Canadian Journal of Anesthesia, Vol 40, 532-541, Copyright © 1993 by Canadian Anesthesiologists' Society

ARTICLES

Epidural morphine reduces the risk of postoperative myocardial ischaemia in patients with cardiac risk factors

WS Beattie, DN Buckley and JB Forrest
Department of Anaesthesia, McMaster University, Hamilton, Ontario.

Perioperative myocardial ischaemia is a predictor of postoperative cardiac morbidity (PCM). Epidural anaesthesia and adequate perioperative analgesia have been shown to improve myocardial oxygen dynamics due to interruption of pain and sympathetic pathways. The aim of the present study was to compare the incidence of ischaemia after either general anaesthesia followed by parenteral analgesia with morphine or combined epidural/general anaesthesia followed by analgesia with epidural morphine. In a prospective observer-blinded analysis of the occurrence of ischaemia, 55 patients (epidural = 29/parenteral = 26) scheduled for elective surgery with defined risks for ischaemic cardiac disease were entered and followed for 24 hr after surgery with two-lead continuous Holter monitoring. Groups were similar with respect to age, weight, modified Goldman (Detsky) risk classification and the use of cardiac medications. Fewer patients receiving the epidural anaesthesia/analgesia had ischaemic episodes (17.2 vs 50.0%, P = 0.01), and tachyarrhythmias (20.7 vs 50.0%, P < 0.05). Epidural patients had a four-fold reduction of the relative risk for either event (P < 0.001). All ischaemic events were asymptomatic and unrecognized (silent). All major morbid events (n = 5) (MI, congestive heart failure and death) occurred in patients who had perioperative episodes of ischaemia. There were three distinct peaks in onset of ischaemia, at 1-4 hr, 9-12 hr and 22-24 hr postoperatively. One third of postoperative ischaemic events occurred within the first four hours after operation and lasted from 1 to 31 min. Forty-two percent of ischaemic episodes were associated with a heart rate > 100 bpm, or an increase of 20% over the baseline heart rate. We conclude that epidural anaesthesia/analgesia reduces but does not eliminate the risk of myocardial ischaemia and tachyarrhythmia. We were unable to determine any associated reduction in the risk of PCM.

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