Cardiorespiratory, anaesthetic and recovery effects of morphine combined with medetomidine and alfaxalone in rabbits

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.

Ketamine-propofol for total intravenous anaesthesia in rabbits: a comparison of premedication with acepromazine-medetomidine, acepromazine-midazolam or acepromazine-morphine

OBJECTIVE

To describe ketamine-propofol total intravenous anaesthesia (TIVA) following premedication with acepromazine and either medetomidine, midazolam or morphine in rabbits.

STUDY DESIGN

Randomized, crossover experimental study.

ANIMALS

A total of six healthy female New Zealand White rabbits (2.2 ± 0.3 kg).

METHODS

Rabbits were anaesthetized on four occasions, each separated by 7 days: an intramuscular injection of saline alone (treatment Saline) or acepromazine (0.5 mg kg^-1) in combination with medetomidine (0.1 mg kg^-1), midazolam (1 mg kg^-1) or morphine (1 mg kg^-1), treatments AME, AMI or AMO, respectively, in random order. Anaesthesia was induced and maintained with a mixture containing ketamine (5 mg mL^-1) and propofol (5 mg mL^-1) (ketofol). Each trachea was intubated and the rabbit administered oxygen during spontaneous ventilation. Ketofol infusion rate was initially 0.4 mg kg^-1 minute^-1 (0.2 mg kg^-1 minute^-1 of each drug) and was adjusted to maintain adequate anaesthetic depth based on clinical assessment. Ketofol dose and physiological variables were recorded every 5 minutes. Quality of sedation, intubation and recovery times were recorded.

RESULTS

Ketofol induction doses decreased significantly in treatments AME (7.9 ± 2.3) and AMI (8.9 ± 4.0) compared with treatment Saline (16.8 ± 3.2 mg kg^-1) (p < 0.05). The total ketofol dose to maintain anaesthesia was significantly lower in treatments AME, AMI and AMO (0.6 ± 0.1, 0.6 ± 0.2 and 0.6 ± 0.1 mg kg^-1 minute^-1, respectively) than in treatment Saline (1.2 ± 0.2 mg kg^-1 minute^-1) (p < 0.05). Cardiovascular variables remained at clinically acceptable values, but all treatments caused some degree of hypoventilation.

CONCLUSIONS AND CLINICAL RELEVANCE

Premedication with AME, AMI and AMO, at the doses studied, significantly decreased the maintenance dose of ketofol infusion in rabbits. Ketofol was determined to be a clinically acceptable combination for TIVA in premedicated rabbits.

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.

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.

A comparison of the pharmacodynamic effects of intravenous ketamine-xylazine with alfaxalone in mute swans (Cygnus olor) presenting at a wildlife veterinary hospital

OBJECTIVE

To compare effects of intravenous (IV) alfaxalone with ketamine-xylazine combination on anaesthetic induction, recovery and cardiopulmonary variables in mute swans.

STUDY DESIGN

Randomized, controlled, clinical study.

ANIMALS

A group of 58 mute swans.

METHODS

Swans were given either alfaxalone (10 mg kg-1; group A) or a combination of ketamine (12.5 mg kg-1) and xylazine (0.28 mg kg-1) (group KX) IV. Heart and respiratory rates, end-tidal carbon dioxide and peripheral haemoglobin oxygen saturation were recorded at 5 minute intervals during anaesthesia. Time from anaesthetic induction to intubation, from cessation of isoflurane to extubation, to lifting head, sternal recumbency and absence of head/neck ataxia were recorded. Anaesthetic and recovery quality were scored (1 = very poor; 5 = excellent). Data are presented as median (interquartile range). Significance was set at p < 0.05.

RESULTS

In group A, 44% (12/27) of swans required mechanical ventilation for 2-14 minutes versus 3.2% (1/31) of swans in group KX (p = 0.0002). Heart rate was higher in group A than in group KX [146 (127-168) versus 65.5 (56-78) beats minute-1, respectively; p < 0.0001]. The isoflurane concentration required to maintain anaesthesia was higher in group A than in group KX [2.5% (2.0-3.0%) versus 1.5% (1.0-2.0%), respectively; p = 0.0001]. Time from cessation of isoflurane administration to lifting head was significantly longer in group A than in group KX [12 (9-17) versus 6 (4-7.75) minutes, respectively; p < 0.0001]. Anaesthesia quality scores were significantly better in group KX than in group A [4 (4-5) versus 4 (3-4), respectively; p = 0.0011], as were recovery scores [4 (3-5) versus 2 (2-3), respectively; p = 0.0005].

CONCLUSIONS AND CLINICAL RELEVANCE

Alfaxalone is a suitable anaesthetic induction agent for use in mute swans. There is a greater incidence of postinduction apnoea and a higher incidence of agitation on recovery with alfaxalone than with ketamine-xylazine.

Hypoventilation following oxygen administration associated with alfaxalone-dexmedetomidine-midazolam anesthesia in New Zealand White rabbits

OBJECTIVE

To investigate the relationship between oxygen administration and ventilation in rabbits administered intramuscular alfaxalone-dexmedetomidine-midazolam.

STUDY DESIGN

Prospective, randomized, blinded study.

ANIMALS

A total of 25 New Zealand White rabbits, weighing 3.1-5.9 kg and aged 1 year.

METHODS

Rabbits were anesthetized with intramuscular alfaxalone (4 mg kg^-1), dexmedetomidine (0.1 mg kg^-1) and midazolam (0.2 mg kg^-1) and randomized to wait 5 (n = 8) or 10 (n = 8) minutes between drug injection and oxygen (100%) administration (facemask, 1 L minute^-1). A control group (n = 9) was administered medical air 10 minutes after drug injection. Immediately before (PRE_oxy/air5/10) and 2 minutes after oxygen or medical air (POST_oxy/air5/10), respiratory rate (f_R), pH, PaCO₂, PaO₂, bicarbonate and base excess were recorded by an investigator blinded to treatment allocation. Data [median (range)] were analyzed with Wilcoxon, Mann-Whitney U and Kruskal-Wallis tests and p < 0.05 considered significant.

RESULTS

Hypoxemia (PaO₂ < 88 mmHg, 11.7 kPa) was observed at all PRE times: PRE_oxy5 [71 (61-81) mmHg, 9.5 (8.1-10.8) kPa], PRE_oxy10 [58 (36-80) mmHg, 7.7 (4.8-10.7) kPa] and PRE_air10 [48 (32-64) mmHg, 6.4 (4.3-8.5) kPa]. Hypoxemia persisted when breathing air: POST_air10 [49 (33-66) mmHg, 6.5 (4.4-8.8) kPa]. Oxygen administration corrected hypoxemia but was associated with decreased f_R (>70%; p = 0.016, both groups) and hypercapnia (p = 0.016, both groups). Two rabbits (one per oxygen treatment group) were apneic (no thoracic movements for 2.0-2.5 minutes) following oxygen administration. f_R was unchanged when breathing air (p = 0.5). PaCO₂ was higher when breathing oxygen than air (p < 0.001).

CONCLUSIONS AND CLINICAL RELEVANCE

Early oxygen administration resolved anesthesia-induced hypoxemia; however, f_R decreased and PaCO₂ increased indicating that hypoxemic respiratory drive is an important contributor to ventilation using the studied drug combination.

Continuous Rate Infusion of Alfaxalone during Ketamine-Xylazine Anesthesia in Rats

Alfaxalone is an injectable anesthetic agent that is used in veterinary medicine for general anesthesia. We evaluated the safety and efficacy of alfaxalone delivered through continuous rate infusion by comparing ketamine-xylazine-alfaxalone (KXA) anesthesia with ketamine-xylazine (KX) anesthesia in Sprague-Dawley rats. Anesthesia was induced in male and female rats by using subcutaneous KX. After induction, rats in the KXA group received alfaxalone (10 mg/kg/h IV) for 35 min, whereas rats in the KX group did not receive alfaxalone. At the end of the trial, alfaxalone was discontinued, and xylazine was reversed in all rats by using atipamezole. Throughout anesthesia, we assessed forepaw withdrawal reflex (FPWR), hindpaw withdrawal reflex (HPWR), response to surgical stimulation, heart rate, respiratory rate, SpO₂, body temperature, and time to standing. KXA produced a reliable surgical plane of anesthesia, as evidenced by the loss of both FPWR and HPWR and lack of response to surgical stimulation in all 16 rats, whereas only 6 of the 16 rats in the KX group lost HPWR. No rat in the KXA group regained a paw withdrawal reflex during alfaxalone administration, whereas 3 of the 12 rats (25%) in the KX group that reached a surgical plane of anesthesia exited that plane within the 35-min timeframe. Neither heart rate, respiratory rate, SpO₂, body temperature, nor time to standing differed between KXA and KX groups; and there were no sex-associated differences in anesthesia response. These results indicate that alfaxalone (10 mg/kg/h IV) delivered through continuous rate infusion, in combination with ketamine and xylazine, provides a safe, prolonged, and reliable surgical plane of anesthesia in rats.

Pharmacokinetics and sedative effects of alfaxalone with or without dexmedetomidine in rabbits

This study aimed to investigate the specific pharmacokinetic profile and effects of alfaxalone after intravenous (IV) and intramuscular (IM) administration to rabbits and evaluate the potential interaction with dexmedetomidine. The study design was a blinded, randomized crossover with a washout period of 2 weeks. Five New Zealand white rabbits were used. Each animal received single IV and IM injections of alfaxalone at a single dose of 5 mg/kg, and single IV and IM injections of alfaxalone (5 mg/kg) combined with dexmedetomidine (100 μg/kg) administered intramuscularly. Blood samples were collected at predetermined times and analysed by high-performance liquid chromatography. The plasma concentration-time curves were analysed by non-compartmental analysis. Sedation/anaesthesia scores were evaluated by a modified numerical rating scale. At pre-determined time points heart and respiratory rates were measured. Times to sternal recumbency and standing position during the recovery were recorded. Concentrations of alfaxalone alone were very similar (slighty smaller) to concentrations when alfaxalone was combined with dexmedetomidine, after both routes of administration. Dexmedetomidine enhanced and increase the duration of the sedative effects of alfaxalone. In conclusion, alfaxalone administered in rabbits provides rapid and smooth onset of sedation. After IV and IM injections of alfaxalone combined with dexmedetomidine, a longer MRT and a deeper and extended sedation have been obtained compared to alfaxalone alone. Consequently, alfaxalone alone or in combination with dexmedetomidine could be useful to achieve respectively moderate to deep sedation in rabbits.

Evaluation of alfaxalone and dexmedetomidine for intramuscular restraint in European hedgehogs (Erinaceus europaeus)

The European hedgehogs may require the use of chemical restraint for clinical examination because of their tendency to roll up as a defensive behaviour. This study evaluated the effects of alfaxalone combined with dexmedetomidine for restraint of hedgehogs undergoing pre-release health checks and atipamezole for recovery.Twenty hedgehogs received alfaxalone 2 mg/kg and dexmedetomidine 0.05 mg/kg intramuscularly in the quadriceps. If the righting reflex was still present, both drugs were administered at half of the initial doses. A semiquantitative scale scored sedation; clinical variables evaluated included pulse rate, respiratory rate, arterial haemoglobin oxygen saturation, end-tidal CO₂ and body temperature.The righting reflex disappeared between 141 and 880 seconds. Overweight animals required one additional injection to achieve adequate relaxation. Pulse rate decreased during the procedure and increased after atipamezole administration. Respiratory rate and end-tidal CO₂ did not change statistically throughout the procedure but one hedgehog showed haemoglobin oxygen saturation lower than 90%. Recovery after atipamezole was smooth and complete. Body temperature decreased over time.The sedation protocol may represent an effective combination to restrain European hedgehogs and atipamezole provides a rapid antagonism. Additional sedatives administration may be required in overweight animals and an external source of oxygen should be available.

Comparison of alfaxalone-medetomidine and tiletamine-zolazepam in rescued common palm civets (Paradoxurus musangus)

Forty rescued common palm civets were anesthetized. Twenty animals received intramuscular injections of alfaxalone 5 mg/kg and medetomidine 0.05 mg/kg (A-M group), whereas twenty animals received 5 mg/kg of tiletamine and zolazepam (T-Z group). The A-M group was reversed with atipamazole 0.25 mg/kg. There were no significant differences in the time from anesthetic injection to induction and intubation between the A-M and T-Z groups. The time from the injection of reversal in the A-M group and the time from cessation of isoflurane in the T-Z group to extubation, first response to recovery and ambulation were longer (P<0.05) in the T-Z group. The T-Z group recorded lower (P<0.05) rectal temperatures compared to the A-M group. This study showed that both drug combinations can be used effectively for the immobilization of civets. The A-M combination provided better anesthetic depth, but with higher incidence of bradycardia and hypoxemia. The recovery time was reduced significantly as atipamezole was used as a reversal agent in the A-M combination.

Effects of buprenorphine, butorphanol or tramadol premedication on anaesthetic induction with alfaxalone in common marmosets (Callithrix jacchus)

OBJECTIVE

To investigate the clinical and physiological effects of intravenous (IV) alfaxalone alone or in combination with buprenorphine, butorphanol or tramadol premedication in marmosets.

STUDY DESIGN

Prospective, randomized, blinded, crossover design.

ANIMALS

Nine healthy marmosets (391 ± 48 g, 3.7 ± 2.2 years old).

METHODS

Meloxicam 0.20 mg kg^-1 subcutaneously, atropine 0.05 mg kg^-1 intramuscularly (IM) and either buprenorphine 20 μg kg^-1 IM (BUP-A), butorphanol 0.2 mg kg^-1 IM (BUT-A), tramadol 1.5 mg kg^-1 IM (TRA-A) or no additional drug (control) were administered to all marmosets as premedication. After 1 hour, anaesthesia was induced with 16 mg kg^-1 alfaxalone IV. All animals received all protocols. The order of protocol allocation was randomized with a minimum 28 day wash-out period. During anaesthesia, respiratory and pulse rates, rectal temperature, haemoglobin oxygen saturation, arterial blood pressure, palpebral and pedal withdrawal reflexes and degree of muscle relaxation were assessed and recorded every 5 minutes. Quality of induction and recovery were assessed. Duration of induction, immobilization and recovery were recorded. Blood samples were analysed for aspartate aminotransferase, creatine kinase and lactate dehydrogenase concentrations. The protocols were compared using paired t tests, Wilcoxon's signed-rank test with Bonferroni's corrections and linear mixed effect models where appropriate.

RESULTS

Out of nine animals, apnoea was noted in eight animals administered protocol BUP-A and two animals administered protocol BUT-A. With TRA-A and control protocols, apnoea was not observed. No other significant differences in any of the parameters were found; however, low arterial blood pressures and hypoxia occurred in TRA-A.

CONCLUSIONS AND CLINICAL RELEVANCE

Our study employing different premedications suggests that the previously published dose of 16 mg kg^-1 alfaxalone is too high when used with premedication because we found a high incidence of complications including apnoea (BUP-A), hypotension and hypoxaemia (TRA-A). Appropriate monitoring and countermeasures are recommended.

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.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.