[Intravenous regional anesthesia of the foot using prilocaine. Clinical aspects, pharmacokinetic and pharmacodynamic studies].

Intravenous regional anesthesia (IVRA) of the foot is a rarely used but alternative method to other regional techniques and general anesthesia, especially when operating on the distal portion of the lower limb. The present report describes our method and experience with this type of anesthesia in approximately 500 patients, including pharmacokinetic and -dynamic aspects. MATERIALS AND METHODS. Pharmacological studies were performed in 17 orthopedic outpatients undergoing operations on the foot following an IVRA technique with prilocaine. A plastic cannula was inserted into a peripheral vein of the forefoot and a pneumatic tourniquet (350 mm Hg) applied proximally and close to the malleoli after achieving exsanguination with an Esmarch bandage. If there was no sufficient analgesia (pinprick testing) 5 min after injection of 200 mg prilocaine, IVRA was supplemented with another 100 mg of local anesthetic. Peripheral venous blood samples were collected at short intervals for up to 2 h before and after cuff release to determine total plasma concentrations of prilocaine (HPLC) and the degree of methemoglobinemia (CO-Oximeter). RESULTS. Administration of 200-300 mg prilocaine resulted in complete analgesia in 15 of 17 cases that was sufficient for operations lasting up to 85 min. The tourniquet was tolerated for up to 105 min without any complaints. Plasma concentrations after 200 (n = 12) and 300 mg prilocaine (n = 3) peaked between 10 and 20 min after cuff release, respectively, with maximum levels of 0.96 micrograms/ml (means = 0.56 micrograms/ml) and 1.45 micrograms/ml. The extent of methemoglobin formation was low (maximum 3.8% of total hemoglobin). DISCUSSION. In addition to conventional anesthetic techniques, IVRA deserves a firm place in modern anesthesiological practice and should be used more widely. In order to avoid systemic toxic reactions, the use of prilocaine is recommended. Prolocaine plasma concentrations and methemoglobin formation were both far below toxic levels. Failure of IVRA was probably caused by premature outflow of the local anesthetic solution, as shown by the course of prilocaine plasma concentrations and methemoglobinemia.