The minimum infusion rate of alfaxalone during its co-administration with lidocaine at three different doses by constant rate infusion in goats

Objective

To determine the minimum infusion rate (MIR) of alfaxalone required to prevent purposeful movement in response to standardized stimulation while co-administered with lidocaine at three different doses by constant infusion rate infusion (CRI) in goats.

Study design

Prospective, blinded, randomized crossover, experimental.

Animals

A total of eight healthy goats: four does and four wethers.

Methods

Anaesthetic induction was with lidocaine at 1 mg kg^?1 low dose of lidocaine (L-Lid)], 2 mg kg^?1 moderate dose (M-Lid)] or 4 mg kg^?1 high dose (H-Lid)] and alfaxalone at 2 mg kg^?1. Anaesthetic maintenance was with alfaxalone initially at 9.6 mg kg^?1 hour^?1 combined with one of three lidocaine treatments: 3 mg kg^?1 hour^?1 (L-Lid), 6 mg kg^?1 hour^?1 (M-Lid) or 12 mg kg^?1 hour^?1 (H-Lid). The MIR of alfaxalone was determined by testing for responses to a stimulation in the form of clamping on a digit with a Vulsellum forceps every 30 minutes during lidocaine CRI. Basic cardiopulmonary parameters were measured.

Results

The alfaxalone MIRs were 8.64 (6.72–10.56), 6.72 (6.72–8.64) and 6.72 (6.72–6.72) mg kg^?1 hour^?1 during L-Lid, M-Lid and H-Lid, respectively, without any significant differences among treatments. Compared to the initial rate of 9.6 mg kg^?1 hour^?1, these reductions in MIR are equivalent to 10, 30 and 30%, respectively. Significant increases in heart rate (HR) and arterial carbon dioxide partial pressure (PaCO₂) and decreases in arterial haemoglobin saturation (SaO₂), arterial oxygen partial pressure (PaO₂) and respiratory frequency (f_R) immediately after induction were observed during all lidocaine treatments.

Conclusions and clinical relevance

Lidocaine reduces the alfaxalone MIR by up to 30% with a tendency towards a plateauing in this effect at high CRIs. Immediate oxygen supplementation might be required to prevent hypoxaemia.