Role of angiotensin II in the development of peripheral vasoconstriction during cardiopulmonary bypass.

The possible relationship between angiotensin II -- the end product of the renin-angiotensin system, and the increase in peripheral vasoconstriction associated with cardiopulmonary bypass, has been investigated in 12 patients undergoing elective open-heart surgical procedures. Plasma angiotensin II (AII) levels were measured by radio-immunoassay at the start and the end of the period of cardiopulmonary bypass. Measurements of peripheral vascular resistance index were made at the times of AII sampling. Plasma AII levels rose during CPB from 78.0 to 231.3 pg.cm-3 (normal values less than 35 pg.cm-3). Peripheral vascular resistance index also rose during perfusion from 20.87 to 27.83 units. The rise in plasma AII levels and in peripheral vascular resistance index were correlated for each of the 12 patients. A highly significant correlation was obtained (r = 0.91; P less than 0.001). These results confirm the presence of parallel rises in plasma angiotensin II levels and in peripheral vasoconstriction during conventional non-pulsatile cardiopulmonary bypass, and suggest that increased plasma AII levels may be principal causative factor in the increased vasoconstriction associated with open-heart surgical procedures.