[Serum bupivacaine concentrations in patients with continuous peridural anesthesia administered by thoracic catheter]

Continuous infusion of a 0.2% solution of bupivacaine via a peridural catheter in a rate of 0.2 ml/kg x h is sufficient to make a patient pain-free for any time required following upper abdominal or abdomino-thoracic surgery. The zone of analgesia extends segmentally from T4 to T12/L1 so that the patient can be mobilized. If necessary an insufficient blockade can be completed by bolus injection of 10 to 15 ml of 0.2% solution. Using this technique over a period of four days after surgery, serum concentrations of bupivacaine were measured in 20 patients. The following values were found (median, range): at the end of the operation 0.85, 0.26-1.72 mg/1, after 24 h 1.70, 0.58-4.04 mg/1, after 48 h 3.46, 1.22-7.62 mg/1, after 72 h 2.80, 0.73-12.15 mg/1 and after 96 h (end of the investigation) 2.39, 0.34-9.92 mg/1. Moderate excitation was sometimes observed, while the patient was in the recovery room (shivering, restlessness) but disappeared completely within 10 h. Later on no signs of intoxication were observed, even when serum bupivacaine concentrations exceeded 6 mg/1. During continuous epidural anaesthesia, when serum bupivacaine concentrations increase gradually this level does not seem to be toxic. We consider this method to be suitable for keeping a patient pain-free following upper abdominal surgery, provided that adequate monitoring is available.