Plasma concentrations of lignocaine after obturator nerve block combined with spinal anaesthesia in patients undergoing transurethral resection procedures.

Bilateral obturator nerve block has become a widely accepted technique to avoid adductor contraction during transurethral resection of prostate or bladder tumours. However, little is known about plasma lignocaine concentrations after the block. We conducted this study to assess a safe dose of lignocaine for injection in obturator nerve block. Bilateral obturator nerve block was performed with the aid of a peripheral nerve stimulator in 12 patients after spinal anaesthesia. In group I (n = 6), patients received 2% lignocaine 10 ml (200 mg) for the block; those in group II (n = 6) received 2% lignocaine 15 ml (300 mg). The block was satisfactory and no single adductor contraction was observed in either group during surgery. The peak plasma concentrations of lignocaine were 2.28 (SD 0.29) micrograms ml-1 and 3.75 (0.79) micrograms ml-1 in groups I and II, respectively. The greatest plasma concentration was 5.07 micrograms ml-1 in a patient of group II. There were no symptoms suggesting systemic toxicity. We conclude that bilateral obturator nerve block may be performed safely and effectively with 2% lignocaine 10 ml with the aid of a peripheral nerve stimulator in patients undergoing transurethral resection procedures with spinal anaesthesia.