Posterior approach to the lumbar plexus combined with a sciatic nerve block using lidocaine

A combination of lumbar plexus block, by a posterior technique, and sciatic nerve block can be a useful technique for outpatient anaesthesia. The purpose of this study was to examine the clinical characteristics of these blocks using lidocaine and to measure the serum lidocaine concentrations. Forty-five patients, undergoing lower extremity surgery, were studied. Sciatic nerve and lumbar plexus blocks were made with lidocaine, 680 mg with adrenaline 0.3 mg. For each patient the following data were collected: weight, age, sex, site of surgery, time to perform each block, needle depth, speed of onset of the sensory and motor blocks in the territories of the sciatic, femoral, obturator and lateral cutaneous (sensory) nerves and postoperative analgesic requirements. Lidocaine serum concentrations were measured in ten of these patients at 0, 2, 5, 10, 30, 60, 90 and 120 min after the second block. Analgesia was complete in 88% (40/45) of the patients. The remaining five patients needed analgesics (fentanyl 150 micrograms or less). Despite the high dose of lidocaine, the serum concentrations were within safe limits (mean +/- SD) (CMAX = 3.66 +/- 2.21 micrograms.ml-1). Only one patient had a serum concentration > 5 micrograms.ml-1 (CMAX = 9.54 micrograms.ml-1). This was associated with a contra-lateral extension of the block. We conclude that this combination of blocks is a valuable alternative for unilateral lower extremity anaesthesia. However, clinicians must be aware of the implications of a contra-lateral extension of the block.