Venoconstrictor Agents Mobilize Blood from Different Sources and Increase Intrathoracic Filling during Epidural Anesthesia in Supine Humans

The authors studied the effects of dihydroergotamine (DHE) and etilefrine hydrochloride (E) on the regional distribution of 99mTc-marked erythrocytes during epidural anesthesia in eight supine men to determine if vasoactive agents with venoconstrictor action would enhance cardiac filling during epidural anesthesia. Radioactivity was recorded with a gamma camera, and its distribution determined in the thorax, abdomen, and limbs. Arterial and central venous pressure, heart rate, and calf volume by plethysmography were measured. During epidural anesthesia with a sensory block up to T4/5, DHE (7.5 micrograms/kg) reduced the radioactivity, i.e., blood volume, in both the innervated (-5.9 +/- 3.5%) and denervated muscle/skin (-16.9 +/- 7%) regions, and increased it in both the intrathoracic (+7.0 +/- 2.3%), and splanchnic vasculature (+4.2 +/- 3.2). In contrast, E (6 micrograms X kg-1 X min-1) decreased the blood volume most markedly in the splanchnic region (-5.4 +/- 0.7%) and increased it in the thorax (+2 +/- 0.6%). All these changes were statistically significant. The combined effects were estimated to be equivalent to a transfusion of nearly 1.01 of blood. Both drugs reversed the hypotensive action of epidural anesthesia. During epidural anesthesia, DHE preferentially constricted the capacitance vessels in skeletal muscle and skin irrespective of the state of innervation, whereas E preferentially constricted the splanchnic vasculature. In the doses used, the two agents replenished in an additive fashion the central circulation during epidural anesthesia.