Is General Anesthesia Safe?

© G.M. Woerlee

Is general anesthesia safe? The thought of undergoing anesthesia, and especially of undergoing general anesthesia strikes terror in the hearts of many people. During my preoperative visits (visits before the operation), and in the preoperative assessment clinic (anesthetic risk assessment clinic), I regularly speak with persons whose main fear is not of the operation, nor of the prospect of pain after the operation, nor of the prospect of crippling complications, infections, or death after the operation, but a fear of general anesthesia. And this fear of general anesthesia is not rare - studies by psychiatrists reveal that about 30% of people are more afraid of general anesthesia than the operation itself (Levenson 2007). Even in developed Western societies, many people appear to equate general anesthesia with a risky form of temporary death. Such a fear always reminds me of a passage in the Koran.

God takes away men's souls upon their death, and the souls of the living during their sleep. Those that are doomed He keeps with Him, and restores the others for a time ordained. Surely there are signs in this for thinking men. (Koran 39:42)

Actually, fear of general anesthesia is no more than a product of an ages old belief that sleep-like states are very similar to death, because a person undergoing general anesthesia is very definitely not dead, nor in a death-like state.

General anesthesia is not death

A person undergoing general anesthesia is far from being nearly dead, or in a death-like state. General anesthesia is actually very safe, and some desperately sick patients are in better condition under general anesthesia than when awake and breathing by themselves. Their vital functions, such as blood pressure, the amount of blood pumped by their hearts, etc are improved by the anesthesia, extra medicines, and extra oxygen administered by the anesthesiologist.

• The anesthesiologist monitors the volume of air entering the lungs, as well as the volumes of air returning out of the lungs.
• The anesthesiologist continually monitors vital signs such as the concentrations of oxygen, carbon dioxide, and anesthetic drugs breathed by the patients.
• The anesthesiologist monitors the circulation, by measuring whether the heart is doing anything (electrocardiogram and pulse rate), measuring whether the pumping action of the heart generates enough pressure to cause a flow of blood through the blood vessels of the body (blood pressure), whether this flow of blood is sufficient to remove waste products (capnogram, urine production), measuring whether the flow of blood transports sufficient oxygen to the organs and tissues of the body (oxygen saturation meter).
• The anesthesiologist monitors and replaces the volumes of various fluids lost during surgery as blood, urine, pus, evaporation from large open wounds, exudation of plasma from wounds or body cavities, or as swelling of wounds, making sure that the blood volume, and fluid composition of the patients' bodies is maintained at normal levels. During some major operations the blood volume of a person may need to be replaced 1-5 times.
• The anesthesiologist monitors the level of consciousness by clinical observation and special measures of the brain electrical activity, such as the electroencephalogram, or a derivative of the electroencephalogram.

So people under general anesthesia are far from being nearly dead. Instead they are very much alive, although they are unconscious, unable to speak, to move, to breathe, or to respond in any way to external stimuli.

Chance of dying due to general anesthesia

So what are the chances of dying as a result of general anesthesia and other events. Look at the chances of dying as a result of general anesthesia, pregnancy, and some relatively common planned operations.

• Chance of dying as a result of pregnancy in the USA or Western Europe = 5-10 deaths per 100,000 live births (0.005-0.01%) (Chang 2003, Hill 2001).
• Chance of dying as a result of general anesthesia alone = somewhat less than 11-16 deaths per 100,000 persons, depending upon general health of the persons (0.01-0.016%) (Lienhart 2006, Arbous 2001).
• Chance of dying due to complications resulting from the operation of removing the womb (hysterectomy) = 120 to 160 deaths per 100,000 operations (0.12-0.16%) (Bachmann 1990, Loft 1991).
• Chance of dying due to complications resulting from the operation of removing the gallbladder = 150 to 1400 deaths per 100,000 operations, depending upon health and technique of operation (0.15-1.4%) (Feldman 1994, Hannan 1999).
• Chance of dying due to complications resulting from the operation of removing the large bowel for cancer = 800 to 5000 deaths per 100,000 operations, depending upon health and technique of operation (0.8-5.0%) (Nelson-2006).

This is a wonderful illustration of how public opinion, socio-cultural factors, and rumor determine perceptions. Most women who are to undergo a hysterectomy are not at all afraid of the most deadly procedure - the operation - yet they are scared out of their wits by the thought of general anesthesia, the least deadly of these two things! Furthermore, these women were ecstatically happy during their reproductive lives when they discovered themselves to be pregnant, a condition whose mortality is comparable to that of general anesthesia. They were happy with pregnancy, but afraid of anesthesia. Curious... I explain these things, hoping to comfort these women, while explaining at the same time that statistics and emotions are two different things. The same principles apply to gallbladder and large bowel operations undergone by women. As regards the men who undergo gallbladder and large bowel operations, they were often also ecstatically happy when their sisters, wives, or daughters announced a pregnancy. In other words, they were happy with the risks undergone by these women, but unhappy with anesthesia which has a similar mortality. Also a strange attitude. Even so, I never tell these people of the mortality of the other types of surgery they are about to undergo - this is the responsibility of the surgeon. Furthermore, some people may refuse surgery upon learning these things, even though the complications of their diseases eventually have a higher mortality than the surgery they are to undergo - so of course surgery is the better choice, even though it does expose these people to some risk.

Anesthesia and surgery - a blind spot

There is a curious blind spot in the perception of many people. Many people seem to just look at anesthesia alone, seemingly forgetting that anesthesia is necessary to make the operation possible. People never undergo anesthesia without undergoing an operation. So when we talk about the risk of anesthesia, we are not talking about the risk of anesthesia alone, but the risk of anesthesia plus the risk of undergoing an operation. The discussion above clearly shows that the risk of dying due to an operation is generally very much higher than the risk of dying due to anesthesia. Moreover, the risk of dying due to undergoing an operation under anesthesia differs for different types of operation, and is also influenced by the health of the person undergoing the operation. In general, the larger the operation, the greater the risk of dying, and the unhealthier the person undergoing the operation, the greater the risk of dying. The health of a person undergoing an operation is usually expressed in terms of the ASA-score (American Society of Anesthesiologists score) (Keats 1978).

• ASA-1: A completely healthy patient.
• ASA-2: A patient with mild systemic disease.
• ASA-3: A patient with severe systemic disease that is not incapacitating.
• ASA-4: A patient with incapacitating disease that is a constant threat to life.
• ASA-5: A moribund patient who is not expected to live 24 hours with or without surgery.
• E: Emergency case suffix. (always a higher risk category)

This is a simple scoring system, which is why there is some variation in how different anesthesiologists score the same patient (Owens 1978). In general, the higher the score, the greater the chance of dying as a result of anesthesia and surgery. This is clearly shown in the table below. The reader should realize that these figures are statistics for large numbers of patients who underwent all manner of operations ranging from trivial to major. Accordingly, they should not in any way be misconstrued as applying to any specific individual, or to any specific combination of anesthesia and surgery. What these figures do show, is that unhealthy individuals are more likely to die as a result of anesthesia and surgery than healthy individuals.

Final remarks

The conclusion is evident - for healthy patients undergoing a planned operation, general anesthesia is about as dangerous as pregnancy in a healthy woman. In other words, general anesthesia is very safe. However, the poorer the health of a person, the older they are, and the higher the risk of the operation - the greater the chance of dying as a result of anesthesia and surgery. There are actually very few conditions where anesthesia is likely to be lethal for a patient, e.g. extremely severe aorta stenosis, major coronary artery stenosis, someone in deep shock, etc. Fortunately, these conditions occur very seldom. In general, for nearly all people, as the discussion above clearly demonstrates, anesthesia is very safe and far less dangerous than the effects of surgery.

© G.M. Woerlee | last updated 5 August 2009