CONTINUOUS BLOCKADE OF THE LUMBAR PLEXUS AFTER KNEE SURGERY - A COMPARISON OF THE PLASMA-CONCENTRATIONS AND ANALGESIC EFFECT OF BUPIVACAINE 0.250-PERCENT AND 0.125-PERCENT

In 20 patients a continuous block of the lumbar plexus was administered after knee joint surgery, and the analgesic effect of two different concentrations of bupivacaine was compared. The same volume of bupivacaine was given to both groups of patients: a bolus dose of 0.4 ml/kg, 0.5% or 0.25%, followed by infusion of 0.14 ml/kg/h, 0.25% or 0.125%, respectively, via a catheter placed in the neurovascular fascial sheath of the femoral nerve according to the “3‐in‐1 block” technique. The median morphine consumption during the first 16 h postoperatively was 6.0 mg when bupivacaine 0.5/0.25% was used and 9.5 mg when 0.25/0.125% was used. This difference is not significant. The visual analogue pain scores were also similar in the two groups (P > 0.05). All plasma concentrations were below 4 μg/ml, the highest concentration measured being 3.6 μg/ml. It is concluded that when used for a continuous block of the lumbar plexus after knee‐joint surgery, bupivacaine in a concentration of 0.125% offers the same pain relief as a concentration of 0.25%, and the risk of toxic reactions is reduced. © 1990 Acta Anaesthesiologica Scandinavica Fonden