Arterial hypoxaemia following premedication in patients with coronary artery disease

The effect of premedication with morphine and scopolamine, morphine alone, and scopolamine alone on arterial oxygen tension has been studied in patients with coronary artery disease undergoing bypass operations. Control arterial blood samples were obtained with the patients in the supine position breathing room air the day before operation. A second arterial blood sample was taken in the induction room with the patient breathing room air in the supine position. In the first group (scopolamine only) and second group (morphine only) cH+ (pH), PaCO2 and PaO2 did not change. In the third group (morphine and scopolamine), however, PaO2 decreased, while PaCO2 and cH+ increased (pH decreased). The changes in cH+ and PaCO2 were statistically significant, but of no clinical importance. The present study suggests that, when morphine and scopolamine premedication is used for patients with coronary artery disease, simultaneous administration of oxygen is important in helping to eliminate a possible cause of preoperative myocardial ischaemia.