SYSTEMIC ABSORPTION AND BLOCK AFTER EPIDURAL INJECTION OF ROPIVACAINEIN HEALTHY-VOLUNTEERS

Background: For local anesthetics, the process of removal from the sit e of administration influences the duration of anesthesia and the risk for systemic toxicity to develop. The systemic absorption of epidural ropivacaine and the time profile of sensory and motor block were stud ied in healthy volunteers. Methods: Nine persons simultaneously receiv ed 150 mg ropivacaine hydrochloride (7.5 mg/ml) epidurally and 40 mg d euterium-labeled (H-2(3))ropivacaine hydrochloride (0.25 mg/ml:) intra venously. Peripheral arterial and venous plasma samples were collected , and assessments of sensory and motor block were made, Results: The a rterial plasma concentrations increased faster than the venous concent rations, with 50% higher maximum concentrations after both intravenous and epidural administration. The absorption was biphasic, A correlati on was seen between the duration of sensory block and the slower absor ption half-life; that is, the longer the half-life, the longer the dur ation. The extent of spread varied among the volunteers, with the medi an upper block level not exceeding T12. The motor block (Bromage score 1) was of slower onset (:median, 0.4 h) and of shorter duration (medi an, 4.1 h) than the sensory block (onset, 0.2 h; duration, 6.5 h at L2 medians), Conclusions: As much as 50% differences were seen in the ar teriovenous plasma concentrations of ropivacaine during the first hour , which has implications for the interpretation of systemic toxic plas ma concentrations. The absorption into the general circulation was bip hasic, with a correlation between the sensory block and the slower abs orption half-life. A faster onset and a longer duration of sensory com pared with motor block was seen.