Caudal anesthesia with lidocaine or bupivacaine: plasma local anesthetic concentration and extent of sensory spread in old and young patients.

Continuous caudal peridural anesthesia with 2% lidocaine (6 mg/kg) or 0.75% bupivacaine (2.2 mg/kg), both with epinephrine 1:200,000, was studied in two groups of male patients, younger than 40 or older than 55 yr old, respectively. Patients receiving lidocaine in the younger group (n = 6) were 32 +/- 5.2 (mean +/- SD) yr old and weighed 75 +/- 12 kg, while those in the older group (n = 16) were 66 +/- 5.3 yr old and weighed 72 +/- 8.2 kg. Patients receiving bupivacaine in the respective groups were 27 +/- 7.0 yr old (n = 5), and 76 +/- 10 kg compared to 69 +/- 10 yr (n = 14) and 75 +/- 10 kg. Anesthesia was satisfactory in all patients. Extent of sensory anesthesia, peak plasma lidocaine or bupivacaine concentrations, and area under the plasma concentration-time curves were independent of age. No local anesthetic toxicity was observed and peak drug concentrations were below those commonly associated with toxicity.