Preoperative fasting guidelines

As a principal investigator in studies of a 2- to 3-hour fast for clear liquids in Calgary in the late 1980s, and a member of the American Society of Anesthesiologists' task force that developed evidence-based fasting guidelines, I wish to discuss the Canadian Association of General Surgeons (CAGS) review and commentary of preoperative fasting for adults.¹

The authors state that the “classical surgical and anesthesia dictum has been that” healthy patients “should be kept NPO from midnight the night before operation.” This is questionable if by “classical” they mean an established pattern of practice sanctioned by a body of literature. In 1883, Lister² recommended that patients should drink clear liquid about 2 hours before surgery, but there should be no solid matter in the stomach. For the next 80 years, textbook fasting guidelines were 2–3 hours for clear liquids and 4–6 hours for easily digestible solids. These were consistent with the known rapid gastric emptying of clear liquids and the slower digestion and emptying of solids. It was only in the 1960s that most American anesthesia textbooks changed, without new evidence, to NPO after midnight.

Our first Calgary study demonstrated wide inter-patient variability in gastric fluid volume at induction of anesthesia in healthy patients. Mean volume was less in those who drank 150 mL water 2–3 hours preoperatively than in those who received NPO from midnight,³ most of whom had had no oral intake for 12–18 hours. Further studies from Calgary and other centres, to which the authors refer, confirmed that drinking 150–450 mL or more of clear liquid (water, black coffee or tea, fruit juice) until 2–3 hours before surgery did not increase gastric fluid volume compared with NPO from midnight. If volume is not increased, the risk of pulmonary aspiration is not increased.

The 1990 guidelines of the Canadian Anaesthetists' Society, quoted by the authors, of a total fast of no less than 5 hours, are long out of date. In 1999, the American Society of Anesthesiologists published preoperative fasting guidelines of 6 hours for easily digested solids and 2 hours for clear liquid for healthy patients scheduled to undergo elective surgery.⁴ The Canadian Anesthesiologists' Society adopted similar guidelines the following year.⁵

Cooperation of anesthesia and surgical colleagues and nurses is essential for a change to evidence-based guidelines. At Foothills Medical Centre in 1988, we presented our evidence of the safety of clear liquids to a joint meeting of surgeons and anesthesiologists and then to head nurses of our ambulatory and surgical nursing units. The clinical heads of anesthesia and surgery provided details of the revised guidelines in a joint letter to all attending and resident surgeons and anesthesiologists, with copies to the head nurses. Fasting instructions in the hospital's nursing policy manual were then revised. Patients may choose to drink from a list of clear liquids until 4 hours before the scheduled time of surgery, so that a change in the surgical schedule can be made and still allow 2 hours before the actual time of surgery.

Competing interests: None declared.