“Almost three million general anesthetics happen each year in the UK alone,” says Peter Odor, a registrar at St George’s Hospital in London. “As a consequence, it is more probable than not that someone, somewhere in the world, right now is aware during their surgery.”
We once knew surprisingly little about why anesthesia works. Now, however, researchers are striving to understand more about the nature of going under and the circumstances in which anesthesia doesn’t work, in the hope of making advances that might reduce the risk of anesthesia awareness. And, with a greater understanding of the anesthetized state, we may even be able to turn a rudimentary awareness to our advantage – in the form of medical hypnosis.
Let’s be clear: anesthesia is a medical miracle. Since at least the time of the Ancient Greeks, physicians and medicine men had hunted for a good way to ease the pain of medical procedures. While drugs such as alcohol, opium and even hemlock could act as sedatives, their efficacy was unreliable; most patients did not escape the torture.
By the 1840s, scientists had discovered various gases that appeared to have sedative effects. One of these, sulphuric ether, had attracted the particular attention of a dentist based in Boston who put it to the test in a public demonstration at the Massachusetts General Hospital in 1846. Although the patient was still able to mutter half-coherent thoughts, he reportedly felt no pain, just the faint sense of his skin being “scratched with a hoe”.
The news of the demonstration soon spread throughout the medical establishment, heralding the start of the anesthetic era. With the subsequent discovery of even more effective anesthetic agents such as chloroform, the agony of the surgical knife seemed to be a thing of the past.
General anesthesia creates a controlled unconsciousness that is deeper and more detached from reality even than sleep. Today, anesthetists have a wide range of pain-killing and consciousness-reducing drugs at their disposal, and the exact choice will depend on the procedure and the patient’s particular needs.
Often, the aim is not to produce a loss of consciousness but simply to remove the sensation from a particular part of the body. So-called “regional anesthetics” include spinal and epidural anesthetics, both of which are delivered between the bones of your back to numb the lower half of your body. These are commonly used during childbirth, bladder operations and hip replacements.
You may also be given a sedative, which produces a relaxed, sleepy state. However, it does not fully eliminate your awareness
Propofol is a creamy white liquid that, at different doses, can act either as a sedative or as an anesthetic
General anesthesia, in contrast, aims to do just that, creating an unresponsive drug-induced coma or controlled unconsciousness that is deeper and more detached from reality even than sleep, with no memories of any events during that period. As Robert Sanders, an anesthetist at the University of Wisconsin–Madison, puts it: “We’ve apparently ablated this period of time from that person’s experience.” (During the operation, the patient may also be given painkillers to ease their recovery when they wake up from surgery.)
We still don’t know exactly why anesthetic agents dim our consciousness, but they are thought to interfere with various brain chemicals called neurotransmitters. These chemicals turn up or turn down the activity of neurons, particularly the widespread communication between different brain regions.
Propofol, for instance – a milky-white fluid used in general anesthetics and some types of sedation – seems to amplify the effects of GABA, an inhibitor that damps down activity in certain areas of the brain, as well as communication between them.
Sanders’s colleagues recently used a form of non-invasive brain stimulation to demonstrate this principle in action, with propofol silencing the waves of activity you would normally see spreading across the brain in response to the stimulation.
“It’s very possible that anesthesia interferes with that ascending transmission of information,” he says. And without it, the mind temporarily disintegrates, becoming a blank screen with no ability to process or respond to the body’s signals.
In the clinic, there are many complicating factors to consider, of course. An anesthetist may choose to use one drug to induce the temporary coma and another to maintain it, and they need to consider many factors – such as the patient’s age and weight, whether they smoke or take drugs, the nature of their illness – to determine the doses.
This all makes anesthesia as much art as science, and in the vast majority of cases, it works astonishingly well. More than 170 years after its first public demonstration, anesthetists across the world plunge millions of people each year into comas and then bring them out safely. This doesn’t just reduce patients’ immediate suffering; many of the most invasive lifesaving procedures would simply not be possible without good general anesthesia.
But as with any medical procedure, there can be complicating factors. Some people may have a naturally higher threshold for anesthesia, meaning that the drugs don’t reduce the brain’s activity enough to dim the light of consciousness.
In some cases, such as injuries involving heavy bleeding, an anesthetist may be forced to use a lower dose of the anesthetic for the patient’s own safety.
It may also be difficult to time the effects of the different drugs, to ensure that the so-called induction dose (which gets you to sleep) doesn’t fade before the maintenance dose (to keep you unconscious) kicks in.
In some situations, you might be able to raise or lower your limb, or even speak, to show the anesthetic is not working before the surgeon picks up their scalpel. But if you have also been given neuromuscular blockers, that won’t be possible. The unfortunate result is that a small proportion of people may lie awake for part or all of their surgery without any ability to signal their distress.
In some emergencies – particularly when the patient has lost a lot of blood – it may be impossible to achieve the perfect dose of the anesthetic drugs
Donner Penner talks about her own experience, during a lengthy telephone conversation from her home in Canada.
She says that she had felt anxious in the run-up to the operation, but she had had general anesthetic before without any serious problems. She was wheeled into the operating theatre, placed on the operating table, and received the first dose of anesthesia. She soon drifted off to sleep, thinking, “Here I go.”
When she woke up, she could hear the nurses buzzing around the table, and she felt someone scrubbing at her abdomen – but she assumed that the operation
to be panicking. I heard them say they were losing me.”
As you might expect, a large majority of the accounts – more than 70% – also contain reports of pain. “I felt the sting and burning sensation of four incisions being made, like a sharp knife cutting a finger,” wrote one. “Then searing, unbearable pain.”
“There were two parts I remember quite clearly,” wrote a patent who had had a wide hole made in his femur. “I heard the drill, felt the pain, and felt the vibration all the way up to my hip. The next part was the movement of my leg and the pounding of the ‘nail’.” The pain, he said, was “unlike anything I thought possible”.
It is the paralysing effects of the muscle blockers that many find most distressing, however. For one thing, it produces the sensation that you are not breathing – which one patient described as “too horrible to endure”.
Then there’s the helplessness. Another patient noted: “I was screaming in my head things like ‘don’t they know I’m awake, open your eyes to signal them’.”
To make matters worse, all of this panic can be compounded by a lack of understanding of why they are awake but unable to move.
“They have no reference point to say why is this happening,” says Christopher Kent at the University of Washington, who co-authored the paper about these accounts. The result, he says, is that many patients come to fear that they are dying. “Those are the worst of the anesthesia experiences.”
Estimates of how often anesthesia awareness happens have varied depending on the methods used, but those relying on patient reports had tended to suggest it was very rare indeed.
One of the largest and most thorough investigations was the fifth National Audit Project carried out by British and Irish anesthetists’ associations, in which every public hospital in the UK and Ireland had to report any incidents of awareness for a year. The results, published in 2014, found that the overall prevalence was just 1 in 19,000 patients undergoing anesthesia. The figure was higher – around 1 in 8,000 – if the anesthesia included paralysing drugs, which is to be expected, since they prevent the patient from alerting the anesthetist that there is a problem before it is too late.
Many more people might be conscious during surgery, but they simply can’t remember it afterwards
These low numbers were comforting news. As the media reported at the time, you were more likely to die during surgery than to become aware during the operation, confirming many doctors’ suspicions that this was a very remote risk.