There is no adequate explanation for the marked fall in blood pressure which accompanies spinal anesthesia. In order to explain the mechanism by which this hypotension is developed, it would be necessary to know in detail all the changes which occur in the circulatory system. Thus far studies have shown conclusively that:
1. Systolic and diastolic blood pressures usually fall to a variable degree.1
2. Sympathomimetic drugs usually either prevent the fall or produce a subsequent rise of blood pressure.2
3. There is a rise in cutaneous temperature of the lower extremities.3
Beside these definite findings, Webb, Scheinfeld and Colin4 reported that there was no significant variation in circulation time during spinal anesthesia in the 6 patients they studied.
We investigated the effect of spinal anesthesia on blood volume, venous pressure, circulation time, viscosity of the blood and cardiac output and its related functions.
GOLDFARB W, PROVISOR B, KOSTER H. CIRCULATION DURING SPINAL ANESTHESIA. Arch Surg. 1939;39(3):429-434. doi:10.1001/archsurg.1939.01200150108005