Sub-topics
Why is fasting important ?
How long do patients go without food or drink ?
Emergency surgery
Why is fasting important ?
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If you vomit when you are awake, or even when you are asleep at night (and not anaesthetised), your reflexes prevent any of that vomit being sucked into your lungs. You cough and splutter to clear the area around the back of your throat and  larynx. Then you can breathe again.
When anaesthetised (or very drunk, or affected by an overdose of sedatives or certain street drugs), you may be able to vomit but some of your protective reflexes do not work. There is therefore a possibility that fluid from the stomach will regurgitate - that is, run up your oesophagus and into the back of your throat. Should this happen when your level of consciousness is decreased, then you cannot protect yourself by swallowing and coughing. The fluid may then pass into your windpipe or trachea and down into your lungs. This is known as aspiration. Should you inhale some stomach contents, then there is the risk of suffocation, particularly if undigested food is present. The acid in your lungs may also cause severe wheezing and a lack of oxygen. Later, pneumonia may develop. This pneumonia is a particularly severe form because of the effect of the acid on the delicate tissue of the lungs.
How long do patients go without food or drink ?
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Until about ten years ago, it was common for patients scheduled for elective surgery to fast from midnight on the night before surgery. If the operation was scheduled in the afternoon, patients had to fast for periods of up to 16 - 18 hours. In the late 1980s, a number of scientific studies were carried out that questioned the validity of this fasting policy. In some countries, professional organisations have changed their recommendations to allow shorter hours of fasting. For example, the Canadian Anaesthetists' Society produced a revision to the Guidelines to the Practice of Anaesthesia in 1996. These new guidelines stated that fasting policies should take into account the age of the patient, as well as any medical problems that the patient might have. The guidelines also recommended that a patient should not eat any solid foods on the day of surgery, but could drink clear fluids up to three hours before the operation. Despite increasing amounts of scientific evidence about the safety of following guidelines such as these, standard textbooks of anaesthesia still recommend that patients be ‘ NPO ’ (‘Nil per os’ or ‘nothing by mouth’) for six to eight hours before anaesthesia and surgery. It is likely that such statements will change in the future, although anaesthetists still recommend in general that patients do not eat any solid food after midnight before the scheduled operation.
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If you have been in an accident, are in pain, or have been given an injection of a painkiller, the speed at which food leaves your stomach and passes downwards is slowed. This results in you having what anaesthetists term a ‘ full stomach’, which increases the possibility of stomach contents being regurgitated back up the throat. Theoretically, your operation could be delayed until your stomach had emptied, although this is not always appropriate. There are ways of minimising the possibility of regurgitation of gastric contents. Some patients may need to have a nasogastric inserted through the nose, down the oesophagus, and into the stomach. The fluid in the stomach can then be suctioned out through the tube, although removing solids is still a problem. This technique is important in patients who have an obstruction of the bowel. Unfortunately, suctioning cannot ensure that the stomach is empty, but only one that is ‘less full’. Drugs that are currently used to lessen the risk of regurgitation include those to neutralise stomach acid, those to decrease acid production, and those to increase the downward emptying of the stomach.
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