Peri-operative body temperatures in isoflurane-anaesthetized rabbits following ketamine-midazolam or ketamine-medetomidine

Retrospective comparison of the effects of laryngeal mask and endotracheal tube on some cardio-respiratory variables in pet rabbits undergoing anaesthesia for elective gonadectomy

BACKGROUND

Endotracheal intubation in rabbits is challenging and supraglottic airway devices, such as laryngeal masks (LMA), represent an alternative as they are easy to insert, and do not stimulate the larynx requiring therefore a lighter plane of anaesthesia for their insertion and positioning than the endotracheal tubes. We investigated whether, compared to an endotracheal tube, the LMA can reduce the negative effects of general anaesthetics on some cardiovascular and respiratory parameters routinely monitored in rabbits anaesthetized for elective gonadectomy. The records of 21 adult mixed breed pet rabbits were collected retrospectively. Rabbits were divided in two groups based on the type of airway device used. A laryngeal mask secured the airway in group LMA (n = 11), and in group ETT (n = 10) an endotracheal tube was used. The amount of propofol used before successful insertion of the airway device was recorded. A pitot-based spirometer was connected and ventilatory variables were measured immediately after insertion. Pulse rate, non-invasive arterial blood pressure, haemoglobin oxygen saturation, respiratory rate, end-tidal carbon dioxide and volatile anaesthetic consumption were also monitored during the surgical procedure; extubation time was noted as well.

RESULTS

The use of LMA required significantly less propofol (0.8 to 4 mg/kg) for insertion than the ETT (1.2 to 5.6 mg/kg), and the difference was statistically significant (P < 0.01). No differences were observed in ventilatory variables measured immediately after airway positioning. Intraoperatively, there were no differences between groups for respiratory and cardiovascular variables, and amount of isoflurane administered. In all rabbits mean and diastolic blood pressure progressively decreased during surgery. Mean extubation time was shorter in group LMA (6 ± 2 min) than group ETT (8 ± 3 min, P < 0.01).

CONCLUSION

The airway device did not clinically affect the cardiovascular and respiratory variables during anaesthesia. Intraoperative hypoventilation was observed in most rabbits regardless of the device being used; therefore ventilatory support may be required. Rabbits with the laryngeal masks were extubated earlier.

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.

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.

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.

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

OBJECTIVE

To compare ketamine-midazolam (KMZ) and ketamine-medetomidine (KMT) anaesthesia in rabbits using anaesthetic induction, maintenance and recovery data.

STUDY DESIGN

Randomized, prospective, blinded clinical trial.

ANIMALS

Fifty rabbits (25 male, 25 female) of different breeds undergoing ovariohysterectomy or castration. Rabbits were 12.7 +/- 9.8 months old with body mass 2.24 +/- 0.61 kg.

STUDY DESIGN

Randomized, prospective, blinded clinical trial.

METHODS

Ketamine (15 mg kg(-1)) and midazolam (3 mg kg(-1)) or medetomidine (0.25 mg kg(-1)) were administered by intramuscular (IM) injection. Ten minutes after IM injection, blind intubation of the trachea was attempted. The time taken, the number of attempts and a subjective score of the ease of intubation were recorded. Isoflurane (range 0-3.6%) in 100% oxygen was delivered via a Jackson Rees modification of an Ayre's T-piece non-rebreathing system. Carprofen (3 mg kg(-1)) and dextrose saline (5 mL kg(-1) hour(-1)) were administered intravenously (IV). During surgery heart rate (HR), respiratory rate (RR) and arterial oxygen saturation of haemoglobin (SpO(2)) were monitored. Times to extubation and first head lift were recorded. Group KMT received atipamezole (0.5 mg kg(-1)) IM 30 minutes after discontinuation of isoflurane. Activity was scored at 30, 60 and 120 minutes after volatile agent discontinuation. Mean time to loss of righting reflex (LRR), body mass, RR and vaporizer setting were compared using a two-tailed t-test. Median values for all other data were compared using a Mann-Whitney test.

RESULTS

Mean time to LRR (+/-SD) was significantly shorter with KMT (1.64 +/- 0.55 minutes) compared with KMZ (2.28 +/- 0.66 minutes). Intubation was not possible in seven rabbits (three with KMT, four with KMZ) and three with KMT developed laryngospasm. Mean HR, SpO(2) and vaporizer settings were all significantly lower in group KMT.

CONCLUSION AND CLINICAL RELEVANCE

KMT has a faster onset of action and a greater isoflurane-sparing effect when compared with KMZ. Rabbits with KMT were more prone to laryngospasm and had significantly lower HR.