A comparison of ketamine-midazolam and ketamine-medetomidine combinations for induction of anaesthesia in rabbits

Comparison of the effects of intranasal and intramuscular midazolam-butorphanol-ketamine on intraocular pressure, tear production and sedation in New Zealand White rabbits

OBJECTIVE

To compare the effects of intranasal (IN) and intramuscular (IM) midazolam-butorphanol-ketamine on intraocular pressure (IOP), tear production (TP) and sedation in rabbits.

STUDY DESIGN

Prospective, randomized, crossover experimental study.

ANIMALS

Fourteen male New Zealand White rabbits, aged 1-2 years, body mass 3.1 ± 0.8 kg (mean ± standard deviation).

METHODS

Rabbits were administered midazolam (1 mg kg-1), butorphanol (1.5 mg kg-1) and ketamine (5 mg kg-1) via IN and IM routes. IOP, TP and sedation scores were assessed at 0 (before drug administration), 5, 15, 30, 45 and 60 minutes after drug administration. Heart rate (HR), respiratory rate (fR), rectal temperature (RT), noninvasive mean arterial blood pressure (MAP) and peripheral hemoglobin oxygen saturation (SpO2) were simultaneously recorded until 45 minutes after drug administration. The onset and duration of sedation and sedation scores were recorded.

RESULTS

Drug delivery route had no significant impact on mean IOP (p = 0.271) or TP (p = 0.062), and there were no significant changes over time for IOP (p = 0.711) or TP (p = 0.372). Similarly, delivery route had no significant impact on HR (p = 0.747), fR (p = 0.872), RT (p = 0.379), MAP (p = 0.217) and SpO2 (p = 0.254). Sedation onset was faster with IN (3.0 ± 1.0 minutes) than with IM administration (4.9 ± 0.7 minutes) (p = 0.011), but sedation duration was significantly longer with IM (52.6 ± 7.2 minutes) than with IN delivery (30.7 ± 6.8 minutes) (p = 0.004). There was no significant difference in sedation scores between the two delivery routes at any of the recorded time points.

CONCLUSIONS AND CLINICAL RELEVANCE

The combination of midazolam-butorphanol-ketamine had minimal impact on physiological and ocular variables regardless of the route of administration, whereas IN drug administration led to a shorter onset and duration of action than IM administration.

Sedation and Anesthesia in Exotic Animal Critical Care

Sedation and anesthesia of exotic animals in inherently challenging, but often facilitates the best care for patients. Critical illness or injury adds on another layer of complexity to their management for obtaining diagnostics and providing treatments. This article serves to review some of the more recent literature of sedation and anesthesia within exotics practice, bringing to light some nuances and considerations for when those patients are critically ill or injured.

Intramuscular alfaxalone with or without buprenorphine or hydromorphone provides sedation with minimal adverse effects in healthy rabbits (Oryctolagus cuniculus) in a randomized blinded controlled trial

OBJECTIVE

To evaluate the effects of alfaxalone administered IM with or without buprenorphine or hydromorphone in healthy rabbits (Oryctolagus cuniculus).

ANIMALS

24 male rabbits undergoing elective orchiectomy between August 21, 2021, and November 6, 2021.

PROCEDURES

In this controlled clinical trial, rabbits were randomly assigned to receive alfaxalone (4 mg/kg, IM) alone (group A; n = 8) or with buprenorphine (0.03 mg/kg, IM; group BA; 8) or hydromorphone (0.1 mg/kg, IM; group HA; 8). Vital signs and sedation scores were recorded immediately prior to (T0) and 10 minutes after (T1) treatment. Ease of IV catheter placement and pain scores were also evaluated. All rabbits received ketamine (2.5 mg/kg, IV), midazolam (0.13 mg/kg, IV), and meloxicam (0.5 mg/kg, SC) before orchiectomy but after IM treatments. Results were compared across groups with ANOVA or Fisher exact tests and across time with paired t tests.

RESULTS

Sedation score, median time to recumbency, and ease of catheter placement did not differ among groups. Supraglottic airway device placement was possible for 1 rabbit in group A, 1 in group BA, and 2 in group HA. Mean respiratory rate at T1 versus T0 was significantly decreased for groups BA (63.8 vs 128.6 breaths/min) and HA (66.7 vs 123.2 breaths/min). Mean postoperative pain scores were significantly lower for rabbits in group HA (0.58), compared with those in groups A (2.25) and BA (2.06).

CLINICAL RELEVANCE

All 3 treatments provided reliable sedation; however, alfaxalone (4 mg/kg, IM) combined with hydromorphone (0.1 mg/kg, IM) may be a better choice for painful procedures.

Intramuscular Alfaxalone-Butorphanol-Midazolam Compared with Ketamine-Butorphanol- Midazolam in New Zealand White Rabbits

Rabbits are a common companion animal and research subject and frequently require sedation to facilitate procedures. The objective of this study was to compare the effects of intramuscular butorphanol and midazolam combined with either alfaxalone or ketamine in rabbits. In a complete crossover study, healthy New Zealand white rabbits (n = 9; age, 6 mo) randomly received midazolam (1 mg/kg IM) and butorphanol (1 mg/kg IM) combined with either alfaxalone (2 mg/kg IM; ABM) or ketamine (5 mg/kg IM; KBM). Time to first effects, recumbency, and standing (recovery) were recorded. Every 5 min during recumbency, an investigator who was blind to treatment group collected serial physiologic parameters and sedation scores. At 5 min after rabbits became recumbent, manipulations were performed to mimic 2-view radiography and a cephalic intravenous catheter was placed. At 30 min after drug injection, flumazenil (0.05 mg/kg IM) was administered for reversal. Food consumption and fecal output were measured for 3 d after each study day. Time to standing and duration of recumbency differed significantly between groups. The median (range) of the total sedation score for ABM was 10 (8 to 10) and for KBM was 10 (6 to 10). Sham radiographs were successful in all rabbits in both groups. Physiologic parameters were not significantly different between groups over time. At 24 h after drug treatment, KBM-treated rabbits showed reduced food intake and both groups showed reduced fecal output. Total sedation scores decreased significantly over time in KBM rabbits ( P < 0.001) but not in ABM rabbits (P = 1). The duration of recumbency was significantly longer in ABM rabbits than in KBM rabbits. Both protocols produced sufficient sedation for radiograph acquisition without clinically significant adverse effects.

Endotracheal intubation in rabbits using a video laryngoscope with a modified blade

Rabbits are being increasingly used as companion animals, and in research; thus, the need for proper veterinary care for rabbits has increased. Surgical access is more challenging in rabbits under inhalation anesthesia compared to other animals, such as dogs and cats. Rabbits have a very narrow and deep oral cavity, large incisors, and a large tongue. Moreover, their temporomandibular joint has limited mobility, making it more difficult to approach the larynx. Various methods have been proposed to overcome this difficulty. The video laryngoscope was introduced in 1999 and is useful when airway intubation is unsuccessful using a conventional laryngoscope. We postulated that a video laryngoscope with a modified size 1 Macintosh blade (McGrath MAC Video Laryngoscope, Medtronic, USA) would facilitate the intubation of New Zealand White rabbits. Sixteen specific-pathogen-free male New Zealand White rabbits weighing 3.45–4.70 kg were studied. All rabbits were intubated using the video laryngoscope. Typically, a 3.0 mm endotracheal tube was used for rabbits weighing < 4 kg, while a 3.5 mm tube was used in those weighing > 4 kg. During surgery, anesthesia was well maintained, and there were no major abnormalities in the animals’ conditions. No rabbit developed breathing difficulties or anorexia after recovering from anesthesia. We established an intubation method using a video laryngoscope with a modified blade and stylet in the supine (ventrodorsal) position and successfully applied it in 16 rabbits. It is useful for training novices and for treating rabbits in veterinary hospitals with few staff members and animal research facilities where there are insufficient human resources.

Effects of a Single Opioid Dose on Gastrointestinal Motility in Rabbits (Oryctolagus cuniculus): Comparisons among Morphine, Butorphanol, and Tramadol

The aim of this study was to evaluate and compare the effects of single doses of butorphanol, morphine, and tramadol on gastrointestinal motility in rabbits (Oryctolagus cuniculus) using non-invasive imaging methods, such as radiographic barium follow through and ultrasonographic contraction counts. Time-lapse radiographic and ultrasound examinations were performed before and after a single intramuscular dose of 5 mg kg⁻¹ butorphanol, 10 mg kg⁻¹ morphine, or 10 mg kg⁻¹ tramadol. Pyloric and duodenal contraction counts by ultrasonography and radiographic repletion scores for the stomach and caecum were analysed using a mixed linear model. No significant effect was noted on ultrasound examinations of pyloric and duodenal contractions after administration of an opioid treatment. Morphine had a significant effect on the stomach and the caecum repletion scores, whereas butorphanol had a significant effect only on the caecum repletion score. Tramadol had no significant effect on the stomach or caecum repletion scores. The present findings suggest that a single dose of 5 mg kg⁻¹ butorphanol or 10 mg kg⁻¹ morphine temporarily slows gastrointestinal transit in healthy rabbits, preventing physiological progression of the alimentary bolus without the induction of ileus. In contrast, a single dose of 10 mg kg⁻¹ tramadol has no such effects.

Rabbit Sedation and Anesthesia

With the increasing frequency of rabbits as veterinary patients, the expectation for high-quality, intensive veterinary care, and resultantly an understanding of anesthesia has been increasing. Sedation and general anesthesia are commonly required for many routine and emergency procedures in rabbits, and this results in the need for a strong awareness of anesthetic principles, knowledge of limitations of anesthesia, and maintenance of high standards of anesthesia.

Assessment of intramuscular administration of three doses of alfaxalone combined with hydromorphone and dexmedetomidine for endoscopic-guided orotracheal intubation in domestic rabbits (Oryctolagus cuniculus)

OBJECTIVE

To determine the dose of alfaxalone for IM administration combined with dexmedetomidine and hydromorphone that would allow endoscopic-guided orotracheal intubation in rabbits without causing a decrease in respiratory rate or apnea.

ANIMALS

15 sexually intact (9 females and 6 males) healthy Miniature Lop rabbits weighing a mean ± SD of 2.3 ± 0.3 kg and ranging in age from 4 to 9 months.

PROCEDURES

In a randomized, controlled clinical trial, rabbits received 0.1 mg of hydro-morphone/kg and 0.005 mg of dexmedetomidine/kg, plus alfaxalone at either 2 mg/kg (5 rabbits), 5 mg/kg (5 rabbits), or 7 mg/kg (5 rabbits). Drugs were mixed in a single syringe and administered IM. Semiquantitative rating scales were used to evaluate quality of anesthesia and intubation. Orotracheal intubation was attempted with endoscopy and confirmed by capnography.

RESULTS

The number of successful intubations was 0, 3, and 4 in rabbits receiving 2, 5, and 7 mg of alfaxalone/kg, respectively. Median (range) anesthesia quality scores (scale, 0 to 12; 12 = deepest anesthesia) were 3 (2 to 5), 6 (5 to 6), and 6 (4 to 9) for rabbits receiving 2, 5, and 7 mg of alfaxalone/kg, respectively. The median (range) intubation quality scores (scale, 0 to 3 [ie, intubation not possible to easiest intubation]) were 0 (0 to 0), 2 (0 to 3), and 2 (0 to 3) for rabbits receiving 2, 5, and 7 mg of alfaxalone/kg, respectively. None of the rabbits experienced a decrease in respiratory rate or apnea.

CONCLUSIONS AND CLINICAL RELEVANCE

Increasing doses of alfaxalone combined with hydromorphone and dexmedetomidine increased the success rate of endoscopic-guided orotracheal intubation. Increasing the dose of alfaxalone had no effect on respiratory rate.

Formulation, characterization, optimization, and in-vivo performance of febuxostat self-nano-emulsifying system loaded sublingual films

Febuxostat (FXS) is a potent antigout drug with poor water solubility and relative high first-pass effect leading to moderate oral bioavailability (<49%). This study aimed to increase FXS solubility and bioavailability by optimizing sublingual fast-dissolving films (SFs) containing a selected FXS self-nano-emulsifying system (s-SNES) previously prepared by our team. The s-SNES was loaded into SFs by solvent casting technique. A full factorial design (3²) was applied to study the effects of polymer and plasticizer types on mechanical characteristics and the dissolution profile of FXS from the SFs. Numerical optimization was performed to select the SF having highest desirability according to predetermined characteristics. The optimized SF (O-SF) contained 1 g of s-SNES, polyvinylpyrrolidone K30 (6%w/v), polyethylene glycol 300 (20%w/w of polymer wt.), and Avicel PH101 (0.5%w/v). O-SF showed good permeation of FXS through sheep sublingual tissue. Storage of O-SF for three months showed no significant change in the FXS dissolution profile. In-vivo performance of O-SF in rabbits was compared to that of oral marketed tablets (Staturic^® 80 mg). A cross-over design was applied and pharmacokinetic parameters were calculated after ensuring absence of sequence effect. Statistical analysis revealed better performance for O-SF with significantly higher C_max, AUC_0–24, AUC_0–∞, apparent t_1/2 together with lower t_max, and apparent k_el than marketed tablets. Relative bioavailability of O-SF compared to the marketed tablet was found to be 240.6%. This confirms the achievement of the study aims of improving dissolution rate and bioavailability of FXS using a patient-wise convenient formula.

A Pharmacokinetic-Pharmacodynamic Study of Intravenous Midazolam and Flumazenil in Adult New Zealand White-Californian Rabbits (Oryctolagus cuniculus)

Flumazenil, a competitive GABAA receptor antagonist, is commonly used in rabbits to shorten sedation or postanesthetic recovery after benzodiazepine administration. However, no combined pharmacokinetic (PK) and pharmacodynamic (PD) data are available to guide its administration in this species. In a prospective, randomized, blinded, crossover study design, the efficacy of IV flumazenil (FLU; 0.05 mg/kg) or saline control (SAL; equal volume) to reverse the loss of righting reflex (LORR) induced by IV midazolam (1.2 mg/kg) was investigated in 15 New Zealand white rabbits (2.73 to 4.65 kg, 1 y old). Rabbits were instrumented with arterial (central auricular artery) and venous (marginal auricular vein) catheters. After baseline blood sampling, IV midazolam was injected (T0). Flumazenil or saline (FLU/SAL) was injected 30 s after LORR. Arterial blood samples were collected at 1 and 3 min after midazolam injection, and at 1, 3, 6, 10, 15, 21, 28, 36, 45 and 60 min after injection with flumazenil. Plasma samples for midazolam, 1-OH-midazolam and flumazenil were analyzed using high performance liquid chromatography-high-resolution mass spectrometry and the time to return of righting reflex (ReRR) was compared between groups (Wilcoxon test). FLU terminal half-life, plasma clearance and volume of distribution were 26.3 min [95%CI: 23.3 to 29.3], 18.74 mL/min/kg [16.47 to 21.00] and 0.63 L/kg [0.55 to 0.71], respectively. ReRR was 25 times faster in rabbits treated with FLU (23 [8 to 44] s) compared with SAL (576 [130 to 1141] s; 95%CI [425 to 914 s]). Return of sedation (lateral recumbency) occurred in both groups (7/13 in FLU; 12/13 in SAL) with return of LORR in a few animals (4/13 in FLU; 7/13 in SAL) at 1540 [858 to 2328] s. In the population and anesthesia protocol studied, flumazenil quickly and reliably reversed sedation induced by midazolam injection. However, the potential return of sedation after flumazenil administration warrants careful monitoring in the recovery period.

Evaluation of subcutaneous administration of alfaxalone-midazolam and ketamine-midazolam as sedation protocols in African pygmy hedgehogs (Atelerix albiventris)

OBJECTIVE

To evaluate SC administration of 2 sedation protocols, ketamine-midazolam (KM) and alfaxalone-midazolam (AM), in African pygmy hedgehogs (Atelerix albiventris).

ANIMALS

9 healthy adult hedgehogs (5 males, 4 females).

PROCEDURES

A randomized, blinded, complete crossover study was performed. Sedation was induced by SC administration of either ketamine (30 mg/kg [14 mg/lb]) with midazolam (1 mg/kg [0.45 mg/lb]) or alfaxalone (3 mg/kg [1.4 mg/lb]) with midazolam (1 mg/kg), including a 2-week washout period between treatments. Flumazenil (0.05 mg/kg [0.02 mg/lb], SC) was administered 45 minutes after administration of either protocol to reverse the effects of midazolam. Physiologic variables, reflexes, and behaviors were monitored. Food intake and body weight were measured before and after sedation.

RESULTS

Deep sedation characterized by complete loss of the righting reflex, decreased jaw tone, decreased pelvic limb withdrawal reflex, and preservation of the palpebral reflex was produced in 7 of 9 hedgehogs after KM administration and all 9 hedgehogs after AM administration. Mean ± SD time to loss of righting reflex was 6.4 ± 2.4 minutes after KM administration and 10 ± 4.0 minutes after AM administration. Following flumazenil administration, no significant difference was found in recovery time between sedation with KM (18.8 ± 12.7 minutes) and AM (14.4 ± 7.8 minutes). No significant differences were found in respiratory rate, oxygen saturation, or body temperature between protocols, whereas heart rate was higher for sedation with KM. Both sedation protocols resulted in a transient reduction in food intake.

CONCLUSIONS AND CLINICAL RELEVANCE

Subcutaneous administration of KM and AM provided deep sedation that might be useful to facilitate routine, noninvasive procedures in hedgehogs.

A comparative study of the cardiopulmonary and sedative effects of a single intramuscular dose of ketamine anesthetic combinations in rabbits

The aim of this prospective, randomized, blinded crossover study was compare the cardiopulmonary and sedative effects of ketamine in combination with acepromazine, diazepam, dexmedetomidine, midazolam or xylazine, injected intramuscularly in rabbits, using eight one-year-old male New Zealand rabbits (4.1 ± 0.40 kg). All treatments included ketamine (K; 30 mg/kg) in combination with one of the following: acepromazine 0.5 mg/kg (treatment KA); diazepam 1 mg/kg (KD); dexmedetomidine 0.025 mg/kg (KDex); midazolam 1 mg/kg (KM); or xylazine 3 mg/kg (KX) mixed in the same syringe and injected intramuscularly. Cardiopulmonary variables, blood gases and sedative scores were measured before injection (T0 or baseline) and every 10 min thereafter, over a 60-min period. There were reductions in heart rate, compared with the baseline, at all evaluation times in treatment KX. Treatments KDex, KM and KX presented reductions in respiratory rate at all evaluation times, in comparison with the baseline. There were reductions in mean arterial pressure in KA and KX at times T10-T60 and in PaO2 in KDex, KM and KX at T10-T50. The sedation scores were similar in KA, KDex, KM and KX at T10-T20. Ketamine in combination with acepromazine, dexmedetomidine, midazolam or xylazine promoted similar sedative effects for twenty minutes, but the α2-agonists can promote hypoxemia.

Anaesthetic and Perioperative Management of 14 Male New Zealand White Rabbits for Calvarial Bone Surgery

Simple Summary

Bone substitutes are commonly used when bone grafts are necessary in human craniofacial surgery. To study the properties and biologic behaviour of those substitutes, they can be implanted in experimental animals. A frequently used model involves the creation of critical-sized defects (defects that are too large to heal by themselves) in the rabbits calvaria (the top part of the skull). The procedure was initially described in 1989 and the authors considered and reported that post-operative analgesia was not necessary. In our experience, this procedure is invasive and can result in severe postoperative pain. The anaesthetic management of rabbits undergoing this procedure is challenging. Most of the recent publications using this model fail to provide sufficient information on perioperative animal management. With this report we have aimed to document a possible practical and simple anaesthetic and postoperative management of rabbits undergoing this procedure. Particular emphasis has been placed on postoperative pain assessment, duration and treatment.

Abstract

Calvarial bone surgery on rabbits is frequently performed. This report aims to document a simple and practical anaesthetic and perioperative management for this procedure. Fourteen male New Zealand white rabbits were included in the study. Subcutaneous (SC) dexmedetomidine, ketamine and buprenorphine ± isoflurane vaporized in oxygen administered through a supraglottic airway device (V-gel^®) provided clinically suitable anaesthesia. Supplemental oxygen was administered throughout recovery. Monitoring was clinical and instrumental (pulse-oximetry, capnography, invasive blood pressure, temperature, arterial blood gas analysis). Lidocaine was infiltrated at the surgical site and meloxicam was injected subcutaneously as perioperative analgesia. After surgery, pain was assessed five times daily (composite behavioural pain scale and grimace scale). Postoperative analgesia included SC meloxicam once daily for four days and buprenorphine every 8 h for three days (unless both pain scores were at the lowest possible levels). Rescue analgesia (buprenorphine) was administered in case of the score > 3/8 in the composite pain scale, >4/10 on the grimace scale or if determined necessary by the caregivers. Airway management with a V-gel^® was possible but resulted in respiratory obstruction during the surgery in two cases. Hypoventilation was observed in all rabbits. All rabbits experienced pain after the procedure. Monitoring, pain assessments and administration of postoperative analgesia were recommended for 48 h.

Postanaesthetic effects of ketamine-midazolam and ketamine-medetomidine on gastrointestinal transit time in rabbits anaesthetised with isoflurane

BACKGROUND

Gastrointestinal stasis is a common perianaesthetic complication in rabbits. The objective of this study was to assess the impact on gastrointestinal transit time of ketamine-midazolam (KMZ) versus ketamine-medetomidine (later antagonised by atipamezole) (KMT-A) in rabbits anaesthetised with isoflurane.

METHODS

This was a cross-over, randomised, single-blinded, controlled, experimental trial. Seven healthy adult New Zealand White rabbits were used. Gastrointestinal transit time was assessed by contrast radiography in awake rabbits. Presence of contrast medium in the small intestine (gastric transit time), in the caecum (small intestinal transit time) and in faeces in the colon was assessed. One week later, 55 minutes isoflurane anaesthesia was induced with ketamine (15 mg/kg) and either midazolam (3 mg/kg) or medetomidine (0.25 mg/kg) by intramuscular injection. Thirty minutes after discontinuation of isoflurane, atipamezole (0.5 mg/kg) was administered only to rabbits in KMT-A treatment. Gastrointestinal transit time was then assessed in both treatment groups, beginning 30 minutes after cessation of isoflurane administration. Two weeks later, the treatment groups were interchanged.

RESULTS

Gastric and small intestinal transit times were significantly longer with KMT-A (92±109 minutes and 214±119 minutes, respectively) than with KMZ (1±0 minutes and 103±6 minutes, respectively) and in the awake state (7±7 minutes and 94±32 minutes, respectively).

CONCLUSION

Clinicians should therefore be aware of the potential gastrointestinal side effects of KMT-A, particularly in rabbits at risk for gastrointestinal stasis.

Comparison of Systemic Effects of Midazolam, Ketamine, and Isoflurane Anaesthesia in Rabbits

Introduction

Clinical doses of anaesthetic agents were administered to rabbits and effects on the brain, heart, and liver were investigated biochemically and histopathologically.

Material and Methods

The rabbits were randomly divided into three main groups (16 rabbits each) and each group into study (n = 8) and control (n = 8) groups. All study group rabbits received 3 mg/kg of midazolam (M) intramuscularly. Group 1.1 (M) received nothing further, group 2.1 (MK) also received 25 mg/kg of ketamine, and group 3.1 (MKI) besides ketamine was also given 2% isoflurane to induce anaesthesia for 30 min. NaCl solution in the same volume as midazolam and ketamine was injected into the controls.

Results

In clinical evaluation significant differences were detected in respiratory and heart rates. In blood gas analysis the PO₂ and PCO₂ values showed statistical differences in anaesthesia intervals. Significant biochemical value changes were recorded in creatine kinase-Mb, glucose, and total protein. Histopathological liver examinations revealed higher total apoptotic and normal cell numbers in the MK than in the M and MKI groups. Apoptotic cell numbers were statistically significant in M and MK groups.

Conclusion

Anaesthetic agents may increase programmed apoptosis. The MKI anaesthetics combination was found to cause less cell destruction in general than the other study groups. It was indicated that MKI was the safer anaesthetic combination in rabbits.

Peri-anaesthetic mortality and nonfatal gastrointestinal complications in pet rabbits: a retrospective study on 210 cases

OBJECTIVE

The aim of this study was to determine the incidence and the associated risk factors of peri-anaesthetic mortality and gastrointestinal complications in pet rabbits.

STUDY DESIGN

Retrospective cohort study.

ANIMALS

A total of 185 pet rabbits admitted to the Exotic Referal Service of Beaumont Sainsbury's Animal Hospital over the period 2009-2016.

METHODS

The clinical records of the rabbits were obtained from the database. To evaluate the incidence of peri-anaesthetic mortality, three possible outcomes were considered: alive, dead or euthanized within the 72 hours following the anaesthetic event. Food intake and stool production during the first 72 hours following the anaesthetic event were evaluated to investigate the occurrence of gastrointestinal complications. Thereafter, various hypothesized risk factors, including administration of alpha-2 agonists, body weight, American Society of Anaesthesiologists classification and endotracheal intubation were tested against peri-anaesthetic mortality and gastrointestinal complications, with both univariate and multivariate binary logistic regression.

RESULTS

Twenty-five out of 185 rabbits underwent two anaesthetic events; therefore, data from 210 cases were used. Of these 210 cases, six died during sedation or general anaesthesia and four (one of which euthanized) died during the first 72 postoperative hours, accounting for an actual mortality rate equal to 4.8% (95% confidence interval, 0.025-0.086). Peri-anaesthetic gastrointestinal complications developed in 77 (38%) out of the 204 anaesthetic events whose outcome was not intraoperative death (95% confidence interval, 0.314-0.446). Species-specific risk factors could not be identified for peri-anaesthetic mortality; however, the odds for post-anaesthetic gastrointestinal complications increased significantly with body weight (p = 0.01).

CONCLUSIONS AND CLINICAL RELEVANCE

Our findings confirm that rabbits continue to have a higher incidence of peri-anaesthetic mortality than dogs and cats, and highlight a high risk for nonfatal peri-anaesthetic gastrointestinal complications in this species.

Comparison of a Supraglottic Airway Device (v-gel®) with Blind Orotracheal Intubation in Rabbits

INTRODUCTION

Achieving a secure airway in rabbits is generally considered more difficult than in cats or dogs. Their relatively large tongue, small oropharyngeal cavity and glottis limit direct visualization. A rabbit-specific supraglottic airway device (SGAD) may offer benefits over blind orotracheal intubation.

ANIMALS AND METHODS

Fifteen adult New Zealand white rabbits were randomized to SGAD or orotracheal intubation (ETT). All animals were sedated with dexmedetomidine (0.1 mg kg^-1 IM) and midazolam (0.5 mg kg^-1 IM), followed by induction with alfaxalone (0.3 mg kg^-1 IV). Two CT scans of the head and neck were performed, following sedation and SGAD/ETT placement. The following were recorded: time to successful device insertion, smallest cross-sectional airway area, airway sealing pressure, and histological score of tracheal tissue. Data were analyzed with a Mann-Whitney test.

RESULTS

Two rabbits were excluded following failed ETT. Body masses were similar [ETT; n = 6, 2.6 (2.3-4.5) kg, SGAD; n = 7, 2.7 (2.4-5.0) kg]. SGAD placement was significantly faster [33 (14-38) s] than ETT [59 (29-171) s]. Cross-sectional area (CSA) was significantly reduced from baseline [12.2 (6.9-3.4) mm²] but similar between groups [SGAD; 2.7 (2.0-12.3) mm², ETT; 3.8 (2.3-6.6) mm²]. In the SGAD group, the device tip migrated into the laryngeal vestibule in 6/7 rabbits, reducing the CSA. ETT airway seals were higher [15 (10-20) cmH₂O], but not significant [SGAD; 5 (5-20) cmH₂O, p = 0.06]. ETT resulted in significantly more mucosal damage [histological score 3.3 (1.0-5.0)], SGAD; 0.67 (0.33-3.67).

CONCLUSION

The SGAD studied was faster to place and caused less damage than orotracheal intubation, but resulted in a similar CSA.

Rabbit analgesia

With the increasing popularity of rabbits as household pets, the complexity of diagnostic and surgical procedures performed on rabbits is increasing, along with the frequency of routine surgical procedures. More practitioners are faced with the need to provide adequate analgesia for this species. Preemptive analgesia prior to planned surgical interventions may reduce nervous system changes in response to noxious input, as well as reduce postoperative pain levels and analgesic drug requirements. Concurrent administration of analgesic drugs to anesthetized rabbits undergoing painful procedures is warranted both pre- and intraoperatively as well as postoperatively. This article discusses the neuropharmacologic and pharmacologic aspects of pain in rabbits, and reviews current protocols for the use of analgesic drugs.

The use of propofol and sevoflurane for surgical anaesthesia in New Zealand White rabbits

New Zealand White (NZW) rabbits ( n = 34) received intravenous propofol (16 ± 5 mg/kg) for induction of anaesthesia followed by maintenance with sevoflurane (4.0 ± 0.5%) in oxygen. All animals underwent ovariohysterectomy. Heart rate, respiratory rate, haemoglobin oxygen saturation, end-tidal carbon dioxide concentration, end-tidal sevoflurane concentration and oesophageal temperature were monitored every 5 min. Time from induction of anaesthesia to tracheal extubation and sternal recumbency were recorded as was the quality of recovery. Direct arterial blood pressure values (mmHg) were recorded every 5 min from 19 rabbits and 22 arterial blood gases analyses were performed (11 postintubation and 11 at the time of recovery). Propofol produced smooth induction of anaesthesia without production of apnoea. Intubation was successfully performed in all but one rabbit in an average of 4 ± 3 min from the beginning of propofol administration. No ventilatory support was required during the anaesthetic period. Respiratory rate averaged 51 ± 8 bpm and end-tidal CO2 (kPa) was 4.0 ± 0.5 mmHg during anaesthesia. Blood gas values were maintained within normal limits and average mean arterial blood pressure was 73.4 ± 7.9 mmHg. Time to regain the swallowing reflex following discontinuation of sevoflurane was 2 ± 1 min and time to sternal recumbency was 8 ± 0.3 min. No anaesthetic-related mortality occurred and all animals recovered uneventfully. Propofol–sevoflurane anaesthesia produced a good quality of surgical anaesthesia for ovariohysterectomy and stable cardiopulmonary conditions. Propofol–sevoflurane anaesthesia in young healthy NZW rabbits appears to be an effective and practically useful method of anaesthesia.

Anaesthesia with a combination of ketamine and medetomidine in the rabbit: effect of premedication with buprenorphine

OBJECTIVE

To assess the effects of premedication with buprenorphine on the characteristics of anaesthesia induced with ketamine/medetomidine.

STUDY DESIGN

Prospective crossover laboratory study.

ANIMALS

Six female New Zealand White rabbits.

METHODS

Rabbits received, on occasions separated by 7 days, either buprenorphine (0.03 mg kg(-1)) or saline subcutaneously (SC) as premedication, followed 1 hour later by SC ketamine (15 mg kg(-1)) and medetomidine (0.25 mg kg(-1)) (K/M). At pre-determined time points reflex responses and cardiopulmonary parameters were recorded and arterial blood samples taken for analysis. Total sleep time was the duration of loss of the righting reflex. Duration of surgical anaesthesia was the time of suppression of the ear pinch and pedal withdrawal reflexes. Wilcoxon signed-ranks tests were used to compare data before (T(0)) and 10 minutes after (T(10)) injection with K/M.

RESULTS

All animals lost all three reflex responses within 10 minutes of injection of K/M. The duration of loss of these reflexes significantly increased in animals that received buprenorphine. At induction, animals that had received buprenorphine tended to have a lower respiration rate but there were no significant differences in arterial PCO(2), PO(2) or pH between treatments. Hypoxaemia [median PaO(2) < 6.0 kPa (45 mmHg)] developed in both treatments at T(10) but there was no significant difference between treatments. Mean arterial pressure (MAP) was lower at T(10) in animals that had received buprenorphine.

CONCLUSION AND CLINICAL RELEVANCE

Premedication with buprenorphine significantly increased the duration of anaesthesia induced by K/M, with no significant depression of respiration further to the control treatment within the first 10 minutes of anaesthesia. The MAP decreased but this was not reflected in a difference in other physiological parameters. These data show that premedication with buprenorphine, before K/M anaesthesia in the rabbit, has few negative effects and may provide beneficial analgesia.

Care of the geriatric rabbit

The average life span reported in laboratory and lay literature for the domestic rabbit is 5 to 10 years. The author and other veterinarians are now regularly seeing rabbits living to 9 or 10 years, the oldest reported in the author's practice being 14 years. Rabbits are herbivorous prey species with continually growing (elodont) teeth. This feature allows the geriatric rabbit to possess teeth that are essentially "new", a distinct advantage over geriatric carnivores. Expanded longevity, while generally desirable, necessarily accompanies an increase in geriatric disorders. This article examines the spectrum of disease that can affect the geriatric rabbit as well as crucial factors concerning the clinical management of the animal up to the end of its life. An improved understanding of geriatric disorders in pet rabbits allows early recognition and the opportunity to improve quality of life.

Induction of anaesthesia with either midazolam or propofol in rabbits premedicated with fentanyl/fluanisone

Fifty-four rabbits that were to be neutered were premedicated with 0.1 ml/kg fentanyl/fluanisone and then randomly allocated to be anaesthetised with either midazolam or propofol. Anaesthesia was then maintained with isoflurane. The ease of orotracheal intubation, the rabbits' cardiorespiratory variables, and the speed and quality of recovery from anaesthesia were assessed by the same anaesthetist who was unaware of the induction agent used. Hypotension was common in both groups. The mean (sd) respiratory rates were 30 (12) breaths per minute in the midazolam group and 43 (15) breaths per minute in the propofol group. The mean (sd) time to first head lift was 36 (21) minutes in the midazolam group and 14 (11) minutes in the propofol group, and the mean (sd) times to the return of the righting reflex were 35 (19) minutes and 15 (eight) minutes, respectively. The quality of recovery was better in the propofol group than in the midazolam group.

Cardiovascular physiology and diseases of the rabbit

This article reviews what is known about the diagnosis and management of cardiovascular diseases in the pet rabbit. Current knowledge is based on anecdotal reports, derived from research data using the rabbit as an animal model of human cardiovascular diseases, but most importantly canine and feline cardiology. It is likely that, as cardiovascular diseases are more often recognized, more specific information will soon become available for the treatment of the pet rabbit with cardiac disease.