Cumulation of bupivacaine, desbutylbupivacaine and 4-hydroxybupivacaine during and after continuous interscalene brachial plexus block.

Desbutylbupivacaine (DBB) and 4-hydroxybupivacaine (4-OHB) are major metabolites of bupivacaine. They may cumulate during continuous infusion blocks. In the present study, all patients received an interscalene brachial plexus block with 20-28 ml of 0.75% bupivacaine plus adrenaline. A catheter was introduced into the interscalene space, and an infusion of 0.25% bupivacaine (5-9 ml/h) was started and continued with ten patients for 24 h and with another ten for 48 h. An infiltration block of the suprascapular and intercostobrachial nerves was performed using 0.5% bupivacaine. Before surgery, light general anaesthesia was induced. For measurement of plasma concentrations of bupivacaine, DBB and 4-OHB blood samples were taken before the block and 30 min, 3 h, 24 h and 48 h after the blocks as well as 30 min, 1 h, 2 h, 4 h and 6 h after the termination of the infusions. The highest plasma concentrations of bupivacaine, mean 1.84 micrograms/ml, were measured 30 min after the block. There was a slight but statistically significant rise in the bupivacaine concentrations between 24 and 48 h. The bupivacaine concentration decreased by 54% and 45%, on average, during the first 6 h following the 24- and 48-h infusions, respectively. On average, the highest DBB concentrations were measured 2 h after the 24-h infusion (0.31 +/- 0.18 micrograms/ml) and 30 min after the 48-h infusion (0.33 +/- 0.13 micrograms/ml). The highest 4-OHB concentrations were measured 1 h (0.18 +/- 0.09 micrograms/ml) and 30 min (0.20 +/- 0.05 micrograms/ml) after the 24- and 48-h infusions, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)