Bupivacaine blood levels after intravenous regional anesthesia of the arm.

Toxic reactions have been reported in patients after immediate release of the tourniquet cuff following intravenous regional anesthesia (I.V.R.A.) with bupivacaine. In this study we induced I.V.R.A. with 0.25% bupivacaine, mean dose 1.8 mg/kg (range 1.4-2.6 mg/kg). The patients were divided into two groups according to the method used to release the cuff; these were immediate release (Group I), or release with an "on and off" technique (Group II). The highest venous bupivacaine concentrations (max. 2.72 micrograms/ml) were measured 10 min after the ischaemic period, but there were not statistically significant differences between the two groups (the highest mean concentration was 0.91 microgram/ml in Group I and 0.93 microgram/ml in Group II). There was a difference in the bupivacaine concentrations between the subgroups of short (less than 40 min) and long (greater than 90 min) periods of ischaemia, but it was not significant. The fact that the bupivacaine concentration peak appeared later and was higher in the latter group might be associated with the lower pH (long ischemia) and its effect on the bupivacaine binding in the tissues. No toxic symptoms were recorded in the 40 patients in our study. Additional analgesics were needed in 11 cases and in 8 of these the reason was an uncomfortable feeling under the cuff. It is concluded that bupivacaine in doses of 1.4 to 2.6 mg/kg is safe for I.V.R.A. The tourniquet cuff could be released without toxic reactions. However, after long periods of ischaemia, the possibility of delayed, potentially toxic blood bupivacaine concentrations is higher.