Single-dose interpleural versus intercostal blockade: nerve block characteristics and plasma concentration profiles after administration of 0.5% bupivacaine with epinephrine.

Analgesic effects and plasma concentration profiles after interpleural (IP) or intercostal (IC) administration of 21 mL of 0.5% bupivacaine with epinephrine (5 micrograms/mL) were studied in 24 patients (IP group: n = 12; IC group: n = 12) who had undergone cholecystectomy or renal surgery. The number of blocked dermatomes, as assessed by pinprick, was more variable between patients in the IP group (2-9 dermatomes) than in the IC group (6-8 dermatomes). The mean time intervals from the injection to two-dermatome regression and to first need for additional pain medication were 4 h (IP) and 5.5 h (IC) (P less than 0.02) and 5.3 h (IP) and 9.8 h (IC) (P = 0.002), respectively. The degree of postoperative pain was evaluated by means of a visual analogue scale. This gradually increased during the first 4 h in the IP group (P less than 0.001), but not in the IC group. Peak bupivacaine concentrations in arterial plasma were approximately 10% higher than those in venous plasma and were attained more rapidly. Peak arterial plasma concentrations after IP injection (2.07 +/- 0.53 micrograms/mL) were significantly higher (P less than 0.005) than those after IC administration (1.36 +/- 0.48 micrograms/mL). Peak venous plasma concentrations showed a similar difference (IP: 1.86 +/- 0.45 micrograms/mL; IC: 1.21 +/- 0.48 micrograms/mL; P less than 0.005). Peak concentrations were attained later after IP injection both in arterial (IP: 16.3 +/- 4.6 min; IC: 8.8 +/- 5.4 min; P less than 0.002) and venous plasma (IP: 20.0 +/- 7.1 min; IC 13.3 +/- 6.9 min; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)