Abstract

Arterial lidocaine concentrations and the duration of motor anesthesia following the subarachnoid injection of 30 or 40 mg of lidocaine with or without epinephrine 0.3 mg were measured in 10 sedated dogs. As the dogs were sedated with ketamine, the duration of sensory anesthesia was not evaluated. Each dog served as its own control with alternating treatments at a 7-day interval. The maximum arterial lidocaine concentration occurred 15 minutes after subarachnoid injection and was not different (p > 0.05) with lidocaine (820 ng/ml) or lidocaine-epinephrine (990 ng/ml). However, the mean duration of motor anesthesia was prolonged 46 percent ( p < 0.05) in the same animal when epinephrine accompanied the lidocaine injection. We conclude that epinephrine added to lidocaine placed in the subarachnoid space of the dog predictably prolongs motor anesthesia. However, the prolongation is significant only in the lower spinal segments. This prolongation occurs despite the absence of evidence that systemic absorption of lidocaine is altered by epinephrine.