Risk factors for colic in horses after general anaesthesia for MRI or nonabdominal surgery: absence of evidence of effect from perianaesthetic morphine

Anaesthesia-related morbidity associated with recumbent, low-field magnetic resonance imaging of horses

CASE HISTORY

Medical records from 2009 to 2021 from a private equine referral hospital in Rochester, NH, USA were analysed for cases that underwent general anaesthesia for low-field MRI of the distal limb. These were used to determine peri-anaesthetic morbidity and mortality.

CLINICAL FINDINGS AND OUTCOME

Two hundred and forty-three anaesthetic episodes were recorded in horses undergoing low-field MRI. The peri-anaesthetic complication rate prior to discharge was 6.2% (15/243). No patients experienced a fatal complication. Ninety two of the 243 patients had multiple sites imaged, 90/243 received pre-anaesthetic dantrolene, 134/243 received intra-anaesthetic dobutamine, and 15/243 were positioned in dorsal recumbency. Complications included: abdominal discomfort ("colic"; 9/243), myopathy (4/243), hyphaema (1/243) and carpal fracture (1/243). At the time of discharge, 14/15 complications had resolved. Of 135 horses for which data were available 55 became hypotensive during the procedure (lowest mean arterial pressure < 65 mmHg). Median body weight was 553 (min 363, max 771) kg. Horses were anaesthetised for a median of 150 (min 45, max 210) minutes. There was no evidence of an association between higher body weight (p = 0.051) or longer duration of anaesthesia (p = 0.421) and development of an anaesthetic complication. For categorical variables (dantrolene administration pre-anaesthesia, dobutamine administration during anaesthesia, hypotension (mean < 65 mmHg) during anaesthesia, dorsal vs. lateral recumbency, and imaging of single vs. multiple sites), the 95% CI for the OR included 1, indicating a lack of effect of the variable on the odds of complication.

CLINICAL RELEVANCE

The cases included in this series suggest that low-field MRI under general anaesthesia is a viable option for diagnostic imaging in otherwise healthy horses. Complications occur, but most resolve before discharge.

The impact of opioid administration on the incidence of postanaesthetic colic in horses

Effective management of postoperative pain is essential to ensure patient welfare, reduce morbidity and optimize recovery. Opioids are effective in managing moderate to severe pain in horses but concerns over their adverse effects on gastrointestinal (GI) motility and associated increased colic risk limit their widespread use. Studies investigating the impact of systemic opioids on both GI motility and colic incidence in horses have yielded inconclusive outcomes. Therefore, this retrospective study aims to assess the influence of systemic administration of butorphanol, morphine, and methadone on post-anaesthetic colic (PAC) incidence. Horses undergoing general anaesthesia for non-gastrointestinal procedures that were hospitalized for at least 72 h post-anaesthesia were included in this study. Anaesthetised horses were stratified by procedure type into horses undergoing diagnostic imaging without surgical intervention, emergency or elective surgery. In addition, patients were grouped by opioid treatment regime into horses receiving no opioids, intraanaesthetic, short- (<24 h) or long-term (>24 h) postoperative opioids. Administered opioids encompassed butorphanol, morphine and methadone. The number of horses showing signs of colic in the 72 h after anaesthesia was assessed for each group. A total of 782 horses were included, comprising 659 undergoing surgical procedures and 123 undergoing diagnostic imaging. The overall PAC incidence was 15.1%. Notably, horses undergoing diagnostic imaging without surgery had a significantly lower PAC rate of 6.5% compared to those undergoing surgery (16.7%, p = 0.0146). Emergency surgeries had a significantly lower PAC rate of 5.8% compared to elective procedures (18%, p = 0.0113). Of the 782 horses, 740 received intraoperative opioids and 204 postoperative opioids, 102 of which long-term (≥24 h). Neither intraoperative (p = 0.4243) nor short-term postoperative opioids (p = 0.5744) increased PAC rates. Notably, only the long-term (≥24 h) administration of morphine significantly increased PAC incidence to 34% (p = 0.0038). In contrast, long-term butorphanol (5.3% PAC, p = 0.8482) and methadone (18.4% PAC, p = 0.6161) did not affect PAC rates. In summary, extended morphine administration was the only opioid treatment associated with a significantly increased risk of PAC.

Incidence and risk factors for complications associated with equine general anaesthesia for elective magnetic resonance imaging

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.

Comparison of hydromorphone and butorphanol for management of pain in equine patients undergoing elective arthroscopy: a randomized clinical trial

OBJECTIVE

To compare the effects of hydromorphone and butorphanol in horses undergoing arthroscopy and describe the pharmacokinetics of hydromorphone in anesthetized horses.

STUDY DESIGN

Randomized controlled clinical trial.

ANIMALS

A total of 40 adult horses admitted for elective arthroscopy.

METHODS

Horses were randomly assigned to be administered intravenous hydromorphone (0.04 mg kg-1; group TxH; n = 19) or butorphanol (0.02 mg kg-1; group TxB; n = 21) prior to surgery as part of a standardized anesthetic protocol. Pain was scored by two observers unaware of group assignment using the Equine Utrecht University Scale for Facial Assessment of Pain (EQUUS-FAP) and a composite pain scale (CPS) prior to surgery (baseline), 2 hours (P2) and 4 hours (P4) following recovery from anesthesia. Blood samples were collected at various time points for determination of plasma hydromorphone concentration using liquid chromatography-tandem mass spectrometry. Data were analyzed with a mixed-effect model.

RESULTS

Median (range) baseline EQUUS-FAP was 1.2 (0.0-4.0) with no effect of group, time points or interaction. Baseline CPS was similar between groups. Group TxH baseline CPS was 2.5 (0.0-10.0), increased at P2 [4.5 (0-10.0); p = 0.046] and returned to baseline values at P4 [3.0 (0.0-11.0)]. Group TxB baseline CPS was 2.0 (0.0-8.0), increased at P2 [3.5 (0.0-11.0); p = 0.009] and P4 [5.0 (0.0-11.0); p < 0.001]. Pharmacokinetic terminal half-life was 774 ± 82.3 minutes, area under the curve was 1362 ± 314 ng minutes mL-1, clearance was 30.7 ± 7.23 mL minute-1 kg-1 and volume of distribution at steady state was 884 ± 740 mL kg-1.

CONCLUSIONS

Hydromorphone, but not butorphanol, decreased CPS back to baseline at P4 after recovery.

CLINICAL RELEVANCE

Hydromorphone may provide superior postoperative analgesia compared with butorphanol in horses undergoing arthroscopy.

Retrospective evaluation of association between perioperative antimicrobial protocol and complications following elective equine synovial endoscopy

Background

Prophylactic perioperative antimicrobial protocols in equine synovial endoscopy have been described but not compared with respect to post‐operative outcomes and complications. Increasing antimicrobial resistance in equine practice and interest in promoting judicious use of antimicrobials has prompted reevaluation of drug selection and dosing strategies.

Objectives

To determine the frequency of and compare post‐operative complications following elective synovial endoscopy between horses receiving different perioperative antimicrobial protocols.

Methods

Records from the Colorado State University Veterinary Teaching Hospital were evaluated (2014–2018) and equine patients undergoing elective synovial endoscopy were identified. Patients undergoing endoscopy for sepsis or internal fixation were excluded. Patient signalment, clinician, joint and limb involved, perioperative antimicrobial regimen, number endoscopic portals and closure technique, and post‐operative complications including incidence of joint infection were recorded. Generalized linear models were used to estimate the odds of post‐operative complications.

Results

Elective synovial endoscopies of 516 horses in 537 procedures evaluating 761 synovial structures were performed. No horses developed post‐operative septic synovitis. Administration of post‐operative antimicrobials, type used and patient sex were all significantly associated with increased risk of complications, which were predominantly gastrointestinal‐related. Complication rates in horses receiving a single preoperative dose of cefazolin were lower than in horses receiving potassium penicillin, gentamicin or multiple doses. Complication rates were lower in females compared to castrated or intact males. Other factors evaluated (breed, age, surgeon, anaesthesia duration or hospitalization, joint/limb operated, number endoscopic portals) were not associated with increased risk of complications post‐operatively in this case population.

Conclusions

Prophylactic perioperative antimicrobial protocols in equine practice deserve periodic reconsideration due to increased antimicrobial resistance. Prolonged antimicrobial usage beyond the time of surgery was unnecessary to prevent septic synovitis following synovial endoscopy in this case population and was furthermore associated with an increased risk of gastrointestinal complications.

Effects of feed deprivation on physical and blood parameters of horses

The objective of this study was to evaluate the effect of feed restriction on some physical and blood parameters in horses kept outdoors under natural conditions. Twenty horses were deprived of food for 48 h. They were closely monitored and examined, and blood samples were taken at the beginning (0) of the experiment and 6, 12, 18, 24, 30, 36, 42 and 48 hours afterward. During the experimental period, the control group (12 animals) had free access to water and hay, while the restricted group had free access to water only. Data were submitted to two-way analysis of variance with repeated measures, and statistical significance was P ≤ 0.05. The horses tolerated feed restriction without complications. Feed restriction had no effect on body mass and body condition score, heart rate, respiratory rate, capillary filling time and body temperature. However, feed restriction decreased the intensity of gastrointestinal sounds (P<0.05) compared to the control horses. Feed restriction did not cause any changes in erythrocyte variables and gamma glutamyl transferase, creatinine, total protein, and albumin concentrations. During fasting, there was a reduction in the leukocyte response (P<0.05). Feed restriction significantly raised the levels of blood urea nitrogen (24 to 48 hours), aspartate aminotransferase (36 to 48 hours) and total cholesterol (42 to 48 hours). During 48 hours of fasting, there was a continuous increase in triglyceride concentration. Feed restriction for 48 h had a marked effect on the intensity of gastrointestinal sounds and was responsible for important metabolic changes in the healthy horses of our sample.

Pharmacokinetics and pharmacodynamics of meperidine after intramuscular and subcutaneous administration in horses

OBJECTIVE

To describe the pharmacokinetics and pharmacodynamics of meperidine after IM and subcutaneous administration in horses.

STUDY DESIGN

prospective, randomized, blinded, crossover trial.

ANIMALS

Six adult horses weighing 494 ± 33 kg.

METHODS

Treatments included meperidine 1 mg/kg IM with saline 6 mL subcutaneously, meperidine 1 mg/kg subcutaneously with saline 6 mL IM, and saline 6 mL subcutaneously and 6 mL IM, with a 7-day washout between treatments. Plasma meperidine concentrations and pharmacodynamic values (thermal and mechanical thresholds, physiological variables, fecal production) were collected at various time points for 24 hours. Accelerometry data were obtained for 8 hours to measure locomotor activity. Data were analyzed with a mixed effects model, and α was set at .05.

RESULTS

Meperidine terminal half-life (T_1/2 ), maximal plasma concentrations, and time to maximal concentration were 186 ± 59 and 164 ± 56 minutes, 265.7 ± 47.2 and 243.1 ± 80.1 ng/mL at 17 ± 6, and 24 ± 13 minutes for IM at subcutaneous administration, respectively. No effect of treatment or time was observed on thermal or mechanical thresholds, heart rate, respiratory rate, locomotor activity, frequency of defecations, or fecal weight (P > .2 for all).

CONCLUSION

Maximum meperidine concentrations were achieved quickly with a short T_1/2 in both treatment groups. Neither IM nor subcutaneous meperidine influenced thermal or mechanical threshold or physiological variables.

CLINICAL SIGNIFICANCE

The short half-life and lack of detectable antinociceptive effect do not support IM or subcutaneous administration meperidine at 1 mg/kg for analgesia in horses.

Clinical magnetic resonance image quality of the equine foot is significantly influenced by acquisition system

BACKGROUND

Investigation of image quality in clinical equine magnetic resonance (MR) imaging may optimise diagnostic value.

OBJECTIVES

To assess the influence of field strength and anaesthesia on image quality in MR imaging of the equine foot in a clinical context.

STUDY DESIGN

Analytical clinical study.

METHODS

Fifteen equine foot studies (five studies per system) were randomly selected from the clinical databases of three MR imaging systems: low-field standing (LF St), low-field anaesthetised (LF GA) and high-field anaesthetised (HF GA). Ten experienced observers graded image quality for entire studies and seven clinically important anatomical structures within the foot (briefly, grade 1: textbook quality, grade 2: high diagnostic quality, grade 3: satisfactory diagnostic quality, grade 4: non-diagnostic). Statistical analysis assessed the effect of anaesthesia and field strength using a combination of the Pearson chi-square test or Fisher's exact test and Mann-Whitney test.

RESULTS

There was no difference in the proportion of entire studies of diagnostic quality between LF St (90%, 95% CI 78%-97%) and LF GA (88%, 76-95%, P = .7). No differences were evident in the proportion of diagnostic studies or median image quality gradings between LF St and LF GA when assessing individual anatomical structures (both groups all median grades = 3). There was a statistically significant difference in the proportion of entire studies of diagnostic quality between LF GA and HF GA (100%, 95% CI lower bound 94%, P = .03). There were statistically significant differences in median image quality gradings between LF GA (all median grades = 3) and HF GA (median grades = 1 (5/7 structures) or 2 (2/7 structures) for all individual anatomical structures (all P < .001). The reasons reported for reduced image quality differed between systems.

MAIN LIMITATIONS

Randomised selection of cases from clinical databases. Individual observer preferences may influence image quality assessment.

CONCLUSIONS

Field strength is a more important influencer of image quality than anaesthesia for magnetic resonance imaging of the equine foot in clinical patients.

A retrospective evaluation of the effect of perianesthetic hydromorphone administration on the incidence of postanesthetic signs of colic in horses

OBJECTIVE

To describe the incidence of postanesthetic signs of colic (PASC) in horses and determine if perianesthetic administration of hydromorphone was associated with an increased risk of PASC.

STUDY DESIGN

Retrospective, cohort study.

ANIMALS

A total of 409 horses.

METHODS

Anesthesia and clinical records of horses admitted for various procedures from July 2018 to September 2019 were reviewed. Signs of colic and interventions were recorded up to 48 hours after anesthesia. A binomial logistic regression model was used to evaluate the association between the type of surgery, administration of hydromorphone, the duration of anesthesia and the incidence of PASC.

RESULTS

Overall, 25 (6.1%) horses developed PASC within 48 hours of general anesthesia. Of 60 horses that underwent colic surgery, 16 (26.7%) developed PASC. Of 349 horses that underwent noncolic procedures, nine (2.6%) developed PASC. Thus, the incidence of PASC was higher in horses that underwent colic surgery than in horses that underwent noncolic procedures [odds ratio (OR) = 13.74 (5.73-32.95)]. No effect of hydromorphone on the incidence of PASC was identified [OR = 1.61 (0.71-3.62)]. Longer procedures (>2 hours) were identified as an independent risk factor for PASC [OR = 4.13 (1.52-11.22)].

CONCLUSIONS

No association between hydromorphone and an increase in the incidence of PASC was identified. Anesthesia for colic surgery and duration of anesthesia were associated with an increased risk of PASC.

CLINICAL RELEVANCE

Hydromorphone did not increase the incidence of PASC in this population.

Pharmacokinetics and pharmacodynamics of hydromorphone hydrochloride in healthy horses

OBJECTIVES

To determine the physiologic and behavioral effects and pharmacokinetic profile of hydromorphone administered intravenously (IV) to horses.

STUDY DESIGN

Prospective, randomized, crossover study.

ANIMALS

A group of six adult healthy horses weighing 585.2 ± 58.7 kg.

METHODS

Each horse was administered IV hydromorphone (0.025 mg kg^-1; treatment H0.025), hydromorphone (0.05 mg kg^-1; treatment H0.05) or 0.9% saline in random order with a 7 day washout period. For each treatment, physiologic, hematologic, abdominal borborygmi scores and behavioral data were recorded over 5 hours and fecal output was totaled over 24 hours. Data were analyzed using repeated measures anova with significance at p < 0.05. Blood samples were collected in treatment H0.05 for quantification of plasma hydromorphone and hydromorphone-3-glucuronide and subsequent pharmacokinetic parameter calculation.

RESULTS

Hydromorphone administration resulted in a dose-dependent increase in heart rate (HR) and systolic arterial pressure (SAP). HR and SAP were 59 ± 17 beats minute^-1 and 230 ± 27 mmHg, respectively, in treatment H0.05 at 5 minutes after administration. No clinically relevant changes in respiratory rate, arterial gases or temperature were observed. The borborygmi scores in both hydromorphone treatments were lower than baseline values for 2 hours. Fecal output did not differ among treatments and no evidence of abdominal discomfort was observed. Recorded behaviors did not differ among treatments. For hydromorphone, mean ± standard deviation for volume of distribution at steady state, total systemic clearance and area under the curve until the last measured concentration were 1.00 ± 0.29 L kg^-1, 106 ± 21 mL minute^-1 kg^-1 and 8.0 ± 1.5 ng hour mL^-1, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Hydromorphone administered IV to healthy horses increased HR and SAP, decreased abdominal borborygmi and did not affect fecal output.

Factors Influencing Equine Gut Microbiota: Current Knowledge

Gastrointestinal microbiota play a crucial role in nutrient digestion, maintaining animal health and welfare. Various factors may affect microbial balance often leading to disturbances that may result in debilitating conditions such as colic and laminitis. The invention of next-generation sequencing technologies and bioinformatics has provided valuable information on the effects of factors influencing equine gut microbiota. Among those factors are nutrition and management (e.g., diet, supplements, exercise), medical substances (e.g., antimicrobials, anthelmintics, anesthetics), animal-related factors (breed and age), various pathological conditions (colitis, diarrhea, colic, laminitis, equine gastric ulcer syndrome), as well as stress-related factors (transportation and weaning). The aim of this review is to assimilate current knowledge on equine microbiome studies, focusing on the effect of factors influencing equine gastrointestinal microbiota. Decrease in microbial diversity and richness leading to decrease in stability; decrease in Lachnospiraceae and Ruminococcaceae family members, which contribute to gut homeostasis; increase in Lactobacillus and Streptococcus; decrease in lactic acid utilizing bacteria; decrease in butyrate-producing bacteria that have anti-inflammatory properties may all be considered as a negative change in equine gut microbiota. Shifts in Firmicutes and Bacteroidetes have often been observed in the literature in response to certain treatments or when describing healthy and unhealthy animals; however, these shifts are inconsistent. It is time to move forward and use the knowledge now acquired to start manipulating the microbiota of horses.

BEVA primary care clinical guidelines: Analgesia

Primary care guidelines provide a reference point to guide clinicians based on a systematic review of the literature, contextualised by expert clinical opinion. These guidelines develop a modification of the GRADE framework for assessment of research evidence (vetGRADE) and applied this to a range of clinical scenarios regarding use of analgesic agents. Key guidelines produced by the panel included recommendations that horses undergoing routine castration should receive intratesticular local anaesthesia irrespective of methods adopted and that horses should receive NSAIDs prior to surgery (overall certainty levels high). Butorphanol and buprenorphine should not be considered appropriate as sole analgesic for such procedures (high certainty). The panel recommend the continuation of analgesia for 3 days following castration (moderate certainty) and conclude that phenylbutazone provided superior analgesia to meloxicam and firocoxib for hoof pain/laminitis (moderate certainty), but that enhanced efficacy has not been demonstrated for joint pain. In horses with colic, flunixin and firocoxib are considered to provide more effective analgesia than meloxicam or phenylbutazone (moderate certainty). Given the risk of adverse events of all classes of analgesic, these agents should be used only under the control of a veterinary surgeon who has fully evaluated a horse and developed a therapeutic, analgesic plan that includes ongoing monitoring for such adverse events such as the development of right dorsal colitis with all classes of NSAID and spontaneous locomotor activity and potentially ileus with opiates. Finally, the panel call for the development of a single properly validated composite pain score for horses to allow accurate comparisons between medications in a robust manner.

Pharmacokinetics and pharmacodynamics of hydromorphone after intravenous and intramuscular administration in horses

OBJECTIVE

To compare the pharmacokinetics and pharmacodynamics of hydromorphone in horses after intravenous (IV) and intramuscular (IM) administration.

STUDY DESIGN

Randomized, masked, crossover design.

ANIMALS

A total of six adult horses weighing [mean ± standard deviation (SD))] 447 ± 61 kg.

METHODS

Horses were administered three treatments with a 7 day washout. Treatments were hydromorphone 0.04 mg kg^⁻1 IV with saline administered IM (H-IV), hydromorphone 0.04 mg kg^⁻1 IM with saline IV (H-IM), or saline IV and IM (P). Blood was collected for hydromorphone plasma concentration at multiple time points for 24 hours after treatments. Pharmacodynamic data were collected for 24 hours after treatments. Variables included thermal nociceptive threshold, heart rate (HR), respiratory frequency (f_R), rectal temperature, and fecal weight. Data were analyzed using mixed-effects linear models. A p value of less than 0.05 was considered statistically significant.

RESULTS

The mean ± SD hydromorphone terminal half-life (t_1/2), clearance and volume of distribution of H-IV were 19 ± 8 minutes, 79 ± 12.9 mL minute^⁻1 kg^⁻1 and 1125 ± 309 mL kg^⁻1. The t_1/2 was 26.7 ± 9.25 minutes for H-IM. Area under the curve was 518 ± 87.5 and 1128 ± 810 minute ng mL^⁻1 for H-IV and H-IM, respectively. The IM bioavailability was 217%. The overall thermal thresholds for both H-IV and H-IM were significantly greater than P (p < 0.0001 for both) and baseline (p = 0.006). There was no difference in thermal threshold between H-IV and H-IM. No difference was found in physical examination variables among groups or in comparison to baseline. Fecal weight was significantly less than P for H-IV and H-IM (p = 0.02).

CONCLUSIONS AND CLINICAL RELEVANCE

IM hydromorphone has high bioavailability and provides a similar degree of antinociception to IV administration. IM hydromorphone in horses provides a similar degree and duration of antinociception to IV administration.

A retrospective study of fecal output and postprocedure colic in 246 horses undergoing standing sedation with detomidine, or general anesthesia with or without detomidine

OBJECTIVE

To determine time to first passage of feces, total fecal piles and incidence of colic in the first 24 hours postprocedure in horses undergoing standing sedation with detomidine, or general anesthesia with or without detomidine.

STUDY DESIGN

Retrospective cohort study.

ANIMALS

A total of 246 horses.

METHODS

Records of all horses that underwent standing sedation or general anesthesia between December 2012 and March 2016 were reviewed. Horses aged <6 months, admitted for colic or cesarean section, with inadequate data, and those not administered xylazine and/or detomidine were excluded. Records included patient signalment, fasting duration, procedure performed, drugs administered, time to first feces, number of fecal piles during 24 hours postprocedure and mention of colic. Chi-square, Fisher's exact and Tukey's post hoc comparison tests were used. Parametric data were reported as mean ± standard deviation with significance defined as p <0.05.

RESULTS

In total, 116 and 57 horses underwent general anesthesia without detomidine (group GA) and with detomidine (group GA-D), respectively, and remaining 73 horses underwent standing sedation with detomidine (group S-D). Detomidine dose was significantly higher in group S-D than in group GA-D. Time to first feces was longer (7.1 ± 4.2 hours), and group S-D horses passed one fewer fecal pile (6.3 ± 2.4) than group GA horses. There was no interaction between detomidine treatment and preprocedure food withholding and the time to first feces or the number of fecal piles in the first 24 hours postprocedure. Overall, seven horses (2.8%) showed signs of colic (five, one and one in GA, GA-D and S-D, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

Detomidine administration, as part of an anesthetic protocol or for standing sedation procedures, should not be expected to contribute to postprocedural colic.

Systemic morphine administration causes gastric distention and hyperphagia in healthy horses

BACKGROUND

There are no data investigating the effect of systemic morphine on the size of the stomach or the food consumption in horses.

OBJECTIVES

To evaluate gastrointestinal side effects of morphine administered systemically in healthy horses by the means of clinical and ultrasonographic evaluations.

STUDY DESIGN

In vivo experiment.

METHODS

On day 1 of the experiment, six healthy French Trotter mares were evaluated clinically and an abdominal ultrasonography was performed three times 4 h apart to record the size of the stomach, the number of contractions per minute of the duodenum, jejunum, caecum, left and right ventral colons. On Day 2, morphine was administered three times 4 h apart at the dose of 0.1 mg/kg i.v. and the same ultrasonographic examinations performed. On Day 3, only clinical and ultrasonographic examinations were performed as on Day 1. Amounts of hay and water ingested, frequency and weight of faeces were recorded throughout the study.

RESULTS

Number of contractions of the duodenum, caecum, left and right ventral colons were significantly decreased after morphine administration. Size of the stomach was increased significantly with a cumulative effect of repeated doses of morphine. Hay (+0.4 kg/h, P<0.001) and water (+1.1 L/h, P<0.001) consumption were significantly increased.

MAIN LIMITATIONS

The study was performed in healthy horses.

CONCLUSIONS

Systemic morphine administration causes gastrointestinal depression, gastric distention and hyperphagia in horses. Clinical and ultrasonographical examinations are valuable tools to identify side effects of morphine administration in horses. Further studies are needed to assess side effects and monitoring in clinically painful cases. Horses receiving systemic morphine administration should be closely monitored for signs of gastric distention and, specifically, the amount of food given while receiving treatment should be controlled to avoid complications.

Factors associated with postoperative complications in healthy horses after general anesthesia for ophthalmic versus non-ophthalmic procedures: 556 cases (2012-2014)

OBJECTIVE To compare complications between healthy horses undergoing general anesthesia for ophthalmic versus non-ophthalmic procedures and identify potential risk factors for the development of complications. DESIGN Retrospective case series. ANIMALS 502 horses (556 anesthetic procedures). PROCEDURES Medical records from January 2012 through December 2014 were reviewed to identify horses undergoing general anesthesia. Signalment, body weight, drugs administered, patient positioning, procedure type (ophthalmic, orthopedic, soft tissue, or diagnostic imaging), specific procedure, procedure time, anesthesia time, recovery time, recovery quality, and postoperative complications were recorded. RESULTS Patients underwent general anesthesia for ophthalmic (n = 106), orthopedic (246), soft tissue (84), diagnostic imaging (110), or combined (10) procedures. Mean procedure, anesthesia, and recovery times were significantly longer for patients undergoing ophthalmic versus non-ophthalmic procedures. Excluding diagnostic imaging procedures, there was a significant positive correlation between surgery time and recovery time. Within ophthalmic procedures, surgery time, anesthesia time, and recovery time were significantly greater for penetrating keratoplasty versus other ophthalmic procedures. There was a significantly higher rate of postoperative colic following penetrating keratoplasty, compared with all other ophthalmic procedures. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that in healthy horses, duration of general anesthesia should be minimized to decrease the risk of postanesthetic complications. Judicious use of orally administered fluconazole is recommended for horses undergoing general anesthesia. For horses undergoing a retrobulbar nerve block during general anesthesia, use of the lowest effective volume is suggested.

Gastrointestinal effects of general anaesthesia in horses undergoing non abdominal surgery: focus on the clinical parameters and ultrasonographic images

The ultrasonographic images of the gastrointestinal tract in horses can be influenced by fasting and sedation but the proper effect of general anaesthesia (GA) on them has not been determined yet. This study aimed to evaluate the effects of GA on ultrasonographic images of the gastrointestinal tract in horses and to compare these effects with a clinical evaluation. Twenty horses undergoing non-abdominal surgeries were evaluated by ultrasonography before and 4 times within 24 h after GA. Each ultrasonographic exam focused on the stomach, the duodenum and on 5 locations on the jejunum. The four-quadrant auscultation and the postoperative faecal output were also recorded. Pre and post anaesthetic values were compared using linear mixed effects models. None of the horses presented colic signs or reduced faecal output. During the first 2 post anaesthetic evaluations, the gut sounds were significantly decreased and, when taking all jejunal locations together, the jejunal diameter and visualisation frequency significantly increased. No intestinal loop appeared thickened and most of their diameters remained within the normal range. Our results suggest that the effects of GA on the ultrasonographic images of the small intestine are mild and of short duration and can therefore be differentiated from a pathological process.

The pharmacokinetics and pharmacodynamics of intravenous hydromorphone in horses

OBJECTIVE

Describe the pharmacokinetics and pharmacodynamics of intravenous hydromorphone in healthy horses.

STUDY DESIGN

Masked, randomized, cross-over, Latin square design.

ANIMALS

A group of eight healthy adult horses METHODS: Horses were administered each of four treatments with an 8 day washout. Treatments groups included intravenous hydromorphone 0.02 mg kg^-1 (LD), 0.04 mg kg^-1 (MD), 0.08 mg kg^-1 (HD) and saline (P). Blood samples for hydromorphone analysis were obtained for 24 hours after treatment. Plasma hydromorphone was quantified and pharmacokinetic parameters were determined using non-compartmental analysis. Pharmacodynamic data collected for 24 hours after treatment included thermal nociceptive threshold, heart rate (HR), respiratory rate (f_R) and rectal temperature, and analyzed using mixed-effects linear models.

RESULTS

Mean (± standard deviation) hydromorphone terminal half-life (t_1/2), systemic clearance and apparent volume of distribution at steady state (Vd_ss) were 18.1 ± 18.6, 34.0 ± 12.8, and 41.3 ± 32.5 minutes, 66.6 ± 5.3, 550.0 ± 76.4, and 92.7 ± 13.9 mL kg^-1 minute^-1, and 1118 ± 369, 1460 ± 325 and 2242 ± 950 mL kg^-1 for treatments LD, MD and HD, respectively. Thermal threshold increased significantly compared to baseline for all treatments for up to 12 hours. HR was elevated above baseline in treatments LD, MD and HD, extending to 30, 15 and 105 minutes after treatment, respectively. Respiratory rate was elevated above baseline in treatments MD and HD from 30 to 195 minutes and from 45 to 480 minutes after treatment, respectively. Temperature was elevated above baseline in treatment HD until 255 minutes after treatment.

CONCLUSIONS

Hydromorphone exhibited a short t_1/2, rapid clearance and large Vd_ss in horses. It also provided a dose-dependent increase in thermal threshold with associated increases in HR, f_R and rectal temperature.

CLINICAL RELEVANCE

Hydromorphone 0.04 mg kg^-1 provided clinically relevant thermal antinociception with minimal adverse effects.

Interval prevalence of and factors associated with colic in horses hospitalized for ocular or orthopedic disease

OBJECTIVE To determine interval (1-year) prevalence of and factors associated with colic in horses hospitalized for ocular or orthopedic disease. DESIGN Cross-sectional study. ANIMALS 105 horses with ocular disease and 197 horses with orthopedic disease admitted to a veterinary teaching hospital between July 1, 2011, and June 30, 2012. PROCEDURES Medical records were reviewed to determine whether colic (abnormal behavior prompting abdominal palpation per rectum or nasogastric intubation) was observed during hospitalization. Data were collected on putative risk factors for colic, including reason for admission, signalment, and medical or surgical interventions received. RESULTS No significant difference in interval prevalence of colic was identified between horses with ocular disease (8/105 [8%]) or orthopedic disease (9/197 [5%]). However, horses with ocular disease differed significantly from other horses in median age (10 vs 3 years, respectively); proportions of sexually intact males (3% vs 30%), Thoroughbreds (28% vs 62%), and those receiving general anesthesia (65% vs 80%); and median duration of hospitalization (3 vs 2 days). For every 1 mg/kg increase in daily NSAID dose, the odds of colic increased by 98%. No difference between groups was identified in median duration of colic (1 day), hospitalization (7 vs 3 days), or systemic NSAID administration (7 vs 5 days). Colic in both groups resolved with medical management for all but 1 horse with ocular disease. CONCLUSIONS AND CLINICAL RELEVANCE Horses hospitalized for ocular disease were at no greater odds for colic than were horses hospitalized for orthopedic disease. Medical management of colic appeared adequate for most horses.

A multicentre, prospective, randomised, blinded clinical trial to compare some perioperative effects of buprenorphine or butorphanol premedication before equine elective general anaesthesia and surgery

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.

Effect of prolonged general anesthesia with sevoflurane and laparoscopic surgery on gastric and small bowel propulsive motility and pH in dogs

OBJECTIVE

To determine if general anesthesia with sevoflurane and laparoscopic surgery changed gastric and small bowel propulsive motility or pH in dogs.

STUDY DESIGN

Prospective, controlled trial.

ANIMALS

Twelve, 19-24 months old, female, Treeing Walker Hound dogs, weighing 23-30 kg.

METHODS

Dogs were anesthetized for a median of 8.5 hours during another study to determine the minimum alveolar concentration of sevoflurane using a visceral stimulus. Gastric and small bowel motility were determined using a sensor capsule that measures pressure, pH and temperature. Gastric transit time and motility index were calculated. For 8/12 dogs, gastric motility, pH and transit time were measured. In 4/12 dogs, small bowel motility and pH were measured.

RESULTS

Anesthesia decreased gastric and small bowel motility but did not change luminal pH. Mean gastric contraction force decreased from median (range) 11 (8-20) to 3 (1-10) mmHg (p < 0.01) and gastric motility index decreased from 0.63 (0-1.58) to 0 (0-0.31; p = 0.01). Frequency of contractions did not change, 3.7 (1.6-4.4) versus 2.8 (0.1-5.1) contractions minute(-1) (p = 0.1). Gastric motility returned to normal 12-15 hours following anesthesia. Gastric emptying was prolonged from 12 (5.3-16) to 49 (9.75-56.25) hours (p < 0.01). Mean small bowel contraction force decreased from 34 (24-37) to 3 (0.9-17) mmHg (p < 0.02) and motility index decreased from 3.75 (1-4.56) to 0 (0-1.53; p = 0.02). Frequency of contractions did not change, 0.5 (0.3-1.4) versus 1.4 (0.3-4.6) contractions minute(-1) (p = 0.11). Small bowel motility returned within 2 hours after anesthesia. Laparoscopy did not result in changes to gastric or small bowel parameters beyond those produced by general anesthesia.

CONCLUSIONS AND CLINICAL RELEVANCE

The force of gastric and small bowel contractions decreased during sevoflurane anesthesia for laparoscopy. Although gastric motility returned to normal within 12-15 hours the impairment of gastric emptying lasted 30-40 hours, predisposing dogs to postoperative ileus.

Outcome and long-term follow-up of 20 horses undergoing surgery for caecal impaction: a retrospective study (2000-2008)

REASONS FOR PERFORMING STUDY

If untreated, caecal impaction may progress to rupture of the caecum and reports of long-term outcome for horses undergoing surgery for caecal impaction are required.

OBJECTIVES

To describe short- and long-term complication rates for horses undergoing surgery for caecal impaction in an otherwise life-threatening gastrointestinal condition.

METHODS

Case records were reviewed for horses undergoing surgery for caecal impaction. Horses were included in the study if an abnormally large, fluid-distended or feed-impacted caecum was the primary diagnosis at surgery and excluded if the caecum had already ruptured upon opening the abdomen, necessitating euthanasia. Short-term follow-up data were obtained from clinical records; and included complications, repeat celiotomy and survival to discharge. Long-term survival was defined as survival for >1 year post operatively. Long-term follow-up data were obtained through telephone interviews with owners and referring veterinary surgeons. Survival, occurrence of post operative colic and subsequent use of the horse were recorded.

RESULTS

Twenty horses underwent surgery for caecal impaction: 16 horses underwent caecal bypass (typhlotomy and removal of caecal contents, ileal transection followed by ileocolostomy); 3 underwent typhlotomy alone; and one horse underwent typhlotomy followed by a second procedure where caecal bypass was performed. Five horses (25%) were admitted for colic evaluation with primary caecal impactions, in 10/20 (50%) of cases the impaction was secondary to previous orthopaedic surgery and in 5/20 (25%) caecal impaction was identified at repeat celiotomy following a previous colic surgery. Sixty-five percent (13/20) of horses survived to discharge; 11/13 (85%) of horses discharged survived long term; 100% (3/3) horses that received typhlotomy alone were discharged and survived long term.

CONCLUSIONS

The prognosis following caecal impaction surgery is fair, if the horse survives to discharge then prognosis for long-term survival is good.

POTENTIAL RELEVANCE

Surgery for caecal impaction carries a fair prognosis for a potentially life threatening disease, in particular where caecal dysfunction is suspected.

Post anaesthetic colic in horses: a preventable complication?

REASONS FOR PERFORMING STUDY

There is little information on the prevalence of, and risk factors associated with, post anaesthetic colic (PAC) in horses undergoing nonabdominal operations.

OBJECTIVES

To undertake the first prospective study of prevalence of PAC and identify risk factors in its development in nonabdominal procedures.

METHODS

A multicentre prospective case-control study was conducted, on every horse undergoing anaesthesia for a nonabdominal procedure between April 2004 and June 2005. Colic cases were defined as any horse with recognised signs of abdominal pain within 72 h of general anaesthesia that could not be attributed to any concurrent disease. Five control horses per case were selected randomly from the study population at all hospitals. Multivariable logistic regression analysis was used to examine the relationship between predictor variables and the risk of developing PAC.

RESULTS

The estimated mean prevalence of PAC in the study population was 5.2% (95% CI, 2.8, 8.0). However, the prevalence of colic varied between each centre. The most commonly diagnosed cause of colic was impaction. Multivariable analyses showed that the centre involved and the type of surgery performed were associated with an increased risk of PAC. Preoperative food deprivation and the use of opioid drugs were confounding factors.

CONCLUSIONS

Prevalence of PAC varied significantly between the 4 hospitals studied; there may be hospital-related covariates that account for this. The type of surgery performed influenced the risk of PAC.

POTENTIAL RELEVANCE

Identifying the risk factors for PAC is a prerequisite for its prevention. This study indicates horses at increased risk of PAC that might benefit from a more critical evaluation of post anaesthetic gastrointestinal function and/or the provision of preventative measures. Further investigation is required to explain the variation in prevalence of PAC between centres.

Postoperative ileus: pathogenesis and treatment

Surgical manipulation of the intestines activates intestinal macrophages that release cytokines and nitric oxide, which results in inhibition of intestinal motility. Subsequent infiltration of circulating leukocytes into the intestinal wall contributes to cytokine and nitric oxide release and exacerbates ileus. Other factors contributing to ileus are endotoxemia; edema of the intestine wall subsequent to excessive fluid therapy; hypocalcemia; and long abdominal incisions. Because treatment of ileus with prokinetic drugs has not proven to be very effective, efforts should be directed at reducing its severity. Strategies which reduce the severity of ileus include pretreatment with a nonsteroidal anti-inflammatory drug, minimizing the length of the abdominal incision, reducing intestinal manipulation, intraoperative lidocaine infusion, correction of hypocalcemia, limiting the volume of intravenous fluids to prevent intestinal edema, and administration of alpha(2) antagonists.