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Randomized, blinded, controlled clinical trial to assess gastroesophageal reflux and regurgitation in dogs undergoing general anesthesia after hydromorphone premedication with or without acepromazine or dexmedetomidine

Renata S. Costa DVM MPhil1, Lois A. Wetmore DVM, SCD1, and Amy Stein PhD2
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  • 1 From the Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536;
  • | 2 From the From the Office of Research and Sponsors Program, Midwestern University, Glendale, AZ 85308.

Abstract

OBJECTIVE

To investigate whether premedication with hydromorphone alone or combined with acepromazine or dexmedetomidine affects the incidence of gastroesophageal reflux (GER) and regurgitation in dogs undergoing general anesthesia for elective orthopedic surgery.

ANIMALS

39 healthy client-owned dogs undergoing general anesthesia for elective orthopedic surgery between November 2016 and November 2018.

PROCEDURES

For this prospective, randomized, controlled, blinded clinical trial, dogs were randomly assigned to be premedicated with hydromorphone (0.1 mg/kg, IM) alone (group H [control group]) or with either acepromazine (0.05 mg/kg, IM; group AH) or dexmedetomidine (6 μg/kg, IM; group DH) before undergoing general anesthesia induced with propofol and maintained with isoflurane. A pH sensor–tipped probe was used to identify episodes of GER (esophageal pH < 4 or > 7.5 for ≥ 30 seconds). Results for GER, regurgitation, vomiting, propofol dose, and durations of food withholding and anesthesia were compiled and compared across groups.

RESULTS

There were 13 dogs in each group, and no meaningful differences were detected in age, body weight, sex, breed, or durations of anesthesia or food withholding across groups. Overall, 16 of the 39 (41%) dogs developed GER: 9 in group H, 6 in group AH, and 1 in group DH. The incidence of GER was significantly lower for group DH versus group H. Six of the 39 (15%) dogs regurgitated: 4 in group H and 2 in group AH.

CONCLUSIONS AND CLINICAL RELEVANCE

The combined use of dexmedetomidine and hydromorphone as premedication may be a better choice to reduce GER in healthy dogs undergoing orthopedic surgery than would the use of hydromorphone with or without acepromazine. Additional research is warranted. (Am J Vet Res 2021;82:695–700)

Abstract

OBJECTIVE

To investigate whether premedication with hydromorphone alone or combined with acepromazine or dexmedetomidine affects the incidence of gastroesophageal reflux (GER) and regurgitation in dogs undergoing general anesthesia for elective orthopedic surgery.

ANIMALS

39 healthy client-owned dogs undergoing general anesthesia for elective orthopedic surgery between November 2016 and November 2018.

PROCEDURES

For this prospective, randomized, controlled, blinded clinical trial, dogs were randomly assigned to be premedicated with hydromorphone (0.1 mg/kg, IM) alone (group H [control group]) or with either acepromazine (0.05 mg/kg, IM; group AH) or dexmedetomidine (6 μg/kg, IM; group DH) before undergoing general anesthesia induced with propofol and maintained with isoflurane. A pH sensor–tipped probe was used to identify episodes of GER (esophageal pH < 4 or > 7.5 for ≥ 30 seconds). Results for GER, regurgitation, vomiting, propofol dose, and durations of food withholding and anesthesia were compiled and compared across groups.

RESULTS

There were 13 dogs in each group, and no meaningful differences were detected in age, body weight, sex, breed, or durations of anesthesia or food withholding across groups. Overall, 16 of the 39 (41%) dogs developed GER: 9 in group H, 6 in group AH, and 1 in group DH. The incidence of GER was significantly lower for group DH versus group H. Six of the 39 (15%) dogs regurgitated: 4 in group H and 2 in group AH.

CONCLUSIONS AND CLINICAL RELEVANCE

The combined use of dexmedetomidine and hydromorphone as premedication may be a better choice to reduce GER in healthy dogs undergoing orthopedic surgery than would the use of hydromorphone with or without acepromazine. Additional research is warranted. (Am J Vet Res 2021;82:695–700)

Introduction

Regurgitation, vomiting, and GER are adverse events associated with anesthesia.1,2 Unlike vomiting, which is an active process involving abdominal contractions, regurgitation is the passive discharge of liquids from the mouth or nose with no abdominal contractions. In 2 large studies, the reported prevalence of regurgitation in healthy anesthetized dogs was 0.63% (27/4,257)3 and 1.3% (75/5,736),4 and dogs undergoing orthopedic procedures were 26 times as likely to regurgitate than were dogs undergoing diagnostic procedures or other surgeries. In contrast, GER is undetectable, unless esophageal pH is measured, and occurs more frequently (17.4% [47/270] to 60% [18/30]) in anesthetized dogs.58

Exposure of the esophageal mucosa to gastric contents may result in ulcers, esophagitis, and postoperative esophageal strictures. In dogs, exposure of the esophageal mucosa to gastric contents (pH, < 2.5), even for durations as short as 20 minutes, results in mucosal damage.9,10 Dogs that regurgitate or develop GER are at a greater risk for developing postanesthetic esophageal stricture and aspiration pneumonia. Although esophageal strictures are uncommon and the reported incidence of aspiration pneumonia is 0.17% (240/140,711)2 for anesthetized dogs, these postanesthetic complications are serious and debilitating conditions. For instance, the reported1,2,11 mortality rate is up to 20% (2/10) for dogs with esophageal strictures and up to 23% (20/88) for dogs with aspiration pneumonia. Although the mechanism of anesthetic-induced GER remains unclear, a decrease in the LES tone and a resulting reduction in the gastroesophageal pressure gradient have been suggested to be the major physiologic cause.12 Perianesthetic agents such as opioids decrease LES tone, and studies5,13,14 show that GER and vomiting are more common in dogs undergoing anesthesia or sedation when treated with morphine or hydromorphone, compared with dogs that did not receive opioids.

Hydromorphone-induced sedation is improved with the administration of sedatives and tranquilizers such as acepromazine or dexmedetomidine. Although these sedatives are commonly administered, there is limited and conflicting data on the effects of these drugs on the incidence of regurgitation. For example, De Miguel Garcia et al4 reported decreased risk of regurgitation in dogs premedicated with acepromazine and an opioid, compared with premedication with medetomidine, and Lamata et al3 reported no association between administration of acepromazine and the risk of regurgitation. On the basis of our clinical experience, the occurrence of regurgitation in healthy anesthetized dogs is reduced when acepromazine or dexmedetomidine is administered along with hydromorphone as premedication, compared with hydromorphone alone.

The aim of the study reported here was to determine the influence of premedication with acepromazine or dexmedetomidine administered concurrently with hydromorphone on the incidence of GER and regurgitation in healthy anesthetized dogs undergoing elective hind limb orthopedic surgery. We hypothesized that premedication with hydromorphone and acepromazine or dexmedetomidine administered IM would result in a lower incidence of GER and regurgitation than would premedication with hydromor-phone alone.

Materials and Methods

Animals

Healthy client-owned dogs undergoing elective hind limb orthopedic surgery at the Foster Hospital for Small Animals at Tufts University between November 2016 and November 2018 were eligible for enrollment. A power analysis based on a z test for differences in proportions determined that 13 dogs/group were required to achieve 85% power with a significance level of 5%. This design would be able to detect a difference of approximately 50% in the proportion of dogs that developed GER between treatment groups. The effect size was based on varying incidence levels detected in previous studies, which were between 17% (47/270)6 and 60% (18/30).5

Enrollment criteria for dogs included that they had to have had an American Society of Anesthesiologists health status classification of 1 or 2 on the basis of physical examination and laboratory blood tests (Hct and concentrations of total solids, BUN, and glucose). Dogs were excluded if they were a brachycephalic breed or obese (body condition score, ≥ 7 on a scale from 1 [emaciated] to 9 [severely obese]), had a history of vomiting or regurgitation within 2 months before the elective procedure, received gastroprotectant medications, required additional intraoperative opioids, or required additional sedation beyond that of their assigned randomized preanesthetic treatment to allow placement of an IV catheter (alone or in combination). The study was approved by the Institution's Clinical Studies Review Committee, and animals were included after informed owner consent was signed.

Study protocol

Food but not water was withheld for 8 to 14 hours before administration of premedication. Dogs were randomly assigned to 1 of 3 groups that received IM administration of hydromorphone (0.1 mg/kg) alone (group H [control group]) or with acepromazine (0.05 mg/kg, IM; group AH) or dexmedetomidine (6 μg/kg, IM; group DH). Group assignment was randomized,a and the investigator (RSC) was blinded to the treatment administered.

For each dog, after the assigned premedication was administered, an 18- or 20-gauge IV catheter was placed in one of the dog's cephalic veins. Anesthesia was induced with propofol (4 mg/kg, IV) titrated to effect to produce jaw muscle relaxation, ventrome-dial rotation of the eyes, and lack of cough reflex during endotracheal intubation, which was performed with the dog in sternal recumbency. Immediately after intubation, fluid therapy with lactated Ringer solution (5 mL/kg/h) and a constant rate infusion of ketamine (0.6 mg/kg/h) and 2% lidocaine (50 μg/kg/min) were started. Sciatic and femoral nerve blocks with bupivacaine (1.5 mg/kg total) were performed with localization by use of anatomic landmarks and a nerve stimulator.

Esophageal pH probe

Following induction of anesthesia, an esophageal stethoscope and a pH sensor–tipped probeb were inserted into the dog's esophagus. The devices were positioned in all dogs by the same investigator (RSC) to ensure consistency. Several pH sensor–tipped probes from the same manufacturer were used during the study and calibrated at pH 4 and 7 within 1 hour before placement. For placement, the probe was measured externally to mark the distance from the dog's incisor teeth to the cranial aspect of its 10th rib so that, when placed, the tip of the pH probe would be positioned cranially to the gastroesophageal junction.6,15 After placement, the pH probe was secured with tape around the rostral end of the endotracheal tube and mouth, then connected to a recorderc for continuous data collection. Correct probe placement was confirmed with radiography.

Patient monitoring

Each dog was monitored perianesthetically for episodes of vomiting and regurgitation. Regurgitation was defined as passive discharge of liquids from the mouth or nose with no abdominal contractions, whereas vomiting was defined as active discharge of liquids from the mouth or nose with abdominal contractions. Vomiting following premedication was recorded, but esophageal lavage was not performed because dogs were awake and still able to swallow. During anesthesia, when an episode of regurgitation was detected, it was also recorded in the anesthesia record, and the oral cavity and cranial portion of the esophagus were immediately suctioned, then lavaged with saline (0.9% NaCl) solution while the contents were simultaneously aspirated until the suctioned fluid was clear.

In the operating room, each dog was positioned in dorsal recumbency for the hind limb procedure elected. Anesthesia was maintained with isoflurane in oxygen delivered through a circle rebreathing system. The concentration of isoflurane delivered was controlled with adjustments to the vaporizer setting to maintain appropriate procedural anesthetic depth as routinely performed in clinical settings. Each dog's heart rate, respiratory rate, end-tidal carbon dioxide, oxygen saturation of hemoglobin as measured with pulse oximetry, oscillometric noninvasive blood pressure, esophageal temperature, isoflurane vaporizer setting, and oxygen flow rate were recorded every 5 minutes. Monitoring continued after surgery. The patients were moved to radiology for postoperative radiographic examination and to recovery. Extubation and removal of the esophageal pH probe were performed after dogs swallowed 2 or 3 times.

Data collection

Data collected included patient age, body weight, sex, and breed; surgical procedure; food withholding duration; dose of propofol required for induction of anesthesia; anesthetic vaporizer setting and duration; time frame of vomiting, regurgitation, or GER, if occurred; and duration of GER, if occurred. For GER, esophageal pH data were uploadedd at the end of each anesthetic procedure, and the data were analyzed. An episode of GER was defined as a ≥ 30-second duration of esophageal pH that decreased to pH < 4 (gastric acid reflux) or increased to pH > 7.5 (bile reflux).15

Statistical analysis

Normally distributed data were reported as mean ± SD, and nonnormally distributed data were reported as median and range. Normality was verified visually and with the Shapiro-Wilk test. The Kruskal-Wallis test was used to compare results for age, body weight, time frame of GER and regurgitation, and duration of GER across groups. An ANOVA was used to compare results for the duration of food withholding before administration of preanesthetic drugs and the duration of anesthesia, starting at induction and ending at extubation. Any differences between results for vomiting and regurgitation detected across groups were presented with 95% CIs. The Fisher exact test was used to compare results for sex, breed, and occurrence of GER across groups. The potential association between the development of adverse events and duration of food withholding was analyzed with t tests in each group independently. A logistic regression model was used to assess whether the treatment group (H, AH, or DH) or required propofol dose was associated with or was a predictor of GER. Values of P ≤ 0.05 were considered significant; analysis was performed with available software.e

Results

There were 13 healthy client-owned dogs in each of the 3 groups: H (dogs premedicated with hydro-morphone alone [control group]), AH (dogs premedicated with acepromazine and hydromorphone), and DH (dogs premedicated with dexmedetomidine and hydromorphone). There were no meaningful differences in age, body weight, sex, or breed across the groups (Table 1).

Sixteen of the 39 (41%) dogs had GER, and treatment group was a significant (P = 0.007) predictor of GER (Table 2). The incidence of GER for dogs in group DH (8% [1/13]) was significantly lower than for those in group H (69% [9/13]; P = 0.004) but did not differ significantly from that for dogs in group AH (46% [6/13]; P = 0.07). On the basis of these findings, GER occurred 89% less often for dogs in the DH group than in the H group. The incidence of GER did not differ significantly (P = 0.43) between groups H and AH. Nonetheless, GER occurred 33% less commonly for dogs in the AH group than in the H group.

The median duration from induction of anesthesia to onset of GER was 24 minutes (range, 7 to 200 minutes), and 14 of the 16 dogs had an episode of GER < 1 hour after induction. The GER episodes were recorded during surgical preparation for 12 of the 16 dogs and during surgery for the remaining 4 dogs. Of these 16 dogs, 15 had a single episode of GER and 1 (a dog in group H) had 2 episodes. The median duration of GER was 61 minutes (range, 6 to 205 minutes). No differences in GER onset (P = 0.79) or duration (P = 0.93) were found across groups.

Thirteen of the 39 (33%) dogs vomited after receiving preanesthetic medication (time range, 5 to 15 minutes; Table 2). Of these 13 dogs, 3 (23%; 95% CI, 2% to 44%) developed GER, whereas 13 of the 26 (50%; 95% CI, 31% to 69%) dogs that did not vomit had GER. Further, none of the 13 (0%; 95% CI, 0% to 16%) dogs that vomited went on to regurgitate, whereas 6 of the 26 (23%; 95% CI, 2% to 44%) dogs that did not vomit regurgitated.

Regurgitation was observed in 6 of the 39 (15%) dogs (Table 2). None of the dogs in group DH regurgitated, whereas 4 in group H and 2 in group AH regurgitated. All 6 dogs had regurgitation events at the end of their surgical procedures while still anesthetized, and 1 dog from group H also had a regurgitation event approximately midway through its procedure. With each regurgitation event, no cough or swallowing was observed. Ten of the 16 (62.5%; 95% CI, 39% to 86%) dogs that had GER did not regurgitate.

Table 1

Characteristics of healthy client-owned dogs that were premedicated with hydromor-phone alone (group H [control group]), acepromazine and hydromorphone (group AH), or dexmedetomidine and hydromorphone (group DH) before undergoing general anesthesia for elective hind limb orthopedic procedures between November 2016 and November 2018.

CharacteristicGroupP value
H (control; n = 13)AH (n = 13)DH (n = 13)
Age (y)*5 (3–8)3 (2–8)6 (2–8)0.06
Body weight (kg)*28.0 (9.8–39.0)23.9 (6.0–34.8)24.6 (6.3–37)0.25
Sex0.63
 Sexually intact female533
 Spayed female465
 Sexually intact male212
 Castrated male233
Breed0.18
 Labrador Retriever446
 Pit bull–type dog422
 Beagle110
 German Shepherd Dog230
 Australian Shepherd001
 Yorkshire Terrier011
 Jack Russel Terrier001
 Havanese021
 Border Collie001
 Golder Retriever200

Data are presented as the number of animals unless indicated otherwise.

Data are presented as median and range.

Although not all dogs had the same anesthetist, anesthetic procedures for all dogs were directly supervised by the investigators (RSC and LAW). Neither the duration of anesthesia nor food withholding before anesthesia differed across groups (Table 2). Further, the mean ± SD duration of food withholding did not differ (P = 0.83) for dogs grouped on the basis of whether they had GER (10.4 ± 2.0 hours; n = 16) versus did not have GER (10.7 ± 2.1 hour; 23).

Table 2

Results for variables of interest for the dogs described in Table 1 stratified by group.

VariableGroup H (n = 13)Group AH (n = 13)Group DH (n = 13)P value
Data valuePercentage (95% CI)Data value95% CI (%)Data value95% CI (%)
GER*9a69 (44–94)6a,b46 (19–73)1b8 (0–22)0.007
Regurgitation*431 (6–56)215 (0–35)00 (0–28)0.135
Vomiting*323 (1–45)539 (12–65)539 (12–65)0.757
Propofol dose (mg/kg)3.7 (2.2–4)a2.8 (1.8–5)b2.9 (1.8–4.8)b0.007
Food withholding duration (h)9.7 ± 2.011.4 ± 2.010.7 ± 2.30.130
Anesthesia duration (min)168.2 ± 38.3180.2 ± 48.9181.2 ± 43.70.700

Data are presented as the number and percentage of affected animals unless otherwise indicated.

Data are presented as median and range.

Data are presented as mean and SD.

Values with different superscripts differ significantly (P < 0.05).

= Not applicable.

The median required dose of propofol was significantly (P = 0.007) higher for dogs in group H (3.7 mg/kg; range, 2.2 to 4.0 mg/kg), compared with those in groups AH (2.8 mg/kg; range, 1.8 to 5 mg/kg) and DH (2.9 mg/kg; range, 1.8 to 4.8 mg/kg). However, even after controlling for propofol dose in logistic regression analysis, group assignment remained a predictor of the incidence of GER in that dogs in group H and AH had significantly (P = 0.041) higher odds (OR, 15.63; 95% CI, 1.74 to 142.59) of developing GER than did dogs in group DH.

Discussion

The overall incidence of GER (41% [16/39]) in dogs of the present study was similar to results reported in previous studies16,d of healthy dogs undergoing elective orthopedic surgery (38% [10/26] to 44% [18/41]). Additionally, in our study, the incidence of GER was lower for dogs premedicated with dexmedetomidine and hydromorphone (group DH), compared with dogs premedicated with acepromazine and hydromorphone (group AH) or hydromor-phone alone (group H [control group]). This finding supported our hypothesis that premedication with hydromorphone and dexmedetomidine administered IM would result in a lower incidence of GER than would premedication with hydromorphone alone. However, our finding that the incidence of GER did not meaningfully differ between dogs in groups H and AH was in contrast to our hypothesis that premedication with acepromazine and hydromorphone (vs hydromorphone alone) would result in a lower incidence of GER in dogs.

In the present study, there was an 89% lower incidence of GER when dexmedetomidine was added to the hydromorphone premedication, compared with premedicating with hydromorphone alone. The effects of α2-adrenoceptor agonists on LES are not well documented and may be drug specific. Studies6,17 show that administration of xylazine reduces LES tone and increases the incidence of GER in anesthetized dogs. In contrast, a study12 of healthy people shows a minimal reduction in LES tone after sedation with dexmedetomidine alone, suggesting that this drug is unlikely to promote GER. Dexmedetomidine is a widely used α2-adrenoceptor agonist in dogs and cats; however, studies evaluating the drug's effects on GER and regurgitation in animals are lacking. On the basis of our recent literature review of the subject, the present study was the first to our knowledge to investigate the effects of dexmedetomidine on the incidence of GER in dogs. Although the specific mechanisms responsible for the decrease in GER were unclear, our results suggested a beneficial and possibly protective effect of premedication with dexmedetomidine administered IM before anesthesia is induced with propofol and maintained with isoflurane in healthy dogs.

The incidence of GER did not meaningfully differ for dogs in the AH versus H groups. Although not statistically significant, the number of dogs with GER in group AH (n = 6) was 33% less than in group H (9). A previous study5 shows that the risk of GER is lower when acepromazine is administered alone than when combined with morphine, a full agonist at μ-receptors. Opioids, especially full agonists at μ-receptors, delay gastric emptying and increase regurgitation and GER in dogs.5,18 The incidence of GER for dogs in the AH group (46% [6/13]) was similar to that found in a previous study19 that evaluated dogs premedicated with hydro-morphone and acepromazine before anesthesia.

The incidence of GER did not differ significantly between the DH and AH groups. However, only 1 of the 13 dogs in the DH group had GER, whereas 6 of the 13 dogs in the AH group had GER. It was possible that the small group sizes did not allow for significance to be found. The small group sizes were the main limitation of our study; however, a relatively high percentage difference in effect size was considered in the power analysis, which led to small group sizes and difficulty in detecting differences. Studies with larger cohorts should be performed to further evaluate the effects of dexmedetomidine and acepromazine on anesthesia-associated GER.

Findings of a previous study20 suggest a theoretical increased risk of GER and regurgitation with the use of propofol, compared with thiopental, for induction of anesthesia. Our findings indicated that the median propofol dose and the incidence of GER were higher in the H group, compared with the DH and AH groups. However, when propofol dose was controlled for in logistic regression analysis, there was still a significant difference in the incidence of GER between these groups. This finding suggested that higher doses of propofol may contribute to the higher incidence of GER in the H group; however, this factor alone could not explain the significantly lower incidence of GER in the DH group. Thus, premedication with dexmedetomidine may substantially reduce the incidence of GER in dogs when hydromorphone and propofol are part of the anesthetic drug regimen.

The overall incidence of regurgitation in dogs of the present study was 15% (6/39) and similar to the incidence (11% [2/18]) in a study16 of healthy dogs undergoing elective orthopedic surgery. Dogs undergoing orthopedic procedures are at a much higher risk of regurgitating, which may be partly explained by the changes in depth of anesthesia when dogs are moved from one location to another and the need for perioperative changes in patient positioning and subsequent changes in abdominal and gastric pressures.3,4 In the present study, none of the dogs in group DH regurgitated and only 4 dogs in group H and 2 in group AH regurgitated, yielding low incidences of regurgitation across groups. Thus, studies with larger cohorts should be performed to allow for the detection of differences in this less frequent adverse event across groups of interest.

In the present study, 13 dogs vomited and only 3 of these 13 developed GER. Also, none of the dogs that vomited went on to regurgitate later. These findings suggested that vomiting induced by premedication could be beneficial because it results in a reduction in gastric contents, potentially decreasing the risk of GER and regurgitation.5,13 However, previous studies5,15,18,19 show no association between preanesthetic vomiting and development of GER in dogs. Further studies investigating the association between vomiting, regurgitation, and GER are required.

Studies evaluating the duration of preanesthetic withholding of food and the incidence of GER are controversial. For instance, findings by Galatos et al6 and Savas et al7 suggest that shorter durations of food withholding could be beneficial for dogs undergoing general anesthesia to decrease the risk of GER; however, a recent study16 shows that consumption of a light meal 3 hours (vs 18 hours) prior to anesthesia is associated with greater odds of GER and regurgitation in dogs. In the present study, the duration of food withholding was standardized to that routinely used in our hospital, between 8 and 14 hours, and no association was detected between the duration of food withholding and the development of GER. This wide range for the duration of food withholding was distributed evenly across the groups but may have caused unwanted variability within the study population.

In the present study, the incidence of GER in healthy dogs undergoing anesthesia for elective hind limb orthopedic procedures was similar for dogs in the H and AH groups but significantly lower for dogs in the DH group versus the H group. Thus, the combined use of dexmedetomidine and hydromorphone as premedication may be a better choice (vs hydro-morphone alone or with acepromazine) to reduce GER in healthy dogs undergoing orthopedic surgery. Additional research is warranted.

Acknowledgments

This study was funded by the Companion Animal Health Fund at Cummings School of Veterinary Medicine, Tufts University.

The authors declare that there were no conflicts of interest.

Footnotes

a.

Excel RAND random number generator, version 2010, Microsoft Corp, Redmond, Wash.

b.

ComforTec Z/pH probes ZPN-BS46, Sandhill Scientific Inc, Highlands Ranch, Colo.

c.

ZepHr pH monitoring system, Sandhill Scientific Inc, Highlands Ranch, Colo.

d.

ZepHr software, Sandhill Scientific Inc, Highlands Ranch, Colo.

e.

SPSS, version 21.0, IBM Corp, Armonk, NY. d. Falender RA, Wetmore LA, Liakouras L, et al. Randomized prospective evaluation of the influence of methadone, hydromorphone, and glycopyrrolate administration on perioperative gastroesophageal reflux and regurgitation in anesthetized dogs (abstr), in Proceedings. Vet Comp Orthop Traumatol 2015;28:A10.

Abbreviations

GER

Gastroesophageal reflux

LES

Lower esophageal sphincter

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Contributor Notes

Address correspondence to Dr. Costa (Rcosta@midwestern.edu).