You Don’t Need to Do a Prolonged Fast Before Surgery

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By the 1960s the term nil by mouth (or its Latin variant NPO, nil per os) after midnight had become the widely accepted guideline for all surgical patients. If you recently had an elective procedure, you might know that it has not changed much since—fasting before surgery, meaning no food and no water, is still advice routinely given to preoperative patients. Yet the evidence—and medical practice, and even the recommendations—have evolved since Mendelson. Medical practice has yet to catch up.

For one thing, anesthesiologists no longer use ether, a substance known to make patients nauseated. They also employ endotracheal tubes, which protect the airways from the aspiration of stomach contents. Knowledge about digestion has increased to the point where the rate of calories leaving the stomach is predictable: A spate of studies on gastric emptying found that patients who consume clear fluids two hours prior to an operation do not have higher gastric volumes than those who fast for longer. In 1999, the tide of mounting evidence pushed the American Society of Anesthesiologists to amend its preoperative fasting guidelines: Patients are now instructed to have a light meal six hours before a procedure and clear fluids—drinks that you can see through, such as pulp-free juices, black coffee, or tea without milk and cream—until two hours prior to the operation. Guidelines in other countries were similarly amended.

Nevertheless, most patients appear to still be getting outdated advice and arrive to surgery thirsty and irritable. A presentation at the 2016 Anesthesiology Annual Meeting found that only 25 percent of hospitals in Michigan adhered to the new guidelines. A 2016 study of oral and maxillofacial surgeons found that 99.1 percent of them did not adopt ASA guidelines, and a worrying analysis of pediatric practices discovered that most children were fasting longer than necessary before their medical procedures, leading to negative experiences. Prolonged fasting can be associated with dehydration, hypoglycemia, and electrolyte imbalance. Some patients experience headaches and nausea before surgery.