Circulatory stability and plasma lidocaine levels during continuous and intermittent thoracic epidural analgesia

Circulatory stability and plasma levels of lidocaine were investigated in 20 patients who received thoracic epidural analgesia with plain lidocaine during elective abdominal surgery under general anesthesia. In one group, bolus injection of 8 ml of 2% lidocaine was followed by volumetric continuous pump-driven infusion (CPI) of 8 ml of 1.5% lidocaine per hour. In the other group, the same initial bolus injection was followed by repetitive intermittent bolus infusions (RII) of 6 ml of 1.5% lidocaine at a 45 min-interval. Circulatory stability was evaluated by a discriminant function. The results showed that epidural analgesia produced smaller circulatory fluctuations with CPI than with RII. Venous plasma lidocaine levels were consistently higher with CPI than with RII. Plasma levels increased stepwise with RII and kept constant with CPI. Differences in plasma levels were significant from 20 min after the initial injection to 135 min. We therefore conclude that epidural analgesia with CPI is superior to that with RII. However, it must be remembered that higher plasma levels may occur with CPI than with RII.