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Background: Complications are a practical consideration for elective magnetic resonance imaging (MRI) studies performed under general anaesthesia but relatively little is known about their distribution and risk factors., Objectives: To describe the incidence of complications associated with MRI performed under general anaesthesia at a large referral facility and evaluate potential risk factors for these complications., Study Design: Retrospective case-control study., Methods: Patient information and details of the MRI procedure were collected retrospectively from medical records of all horses that had undergone an MRI under general anaesthesia at the University of Pennsylvania, New Bolton Center, between September 2005 and April 2012. Complications and categorical variables were examined by chi-squared or Fisher's exact tests as appropriate. A mixed-effects logistic regression approach was used to evaluate associations between explanatory variables and the outcome variable (complications or pyrexia). A univariable screen was used to select variables (likelihood ratio test p < 0.2) for inclusion in the multivariable analysis. Statistical significance was inferred when p ≤ 0.05., Results: Complications were noted after MRI in 51 (17.4%) of 293 events eligible for inclusion. Complications included pyrexia (n = 35), pneumonia (n = 14), colic (n = 10), facial/nerve paralysis (n = 6), diarrhoea (n = 4), and other (n = 3). The odds of developing a post-anaesthetic complication were significantly decreased in horses that received peri-anaesthetic antimicrobials (OR 0.29, 95% CI 0.14-0.63, p = 0.002). Increased age (OR 0.87, 95% CI, 0.76-0.99, p = 0.03) and peri-anaesthetic antimicrobial administration (OR 0.23, 95% CI 0.08-0.65, p = 0.005) were associated with a decreased odds of developing pyrexia., Main Limitations: Single centre retrospective design., Conclusions: Potential complications including pyrexia, pneumonia and colic should be recognised when pursuing MRI under general anaesthesia. The administration of peri-anaesthetic antimicrobials decreased the odds of a complication and warrants consideration, particularly in horses that might be classified as high risk., (© 2023 The Authors. Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.)

Background: Post-anaesthetic fever is a known complication of general anaesthesia, however, its incidence in horses undergoing elective magnetic resonance imaging (MRI) is unknown., Objective: To determine the incidence of post-anaesthetic fever in horses undergoing elective orthopaedic MRI and determine whether prophylactic antimicrobial therapy would be associated with a reduction in the incidence of post-anaesthetic fever. We hypothesised that prophylactic antimicrobials would be associated with a reduction in the incidence of post-anaesthetic fever., Study Design: Retrospective cross-sectional study., Methods: This retrospective study included 791 elective orthopaedic MRIs in systemically healthy horses between June 2006 and March 2020 that recovered from general anaesthesia and did not undergo surgery or intensive medical therapy soon after recovery. Potential factors associated with post-anaesthetic fever were evaluated using multivariable logistic regression. Case signalment, travel time, preanaesthetic haematology and fibrinogen abnormalities, use of prophylactic antimicrobials, peri-anaesthetic nonsteroidal anti-inflammatories, anaesthesia time and recovery time were all evaluated for association with post-anaesthetic fever., Results: Of 791 MRI cases, 44 (5.6%) developed a post-anaesthetic fever. Horses that received prophylactic antimicrobials were [odds ratio (OR) 3.8, 95% confidence interval (CI) 1.98-7.46; p ≤ 0.001] more likely to develop a post-anaesthetic fever than those that did not receive antimicrobials. Young horses (1-4 years of age) were (OR 2.8, 95% CI 1.26-6.17; p = 0.01) more likely to develop fever compared with adult horses (≥5 years of age)., Main Limitations: Limitations of this study pertain to retrospective analysis including nonrandomised case selection and incomplete data records., Conclusions: While fever may indicate infection, the majority of early post-anaesthetic fevers resolved before discharge from the hospital with no identified cause. The use of prophylactic antimicrobials to reduce the risk of post-anaesthetic fever for elective MRI is not supported by this study., (© 2023 EVJ Ltd.)

Background: Hypoxaemia is a common concern during equine general anaesthesia. The prevalence and predictors of hypoxaemia in horses undergoing elective anaesthesia in particular are poorly documented., Objectives: To determine and compare the prevalence of hypoxaemia (defined as PaO 2  ≤ 80 mm Hg, on the lowest value recorded) in horses undergoing anaesthesia for exploratory laparotomy and elective procedures, and to identify risk factors in both subpopulations., Study Design: Retrospective cohort study., Methods: Data were collected from 774 records of 708 horses undergoing general anaesthesia between April 2017 and August 2020. Potential predictors of hypoxaemia in horses undergoing anaesthesia for exploratory laparotomy or elective procedures were investigated separately by univariable penalised maximum likelihood logistic regression, followed by multivariable analysis. The lowest recorded PaO 2 was used as a single data point for the determination of hypoxaemia and arterial oxygen partial pressure to fractional inspired oxygen ratio analysis., Results: Hypoxaemia was recorded in 23% horses undergoing exploratory laparotomy compared with 3.8% horses undergoing elective anaesthesia (P < .001). Multivariable analysis showed that weight above 550 kg, large intestinal lesions, and peak inspiratory pressure (PIP) above 30 cmH 2 O were significantly associated with hypoxaemia in horses undergoing exploratory laparotomy. Soft tissue procedures and PIP >30 cmH 2 O were significantly associated with hypoxaemia during elective anaesthesia., Main Limitations: This study only considered the minimum PaO 2 recorded during anaesthesia. Duration and treatment of hypoxaemia were not considered., Conclusions: Based on the lowest PaO 2 value during anaesthesia, in our population, horses undergoing anaesthesia for exploratory laparotomy were over six times more likely to become hypoxaemic than horses undergoing elective procedures. Bodyweight, type of procedure, and high PIP were predictors of hypoxaemia., (© 2021 EVJ Ltd.)

Background: In equine anaesthesia, the recovery period is critical, accounting for most anaesthesia-related fatalities reported. Horses may recover unassisted or may be assisted, for example, using a head and tail rope recovery method., Objectives: To compare the impact of head and tail rope and unassisted recovery method on quality of recovery in horses undergoing colic surgery under general anaesthesia (GA)., Study Design: Single centre retrospective cross-sectional study, with prospective model performance analysis., Methods: Clinical data were obtained from horses undergoing emergency exploratory laparotomy over a 6-year period. Multivariable logistic regression analysis was used to identify the perioperative factors that affect quality of recovery. The final prediction model was assessed prospectively., Results: Records from 502 general anaesthetics (490 horses) were included. Multivariable logistic regression analysis showed that head and tail rope recovery (OR 2.2, 95% CI 1.4-3.3, P < .001) and sevoflurane administration (OR 1.6, 95% CI 1.2-2.3, P = .02) were associated with better quality of recovery when compared with unassisted recovery and isoflurane administration respectively. Increasing GA duration (OR 1.0, 95% CI 0.99-1.0, P = .03), increasing intraoperative dosages (in mg/kg) of thiopental (OR 0.85, 95% CI 0.75-0.98, P = .02) or ketamine (OR 0.67, 95% CI 0.46-0.99, P = .04) were linked to poor quality of recovery. No statistically significant difference was found between recovery groups in terms of mortality., Main Limitations: The clinical prediction model obtained is only applicable to the specific facilities, recovery methodology, referral population and anaesthetic protocols practiced at our institution., Conclusions: Head and tail rope recovery is significantly associated with better quality of recovery, compared with unassisted recovery, in horses undergoing emergency exploratory laparotomy. Sevoflurane administration, in detriment of isoflurane, was associated with better quality of recovery. Other risk factors, such as increasing GA duration, the use of higher intra-operative dosages of ketamine and/or thiopental, were associated with poor quality of recovery., (© 2021 EVJ Ltd.)

Background: Standing flank laparotomy can be an alternative to ventral midline laparotomy in horses with colic. Standing flank laparotomy avoids general anaesthesia, provides excellent access to some regions of the abdominopelvic cavity and costs less than ventral midline laparotomy., Objective: To report a series of cases of peritoneal and intestinal diseases other than SC diseases managed with standing flank laparotomy., Study Design: Retrospective case series., Methods: Records from equids with colic subjected to standing flank laparotomy at five hospitals (2003-2020) were reviewed. Descriptive data analysis was performed., Results: Thirty horses (sixteen survived to discharge), six ponies (four survived) and one donkey (euthanised) were subjected to standing flank laparotomy via the left flank (n = 31), right flank (n = 2) or both flanks (n = 4). The primary disease affected the peritoneum (0/5 survived), SI (5/9 survived) and caecum and/or LC (15/23 survived). Enterotomy was performed in four animals (all survived). Partial typhlectomy was performed in one horse (euthanised). Resection-anastomosis of the SI or LC was performed in three animals (one survived). Three animals had intraoperative complications that negatively affected the outcome: Two ponies had intolerance to abdominopelvic exploration; one mare had spontaneous exteriorisation of a long segment of the SI leading to a large tear in the mesentery. In seven cases, severe/extensive lesions found during standing flank laparotomy warranted immediate euthanasia. The survival rate was 54%. All owners were satisfied with the decision to perform standing flank laparotomy., Main Limitations: The retrospective design, lack of a control group, small number of cases and lack of standardised protocols between hospitals., Conclusions: Although ventral midline laparotomy is the standard of care for horses with colic, standing flank laparotomy is a viable approach for some types of colic. Systemic administration of analgesics may not produce sufficient peritoneal analgesia, which can lead to intolerance to abdominopelvic exploration during standing flank laparotomy in horses with colic and may negatively affect the outcome., (© 2021 EVJ Ltd.)

Background: The recovery phase after equine general anaesthesia (GA) is a time of considerable risk and therefore has been the subject of extensive research over the last 20 years. Various pharmacological interventions have been developed and studied with the objective of improving recovery quality and reducing anaesthetic-related mortality and morbidity. Nevertheless, some controversy remains regarding the influence of anaesthetic protocol choice on recovery quality from GA and its implications for recovery-related mortality and morbidity. A systematic review of the literature investigating the influence of anaesthetic protocol choice on recovery quality is currently lacking., Objectives: To perform a detailed evaluation of the equine veterinary literature investigating the effect of anaesthetic protocol choice on equine recovery quality utilising the GRADE framework., Study Design: A systematic evaluation of the equine veterinary literature was performed using the GRADE framework., Methods: A literature search was performed and studies were assessed for eligibility by both authors utilising PRISMA guidelines. Studies meeting inclusion criteria were evaluated by both authors, categorically summarised and the quality of evidence for each sub-topic was assessed using the GRADE framework., Results: A total of 124 studies were identified which directly assessed the impact of anaesthetic protocol choice on recovery quality after GA in horses. Evaluation of the available evidence indicated that certain partial intravenous anaesthesia (PIVA) agents, cessation of intravenous lidocaine 30 minutes prior to recovery and provision of adequate analgesia improves recovery quality., Main Limitations: The validity of the results of some studies may have been compromised by missing data and small sample sizes., Conclusions: There is evidence to indicate that certain PIVA agents, cessation of intravenous lidocaine 30 minutes prior to recovery and provision of adequate analgesia improves recovery quality., (© 2021 EVJ Ltd.)

Background: In equine anaesthesia, the recovery period is a time of considerable risk and has been the focus of prolific research. Risk factors, including age, type and duration of procedure or temperament may influence recovery quality. Unfortunately, the anaesthetist is unable to control for these factors, therefore various pharmacological interventions and recovery methods have been developed with the objective of improving recovery quality. However, no consensus among anaesthetists has been reached for many of these interventions and their implications for recovery-related mortality and morbidity., Objectives: To conduct a systematic review of the published evidence relating to risk factors and interventions in the recovery period which may influence recovery quality from equine general anaesthesia (GA)., Study Design: A systematic evaluation of the equine veterinary literature using the GRADE framework., Methods: A literature search was performed and studies were assessed for eligibility by both authors utilising PRISMA guidelines. Studies meeting inclusion criteria were evaluated by both authors, categorically summarised and the quality of evidence for each sub-topic was assessed using the GRADE framework., Results: Thirty-nine studies were identified which directly assessed the impact of risk factors and recovery interventions on recovery quality after equine GA. There was evidence to support that peri-anaesthetic risk factors such as anaesthesia duration, American Society of Anesthesiologists (ASA) physical status and surgical procedure influenced recovery quality. We also identified sufficient evidence that administration of α-2 adrenoreceptor agonists immediately prior to recovery, improves recovery quality., Main Limitations: The validity of the results of some studies may have been compromised by missing data and small sample sizes., Conclusions: Recovery quality is influenced by factors including: anaesthesia duration, ASA physical status and surgical procedure. Recovery quality can be improved by the administration of an α-2 adrenoreceptor agonist immediately prior to recovery., (© 2021 EVJ Ltd.)

Background: The bispectral index (BIS) has been evaluated as an indicator of central nervous system (CNS) depression in horses during general anaesthesia. The spectral entropy is another electroencephalographic device and it has not been evaluated yet in horses., Objectives: To determine if spectral entropy can assess anaesthetic depth during the different phases of anaesthesia, define the value of state and response entropy during surgical plane of anaesthesia and compare them with BIS., Study Design: Clinical, prospective, non-blinded observational study., Methods: Thirty-five horses ASA I or II undergoing scheduled surgical procedure were used. BIS and electromyography (EMG) with a BIS monitor and state and response entropy with a spectral entropy monitor were recorded at baseline after receiving 5 µg/kg bwt i.v. of medetomidine (sedation period), during the anaesthetic maintenance with isoflurane and medetomidine (intraoperative period) and once the trachea was extubated (recovery period). A general linear model for repeated measurements was employed. Correlation and agreement between methods were also assessed. Data are presented as mean ± SD., Results: State entropy, response entropy and EMG showed significant differences according to the anaesthetic period (P < .001). There was no significant difference in BIS between baseline and sedation period, but there were differences between the remainder of the periods (P < .001). BIS (53.4 ± 11.2) was significantly higher (P < .001) than response entropy (35.1 ± 7.1) and state entropy (27.4 ± 4.8) during surgical plane of anaesthesia. The ICC between BIS and response entropy was 0.56 and between BIS and state entropy was 0.43, without agreement between them., Main Limitations: The need to shave the skin in contact with the sensors and the difficulty in taking measurements during recovery period., Conclusions: Spectral entropy can be used to detect the different periods of an anaesthetic protocol, with the lowest values during the intraoperative period. A low correlation and no concordance were observed between both methods., (© 2020 EVJ Ltd.)

Background: Arterial hypoxaemia is common in anaesthetised horses, but little information exists regarding restoration of arterial oxygen tension (PaO 2 ) during recovery from anaesthesia, or if intra-operative management factors exert any longer-term effect., Objectives: To evaluate PaO 2 in horses recovering from general anaesthesia up to 1 h after resuming standing., Study Design: Prospective observational clinical cohort study., Methods: Systemically healthy adult horses undergoing inhalational general anaesthesia for elective surgical procedures were studied. Arterial blood samples were obtained anaerobically prior to pre-anaesthetic medication, at end of anaesthesia, immediately following positioning in the recovery box, then at 10-min intervals until standing. Additionally, samples were taken when horses achieved sternal recumbency, at standing (STAND) and 1 h after standing (STAND+1). Data were analysed using ANOVA and mixed-effects linear regression, with significance set at P<0.05., Results: Data from one hundred and two horses were analysed. Forty horses received controlled mandatory ventilation (CMV) throughout anaesthesia, 47 breathed spontaneously (SV) and 15 initially breathed spontaneously before CMV was imposed (S-CMV). Overall, PaO 2 , P(A-a)O 2 and PaCO 2 remained significantly lower than baseline at STAND+1 (P<0.01). CMV resulted in higher PaO 2 at the end of anaesthesia (P = 0.03) and during early recovery (P<0.01) than SV. Only in group S-CMV did PaO 2 , P(A-a)O 2 and PaCO 2 return to baseline values at STAND+1. Highest PaO 2 values associated with CMV were also associated with early recovery apnoea., Main Limitations: Non-standardised anaesthetic management, temporal and quantitative variation in oxygen delivery during early recovery and lack of control group where oxygen was electively withheld during recovery., Conclusions: Controlled mandatory ventilation results in better pulmonary function in horses as assessed by PaO 2 , P(A-a)O 2 and PaCO 2 , an effect enhanced by an initial period of SV and still evident 1 h after standing. High PaO 2 values may contribute to early recovery apnoea but this does not adversely affect outcome. The Summary is available in Portuguese - see Supporting Information., (© 2019 EVJ Ltd.)

Background: Although rare, 70% of equine fatalities during recovery from general anaesthesia (GA) are due to catastrophic fractures from poor recovery quality., Objective: To determine the effect of repeated GA recovery on GA recovery quality., Study Design: Experimental blinded trial., Methods: Eight adult horses underwent six GA events on sevoflurane for distal limb MRI examination over a 14-week period. Prior to GA recovery, xylazine was administered. Randomly ordered video-recorded GA recoveries were scored by three blinded board certified veterinary anaesthesiologists, unaware of patient identity or GA event number, for nine parameters using a 100 mm visual analogue scale (VAS) where 0 = worst and 100 = best. The number of attempts to stand, duration of lateral and sternal recumbency, total recovery duration and physiologic parameters during each GA event were recorded. Repeated measures ANOVA were used to detect differences. Agreement between observer VAS scores was determined via inter-rater reliability using an intraclass correlation., Results: With GA recovery experience, VAS scores for balance and coordination, knuckling, and overall quality of recovery were improved and the duration of lateral recumbency was increased. There were no differences in total recovery duration, number of attempts to stand, physiologic parameters other than heart rate during GA, or VAS scores for activity in lateral recumbency, move to sternal, move to stand, or strength., Main Limitations: Each GA event was relatively short and there was no surgical stimulation. The same results may not occur if there was surgical stimulation and pain during each GA event., Conclusion: Recovery from GA improves with multiple anaesthetic episodes in horses. Clinicians can advise clients that horses are likely to have better GA recovery on repeated GA recovery due to improved balance and coordination and reduced knuckling. Additionally, there is no change in anaesthetic morbidity with six repeated GA events over a 14-week period., (© 2017 EVJ Ltd.)

Reasons for Performing Study: Hypoventilation or apnoea, caused by the induction of general anaesthesia, may cause hypoxaemia. Preoxygenation may lengthen the period before this happens. No scientific studies are published on preoxygenation in equine anaesthesia., Objectives: To determine whether supplementation of oxygen at a flow rate of 15 l/min for 3 min via a nasal cannula before induction of general anaesthesia is effective in elevating the arterial partial pressure of oxygen (PaO 2 ) directly after induction., Study Design: Randomised, prospective clinical trial., Methods: A total of 18 American Society of Anesthesiologists physical status 1 or 2 adult horses undergoing elective anaesthesia were randomly allocated to one of 2 groups. The first group (control) received no oxygen supplementation before induction of general anaesthesia, whereas the second group (oxygen) did. All horses were anaesthetised with intravenous detomidine, butorphanol, ketamine, midazolam and isoflurane. Directly after induction (T = 0) and 30 min later (T = 30) an arterial blood sample was taken for blood gas analysis. At T = 30 an estimate of intrapulmonary shunt fraction (Qs/Qt) was calculated., Results: At T = 0 arterial partial pressure of oxygen (PaO 2 ) was significantly higher in the oxygen group compared with the control group (11.0 ± 2.6 kPa vs. 7.4 ± 1.6 kPa; mean ± s.d., P = 0.005) and at T = 30 differences were not statistically significant. Partial pressure of carbon dioxide (PaCO 2 ) and Qs/Qt did not differ between groups., Conclusions: Supplementing oxygen by a nasal cannula before induction of general anaesthesia in horses is feasible and does effectively elevate the PaO 2 immediately after induction. Future research is needed to determine whether supplementation of oxygen before induction of general anaesthesia in horses will affect outcomes., (© 2015 EVJ Ltd.)

Reasons for Performing Study: Buprenorphine, a μ-agonist opioid, has recently been licensed for equine use, but butorphanol, a κ-agonist opioid, is more commonly used in horses. The effect of the 2 opioids has not previously been compared in a large clinical study., Objectives: To compare post operative analgesia and physiological variables in horses undergoing elective surgery following premedication with either buprenorphine or butorphanol in a conventional clinical setting., Study Design: Multicentre, prospective, randomised, blinded clinical investigation., Methods: Eighty-nine healthy horses admitted for elective surgery to one of 6 UK equine veterinary clinics were premedicated with acepromazine, a nonsteroidal anti-inflammatory drug, and romifidine followed by intravenous (i.v.) buprenorphine or butorphanol. Anaesthesia was induced with diazepam/ketamine and maintained with isoflurane in oxygen. A range of surgical procedures were performed and supplementary anaesthetic agents given as required. Physiological variables were monitored during anaesthesia and pain, ataxia, sedation and vital function were assessed post operatively. Data were analysed using t-tests, ANOVA, Mann-Whitney U-test and Chi-squared test as appropriate and P<0.05 was regarded as significant, except for multiple comparisons, when P<0.01 was used., Results: Surgery was carried out successfully in all cases and no mortality or serious morbidity occurred. Physiological variables remained within normal limits and all horses recovered successfully, most standing within 1 h of ceasing anaesthesia. There were no significant differences between groups in any variable except post operative pain when scores (simple descriptive scale) between 3 and 6 h were significantly lower after buprenorphine than after butorphanol., Conclusions: Horses experienced less post operative pain after buprenorphine than after butorphanol premedication. Compared with butorphanol, buprenorphine did not cause any different effects on vital function., (© 2015 The Authors. Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of British Equine Veterinary Association.)

Reasons for Performing Study: Accurate blood pressure measurement is essential for effective clinical assessment and appropriate interventions in anaesthetised horses. Information on the accuracy of oscillometry for blood pressure measurement on the appendages of mature horses is limited., Objectives: To assess equivalence between invasive and oscillometric blood pressures at different anatomic locations in horses., Study Design: Prospective experimental study using 6 healthy mature horses., Methods: Blood pressure was measured invasively in the right transverse facial artery and noninvasively by oscillometry in nondependent limbs and tail of laterally recumbent sevoflurane- or desflurane-anaesthetised horses. Cuff widths of 5-12 cm were tested on the tail, metatarsus, metacarpus and distal radius/ulna. Equivalence between mean arterial pressure (MAP) oscillometric and MAP invasive was assessed using a linear mixed effects model with a significance level of P≤0.05., Results: Twenty paired measurements were obtained for each cuff size in each of the locations, totalling 340 measurements. There was only one location (tail) and one cuff width (6 cm; cuff width-to-tail circumference ratio of 0.25) that resulted in equivalence between MAP measured with the oscillometric and the invasive methods (P = 0.8). All other locations (metacarpus, radius/ulna, metatarsus) and cuff widths were not equivalent (P≤0.01)., Conclusions: A cuff width-to-tail circumference ratio of 0.25 is recommended for accurate oscillometric blood pressure measurement in mature, laterally recumbent anaesthetised normotensive horses. Studies with variable haemodynamics are warranted. Oscillometric measurements at other extremities and/or with other cuff sizes cannot be recommended for clinical use., (© 2015 EVJ Ltd.)

Reasons for Performing Study: Antimicrobial i.v. regional limb perfusion (IV-RLP) is clinically performed on anaesthetised or sedated horses with or without regional anaesthesia. To date, no scientific data are available on the clinical and pharmacokinetic effects of these anaesthetic protocols on antimicrobial IV-RLP, which is believed to result in better tourniquet efficiency due to decreased movement., Objective: To determine the effects of regional or general anaesthesia on the clinical and synovial pharmacokinetic parameters of amikacin administered by IV-RLP to horses., Study Design: Experimental crossover study., Methods: Eight healthy horses received 4 treatments of amikacin IV-RLP in a randomised, blinded, crossover design: standing sedation without regional anaesthesia (CNT); standing sedation with i.v. regional anaesthesia; standing sedation with perineural regional anaesthesia (PNA); or general anaesthesia. Synovial fluid amikacin concentrations were measured over 24 h and regional pharmacokinetic parameters calculated. Heart and respiratory rates, visual analogue scale of discomfort, number of times the limb was lifted and number of additional sedations administered were recorded. Analysis of variance crossover analysis was applied with significance level at P < 0.05., Results: Amikacin concentrations and regional pharmacokinetic parameters did not differ significantly among treatments. Visual analogue scores (mean ± s.d.) were significantly lower with PNA (19 ± 15) vs. i.v. regional anaesthesia (69 ± 36) or CNT (81 ± 13; P < 0.001). Significantly less lifting of the limb (mean ± s.d.) occurred with PNA (20 ± 20) vs. CNT (54 ± 22; P < 0.04)., Conclusions: Perineural regional anaesthesia before IV-RLP was most effective in providing comfort to standing, sedated horses without significantly affecting the regional pharmacokinetic parameters of amikacin. High variability of synovial amikacin concentrations was present. The use of general anaesthesia for IV-RLP is not justified based on this study., (© 2013 EVJ Ltd.)

Reasons for Performing Study: A significant effect of gender, experience and background, i.e. an evaluator's relationship with horses as equine anaesthetists, orthopaedic surgeons, practitioners or owners, on perceptions of recovery quality after anaesthesia would reduce the validity of recovery quality scoring systems., Objectives: To determine the effects of evaluator background, experience and gender on their perceptions of recovery quality; and questionnaire response rate as a function of background., Study Design: Cross-sectional survey., Methods: A total of 440 potential evaluators were invited to evaluate the video-recorded recoveries of 24 horses using a visual analogue scale (VAS) in which 0 = worst, 100 = best possible recovery. A mean score was generated for each of the 1-24 recoveries within each background group. These were compared using Spearman's rank correlation. The effect of gender and experience on VAS scores were analysed using an ordinal logistic regression after scores were categorised into 'intermediate, 'worst' and 'best' recovery categories based on median, 25th and 75th percentile VAS scores, respectively., Results: The overall response rate was 35%. The greatest was from the anaesthetists (78%) followed by surgeons (43%). The response rate among owners and practitioners was 26%. Correlation among VAS scores across all background groups was high (Spearman rank > 0.90; P < 0.001). Among the combined veterinarians, there was no significant gender (P = 0.551) or experience (P = 0.103) effect. Among horse owners, the effect of experience was not significant (P = 0.116) although gender was (P = 0.027). Male horse owners awarded significantly greater scores than females., Conclusions: When VAS are used to grade recovery quality, neither the background nor the gender of veterinary evaluators affects quality perception. Male owners awarded greater scores than female owners, implying that they are less critical of recovery quality and a gender effect among horse owners must be considered when VAS are used to score recovery quality., (© 2013 EVJ Ltd.)

Reasons for Performing Study: Alterations in cerebral haemodynamics may contribute to perianaesthetic complications in horses. Near-infrared spectroscopy (NIRS) is frequently used intraoperatively in man to provide information regarding cerebral perfusion., Objectives: To determine whether NIRS can identify trends in regional cerebral oxygen saturation (rSO2) in horses and whether there is a correlation between rSO2 and venous oxygen tensions., Methods: A cerebral oximeter sensor recorded rSO2 from the dorsal sagittal sinus of 6 healthy horses. Values for rSO2, arterial and venous oxygen and carbon dioxide tensions (PaO2, PvO2, PaCO2 and PvCO2 respectively), along with arteriovenous oxygen saturations (SavO2) were recorded in unsedated (recording period [RP] 1), sedated (RP2) and anaesthetised horses (RP3-5) and during recovery (RP6-8). During anaesthesia, horses were ventilated to achieve states of normo- (RP3), hyper- (RP4) and hypocapnoea (RP5). Data were evaluated descriptively and analysed using linear mixed-effects models and Pearson's correlation coefficient., Results: Overall mean ± s.d. values for rSO2, PaO2, PvO2, PaCO2, SavO2 and mean arterial pressure varied significantly by RP (P<0.001). Significant decreases in rSO2 were identified between RP1 and the post anaesthetic periods (P<0.001). No significant differences in rSO2 values were identified between RP1 and the intra-anaesthesia periods or between RP3, RP4 and RP5. Significant correlations were identified between rSO2 and PaO2 (r = 0.448, P<0.001), rSO2 and PvO2 (r = 0.512, P<0.001) and rSO2 and SavO2 (r = 0.469, P<0.001)., Conclusions: This is the first study to identify trends in rSO2 in horses using NIRS. A positive correlation was identified between rSO2 and PvO2, suggesting that alterations in cerebral oxygenation may be reflected in PvO2 ., Potential Relevance: Near-infrared spectroscopy may be used to monitor trends in rSO2 during equine anaesthesia. Decreasing rSO2 values may act as an early warning signal, alerting clinicians to potential cerebral desaturation events and indicating a need for intervention., (© 2012 EVJ Ltd.)

Reasons for Performing Study: Hypoxaemia is a common problem during equine anaesthesia. Continuous positive airway pressure (CPAP) is a ventilation mode routinely employed in man to overcome hypoxaemia but has not been objectively assessed in horses., Objectives: To test the effects of CPAP on oxygenation and its indices in anaesthetised horses in a clinical setting., Methods: Twenty-four healthy horses requiring anaesthesia in dorsal recumbency were anaesthetised using a standard protocol. Following orotracheal intubation and connection to an anaesthetic machine capable of applying CPAP, horses were randomly allocated to ventilate at physiological airway pressure measured at the airway opening (Group PAP) or to receive CPAP of 8 cmH2O (Group CPAP). Arterial blood gas analysis was performed as soon as arterial cannulation was achieved and 30, 60 and 90 min after induction. If PaCO2 increased above 9.31 kPa controlled ventilation was initiated. Groups were compared using a general linear model., Results: Horses receiving CPAP had significantly higher PaO2 and calculated oxygen indices than horses receiving PAP. No significant differences in ventilation indices were observed between the 2 groups. Eight horses receiving PAP and 5 receiving CPAP required controlled ventilation. No differences in dobutamine requirements or mean arterial pressures were recorded., Conclusions: Continuous positive airway pressure of 8 cmH2O improved oxygenation indices in dorsally recumbent horses without significantly influencing ventilation., Potential Relevance: Continuous positive airway pressure reduces the incidence of hypoxaemia in anaesthetised horses. Further research is warranted to elucidate the effects of CPAP on the cardiovascular system., (© 2012 EVJ Ltd.)

Reason for Performing Study: The recovery quality scoring systems (RQSSs) in current use have not been critically reviewed for reliability., Objective: To examine reliability (reproducibility) of 4 RQSSs when applied to a ranked series., Methods: A DVD incorporating the recordings of 9 horses recovering from general anaesthesia was evaluated by final year students over 5 days. On Day 1, each evaluator ranked recoveries from 1-9 (1 = best). Over the following 4 days, each evaluator scored the same recoveries using 4 different RQSSs (3 of them in common usage and previously published) applied in random order. The scores from each RQSS were ranked and plotted against the Day 1 ranking of each evaluator to establish the extent of agreement using generalisability theory. The same 9 recoveries were also ranked by 12 experienced equine anaesthetists and the Spearman Rank Correlation coefficient calculated to determine the agreement between experienced and inexperienced evaluators., Results: The recoveries were evaluated by 117 students. All 4 RQSSs were equally reliable with low (<4%) interobserver variability. The main (80%) source of total variation arose from differences between horses. The overall ranking within each RQSS was strongly correlated with Day 1 ranking. There was strong correlation (r = 0.983) between the students' ranking and that established by experienced anaesthetists. Interobserver reliability was similar with all 4 RQSSs., Conclusion: All 4 RQSSs studied were similarly reliable., Potential Relevance: The selection of a universally acceptable RQSS from amongst the 4 examined can be based on criteria other than reliability, e.g. ease of use. This will facilitate wider scale multi-centre studies in recovery quality after anaesthesia in horses.

Reasons for Performing Study: The effects of lidocaine combined with medetomidine or lidocaine alone on cardiovascular function during anaesthesia and their effects on recovery have not been thoroughly investigated in isoflurane-anaesthetised horses., Objectives: To determine the effects of an intraoperative i.v. constant rate infusion of lidocaine combined with medetomidine (Group 1) or lidocaine (Group 2) alone on cardiovascular function and on the quality of recovery in 12 isoflurane-anaesthetised horses undergoing arthroscopy., Hypothesis: The combination would depress cardiovascular function but improve the quality of recovery when compared to lidocaine alone in isoflurane-anaesthetised horses., Methods: Lidocaine (2 mg/kg bwt i.v. bolus followed by 50 microg/kg bwt/min i.v.) or lidocaine (same dose) and medetomidine (5 microg/kg bwt/h i.v.) was started 30 min after induction of anaesthesia. Lidocaine administration was discontinued 30 min before the end of surgery in both groups, whereas medetomidine administration was continued until the end of surgery. Cardiovascular function and quality of recovery were assessed., Results: Horses in Group 1 had longer recoveries, which were of better quality due to better strength and overall attitude during the recovery phase than those in Group 2. Arterial blood pressure was significantly higher in Group 1 than in Group 2 and this effect was associated with medetomidine. No significant differences in cardiac output, arterial blood gases, electrolytes and acid-base status were detected between the 2 groups., Conclusions and Potential Relevance: The combination of an intraoperative constant rate infusion of lidocaine and medetomidine did not adversely affect cardiovascular function in isoflurane-anaesthetised horses and improved the quality of recovery when compared to an intraoperative infusion of lidocaine alone.

Reason for Performing Study: It is unknown whether administration of gas-mixtures high in inspired fraction of oxygen (FiO2) under general anaesthesia may increase formation of pulmonary atelectasis and impair gas exchange., Objective: To evaluate the effects of different FiO2 on pulmonary gas exchange in isoflurane-anaesthetised horses breathing a helium/oxygen (He/O2) mixture., Methods: Thirty healthy mature horses were sedated with i.v. acepromazine (0.02 mg/kg bwt), detomidine (0.002 mg/kg bwt) and xylazine (02-0.4 mg/kg bwt). General anaesthesia was induced with i.v. 5% guaifenesin to effect, diazepam (0.1 mg/kg bwt) and ketamine (2 mg/kg bwt), and maintained with isoflurane. Fifteen horses (Group HX) were ventilated mechanically with gas mixtures of successively increasing FiO2 (0.25-030, 0.50-0.55, > 0.90), obtained by blending 02 with Heliox (70% He/30% O2). The other 15 horses (Group O) were ventilated immediately with 100% O2 (FiO2 > 0.90). After 20 min of ventilation at the different FiO2 levels in Group HX and after 60 min in Group O, PaO2 and PaCO2 were measured and the alveolar to arterial PO2 gradient (P(A-a)O2) was calculated. Data analysis included robust categorical regression with clustering on horse (P < 0.05)., Results: Inhalation of a He/O2 mixture with FiO2 as low as 0.25-030 ensured adequate arterial oxygenation and was associated with a smaller P(A-a)O2 gradient than inhalation of pure O2 (P < 0.05). In Group HX, PaO2 increased with each rise in FiO2 and so did P(A-a)O2 (P < 0.05). The PaO2 was significantly lower and the P(A-a)O2 higher in Group O compared to Group HX at a FiOz >0.90 (P < 0.05)., Conclusions and Potential Relevance: Administration of a He/O2 gas mixture low in FiO2 can better preserve lung function than ventilation with pure oxygen. A step-wise increase of FiO2 using a He/O2 gas mixture might offer advantages with respect to pulmonary gas exchange over an immediate exposure to 100% 2O2.

Reasons for Performing Study: Studies have demonstrated the clinical usefulness of propofol for anaesthesia in horses but the use of a concentrated solution requires further investigation., Objectives: To determine the anaesthetic and cardiorespiratory responses to a bolus injection of 10% propofol solution in mature horses., Methods: Three randomised crossover experimental trials were completed. Trial 1: 6 horses were selected randomly to receive 10% propofol (2, 4 or 8 mg/kg bwt i.v.). Trial 2: 6 horses received 1.1 mg/kg bwt i.v. xylazine before being assigned at random to receive one of 5 different doses (1-5 mg/kg bwt) of 10% propofol. Trial 3: 6 horses were sedated with xylazine (0.5 mg/kg bwt, i.v.) and assigned randomly to receive 10% propofol (3, 4 or 5 mg/kg bwt, i.v.); anaesthesia was maintained for 60 min using an infusion of 1% propofol (0.2-0.4 mg/kg bwt/min). Cardiorespiratory data, the quality of anaesthesia, and times for induction, maintenance and recovery from anaesthesia and the number of attempts to stand were recorded., Results: Trial 1 was terminated after 2 horses had received each dose of 10% propofol. The quality of induction, anaesthesia and recovery from anaesthesia was judged to be unsatisfactory. Trial 2: 3 horses administered 1 mg/kg bwt and one administered 2 mg/kg bwt were not considered to be anaesthetised. Horses administered 3-5 mg/kg bwt i.v. propofol were anaesthetised for periods ranging from approximately 10-25 min. The PaO2 was significantly decreased in horses administered 3-5 mg/kg bwt i.v. propofol. Trial 3: The quality of induction and recovery from anaesthesia were judged to be acceptable in all horses. Heart rate and rhythm, and arterial blood pressure were unchanged or decreased slightly during propofol infusion period., Conclusions: Anaesthesia can be induced with a 10% propofol solution and maintained with a 1% propofol solution in horses administered xylazine as preanaesthetic medication. Hypoventilation and hypoxaemia may occur following administration to mature horses., Potential Relevance: Adequate preanaesthetic sedation and oxygen supplementation are required in horses anaesthetised with propofol.

Reasons for Performing Study: Lidocaine single boluses and/or constant rate infusions are commonly administered intraoperatively during inhalant anaesthesia to lower inhalant concentrations, promote or maintain gastrointestinal motility, and potentially supplement analgesia. The benefits of using lidocaine with injectable anaesthesia for field surgeries has not been fully explored to determine advantages and disadvantages of lidocaine as an anaesthetic and analgesic adjunct in these conditions and impact on recovery quality., Objectives: To evaluate the use of systemic lidocaine with a standard field injectable anaesthetic protocol related to the need for additional drug administration as well as overall recovery score and quality., Hypothesis: The administration of systemic lidocaine with xylazine-diazepam/ketamine anaesthesia for castration in the field decreases the need for additional injectable doses required for maintenance, but prolong and potentially impact the overall recovery score and quality in horses., Methods: Thirty client-owned horses underwent standard injectable anaesthesia for field castration. Fifteen horses received lidocaine 3 mg/kg bwt, i.v. as a single bolus, and 15 received saline equal volume. The horses were monitored for the need for additional injectable anaesthetics and scored for overall recovery and quality by a blinded anaesthetist., Results: There were no statistically significant differences in the overall recovery score and quality, or need for additional injectable anaesthetic between horses receiving lidocaine and those receiving saline. There was a significantly longer time for the horses to stand after induction in the lidocaine group (mean 30.7 min) vs. saline group (mean 22.5 min) (P<0.04)., Conclusions: Lidocaine, 3 mg/kg bwt i.v., does not adversely affect recovery using injectable field regimes, but the overall recovery period was longer. Lidocaine does not appear to reduce the need for additional injectable administration during surgery., Potential Relevance: Further research is warranted to define the benefit of systemic lidocaine with field anaesthesia in horses by exploring the ideal dose and plasma level of lidocaine with injectable anaesthesia.

Reasons for Performing Study: In order to evaluate its potential as an adjunct to inhalant anaesthesia in horses, the pharmacokinetics of fentanyl must first be determined., Objectives: To describe the pharmacokinetics of fentanyl and its metabolite, N-[1-(2-phenethyl-4-piperidinyl)maloanilinic acid (PMA), after i.v. administration of a single dose to horses that were awake in Treatment 1 and anaesthetised with isoflurane in Treatment 2., Methods: A balanced crossover design was used (n = 4/group). During Treatment 1, horses received a single dose of fentanyl (4 microg/kg bwt, i.v.) and during Treatment 2, they were anaesthetised with isoflurane and maintained at 1.2 x minimum alveolar anaesthetic concentration. After a 30 min equilibration period, a single dose of fentanyl (4 microg/kg bwt, i.v.) was administered to each horse. Plasma fentanyl and PMA concentrations were measured at various time points using liquid chromatography-mass spectrometry., Results: Anaesthesia with isoflurane significantly decreased mean fentanyl clearance (P < 0.05). The fentanyl elimination half-life, in awake and anaesthetised horses, was 1 h and volume of distribution at steady state was 0.37 and 0.26 l/kg bwt, respectively. Anaesthesia with isoflurane also significantly decreased PMA apparent clearance and volume of distribution. The elimination half-life of PMA was 2 and 1.5 h in awake and anaesthetised horses, respectively., Conclusions and Potential Relevance: Pharmacokinetics of fentanyl and PMA in horses were substantially altered in horses anaesthetised with isoflurane. These pharmacokinetic parameters provide information necessary for determination of suitable fentanyl loading and infusion doses in awake and isoflurane-anaesthetised horses.

Reasons for Performing Study: Patient positioning and long anaesthetic duration required for magnetic resonance imaging (MRI) may result in a higher frequency of post anaesthetic myopathy/neuropathy syndrome (PAMNS) as compared to horses undergoing anaesthesia for surgery., Hypothesis: Equine anaesthesia for MRI is associated with a higher frequency of PAMNS than anaesthesia for nonemergency, nonabdominal surgery., Methods: Anaesthetic and medical records of horses (n = 633) undergoing MRI or surgery between January 2001 and January 2005 (inclusive), were reviewed. Information obtained included patient details (breed, sex, age, bodyweight), area of body scanned or involved in surgery, body position, anaesthetic and inotropic agents administered, anaesthetic duration, adverse events during anaesthesia and outcome at 7 days. Data were examined by cross tabulation and Chi-square or Fisher's exact test of association. The influence of individual variables was examined by univariant and multivariant analysis models., Results: There were no statistically significant differences between the 2 groups in parameters examined, except that horses in the MRI group were heavier (P<0.0001) and anaesthetic duration longer in the surgery group (P<0.004). Eight horses (2.3%, 95% Confidence interval [CI]: 1.1-4.2) in the MRI group had clinical signs of PAMNS in the post anaesthetic period, whereas only 2 horses (0.98%, 95% CI: 0.2-2.8) in the surgery group were affected. This was not statistically significantly different (odds ratio = 2.7, 95% CI: 0.8-13, P = 0.3). Two horses undergoing MRI were subjected to euthanasia due to the severity of PAMNS., Conclusions: There was no difference in the occurrence of PAMNS between the 2 groups., Potential Relevance: The risk of performing general anaesthesia for diagnostic procedures such as MRI may not be greater than that for a surgical procedure. However, the benefits should be carefully weighed against the risks involved.

Reason for Performing Study: Post anaesthetic colic is a recognised risk of general anaesthesia (GA), but causes are poorly understood., Objectives: To identify risk factors for development of colic following GA for magnetic resonance imaging (MRI) or nonabdominal surgery and to test whether the use of perianaesthetic morphine was associated with an increased risk of post anaesthetic colic., Methods: A total of 553 anaesthetic and clinical records of 500 horses anaesthetised at the Animal Health Trust were analysed, 342 (62%) involved MRI and 211 (38%) nonabdominal, predominantly orthopaedic surgery. Multivariable logistic regression analysis was used to examine the association between post anaesthetic colic and explanatory variables, including use of perianaesthetic morphine., Results: Twenty horses (3.6%) developed colic within 7 days of GA. A significantly larger (P = 0.001) proportion of the surgical cases developed post anaesthetic colic (7.1%) compared with MRI cases (1.5%). Having controlled for the effect of MRI/surgeon, there was evidence for a significantly increased risk of colic associated with maintenance of anaesthesia with isoflurane and administration of benzyl penicillin and/or ceftiofur. A reduction in risk of colic was associated with premedication with romifidine, longer duration of anaesthesia and sedation within 2 days of GA. Perianaesthetic morphine administration was not associated with increased risk., Conclusions: This study identified apparently novel risk factors for colic in horses following GA. Use of morphine was not found, after controlling for other MRI and surgery related risk factors, to be associated with an increased risk. The low prevalence of colic after GA and resulting low study power mean that further larger, multicentre collaborative studies are warranted to corroborate findings in this study., Potential Relevance: Better knowledge of risk factors should lead to achievable measures to reduce frequency of occurrence.

Reasons for Performing Study: Lidocaine constant rate infusions (CRIs) are common as an intraoperative adjunct to general anaesthesia, but their influence on quality of recovery has not been thoroughly determined., Objectives: To determine the effects of an intraoperative i.v. CRI of lidocaine on the quality of recovery from isoflurane or sevoflurane anaesthesia in horses undergoing various surgical procedures, using a modified recovery score system., Hypothesis: The administration of intraoperative lidocaine CRI decreases the quality of recovery in horses., Methods: Lidocaine (2 mg/kg bwt bolus followed by 50 microg/kg bwt/min) or saline was administered for the duration of surgery or until 30 mins before the end of surgery under isoflurane (n = 27) and sevoflurane (n = 27)., Results: Horses receiving lidocaine until the end of surgery had a significantly higher degree of ataxia and a tendency towards significance for a lower quality of recovery. There was no correlation between lidocaine plasma concentrations at recovery and the quality of recovery., Conclusions: Intraoperative CRI of lidocaine affects the degree of ataxia and may decrease the quality of recovery., Potential Relevance: Discontinuing lidocaine CRI 30 mins before the end of surgery is recommended to reduce ataxia during the recovery period.

Reasons for Performing Study: Extraction of cheek teeth (CT) by the conventional repulsion technique requires general anaesthesia and carries a high rate of post operative complications. Consequently, an alternative method of extraction, i.e. orally in standing horses, was evaluated., Hypothesis: The need for and risks of general anaesthesia could be avoided and post extraction sequelae reduced by performing extractions orally in standing horses., Methods: One hundred mainly younger horses (median age 8, range 2-18 years) with firmly attached CT that required extraction because of apical infections, displacements, diastemata, idiopathic fractures and the presence of supernumerary CT had the affected teeth (n = 111) extracted orally under standing sedation. Follow-up information was obtained for all cases, a median of 16 months later., Results: Oral extraction was successful in 89 horses and unsuccessful in 11 due to damage to the CT clinical crown (n = 9) during extraction, for behavioural reasons (n = 1) and because the apex of a partly extracted CT fell back into the alveolus following sectioning (n = 1). Predispositions to extraction-related CT fractures were present in 5 of the 9 cases, i.e. advanced dental caries (n = 2) and pre-existing 'idiopathic' fractures (n = 3). The iatrogenically fractured CT were later repulsed under standing sedation (n = 3) and under general anaesthesia (n = 6). Eighty-one of the remaining 89 horses had successful oral CT extraction with no or minimal intra- or post operative complications occurring. Post operative complications in the other 8 cases included post extraction alveolar sequestration (n = 3), alveolar sequestration and localised osteomyelitis (n = 1), localised osteomyelitis (n = 1), incorporation of alveolar packing material into alveolar granulation tissue (n = 1), and nasal discharge due to continued intranasal presence of purulent food material (n = 1) and to ongoing sinusitis (n = 1). The above sequelae were treated successfully in all cases, with general anaesthesia required in just one case. Following oral extraction, significantly (P<0.001) fewer post operative problems developed in 54 horses with apically infected CT in comparison with 71 previous cases that had repulsion of apically infected CT at our clinic., Conclusions and Potential Relevance: Oral extraction of cheek teeth is a successful technique in the majority of younger horses with firmly attached CT and greatly reduces the post operative sequelae, compared with CT repulsion. Additionally, the costs and risks of general anaesthesia are avoided. Further experience and refinement in the described protocol could potentially increase the success of this procedure and also reduce the incidence of post operative sequelae.

Reasons for Performing Study: Recovery from inhalant anaesthesia in the horse is a critical and difficult period to manage; however, several factors could help to obtain a calm recovery period including choice of anaesthetic and analgesic procedure used and the conditions under which anaesthetic maintenance and recovery occur., Objectives: The objective of this study was to evaluate and compare the quality of recovery in horses administered saline, xylazine, detomidine or romifidine during recovery from isoflurane anaesthesia., Methods: Six mature and healthy horses were premedicated with i.v. xylazine and butorphanol, and anaesthesia induced using ketamine. After 2 h of inhalant anaesthesia with isoflurane vaporised in oxygen, saline solution, xylazine (0.1 mg/kg bwt), detomidine (2 microg/kg bwt) or romifidine (8 pg/kg bwt) were administered. The quality of recovery of each horse and the degree of sedation and ataxia were evaluated. Cardiovascular and respiratory parameters were recorded, and arterial blood samples obtained and analysed for pH, PO2 and PCO2 during recovery., Results: Quality of recovery was better in groups treated with alpha-2 adrenergic receptors agonists, showing less ataxia. Degree of sedation was greater in the romifidine group., Conclusions: We concluded that the administration of alpha-2 adrenoceptor agonists during recovery from isoflurane anaesthesia in horses prolonged and improved the quality of recovery without producing significant cardiorespiratory effects., Potential Clinical Relevance: Administration of alpha-2 adrenoceptor agonists after inhalent anaesthesia could prevent complications during the recovery period.

Data from 116 mares that had caesarean section or vaginal delivery at 2 university hospitals were analysed in 5 groups, as follows: dystocia corrected by caesarean section, Group DCS (n = 48); elective caesarean section, Group ECS (n = 10); caesarean section concurrently with colic surgery, Group CCS (n = 8); assisted vaginal delivery, Group AVD (n = 22); and controlled vaginal delivery under general anaesthesia, Group CVD (n = 28). Survival rate in all mares that had caesarean section, excluding Group CCS, was 88% (51/58). All mares in Group ECS survived and Group CCS had the lowest survival rate (38%). In 98 mares with dystocia, Groups DCS (15%) and AVD (14%) had significantly lower (P<0.05) mortality rates than Group CVD (29%). There were no differences between groups for duration of dystocia. The placenta was retained in 75 (65%) of 116 mares, and for a longer period following elective caesarean section than following assisted vaginal delivery. Multiple complications (> or = 3) were recorded in 6 mares in Group CVD but not in the other groups. Of the 102 foals delivered from 98 mares with dystocia, 11 (11%) were alive at delivery and 5 (5%) survived to discharge. Survival rate for foals was 38% in Group CCS, and 90% in Group ECS. Under conditions similar to those in this study, it is calculated that caesarean section is preferable to CVD if dystocia is protracted and great difficulty and trauma is involved, even if CVD allows delivery of the foal.

Thirty-two thoracoscopies were performed in 28 horses. Sixteen horses were affected with pleuropneumonia whereas 12 were affected with various other thoracic conditions. The indications for thoracoscopy was diagnostic in 19 cases, therapeutic in 11 cases and both diagnostic and therapeutic in 2 cases. Twenty-six thoracoscopies were done standing whereas 6 were performed under general anaesthesia. The specific procedures performed during thoracoscopy were exploratory only (7), biopsy of the lung and lymph nodes (10), drain placement into pleural effusions (2) and abscesses (5), exploration prior to thoracotomy (2), transection of pleural adhesions and decortication (1) and window pericardectomy (2). Diaphragmatic hernia repair (2) and partial pneumonectomy (1) were initiated thoracoscopically but conversion to thoracotomy was necessary for completion. Standing thoracoscopy was well tolerated in most horses. Transient exacerbation of pulmonary compromise evidenced by tachypnoea was readily alleviated by reinflation of the lung. Standing thoracoscopy provided good visualisation of the dorsal and lateral structures of the thorax. The ventral thoracic structures and the cranial ventral diaphragmatic surfaces of the lungs were best visualised in dorsal or lateral recumbency under general anaesthesia. Thoracoscopy is a safe and useful diagnostic and therapeutic tool in horses with thoracic diseases.

The use of laparoscopy for the diagnosis or therapeutic management of abdominal disease in the horse has distinct advantages when it allows the horse to remain standing. However, distending the abdomen by insufflation of a biologically active gas in an anaesthetised horse may add to the physiological challenge of general anaesthesia and recumbency. The cardiopulmonary responses to abdominal insufflation with carbon dioxide (CO2) to 15 mmHg pressure were evaluated in 6 horses in dorsal recumbency anaesthetised with halothane in oxygen and subjected to laparoscopic colopexy. Vaporiser settings targeted a fractional expired halothane of 1.5 MAC and a clinically acceptable depth of anaesthesia. Pressure and rate controlled positive pressure ventilation was adjusted to an ETCO2 of 35 mmHg before abdominal insufflation and was not changed thereafter. Cardiopulmonary data were collected before, at 30 and 60 min during and 30 min after CO2 insufflation. ANOVA for repeated measures followed by Tukey's protected t test were used to determine differences. Partial pressure of oxygen and pH of arterial blood, tidal volume and systemic vascular resistance decreased during abdominal insufflation and laparoscopic surgery whereas mean arterial blood pressure, right atrial pressure, cardiac index, stroke index, partial pressure of CO2 in arterial blood and end tidal respiratory gases, and calculated physiological shunt increased significantly. Only systemic vascular resistance returned to the pre-insufflation level after desufflation. The hypercapnia, acidosis and apparent increase in cardiac work that accompany CO2 pneumoperitoneum for laparoscopic surgery could place the anaesthetised horse at additional risk of perioperative complications.

The ultrasonographic appearance of the equine triceps muscle of clinically normal horses, before and after general anaesthesia, was investigated and compared with 5 cases of post anaesthetic myopathy. The triceps muscle areas were examined bilaterally using a 7.5 MHz linear array probe in 2 different planes, with each limb both weightbearing and nonweightbearing. The triceps muscles of 4 unanaesthetised horses were scanned twice, 24 h apart. Six horses underwent general anaesthesia and were scanned pre-anaesthesia and at 1 and 24 h intervals after recovery. Blood samples were obtained in the unanaesthetised group at each scan time and, in the anaesthetised group, pre-anaesthesia and at 10 min, 5 and 24 h after recovery. Creatine kinase (CK) and aspartate aminotransferase (AST) concentrations were measured. Anaesthetic details and recovery were related to the ultrasonographic and muscle enzyme findings. Five horses with post anaesthetic myopathy were scanned at intervals after the onset of clinical signs. In normal horses, the triceps muscle appeared ultrasonographically as echoic striations separated by anechoic areas. The fascia dividing muscle bellies was visible as an echoic line. Ultrasonographs obtained with the limb nonweightbearing had no change or a slight overall increase in echogenicity. The scans of control unanaesthetised horses were unchanged on successive days. All anaesthetised horses had uncomplicated anaesthesia and recoveries and did not exhibit any clinical signs of post anaesthetic myopathy. Elevated CK and AST values were found up to 342 and 195%, respectively, of the pre-anaesthetic values but no significant alterations in the ultrasonographic appearance of the muscles were detected. Clinical cases of post anaesthetic myopathy had disruption of the normal ultrasonographic pattern. There was an overall increase in echogenicity with a loss of the normal striated pattern. In 3 cases, there was localised increased echogenicity within the muscle. One of these horses was humanely destroyed for other reasons and histological examination of the affected muscle revealed a necrotic area correlating with the hyperechoic region. Two horses had bilateral involvement of the triceps musculature. Four horses recovered clinically from the myopathy and the ultrasonographic appearance returned to normal except in 1 horse where focal hyperechoic regions remained 10 weeks after the onset of the clinical signs.

The Confidential Enquiry into Perioperative Equine Fatalities (CEPEF-1) is an observational multi-institutional prospective study of recovery outcome at 7 days post operatively, as called for by Steffey (1991). Data from 6,255 general anaesthetics (February 91-March 93) were submitted confidentially by 62 clinics. The outcomes of 333 cases which were subjected to euthanasia and which were not classified 'alive' or 'died' at 7 days, were excluded from the analysis. The remaining 5922 cases were analysed to identify risk ratios (RR) between survivors and nonsurvivors for a variety of factors. These preliminary results indicate an overall death rate, for equine patients dying or being subjected to euthanasia within 7 days of a general anaesthetic because of perioperative complications, of 102/6255 (1.6%). This mortality rate decreased to 46/5220 (0.9%) when all colic surgery and delivery of foals under general anaesthesia were excluded. There was an increased risk for mares in the last trimester of pregnancy (RR = 6.4). Patients undergoing emergency abdominal procedures (colic patients and pregnant mares undergoing controlled or caesarean section delivery of foals) under general anaesthesia were at increased risk (RR = 12.9) compared to ear, nose and throat surgery. Within orthopaedic surgery, patients requiring internal fixation were at increased risk (RR = 3.2) compared to those undergoing miscellaneous orthopaedic surgery. There was no difference in risk between breeds. Patients not placed in dorsal recumbency were at reduced risk (RR = 0.3-0.5) compared to those which were in dorsal recumbency.(ABSTRACT TRUNCATED AT 250 WORDS)

General anaesthesia was maintained in 40 horses by the continuous intravenous infusion of a mixture of 500 ml 10% guaifenesin solution, 1 g ketamine and 500 mg xylazine. The median duration of infusion was 65 mins (interquartile range 51-95 mins). Anaesthesia was characterised by active palpebral reflexes, variable degrees of nystagmus and occasional swallowing. Swallowing was considered to be undesirable in horses undergoing laryngeal surgery, but the infusion produced satisfactory conditions for all other surgical procedures performed. Arterial blood pressure was well maintained in all cases (median mean arterial blood pressure = 85 mmHg after 30 mins anaesthesia). Heart rate and PaCO2 were significantly lower, whilst PaO2 was significantly higher in the infusion group than in a group of paired control horses which were anaesthetised with halothane. Recovery from anaesthesia was good (Grades 1-2) in 33 horses. Median times to sternal recumbency and to standing were 24 and 38 mins respectively. The infusion caused a significant fall in packed cell volume, haemoglobin concentration and red blood cell count (P < 0.01) and a significant rise in plasma glucose concentration (P < 0.01). These variables returned to pre-infusion values within 24 h.

The uterine and umbilical vessels of 12 pregnant ponies were catheterised to study foetal metabolism. The effects of this procedure on maternal and foetal cardiovascular, respiratory, metabolic and adrenocortical activity were monitored during and after surgery. Premedication with acepromazine-butorphanol-detomidine was followed by induction of anaesthesia with detomidine and ketamine and maintenance, using mechanical ventilation, with halothane in oxygen and nitrous oxide. Mean maternal arterial blood pressure was greater than 70 mmHg during anaesthesia and arterial oxygen tension remained over 100 mmHg. The foetuses were adequately oxygenated but were hypercapnic and lactic acidaemic. Most maternal and foetal blood gases and metabolites had returned to normal by 24 h, although foetal plasma lactate fell more slowly. The maternal adrenocortical discharge was less severe than reported previously and plasma cortisol had fallen to basal levels by 48 h after surgery. Foetal plasma cortisol remained low and did not change during or after surgery. Arterio-venous metabolite and gas tension differences across the uterine and umbilical circulations were slightly greater at operation than in the recovery period, suggesting that uteroplacental perfusion may have been impaired during surgery. Post-operative recovery of the mare and foetus was satisfactory and subsequent problems associated with the foetal catheters were not related to the anaesthesia or surgery.

Circulatory and respiratory effects of five h of constant 1.06 per cent alveolar halothane in oxygen were identified in eight healthy horses, which breathed spontaneously, were otherwise unmedicated and positioned in sternal recumbency. Only a few important significant (P less than 0.05) changes occurred with time. Total peripheral resistance was about 15 per cent lower after two hours of constant dose halothane than after 30 mins of constant dose (P less than 0.05) and accounted for the significant 10 per cent reduction in mean carotid arterial blood pressure. By 5 h, the reduction in resistance and arterial blood pressure was 20 and 25 per cent respectively. Heart rate increased progressively with time and the increase became significant at 5 h (15 per cent increase). However, the heart rate change was not large enough to alter cardiac output. There were no major time-related changes in PaO2 or PaCO2. Three of four horses recovered from anaesthesia had markedly elevated serum creatine kinase levels and clinical signs of severe post anaesthetic myopathy.

Information on the equine stress response to anaesthesia and surgery is sparse but offers a promising approach to elucidating the high anaesthetic risk in this species. Previous work has shown that halothane anaesthesia induces substantial metabolic and endocrine changes. This paper reports the effects of barbiturate anaesthesia. Anaesthesia was induced with thiopentone in six ponies and no further agents were given. They stood within 30 mins. On another occasion, these animals, and three further ponies, were anaesthetised with pentobarbitone and anaesthesia was maintained for 2 h. No surgery was performed on either occasion. Plasma concentrations of glucose, lactate, non esterified fatty acids, cortisol, insulin, catecholamines and adrenocorticotrophic hormone were measured at the same time intervals in both groups before, during and after anaesthesia. There were no significant changes in hormones or metabolites during either period of anaesthesia and normotension was maintained. This was in marked contrast to the substantial stress response and hypotension under halothane anaesthesia in the same ponies. These results suggest that barbiturates may induce less of a stress response than halothane in horses. Recovery after 2 h of pentobarbitone anaesthesia was poor, precluding its clinical use. The need for a non-cumulative intravenous agent or a non-hypotensive volatile agent for use in equine anaesthesia is discussed.

The effect of general anaesthesia and arthroscopic surgery on blood glucose and lactate, plasma non-esterified fatty acids, insulin, beta-endorphin and cortisol was investigated in seven horses. Animals were premedicated with xylazine and anaesthesia was induced with guaifenesin and sodium thiamylal and maintained with halothane vaporised in oxygen. Blood samples were collected in the pre-, intra- and post operative period. Induction of anaesthesia was associated with a transient hyperglycaemia and a significant rise in plasma insulin levels. Plasma insulin values fell during surgery but showed a significant increase post operatively. Surgery stimulated a small but significant rise in plasma beta-endorphin and cortisol values but these had returned to baseline values in the early post operative period. No changes in blood lactate were recorded.

Techniques and normal radiographic anatomy for positive and double contrast shoulder arthrography in horses were evaluated. General anaesthesia was used for most radiographic projections of the shoulder. The mediolateral projection provided the most information during arthrography, although the supinated mediolateral view occasionally allowed better definition of the cartilage surfaces on the medial aspects of the humeral head. The craniocaudal mediolateral oblique and caudocranial projections provided limited additional information. Water soluble non-ionic contrast agents, such as metrizamide and iohexol, were suitable for shoulder arthrography; iohexol resulted in less synovitis and lameness. Arthrography in cases of osteochondrosis and osteochondritis dissecans allowed better evaluation of cartilage attachment to subchondral bone, better evaluation of the length and depth of cartilage lesions and more accurately defined the site and shape of osteocartilaginous free bodies. Cartilage thickening without detachment from the subchondral bone could only be determined by arthrography. Although these thick cartilage regions may later dissect from the subchondral bone, most cases where the cartilage was firmly adherent were not candidates for surgical debridement and carried a favourable prognosis. The determination of a free flap by arthrography indicated the need for surgery. Extensive humeral and glenoid cavity lesions were better defined by arthrography, allowing a rational decision between surgical debridement or euthanasia. Using arthrography, evaluation of the size and patency of the communicating canal to a subchondral cystic defect better separated cases with long, narrow and poorly patent canals for conservative rather than surgical therapy.

A practical and safe method of angiocardiography for the horse is described. The technique involved the rapid injection of 50 to 150 ml contrast agent via catheters in the right and left heart, pulmonary artery and aorta. The examination was carried out with the horse in the standing position or under general anaesthesia. Angiocardiograms were performed on 10 normal horses and satisfactory pictures of the right and left ventricles, pulmonary arteries, aorta and coronary circulation were obtained. The technique was also used in a foal with severe congenital heart disease. The most practical methods of recording the images in the standing position were cinefilm or video taperecording. In the recumbent position both cinefilm and radiographs were taken. No damage to the heart was inflicted by the catheters and only a few ventricular premature contractions (less than five) were produced by the pressure of injection. No signs of toxicity were recorded using repeated injections of contrast material (ie, less than 600 ml).

Ketamine was used on 80 occasions to induce anaesthesia in 77 animals. Xylazine premedication was used alone on 75 occasions, in conjunction with methadone once, in conjunction with methadone and acepromazine once and, on three occasions, methadone and acepromazine only were used. Anaesthesia was maintained in seven cases with halothane and oxygen. Premedication with xylazine 5 mins previously or concurrently with ketamine gave similar results but an interval of more than 5 mins between the drugs produced less deep anaesthesia and this protocol is, therefore, not advised. Induction and recovery were judged to be good in 82 per cent and 78 per cent of cases, respectively, and analgesia and muscle relaxation were judged as adequate in 79 per cent of cases.

Three different anaesthetic techniques were studied in normal, healthy Thoroughbred or Thoroughbred type horses. These were (a) acepromazine, thiopentone and suxamethonium; (b) acepromazine, glyceryl guaiacolate and a 'half-dose' of thiopentone; and (c) xylazine and ketamine. Anaesthesia was maintained with halothane vaporized in oxygen and nitrous oxide. All horses underwent either laryngeal or body surface surgery. Heart rate, packed cell volume, blood glucose and lactate, plasma non-esterified fatty acids, insulin and cortisol were measured before, during and after surgery. The greatest metabolic and hormonal changes occurred immediately after anaesthetic induction and were different in each group. The combination of acepromazine, glyceryl guaiacolate and a 'half-dose' of thiopentone was associated with the least change in the physiological and metabolic variables measured.