Review Articles

Overview of preoperative fasting for general anaesthesia

The primary goal of fasting prior to general anaesthesia is to reduce the risk of pulmonary aspiration, displacement of gastric contents into the lungs. As gastric volume, alongside patient age, current medications and type of surgery are associated with increased incidence of pulmonary aspiration. The preoperative fasting guidelines have been developed to reduce total fasting duration. Most recommend clear fluids up to two hours prior to surgery and solid food up to six hours prior to surgery. Reducing fasting time aims to minimize the negative metabolic effects of prolonged fasting, such as insulin resistance, catabolism, increased gastric acidity, discomfort, hypotension and dehydration. When combined with the negative effects associated with surgical trauma, many of these, particularly insulin resistance, have been associated with poor postoperative outcomes. Preoperative carbohydrate loading through the use of a glucose beverage has been examined as a method of reducing insulin resistance. There is a large amount of evidence suggesting it is a safe and effective preoperative tool. Patient compliance has been identified as a limitation of preoperative fasting guidelines, associated with a lack of understanding regarding their risk of pulmonary aspiration. Altering guidelines to include a default treatment program, consisting of carbohydrate treatment, minimum hydration requirements and enhancements in preoperative assessments to improve patient understanding, would likely improve patient outcomes.

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