10 20 μg kg(-1) medetomidine, 0.5 mg kg(-1) midazolam and 10 mg kg(-1) ketamine SC. Following instrumentation, cardiorespiratory parameters and plasma drug concentrations were measured every 5 minutes (T5-T30) for 30 minutes Ferrets were then euthanased. Data were analysed using anova for repeated measures. p<0.05 was considered significant., Results: Results are mean ± SD. Induction of anaesthesia (minutes) in IM07 and IM10 [2 (1)] was significantly faster than in SC10 [5 (2)]. All groups demonstrated the following: results given as groups IM07, IM10 and SC10 respectively. Mean arterial blood pressures (mmHg) were initially high [186 (13); 174 (33) and 174 (9) at T5] but decreased steadily. Pulse rates were initially 202 (20), 213 (17) and 207 (33) beats minute(-1) , decreasing with time. PaO(2) (mmHg) was low [54.0 (8), 47.7 (10) and 38.5 (1)] at T5, although in groups IM07 and IM10 it increased over time. Plasma concentrations of all drugs were highest at T5 (36, 794 and 8264 nmol L(-1) for medetomidine, midazolam and ketamine, respectively) and decreased thereafter: for both midazolam and ketamine, concentrations in IM07 and IM10 were higher than SC10., Conclusions and Clinical Relevance: MMK combinations containing either 7 or 10 mg kg(-1) ketamine and given IM are suitable combinations for anaesthetising ferrets, although the observed degree of hypoxaemia indicates that oxygen administration is vital., (© 2011 The Authors. Veterinary Anaesthesia and Analgesia. © 2011 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists.)

Objective: To quantify the respiratory and cardiovascular effects of intravenous or subcutaneous buprenorphine in conscious rabbits., Study Design: Prospective experimental trial., Animals: Eight healthy, young adult New Zealand white rabbits (four female)., Methods: Rabbits were instrumented with intraabdominal arterial and venous catheters and diaphragmatic electromyographic electrodes 2 weeks before experiments. Arterial blood pressure, arterial blood gases, heart rate and respiratory rate were monitored during experiments. Buprenorphine (0.06 mg) was administered either intravenously or subcutaneously to conscious rabbits. Respiratory and cardiovascular parameters were compared to baseline at 10 and 22 minutes after intravenous buprenorphine administration, and at 30, 60, and 90 minutes after subcutaneous buprenorphine administration., Results: Buprenorphine administration, at a dose of approximately 0.02 mg kg(-1), did not change blood pressure or heart rate. However, respiratory rate decreased from 252 +/- 26 to 39 +/- 26 breaths minute(-1) (mean +/- SD), and from 306 +/- 38 to 90 +/- 38 breaths minute(-1) following intravenous and subcutaneous administration of buprenorphine, respectively. Subsequent to intravenous and subcutaneous buprenorphine, arterial oxygen tension decreased from 88 +/- 4 to 72 +/- 4 mmHg (11.7 +/- 0.5 to 9.6 +/- 0.5 kPa) and from 87 +/- 3 to 77 +/- 3 mmHg (11.6 +/- 0.4 to 10.3 +/- 0.4 kPa), respectively. Buprenorphine, by either route of administration, increased arterial carbon dioxide tension from 36 to 41 mmHg (4.8-5.5 kPa) and increased the alveolar-arterial oxygen gradient from 15 to > or =20 mmHg (2 to > or =2.7 kPa)., Conclusions and Clinical Relevance: Buprenorphine administration decreased respiratory rate and produced mild hypoxemia in conscious rabbits. While these changes were well tolerated by healthy animals, caution should be exercised when administering buprenorphine to rabbits predisposed to respiratory depression.

Objective: Hypoxaemia accompanies dorsal recumbency in the horse and frequently complicates general anaesthesia. The physiology associated with this phenomenon is poorly understood. One possible cause of poor tolerance to dorsal recumbency is an absent or reduced response to hypoxic pulmonary vasoconstriction (HPV). This study compared the HPV response in isolated pulmonary artery vessels from equivalent regions of equine and bovine lung., Animals: Equine and bovine, in vitro study., Materials and Methods: Equine and bovine pulmonary arteries were removed from the lungs of euthanased horses and cattle. Measurements of isometric tension were made on isolated rings of pulmonary vessels at 37 degrees C in a Krebs' saline solution. Hypoxia was induced by bubbling with a nominally 0% O(2) gas mixture., Results: A significant HPV response was observed above a baseline tension induced by phenylephrine (PE; 0.3 microm) or 5-hydroxytryptamine (5-HT; 0.1 microm). The HPV response in equine pulmonary vessels was approximately 33% less than the response observed in equivalent bovine vessels (equine 196 +/- 20%versus bovine 290 +/- 32%; p < 0.05). Removal of the endothelium (by rubbing the luminal surface) significantly reduced but did not abolish the HPV response. Incubation with the nitric oxide (NO) synthase inhibitor N-nitro-l-arginine methyl ester (L-NAME; 100 microm), or COX-1/COX-2 inhibitor indomethacin (10 microm) markedly attenuated the HPV response in equine vessels., Conclusions: These results suggest that a significant HPV response exists in isolated equine pulmonary vessels; a component of this response requires a functional endothelium. Inhibition of cyclooxygenase and NO synthase attenuated the response, suggesting the involvement of a COX product and/or NO in mediating this effect either directly or indirectly. Alternatively, a non-COX related action of the nonsteroidal anti-inflammatory drug, indomethacin, may be involved.