Humoral changes during and following coronary bypass surgery: relationship to postoperative blood pressure

In this study we investigated the role of the renin-angiotensin system and the adrenergic system in the hypertensive response during and following coronary bypass surgery. Arterial blood samples for measurement of active renin, angiotensin II, aldosterone and catecholamines were drawn before, during and in the first period after coronary artery grafting. Both noradrenaline and adrenaline rose significantly during extracorporeal circulation and remained elevated afterwards, the rise in adrenaline preceding that of noradrenaline. During cardiopulmonary bypass renin also increased while angiotensin II increased after an initial fall. Postoperatively, renin tended to return to control levels. However, angiotensin II fell in some patients but remained elevated in others. The latter group had significantly lower blood pressure during cardiopulmonary bypass, but higher pressure thereafter. Aldosterone levels were markedly reduced during cardiopulmonary bypass. The results suggest that low pressure during extracorporeal circulation may trigger enhanced formation of angiotensin II, apparently involving extrapulmonary converting enzyme. This mechanism may, when acting in concert with an activated sympathetic nervous system, produce significant blood pressure elevation postoperatively.