Low-dose thoracic epidural anesthesia induces discrete thoracic anesthesia without reduction in cardiac output

The sensory spread and hemodynamic effects of low-dose thoracic epidural anesthesia were closely studied in 13 elective preoperative patients undergoing thoracotomy. An epidural catheter was inserted at the T4-5 or T5-6 intervertebral space and 5 ml 0.5% plain bupivacaine was injected. Cardiac output was measured by suprasternal Doppler method in all patients and also by thermodilution method with a Swan-Ganz catheter in six subjects. The cardiac outputs measured by suprasternal Doppler (Y) and thermodilution (X) methods showed a high correlation (Y = 0.74X + 0.99, r = 0.90, n = 24). Cephalad and caudad levels of hypesthesia at 15 minutes after bupivacaine injection were C8.4 +/- 2.1 (mean +/- SD) and T7.8 +/- 2.6, and those of anesthesia, T1.9 +/- 2.4 and T5.7 +/- 2.6, respectively. After epidural injection of 0.5% plain bupivacaine, a mean decrease in heart rate of 12 was observed in 15 minutes, which while clinically insignificant, was statistically significant (p less than 0.001). The decreased heart rate returned to control level after endotracheal intubation. Mean arterial blood pressure decreased slightly and only a slight elevation was seen after endotracheal intubation. Cardiac index and pulmonary capillary wedge pressure were essentially unchanged during the study period. Central venous pressure increased gradually and significantly, but within the normal range. Pulmonary vascular resistance slightly decreased in 15 minutes and returned to the control level after endotracheal intubation. Thus, low-dose thoracic epidural anesthesia was associated with minimal cardiovascular changes.