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The Real Risk

Operations: The risks of going under the knife

About the author

David Spiegelhalter is Winton Professor of the Public Understanding of Risk at the University of Cambridge, UK. His professional background is in medical statistics. He is a frequent contributor to the media, and has been an advisor on risk issues as diverse as breast implants, volcanic ash, clinical trials, surgical mortality, and the inquiry into mass murderer Harold Shipman. He is a Fellow of the Royal Society and was awarded an OBE in 2006. You can see more of David’s explorations of risk at the Understanding Uncertainty website, or follow him on Twitter at @undunc

Operations: the risks of going under the knife

(Copyright: Thinkstock)

Our resident statistician David Spiegelhalter looks at the often-gruesome history behind some of the procedures carried out in the name of medicine.

It is hard to read about surgery over the centuries without flinching: the crudity of the tools, the lack of anaesthetic, and not least what seems like astonishing guts (metaphorically speaking) in carrying out techniques that nowadays seem indistinguishable from butchery.

The past saw such gruesome and widely practiced techniques like trepanation, in which part of the skull is removed to reveal the brain to provide relief for headaches or following injury. Excavations reveal that in Neolithic times up to one in three skulls have holes drilled or scraped out. The head was particularly prone to damage from slings and clubs and other primitive weapons, and the aim of trepanation was to relieve what felt like extreme pressure, release blood and ‘evil air’, and leave the brain nicely aerated.

The even more remarkable finding is that many of these skulls – between 50% and 90% according to some sources – belonged to people who survived. We know this because the edge of the hole has healed. The procedure was popular in Europe as a treatment for epilepsy and mental illness up to the 18th century, and afterwards for head injury. Cornish miners in the 19th century apparently insisted on having their skulls bored after even minor head injuries, as a precautionary measure.

But when hospitals began to flourish in the 19th century, holes in the head became even more dangerous. The problem was hygiene: the infection risk was so high in these hospitals that doctors managed to make a mad idea even worse. As a result the mortality rate shot up to about 90%.

Ether frolics

If this wasn’t bad enough, the only pain relief available for having your head excavated with a sharp instrument was intoxication. Alcohol, cannabis and opium were the basic anaesthetics until Humphrey Davy personally experimented with nitrous oxide or laughing gas. In 1800, he had the foresight to write: “As nitrous oxide in its extensive operation appears capable of destroying physical pain, it may probably be used with advantage during surgical operations in which no great effusion of blood takes place.”

Naturally for such a wildly innovative idea, nobody in medicine took any notice for 50 years. But during this time laughing gas and ether were used as party tricks: so-called ‘ether frolics’ were hugely popular in the US. (Over a century later, the American journalist and author Hunter S Thompson described ether’s effects as making you behave “like the village drunkard in some early Irish novel”.) Then it finally dawned on some medical students that the frolickers appeared not to care about injury. Could this be put to practical use, they wondered.

The first public anaesthetic using ether was thought to have been delivered by William Morton on 16 October 1846 at Massachusetts General Hospital. The idea soon spread, especially after Queen Victoria welcomed the use of chloroform for the birth of Prince Leopold in 1853, although chloroform later lost favour due to sudden deaths from heart arrhythmias, now known as ‘sudden sniffer’s death’ among teenage solvent abusers.

Nowadays, being numbed and put to sleep for an operation is routine in many parts of the world – the World Health Organisation reports that each year there are 230 million major surgical procedures under anaesthesia.

But anaesthetics still come with their own risks, and rates appear to be strongly dependent on health care expenditure levels. The UK Royal College of Anaesthetists says that there are life-threatening allergic reactions in less than 1 in 10,000 people and that most recover. But not all. Around 1 in 100,000 general anaesthetics still lead to the death of the patient.

If we translate these figures into the chance in a million of dying, or micromorts, this becomes a risk of 10 micromorts – equivalent to travelling around 60 miles on a motorbike, or a bit more than a parachute jump. Around half of that risk, 5 micromorts, arises from errors made in administering the anaesthetic, which is nice to know. Risks for day-cases are lower, and higher if you are older or it’s an emergency operation. 

Framing device

OK, so you survive the anaesthetic, but what about the operation itself? One of the most commonly performed procedures is a coronary artery bypass graft (known as CABG, and pronounced like the green vegetable), which relieves symptoms of angina by improving the bloodstream to the heart using a piece of artery or vein removed from elsewhere in the body. The risks have been carefully studied. This type of operation started in 1960, and mortality in the US was down to 3.9% in 1990 and to 3.0% in 1999. The UK now reports a ‘98.4% survival rate’, based on 21,248 operations in 2008.

Note the different framing of this information: The UK figures describe survival rather than mortality. In the US, people die from surgery while in the UK they do not survive. This change of framing is a neat device that tends to make performance look better and obscure differences: the difference between two hospitals with 98% and 96% survival, as we would describe it in the UK, looks negligible, while the same comparison expressed as it would be in the US as 2% versus 4% mortality is a doubling and looks far more serious. The sort of figures that news outlets are more likely to pick up on, for instance.

Whichever way we choose to frame it, the fact that some states in the US mandate mortality reporting mean we can explore the risks of the procedure in further detail. For instance, all hospitals in New York State that perform cardiac surgery must file details of their cases with the State Department of Health. In 2008 there were 10,707 CABG operations in 40 hospitals, and 194 patients died either in hospital or within 30 days – a mortality rate of 1.8%. Or, as they would say in the UK, a survival rate of 98.2%.

Surgery on heart valves was a higher risk: of 21,445 operations in New York State between 2006 and 2008, 1,120 patients died, a mortality rate of 5.2%, or more than 1 in 20. That’s an average of 52,000 micromorts per operation, equivalent to around 10,000 scuba dives or two RAF bombing missions in World War II.

As stark as the risk might seem, presumably the risk without an operation is higher. So you may want to go under the knife like you’d want a hole in the head. But at least thank your lucky stars that the days of actually receiving a hole in the head in the name of medicine are long gone.

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