Anaesthesia: still a medical mystery

My experience leaves me with a renewed sense of awe for what anaesthetists do as a matter of routine. Without really understanding how, they guide hundreds of millions of people a year as close to the brink of nothingness and bring them back to normal state.

Anesthesia is a major medical breakthrough, allowing us to lose consciousness during surgery and other painful procedures. The anaesthetist, in green scrubs, deftly slides a needle into your left hand. You begin to feel light-headed. It’s likely that you are told to count backward from 100 — and that you’ll wake up after a nice ‘deep sleep’. People rarely get beyond 90. But sleep is not the state you’re going into, nor would it be the state in which someone could perform an operation on you.

Recent years have seen the development of brain monitors that translate the brain’s electrical activity into a numeric scale – a sort of ‘consciousness meter’. For all that, doctors still have no way of knowing for sure how deeply an individual patient is anaesthetised!

A typical subject first experiences a state similar to drunkenness, which they may or may not be able to recall later, before falling unconscious, failing to move in response to commands. As they progress deeper into the twilight zone, they now fail to respond to even a scalpel, and at the deepest levels, may need ventilator breathing.

What surgeons need to do in order to be able to operate on you is to put you in a state of coma which we can readily reverse. It has five components. You’re supposed to be unconscious. You’re not supposed to have pain. You’re not supposed to remember. We want you to not move while someone is operating on you. And we want you to be stable — stable heart rate, stable blood pressure, temperature and breathing.

The anaesthesiologist takes over the physiology of the patient and controls it for the duration of the time that the patient is having surgery. Then, by titrating very carefully the way the medications are given, when the surgery is over, we can reverse the coma.

Anaesthesia is initiated with the injection of a drug called propofol, which induces a quick and smooth transition into unconsciousness. For longer operations, an inhaled anaesthetic, like isoflurane, is added to give better control of the depth of anaesthesia.

General anaesthetics are so called because the administered drug is transported via the blood into the brain. The first general anaesthetic used clinically was nitrous oxide, a gas still known as ‘laughing gas’.

In the 1940s, anaesthesia was a dicey proposition. Back then, one in every 1,500 deaths was attributed to anaesthesia. Today, the chances of a patient suffering death due to anaesthesia are less than 1 in 2,00,000. That’s a 0.0005% chance of a fatality. After decades of decline, the worldwide death rate during anaesthesia has risen to about 1.4 deaths per 2,00,000 — and the aging population has a lot to do with it. Anaesthesia can be stressful for older patients with heart problems or high blood pressure.

The development of general anaesthesia has transformed surgery from a horrific ordeal into a gentle slumber. 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 that prevents you from moving on the operating table.

Post-operative delirium is a state of serious confusion and memory loss. Researchers speculate that it’s not the quality of the anaesthetics, but rather the quantity; the greater the amount, the greater the delirium.

Waking up during surgery

“Does it happen, despite our best efforts? Sometimes. It may happen in emergency settings. There’s one situation historically where there had been a fair amount of recall or awareness under anaesthesia, with heart surgery as it was done primarily using large doses of opioids. Even though patients were quite comfortable and there was no evidence of stress overtly, they’d report having recall or having been aware during parts of the surgery. Anaesthetics are fairly selective, erasing consciousness while sparing non-conscious brain activity.

Although anaesthesia undoubtedly induces unresponsiveness and amnesia, the extent to which it causes unconsciousness is harder to establish. Unconsciousness is likely to ensue when a complex of brain regions in the posterior parietal area is inactivated. The fundamental question for anaesthesiology research is, how can this state be created by making physiologically sound, reversible manipulations of the neural circuits in the central nervous system? Anaesthesia remains an inexact science. It really is art more than science — to give the right doses of the right drugs and hope the patient is unconscious.

Recovery from anaesthesia is not simply the result of the anaesthetic ‘wearing off’ but also of the brain finding its way back through a maze of possible activity states to those that allow conscious experience. Put simply, the brain reboots itself.

(The writer is a former director of Sri Jayadeva Institute of Cardiology, Bengaluru, and a former vice chancellor of Bangalore University)