Preoperative fasting is the practice of a patient. This is intended to prevent pulmonary aspiration of the stomach contents during general anesthesia.
The main reason for preoperative fasting is to prevent pulmonary aspiration of the stomach while under the effects of general anesthesia. Aspiration of as little as 30-40 mL can be a significant cause of suffering and death during an operation and therefore fasting. Several factors can be predisposed to aspiration of stomach contents including inadequate anesthesia, pregnancy, obesity, difficult airways, emergency surgery (since fasting time is reduced), full stomach and altered gastrointestinal mobility. Increased fasting times leads to
In addition to fasting, antacids are used in the night before and again after surgery. This is to increase the pH (make more neutral) of the acid present in the stomach, should it occur. H2 receptor blockers should be used in high-risk situations and should be used in the same timing as antacids. Gastroparesis (delayed gastric emptying) may be due to metabolic causes (eg poorly controlled diabetes mellitus), decreased gastric motility (eg due to head injury) or pyloric obstruction (eg pyloric stenosis). Delayed gastric emptying usually only affects the emptying of the stomach of high-cellulose foods such as vegetables. Gastric emptying of clear fluids such as water or black coffee is only affected in highly progressed delayed gastric emptying. Occasionally, gastroesophageal reflux (GERD) may be associated with delayed gastric emptying of solids, but clear liquids are not affected. Raised intra-abdominal pressure (eg in pregnancy or obesity) predisposes to regurgitation. Certain drugs such as these can be marked in gastric emptying, as can be trauma, which can be determined by certain indicators such as normal bowel sounds and patient hunger.
The minimum fasting times have been debated. The first proposal came from British anesthetists stating that patients should be nil by mouth from midnight. However, since then, the American Society of Anesthesiologists (ASA), followed by the Association of Anaesthetists of Great Britain and Ireland (AAGBI), recommended new fasting guidelines for the minimum fast prior to surgery. This study was conducted by the Canadian Institute of Anesthesiology. The following are the recommendations for nil by mouth before surgery in healthy patients: When anesthesia is required in an emergency,
Fasting guidelines often restrict the intake of any oral fluid after two to six hours preoperatively. However, it has been demonstrated in a large retrospective analysis in Torbay Hospital that unrestricted clear oral fluids can not be significantly reduced in the incidence of postoperative adverse events.