Impact of procedural handling on the physiological effects of alfaxalone anaesthesia in the ball python (Python regius).

To describe the cardiovascular changes following intramuscular (handled) and intravascular (undisturbed, via intraarterial catheter) alfaxalone administration, we studied 20 healthy ball pythons (Python regius) in a randomised, prospective study. The pythons were instrumented with occlusive arterial catheters to facilitate undisturbed, continuous monitoring of heart rate and blood pressure. Six pythons were administered intramuscular (IM) saline, followed by 20 mg/kg IM alfaxalone, and were manually restrained for both injections. Six pythons received intraarterial (IA) saline, followed by 10 mg/kg IA alfaxalone, and remained undisturbed for both injections. Arterial blood samples were taken at 0, 12 and 60 min post-injection, and heart rate and blood pressure were recorded for 60 min. The remaining eight snakes received 20 mg/kg IM or 10 mg/kg IA alfaxalone (n = 4 per treatment) and were not handled for intubation 10 min post-injection, to examine the effects of handling during anaesthesia. IM administration of 20 mg/kg alfaxalone or an equivalent volume of saline elicited a profound tachycardia and hypertension, which recovered to resting values after 20 min. However, when 10 mg/kg alfaxalone or saline were injected IA, mild hypotension and a lower magnitude tachycardia occurred. Arterial PCO2 and PO2, pH and lactate concentrations did not change following IA alfaxalone, but an acidosis was observed during IM alfaxalone anaesthesia. There were no significant changes in plasma catecholamines and corticosterone among treatments. Handling for injection and during anaesthesia associated with intubation significantly affects cardiovascular parameters, whereas alfaxalone per se only elicits minor changes in cardiovascular physiology.

Anaesthetic induction with alfaxalone in the ball python (Python regius): dose response and effect of injection site.

OBJECTIVE: To characterise the minimum dose of intramuscular alfaxalone required to facilitate intubation for mechanical ventilation, and to investigate the impact of cranial versus caudal injection on anaesthetic depth. STUDY DESIGN: Randomised crossover study. ANIMALS: Six healthy juvenile ball pythons (Python regius). METHODS: Three dosages (10, 20 and 30 mg kg-1) of alfaxalone were administered to each python in a caudal location with a minimum 2 weeks washout. Induction and recovery were monitored by assessing muscle tone, righting reflex, response to a noxious stimulus and the ability to intubate. A subsequent experiment assessed the influence of injection site by comparing administration of 20 mg kg-1 alfaxalone in a cranial location (1 cm cranial to the heart) with the caudal site. Respiration rate was monitored throughout, and when intubation was possible, snakes were mechanically ventilated. RESULTS: Regardless of dose and injection site, maximum effect was reached within 10.0 ± 2.7 minutes. When administered at the caudal injection site, intubation was only successful after a dosage of 30 mg kg-1, which is higher than in previous reports for other reptiles. However, intubation was possible in all cases after 7.2 ± 1.6 minutes upon cranial administration of 20 mg kg-1, and anaesthetic duration was significantly lengthened (p < 0.001). Both 30 mg kg-1 at the caudal site and 20 mg kg-1 at the cranial site led to apnoea approximately 10 minutes post-injection, at which time the snakes were intubated and mechanically ventilated. CONCLUSIONS AND CLINICAL RELEVANCE: Alfaxalone provided rapid, smooth induction when administered intramuscularly to pythons, and may serve as a useful induction agent prior to provision of volatile anaesthetics. The same dosage injected in the cranial site led to deeper anaesthesia than when injected caudally, suggesting that shunting to the liver and first-pass metabolism of alfaxalone occur when injected caudally, via the renal portal system.

EVALUATION OF FEEDING BEHAVIOR AS AN INDICATOR OF PAIN IN SNAKES.

The necessity to prevent and manage pain in reptiles is becoming increasingly important, as their use in scientific research and popularity as exotic pets continues to rise. It was hypothesized that feeding behavior would provide an adequate indicator of pain perception in the ball python (Python regius). Normal feeding was defined the previous week, where a dead rodent was struck within 12 sec (n = 10). Eighteen pythons were randomly assigned to one of three treatments: anesthesia only (AO), chemical noxious stimulus (CS; capsaicin injection), or surgical noxious stimulus (SS; surgical incision). The time to strike was recorded 4 hr after the procedure and weekly during the subsequent 3 wk. Delayed feeding was observed in animals in the CS and SS groups, and normal feeding resumed after 1 and 3 wk, respectively. Spontaneous feeding remained uninterrupted for the AO group. These findings demonstrate feeding behavior as a potential model to assess pain in snakes.

Tachycardia in response to remote capsaicin injection as a model for nociception in the ball python (Python regius).

OBJECTIVES: To quantify the effect of subcutaneous (SC) capsaicin injection on heart rate (HR) in ball pythons (Python regius) and to assess the efficacy of two opioids (morphine and butorphanol) in modifying this response. STUDY DESIGN: Prospective, randomized, unmatched study. ANIMALS: Eleven mixed-sex, captive-bred ball pythons. METHODS: Snakes were randomly assigned to three groups (n = 6) by intramuscular premedication: 1) control: saline (0.9 mL); 2) morphine (10 mg kg(-1) ); and 3) butorphanol (10 mg kg(-1) ). Three snakes were tested twice and another two were tested three times in different treatments administered 1 month apart. Under isoflurane anaesthesia, snakes were instrumented with SC electrocardiogram (ECG) electrodes and an SC catheter for remote stimulus delivery. After recovery from anaesthesia, all snakes, in visual and audial isolation from the experimenter, received a sham stimulus of saline (0.4 mL) via the SC catheter. A nociceptive stimulus of SC capsaicin (3 mg in 0.2 mL saline with 7% Tween 80) was then applied by catheter at 7 hours after premedication. In a subset (n = 3), two sham injections (saline 0.2 mL) preceded the capsaicin treatment. HR was recorded via ECG, and changes in HR (ΔHR) from baseline were calculated for all stimulations. RESULTS: Capsaicin injection was associated with a significant increase in HR [peak ΔHR: saline group: 8.8 ± 7.1 beats minute(-1) ; capsaicin group: 21.1 ± 5.8 beats minute(-1) (p = 0.0055)] and integrated ΔHR as a function of time. The administration of morphine or butorphanol 7 hours prior to nociception failed to significantly reduce the peak and integrated ΔHR. Butorphanol caused marked, long-lasting sedation as assessed by muscle tone. CONCLUSIONS AND CLINICAL RELEVANCE: The HR response to an SC capsaicin injection can serve as a nociceptive model in P. regius. Morphine and butorphanol administration did not reduce HR response to capsaicin stimulation but produced significantly different effects on pre-stimulation HR and sedation.