The use of b adrenoreceptor antagonists (b blockers) during coronary artery bypass surgery reduced postoperative stroke and coma by almost half.
A study from Duke University Medical Center compared outcomes in 2575 consecutive patients who had elective cardiac bypass surgery between June 1994 and December 1996 (Journal of Cardiothoracic and Vascular Anesthesia 2002; in press).
“We were surprised to see as much effect as we did, even controlling for other factors. Stroke occurred in 1.9% of patients receiving b blockers compared with 4.3% in those who did not. That's almost a 50% reduction,” said Dr Mark Newman, lead author and professor and chairman of the department of anaesthesiology at the Duke centre.
The authors state: “This effect (reduction in stroke and coma p=0.016) persisted in the multivariable logistic regression after adjustments for the 5 risk factors identified previously (p=0.0238; odds ratio, 0.463, 95% confidence interval 0.238 to 0.903; c-index = 0.791).”
Confusion, delirium, and transient ischaemic attacks occurred in 3.9% of patients receiving b blockers and in 8.2% of patients not receiving them.
The Duke cardiovascular database contains prospectively entered patient data since 1971, and an automated anaesthesia information system has been used since 1988. Drug treatments for patients before, during, and after surgery were recorded. Patient outcomes at discharge, as evaluated by the heart team and by a neurologist, were entered in the database.
Most patients at the Duke centre—89
—received b blockers preoperatively or intra-operatively. Those not receiving bblockers tended to be older and to have a preoperative diagnosis of congestive heart failure or chronic obstructive pulmonary disease. Of the entire 2575 patients, 113 (4%) had postoperative neurological complications. These included 44 strokes, 12 comas, 3 transient ischaemic attacks, and 54 cases in which the patient had cognitive changes such as confusion or delirium.
Other studies show that 0.4% to 5.4% of bypass patients have a stroke and that cognitive dysfunction ranges from 24% to 70% and remains a year after surgery in 35% of cases.
“People have advocated use of b blockers in the perioperative period for myocardial protection and the prevention of atrial fibrillation, but many are reluctant to use them. Nationally, only 60% to 70% of bypass patients are on b blockers or are started on them before surgery,” Dr Newman said.
The reason for reluctance is the belief that during cardiac surgery there is downregulation of b receptors as part of the stress response. Giving a b blocker was thought to make matters worse. “It's not the case,” he said. “Patients do better. The b blockers prevent downregulation.”
The b blockers most commonly used by patients were metoprolol and atenolol. During surgery, anaesthesiologists could administer b blockers at their discretion to continue the treatment in patients already taking them or to start them in response to heart rate responses to surgery or to increase myocardial protection. Atenolol, metoprolol, and propranolol were used.
b Blockers reduced the incidence of atrial fibrillation, a common complication of cardiac surgery that increases the risk of stroke. Older patients had less protective effect from b blockers than younger patients.
“Patients today are typically at greater risk,” Dr Newman told the BMJ. “They are older, they have more co-morbidities such as atherosclerosis, diabetes, a previous stroke. Ten years ago they would have been at too high a risk for surgery. The implications of the study are that patients who receive pre-operative, intra-operative, and post-operative beta blockers have an improved outcome.”
The study does not indicate the best timing, dosing, or type of beta blocker.