About 200 million adults a year undergo major surgery that is not cardiac surgery, and about 5 million of those people suffer a major vascular complication. That, said P J Devereaux from McMaster University at the Oxford Health Alliance meeting in Delhi last week, is about the same as the number of people contracting HIV each year. But have you ever heard or thought about it? Probably not.

All doctors know that a heart attack or a stroke can be a complication of major surgery, but very few appreciate the scale of the problem. That’s probably because they are unaware of the degree of risk and of the global scale of surgery. Surgery puts extreme stress on a patient.

Studies conducted a long time ago showed that about 4% of patients with cardiovascular disease or at high risk of such disease and about 1.5% of others suffered a major vascular complication. But these were small studies with a poor method for diagnosing heart attacks: many heart attacks go undetected because they are most likely to happen soon after surgery when patients are sedated and been given large doses of painkillers.

Now Devereaux is leading a major international study that will include 40 000 patients. They have already recruited over 15 000 patients and at this point they are confident that they will have over a 6% incidence of major cardiovascular complications at 30 days after surgery. This higher rate probably has two main causes: a better method of diagnosing heart attacks, and the fact that surgeons are operating on older and sicker patients.

A previous study found that 415 of 8351 surgical patients had a heart attack and that two thirds of them were asymptomatic. Mortality among those who suffered a heart attack was five times higher than among those who did not, and it didn’t make any difference whether the heart attack was symptomatic or not.

What should we do about this problem? The first thing is to be aware of it. Secondly, patients should be told of the risks, and when the large study is complete it should be possible to give patients a clear picture of the risks they face. Some may decide to forego the surgery. Thirdly, Devereaux is launched into major studies to try and find treatments that can reduce the risk. An initial trial of using beta-blockers found that they reduced heart attacks but at the cost of increasing strokes and overall deaths.

I couldn’t help thinking of the many studies I’ve read over the years that show that much surgery is inappropriate. “Good surgeons,” as the famous aphorism says, “know how to operate, better surgeons when to operate, and the best surgeons when not to operate.” Maybe there shouldn’t be 200 million major operations a year but 150 million.