ScienceTalk

Anaesthesia: Have a safe flight

A nurse at a hospital's post-anaesthesia care unit checking the monitor which displays the vital signs of a patient who has just emerged from surgery. Under a general anaesthetic, a person should have no recall of intra-operative events.
A nurse at a hospital's post-anaesthesia care unit checking the monitor which displays the vital signs of a patient who has just emerged from surgery. Under a general anaesthetic, a person should have no recall of intra-operative events.ST PHOTO: STEPHANIE YEOW

The procedure has been likened to aviation, with millions getting high but landing safely

"Then a cold, sleep-inducing drug will run through your veins, and your pulse will stop. Your flesh will be cold, and you'll stop breathing. The red in your lips and your cheeks will turn pale, and your eyes will shut. It will seem like you're dead. You won't be able to move, and your body will be stiff like a corpse. You'll remain in this death-like state for 42 hours, and then you'll wake up as if from a pleasant sleep."

- Friar Laurence, Romeo And Juliet.

From as early as 2000 BC, mankind has known the hypnotic effects of the opium poppy and the mandrake root. These have been used, with varying degrees of success, to induce a state of unconsciousness to facilitate surgical procedures.

Often, inducing a comatose state was rarely the issue. Rather, the ability to control the adverse effects of these substances, and reversing these effects after the procedure, were key to a successful outcome.

Th early practitioners of anaesthesia were dentists, surgeons and obstetricians, who would render their patients unconscious with nitrous oxide, ether or chloroform before proceeding to practise their craft.

  • A guide on surgery care management

  • Dr Bryan Ng, 40, is a consultant with the Department of Anaesthesia at the National University Hospital (NUH) and an assistant professor at the Yong Loo Lin School of Medicine at the National University of Singapore.

    His dual sub-speciality interests are obstetric anaesthesia, for which he is a member of the NUH Obstetric Risk Management Committee; and perioperative medicine - an emerging field of medicine that focuses on the care a patient may receive before, during and after surgery - for which he has formulated guidelines on perioperative management of various medical conditions.

    Dr Ng has produced patient information leaflets and videos to help them and their loved ones make informed decisions regarding their anaesthetic options.

But it became apparent that this was less than ideal as it left the hapless patient unmonitored for the duration of the procedure. Delayed recognition of surgical and anaesthetic complications frequently meant that these procedures did not end well.

This gradual realisation led to the world's first anaesthesia department being established at the Massachusetts General Hospital in 1917, almost 70 years after the first public demonstration of the procedure at the location.

The word anaesthesia is derived from the Greek words "an" meaning without and "aesthesis" meaning sensation.

So similar to death was the anaesthetised patient that in parts of Europe, the practice of anaesthesia became synonymous with reanimation, as the "dead" were awakened after surgery. It is probably this likeness to death that - till today - still strikes fear in some people's hearts.

In a study done at the Anaesthetic Outpatient Consultation Clinic of the National University Hospital, 117 patients scheduled for elective surgery were interviewed. Nearly 70 per cent of them expressed significant levels of anxiety. Their fears included failure to awaken after the procedure and accidental awareness during surgery.

The micromort is a concept introduced by Professor Ronald Howard, an expert in decision analysis. It is a unit of risk representing a one-in-a-million chance of death. This concept allows us to compare the risk of mortality arising from various activities, and put mortality risk into perspective.

Assuming that we live till 80 years (29,200 days), the risk of mortality on any given day is one in 29,200 - a 33 in a million chance of death, or 33 micromorts.

Having a general anaesthetic for an elective procedure exposes a person to 10 micromorts, which is three times lower than our chance of mortality on any given day.

Given the unlikely event of an anaesthetic-related death, should we take the decision for surgery or anaesthesia lightly?

Anaesthesia and surgery cannot be taken in isolation. It is unlikely that anyone would undergo anaesthesia without undergoing a surgical procedure. Tissue damage from surgery incites an inflammatory response in the body. To avoid excessive haemorrhage, the blood clots more readily.

  • Free forum tomorrow

  • In conjunction with World Anaesthesia Day today, the Singapore Society of Anaesthesiologists is organising a public forum tomorrow: Anaesthesia Unmasked: Myths and Truths. It will be held at Academia, Singapore General Hospital, 20 College Road, from 10am to noon (English), and 1pm to 3pm (Mandarin).

    Admission is free.

    •To register, go to www.facebook.com/WAD singapore or contact Jessie Tan on 9450-8395 or e-mail sgwad2015@gmail.com

However, if blood should clot within the coronary or cerebral vessels, it will cause a heart attack or stroke. It is the body's response to tissue injury, interplayed with an individual's medical condition, that determines the true likelihood of complications.

Although one is likely to wake up from anaesthesia, those burdened by chronic medical conditions such as diabetes, or kidney and heart disease are at higher risk of post-operative complications.

Awake was a 2007 film that sensationalised the fear of accidental intra-operative awareness. In this film, the protagonist, undergoing a heart transplant, became aware during his surgery, uncovering a twisted plot involving his wife and cardiac surgeon to murder him.

The fear of awareness has been perpetuated by a common misunderstanding between sedation and anaesthesia. Sleep, sedation and anaesthesia exist along a continuum. When physiologically asleep, we may be roused by external stimuli such as voices or internal stimuli like a full bladder.

Simple procedures like cataract surgery and endoscopy may be done under sedation. The site of surgery may be numbed with local anaesthetics, and a light sleep is induced with pharmacological agents. Under sedation, we would require a stimulus of higher intensity to rouse us.

For example, we might awaken briefly if we experienced discomfort at certain points during the procedure, but would quickly fall asleep again once the stimulus was removed. A person may be able to recall some or all of the procedure, depending on the amount of sedatives used.

Under a general anaesthetic, a person should have no recall of intra-operative events. This is achieved by a larger dose of sedatives to induce a state of anaesthesia. Anaesthesia is then maintained for the duration of surgery using intravenous or inhaled agents.

Accidental awareness can result in a patient's recall of intra-operative events. Patients with such experiences may need psychological support to cope with this emotionally traumatic event.

Equipment failure can result in an interruption in the delivery of the anaesthetic agent. This is one of the reasons why anaesthetic equipment is checked daily and also before the start of each procedure.

Most anaesthetic agents will lower the blood pressure. During periods of haemodynamic instability (such as sudden blood loss), the dosage of anaesthetic agents may be reduced transiently to maintain the blood pressure. This may increase the risk of awareness.

Last year, the United Kingdom and Ireland published the largest cross-sectional study of awareness to date, involving three million operations that required general anaesthesia.

In this National Audit Project, the reported incidence of awareness was one in 20,000 such operations. This report also proposed 64 recommendations to minimise the risk of accidental awareness, many of which are already in place in our local hospitals.

To reiterate, in operations that do not require general anaesthesia, the aim is to allow the patient to be relatively pain-free and calm. Hence, the patient may recall events during the procedure.

In contrast, under general anaesthesia, the intent is to induce a state of complete amnesia, so it would be out-of-the-ordinary if the patient were to recall intra-operative events.

Modern anaesthesia has been likened to modern aviation, with millions getting high but landing safely annually, with your anaesthetist ever-present for your safety and comfort. When preparing for surgery, a visit to the anaesthetic clinic would be similar to your online check-in before your flight.

Here, your medical issues can be optimised, and your anaesthetist may then present you with the anaesthetic options available for your procedure. You may also wish to discuss your concerns with him or her to fully understand the anaesthetic choices available.

Have a pleasant journey.

A version of this article appeared in the print edition of The Straits Times on October 16, 2015, with the headline 'Anaesthesia: Have a safe flight'. Print Edition | Subscribe