Routinely used for surgery , general anaesthesia is now very safe, even if the details of how it works aren’t fully understood. The risk of death from anaesthesia is estimated at . The most common complications are mild: nausea, sore throat, headache and temporary confusion (see below).
There’s a degree of trial and error in finding the right dose for each patient, says anaesthesiologist Nikolaus Gravenstein of the University of Florida College of Medicine. “We look to see if that response is about what we expect, or more or less, and adapt accordingly.” You can track the effect of anaesthetic using a technique called bispectral index monitoring, which measures several brain parameters, but this is expensive and only used in high-risk cases.
There’s always the chance of equipment failures or human error, such as forgetting to refill a medication that has run out, says Gravenstein. But genetics can also influence our response to anaesthetics. People with Down’s syndrome can be particularly at risk of complications. And there are many rare genetic diseases that increase the risk of problems such as airway blockages and heart, liver or kidney disorders.
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Variants in the 60 or so genes that make the enzymes responsible for breaking down certain drugs can also cause problems, says Merlin Butler at Kansas University Medical Center. “If a person is an ultra-rapid metaboliser or poor metaboliser of drugs such as anaesthetics, they can be become toxic leading to serious side effects,” he says. Because they are so rare, such genetic conditions are not yet routinely screened for before anaesthesia, but this may change as personalised genetic profiling becomes a regular aspect of medicine.
Most major complications aren’t related to the fact that we don’t understand the molecular mechanisms of anaesthesia, says Gravenstein. “Although clearly, as we understand them better, we can design better medications to target them.”
When anaesthesia goes wrong
Anaesthesia for surgery is routine and safe – but in very few cases, problems can arise
Nerve damage
About 1 in 5000 people get of some peripheral nerves, often in the hands or feet, while under anaesthetic. And 1 in 2000 patients will have temporary nerve damage. This can happen either if a nerve is injured during the operation itself, or because it is stretched or squashed when the person is lying down in an awkward position for a long time. If you were awake, this would make you uncomfortable and you would move, alleviating the pressure. When you’re under, that’s not an option.
Delirium
After an operation, some people emerge from the anaesthetic into a bewildered state of delirium. This is especially common among older patients or people taking medicines such as antidepressants, but usually resolves within a day or two. In many cases, it may be preventable. Some research suggests that using a lighter level of anaesthesia can afterwards.
Waking mid-operation
Perhaps one of the most worrisome problems is accidental awareness – partially waking up mid-operation because you are not getting enough anaesthetic. That might not be as bad as it sounds, though: most patients who experience it feel no pain, but may remember being in theatre. Often the waking episodes happen before or after an operation.
Still, it can be very alarming. As a child, Fredrik Lloyd, a poet now living in Oslo, had several operations on his foot and stomach at Great Ormond Street Children’s Hospital in London. One of them he never forgot. “I woke quite suddenly and sat up during an operation. I was wide awake, and someone was cutting into me,” he says.
“I remember the green walls, which had all sorts of instruments hanging on them. I remember large saws, drills, pliers and so on. The person cutting me up started telling someone on the other side of the table off, shouting at them… I must have fallen unconscious again. I wasn’t aware of any pain.”
It’s estimated that one or two out of every thousand patients experience a degree of awareness under general anaesthesia. Some, unlike Lloyd, find they are paralysed and can’t signal their condition. Fortunately this rarely lasts more than a few minutes, but some people who wake during surgery later develop post-traumatic stress.
Death
The vast majority of deaths that occur under general anaesthesia aren’t caused by the anaesthetic itself, but it does happen. In very rare cases – one out of every 20,000 patients – people can have severe allergic reactions to the drugs. For five per cent of these people it can prove fatal, although most make a full recovery.
More often, people die because of complications related to the condition the surgery is intended to treat. It is very rarely due to errors made by the medical staff that aren’t recognised in time. Perhaps the most famous case in recent years was that of the American comedian Joan Rivers, who died during an operation on her throat. An examination of that case suggests it was , and not an adverse reaction to anaesthesia, that proved deadly.
This article appeared in print under the headline “When the lights go out”
