Ventilatory and circulatory responses to carbon dioxide and high level sympathectomy induced by epidural blockade in awake humans.

In order to examine the effects of cervico-thoracic epidural block with 1.5% lidocaine on ventilatory and circulatory responses to carbon dioxide, the authors studied the CO2-ventilatory response curves and the changes in heart rate (HR) and blood pressure (AP) to rebreathing of exhaled gas before and after the block in healthy volunteers. Neither resting ventilation nor ventilatory response to CO2 was affected by the epidural block (mean analgesic level extended from C4 to T7); the slope of the CO2-ventilatory response curve averaged 2.38 +/- 0.81 L X min-1 X mm Hg-1 (mean +/- SD) before and 2.32 +/- 0.82 L X min-1 X mm Hg-1 after the block. Resting HR and AP decreased significantly (P less than 0.01) after the block, but responses in HR and AP to CO2 rebreathing were not significantly changed by the block. Plasma concentrations of norepinephrine and epinephrine were similar before and after the block both with and without CO2 rebreathing. These results indicate that high levels of sympathetic denervation induced by epidural block do not impair circulatory and ventilatory responses to carbon dioxide in awake, healthy humans.