[Behavior of plasma concentrations of prilocaine following intravenous regional anesthesia and their relation to methemoglobinemia].

In a previous investigation we were able to demonstrate quite different methemoglobin levels after axillary plexus blockade on one side and intravenous regional anesthesia (IVRA) on the other using prilocaine (Fig. 1). At that time we tried to explain this observation by prolonged mobilization of the local anesthetic after tourniquet release, causing only minimal stress to the erythrocyte-related reduction system. In order to study prilocaine mobilization after tourniquet release in the upper limb following IVRA, prilocaine and methemoglobin concentrations were measured in 8 patients. All patients received 400 mg prilocaine; IVRA lasted 30 min in all cases. In each patient we inserted an intra-venous line via the cubital vein with its orifice in the region of the venous outflow of the blocked upper extremity (Fig. 2). Simultaneously, blood samples were taken for measurement of plasma prilocaine concentrations in the axillary region of the blocked limb and from the contralateral upper limb. Following tourniquet release, samples were collected at short intervals for 15 min; starting with the 15th min methemoglobin concentrations were also determined for up to 5 h. The results of the outflow and systemic prilocaine concentrations are presented in Figure 3. Remarkable differences in peak prilocaine concentrations (64 micrograms/ml vs 7.9 micrograms/ml after the 1st min) were found during the 3-h study period. The course of methemoglobin formation was similar to that in a group of patients we had studied previously (Fig. 4). Our findings confirm the assumption that the low and plateau-like methemoglobin formation following intravenous regional anesthesia of the arm is the result of delayed prilocaine release.(ABSTRACT TRUNCATED AT 250 WORDS)