Ventilatory response to carbon dioxide after epidural clonidine injection.

The authors studied the effects of epidural clonidine (300 micrograms) on circulation and ventilatory control in seven healthy unpremedicated subjects. After clonidine injection, arterial blood pressure decreased significantly in all subjects (range, 13%-25% for systolic blood pressure and 13%-32% for diastolic blood pressure). Heart rate decreased significantly by 10%-16% between 75 and 105 min after injection. The slope of the ventilatory response to CO2 decreased significantly from 2.06 +/- 0.70 (baseline) to 1.37 +/- 0.68, 1.25 +/- 0.65, and 1.33 +/- 0.67 L.min-1.mm Hg-1 (mean +/- SD, P less than 0.05) at 15, 60, and 120 min. The authors conclude that epidural clonidine induces mild ventilatory and circulatory depression.