Clonidine and the sympatico-adrenal response to coronary artery by-pass surgery

Clonidine was administered intravenously in an attempt to limit sympatico-adrenal activity and thereby reduce the incidence of arterial hypertension associated with coronary artery by-pass graft surgery (CABG). Forty patients scheduled for CABG were assigned to two groups. Twenty patients received clonidine 4 micrograms kg-1 before surgery, 2 micrograms kg-1 after cardiopulmonary by-pass and 1 microgram kg-1 when the skin was sutured. The other 20 patients served as controls. All patients were anesthetized with fentanyl, droperidol, nitrous oxide and alcuronium. During surgery 5 min after sternotomy, mean arterial pressure was 13 mmHg lower (P less than 0.01) in the clonidine group, while after operation the difference between the groups was negligible. Both during and after surgery the plasma catecholamine concentrations were significantly lower in the clonidine group (P less than 0.01). The greatest difference between the groups was seen 90 min after operation, when plasma noradrenaline and plasma adrenaline concentrations in the clonidine group were less than 1/3 of those in the control group (P less than 0.01). As judged by catecholamine concentrations clonidine was effective in attenuating sympatico-adrenal hyperactivity during and after surgery. Postoperative arterial hypertension was not reduced, however, and it is concluded that other factors besides sympatico-adrenal hyperactivity must be important.