I developed a dread of the moment when the anaesthetic drugs would take effect and I would cease to be. I pictured myself in a stark, poorly lit room with two doors, one in, one out, neither of which I could open from within. Otherwise the room was empty. No windows, no furniture. In this darkness – which I now realise had the same sinuous quality as the shadows beneath my childhood bed – I would be trapped alone. Perhaps forever. At least until such time as someone else chose to release, not me but some other version of me who would slip soundlessly into the life that had once been mine. Shortly after making my decision, I rang a separate Brisbane medical practice. I asked to speak to the doctor whose job it would be to render me unconscious and keep me that way during the long operation. Halting, almost apologetic, I explained to the receptionist that I had spent some years researching the process known as anaesthesia, and that I was now rather nervous about what was going to happen to me. "I think I know too much," I said. "Oh dear," they said. "That's not good." Not so long ago, if you were unlucky enough to need surgery and strong enough to withstand it, you would be tied down and cut open, usually conscious and probably screaming. Poppy. Hemlock. Hemp. Over the centuries, healers tried every imaginable way of preventing or deadening pain: pressing on arteries, pinching nerves, soaking sponges in narcotic herbs for patients to breathe through. Some practitioners favoured a blow to the jaw; others rubbed stinging nettles on one part of the body to distract from another. Alcohol. Opium. Hypnosis. Prayer. Until the mid-1800s, surgery was almost always an agonising last resort. Most of today's routine operations were impossible, and even when they weren't, many patients chose death in preference. "Suffering so great as I underwent cannot be expressed in words," wrote one survivor. "The particular pangs are now forgotten; but the blank whirlwind of emotion, the horror of great darkness and the sense of desertion by God and man … I can never forget." In the end a patient's best hope was often simply speed. A Napoleonic surgeon called Langeback claimed he could amputate a shoulder "in the time it took to take a pinch of snuff". The brutality of their trade made some surgeons wretched and others hard-hearted, but even amid the burgeoning humanism of the Enlightenment, pain was considered so integral to life that few could imagine surgery without it. "To avoid pain, in surgical operations, is a chimera," said the French surgeon Velpeau in 1839. " 'Knife' and 'pain', in surgery, are two words which never suggest themselves the one without the other … and it is necessary to admit the connection."

Surgical anaesthesia brought the gift of oblivion. Yet 170-odd years after a Boston dentist named William Morton gave the first successful public demonstration – removing a lump from the jaw of 20-year-old Gilbert Abbott – we still don't understand fully how anaesthetics work. Each day, specialist doctors known as anaesthetists put hundreds of thousands of people into chemical comas to enable other doctors to enter and alter our insides. Then they bring us back again. It is mind-blowing. But quite how this daily extinction happens and un-happens remains uncertain. Researchers know that a general anaesthetic acts on the central nervous system, reacting with the slick membranes of the nerve cells in the brain to hijack responses such as sight, touch and awareness. They have nominated areas and processes they know are important: the microscopic channels through which neurons blast their chemical relays; the electrical circuits that pulse and groove between different regions of the brain. But they still can't agree on just what it is that happens in those areas, or which of the things that happen matter the most, or why they sometimes happen differently with different anaesthetics, or even on the manner – a sunset? an eclipse? – in which the human brain segues from conscious to not. In a way, the art of anaesthesia is a sophisticated form of guesswork. We try to give the right doses of the right drugs and hope the patient is unconscious. Nor, as it turns out, can anaesthetists ultimately measure what it is they do. For as long as doctors have been sending people under, they have been trying to fathom how deep they have sent them. In the early days, this meant relying on signals from the body; later, on calculations based on the blood concentration of the various gases used. More recently, brain monitors have come on the market that translate the brain's electrical activity into a numeric scale – a de facto consciousness meter. For all that, however, doctors still have no way of knowing for sure how deeply an individual patient is anaesthetised – or even if that person is unconscious at all.

More than a decade ago, I found this quote in an introductory anaesthesia paper on a University of Sydney website: "There is no way that we can be sure that a given patient is asleep, particularly once they are paralysed and cannot move." Last time I searched, the paper had been adjusted slightly to acknowledge recent advances in brain monitoring, but the message remained the same. Just because a person appears to be unconscious does not mean they are. Equipment can fail – a faulty monitor, a leaking tube. Then there are certain operations such as caesareans, heart and trauma surgery that require relatively light anaesthetics: there the risk is increased as much as tenfold. One study in the 1980s found that close to half of those interviewed after trauma surgery remembered parts of the operation, although these days, with better drugs and monitoring, the figure for high-risk surgery is generally estimated at closer to one in 100. Certain types of anaesthetics (those delivered into your bloodstream rather than those you inhale) raise the risk if used alone. Certain types of people, too, are more likely to wake during surgery: women, fat people, redheads; drug abusers, particularly if they don't mention their history. Children wake far more often than adults, but don't seem to be as concerned about it (or perhaps are less likely to discuss it). Some people might simply have a genetic predisposition to awareness. Human error plays a part. But even without all this, anaesthesia remains an inexact science. An amount that will put one robust young man out cold will leave another still chatting to surgeons. "In a way," continued the original version of the introductory paper, "the art of anaesthesia is a sophisticated form of guesswork. It really is art more than science … We try to give the right doses of the right drugs and hope the patient is unconscious." I tracked down the paper's author, anaesthetist Chris Thompson, at the Royal Prince Alfred Hospital in Sydney. It was a quick encounter, as he was in surgery that day. We met in a small waiting room outside the operating theatre. He was still in his scrubs and surgical mask, and my first impression was of a pair of eyes so startlingly intense that for a moment I could not speak.

Without the mask, Thompson turned out to have a handsome regular face in which the eyes – I think they were blue – assumed more manageable proportions. He was quick to reassure me that anaesthetists are very good at giving the right doses of the right drugs. Today's specialist anaesthetists train for 12 to 13 years. They can put you to sleep in seconds, keep you that way for hours and wake you up again in minutes. They administer increasingly specific drugs in increasingly refined combinations; they have equipment to monitor your physical responses and are trained to look out for signs – such as tears or sweating or increased heart rate or blood pressure – that you might be more awake than you look. Applied anaesthesia, he said, was a blend of technical skill, compassion and science. "Experience is far more important than knowledge alone." Chris Thompson was in every way reassuring. He was knowledgeable and articulate and engaged. But a strange thing happened on both of the occasions that I spoke with him. I went into a kind of trance. I don't think it was just his eyes; perhaps it was the cadence of his voice, or the rhythms of his speech, or the things he was saying, some of which were quite technical. He would talk and I would try to focus, to lean in, to concentrate, and instead I would find myself drifting. When I tried to form words or sentences, they sounded as if they came from somewhere else, or as if someone else were saying them. It was bizarre. When I think of Chris Thompson I think of him as Mr Anaesthesia. Today's anaesthetic cocktails have three main elements: 'hypnotics' designed to render unconsciousness, analgesics to control pain, and in many cases, a muscle relaxant to prevent movement on the operating table. Credit:iStockphoto Anyway, all of this training helps explain why the death rate from general anaesthesia has dropped from about one in 20,000 in the 1970s to one, maybe two, in 200,000 by early this century; and the incidence of awareness from one or two cases per 100 to one or two per 1000. But it doesn't change the fact that anaesthesia is still, in some senses, as close to alchemy as to arithmetic. "Obviously we give anaesthetics and we've got very good control over it," another senior anaesthetist told me, "but in real philosophical and physiological terms we don't know how anaesthesia works." Today's anaesthetic cocktails have three main elements: "hypnotics" designed to render you unconscious and keep you that way; analgesics to control pain; and, in many cases, a muscle relaxant ("neuromuscular blockade") that prevents you from moving on the operating table.

Hypnotics such as ether, nitrous oxide and their modern pharmaceutical equivalents are powerful drugs – and not very discriminating. In blotting out consciousness, they can suppress not only the senses, but also the cardiovascular system – heart rate, blood pressure: the body's engine. When you take your old dog on its last journey, your vet will use an overdose of hypnotics to put them down. Every time you have a general anaesthetic, you take a trip towards death and back. The more hypnotic your doctor puts in, the longer you take to recover and the more likely it is that something will go wrong. The less your doctor puts in, the more likely that you will wake. It is a balancing act, and anaesthetists are very good at it. But it doesn't alter the fact that people have been waking during surgery for as long as other people have been putting them to sleep. I have to say that, having now had considerably more personal experience of anaesthesia than when I began writing my book on the subject, my recent impressions of anaesthetists have been uniformly positive. I have found each to be accessible, intelligent and more than happy to talk about what it is that they do, and are proposing to do to me. Perhaps this is because they know I am already interested in the subject, although I suspect a lot of people simply don't ask. Yet the reality is that anaesthetists remain for the large part the invisible men and women of surgery. For the doctors who each day make possible the miraculous vanishing act at the heart of modern surgery, this invisibility can be galling. It is not surgeons who have enabled the proliferation of surgical operations – numbering in the hundreds 170-odd years ago and the hundreds of millions today. It is anaesthetists. In hospital emergency rooms in Australia and other countries, it is not surgeons who decide which patient is most in need of and mostly likely to survive emergency surgery: anaesthetists increasingly oversee the pragmatic hierarchy of triage. And if you have an operation, although it is your surgeon who manages the moist, intricate mechanics of the matter, it is your anaesthetist who keeps you alive. In 2006 I met Greg Deacon, then head of the Australian Society of Anaesthetists (ASA). It can be a tricky job, balancing the interests (pecuniary and otherwise) of Australia's anaesthetists with the need to maintain their public professional standing. On the day I met him, in the library of the ASA's Sydney headquarters, he looked the part. Black suit, grey-and-white striped tie, slightly greying hair and a neatly trimmed beard. He did not look at all the sort of person who would knowingly allow a man to have his chest cut open without anaesthetic. Throughout the interview he was polite and helpful, although at times barely concealing frustration at the media attention surrounding the question of anaesthetic awareness, which he said was extraordinarily rare. The point he wanted to make, and to which he kept returning, was that on a scale of the things that could go wrong in anaesthesia, awareness was by no means the worst. Sometimes, said Deacon, when patients asked him if there was a chance they might wake up during their operation, he wanted to say to them: "If you purely want to worry, worry about not waking up: don't worry about waking up!"

One of the problems, he said, was that modern anaesthesia had become so safe we now took it for granted. Fifty years ago, if Grandma didn't wake up after her anaesthetic, well … sad, but not so surprising. Or if she woke up, but was never quite herself afterwards. "Again, that wasn't considered unusual." Those were the risks you took. These days, he said, they expect "perfection". Sure, awareness was an issue. "But it's not the main thing that I would be worrying about when I have an anaesthetic." He paused, then added: "I've had an episode myself." At first I thought he himself had woken during an operation. But he meant that one of his patients had, a man waiting to have open-heart surgery. Deacon had been preparing to anaesthetise him, he said, when the man went into cardiac arrest. The team managed to restart the recalcitrant heart and then raced the patient into surgery where they operated immediately. It was only once the operation had begun, the man's heart now beating steadily, that they could safely administer an anaesthetic. It all went well, said Deacon, and the man made an excellent recovery. Some days later, the patient told doctors he remembered the early parts of the procedure before he was given the drugs. "That is a sort of incidence of awareness which was thoroughly understandable and acceptable," Deacon told me: he had not even known if the man's brain was still working, let alone whether he would survive an anaesthetic. "We were trying to keep him alive." This is the tightrope that anaesthetists walk every day. They just tend not to talk about it. Despite some media hype, the likelihood of waking up while still in surgery is extremely rare, says one specialist: 'If you purely want to worry, worry about not waking up, don't worry about waking up!' Credit:FDC

It is not just doctors who sometimes find it hard to admit it when a patient wakes during anaesthesia. In the early-'90s, a Dutch team tracked down and interviewed 26 people who had reported waking during surgery. Most of them had mentioned the experience in preoperative interviews before subsequent operations. The records of the initial operations were unremarkable: experienced anaesthetists who later examined them – side by side with records of other, uneventful surgical procedures – were unable to reliably pick which patients had been aware. But what startled the researchers was that only nine of these patients had told their original anaesthetists what had happened. "Anaesthesiologists may well ask themselves," they wrote, "whether they really know what happens to their patients …" As it turned out, all the patients they approached were grateful, even eager, for the chance to talk. But other patients don't want to talk at all. Some are afraid of being disbelieved. Some don't want to make trouble. Some feel guilty, as though they have been a bad patient. Some can't see the point. Others may be too traumatised to revisit the experience. Michael Wang is a British psychologist who has built a career investigating the impact on patients' lives of being awake when they are supposed to be under anaesthesia. He was one of the first writers I came across when I started investigating stories about people waking under the knife. Some people think he – or at least his area of interest – is a bit wacky. That he is slightly obsessive. Certainly he has been a persistent and outspoken advocate for anaesthetised patients. "It is difficult to imagine a more exquisite form of torture than major surgery with consciousness, pain perception and complete paralysis," he wrote in a 1998 paper. "Clinical psychologists and the patient's family are then left to pick up the pieces." In a 2005 interview, Wang, who was by then working at Hull University in England's north, recounted an incident in which he had been called to the Hull Royal Infirmary after staff realised that a ventilator supposedly delivering anaesthetic gas to surgical patients had been dispensing only oxygen. Two patients had already undergone operations with the faulty equipment, one a woman having her stomach stapled, the other a man having a hernia operation. Both had been paralysed. Wang spoke first to the woman. "I went to the ward to meet her and she was extremely distressed," he said. "She was completely awake during the operation, but couldn't move. She felt every one of those staples going in." He never got to speak to the man. "I got to the ward about 24 hours after his operation had finished, but he'd already discharged himself against medical advice and all attempts to contact him failed," said Wang. "It might be that men assume they're going to experience some degree of pain and distress if they're having an operation, but my suspicion is, they think it's somehow not very macho to complain."

Even in those patients willing or able to talk about their experiences, the events can be strangely elusive. In a study published in UK medical journal The Lancet in 2000, a team led by Swedish anaesthetist Rolf Sandin interviewed nearly 12,000 people who had just undergone general anaesthesia, and asked them if they remembered anything of their surgery. Three times they asked. First, shortly after the operation; then again one to three days later; and again seven to 14 days after the event. They found 18 patients they were confident had been aware – and who themselves reported having been awake – for at least part of the surgery. What seemed odd was that only six had mentioned – and, it seemed, even remembered – this when they were first asked soon after waking. Five reported no memories until the third time researchers inquired. One patient who remembered nothing at the first interview, at the second recalled hearing voices and noises from surgical equipment, trying to get the attention of surgical staff but being unable to speak or move. By 12 days after the surgery she had forgotten again but, at a follow-up interview 24 days after the operation, could remember it all in detail. Less than a third reported memories at all three interviews. It seemed very strange, I thought, that you might be able simply to forget an event as compelling as finding yourself a surprise guest at your own surgery. It suggested for a start that people's experiences of awareness might be significantly under-reported, depending on how long or how often after their operations they were questioned. Then there was the matter of what happened to these erratic memories when they weren't in the process of being remembered. Where did they go? How long did they stay there? And what, in any case, were they? Edited extract from Anaesthesia: The Gift of Oblivion, The Mystery of Consciousness by Kate Cole-Adams (Text Publishing, $33), in shops on Monday.