Does systemic lidocaine reduce ketamine requirements for endotracheal intubation in calves?

To investigate whether an intravenous (IV) lidocaine bolus in calves premedicated with xylazine-butorphanol reduces the amount of ketamine required to allow endotracheal intubation.

Randomized, prospective clinical study.

In total, 41 calves scheduled for elective umbilical surgery.

Calves were randomly assigned to one of two groups (L: lidocaine or S: saline). The calves were administered xylazine (0.07 mg kg^-1) and butorphanol (0.1 mg kg^-1) intramuscularly and 10 minutes later lidocaine (2 mg kg^-1; group L) or saline (group S) IV over 1 minute. After 2 minutes, ketamine (2.5 mg kg^-1) was injected IV. If the depth of anaesthesia was insufficient for intubation, additional ketamine (1 mg kg^-1) was administered every minute until intubation was successful. The amount of ketamine required for intubation, respiratory rate, pulse rate, arterial pressures, the depth of sedation and conditions of endotracheal intubation after induction of anaesthesia were compared between the two groups.

The calves in group L were sedated more deeply than those in group S; however, neither the median (range) amount of ketamine required for intubation, 3.5 (2.5-4.5) mg kg^-1 and 3.5 (2.5-3.5) mg kg^-1, respectively, nor the induction quality differed significantly between the groups.

A bolus of lidocaine (2 mg kg^-1) administered 10 minutes after xylazine-butorphanol in calves deepened the degree of sedation but did not decrease the requirement of ketamine for endotracheal intubation. No adverse effects were recorded in the physiological variables measured.