© Springer International Publishing Switzerland 2017Basavana G. Goudra and Preet Mohinder Singh (eds.)Out of Operating Room Anesthesia10.1007/978-3-319-39150-2_5
5. Fasting Guidelines: Do They Need to Be Different?
Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, 1400 Holcombe Boulevard, Unit 409, Houston, TX, USA
The purpose of fasting guidelines is to reduce the incidence of aspiration during induction and maintenance of anesthesia. Although the traditional dogma of ‘nothing by mouth for 8 hours’ has been accepted for years, there is a lack of scientific evidence in support of this practice. Furthermore, preoperative fasting has been shown to be associated with some unintended unfavorable metabolic and psychological consequences. As a result, patients may be better served if fasting guidelines were approached from a patient and/or procedure specific perspective. Differences in fasting recommendations may therefore have to be accepted as the norm, rather than an exception.
Due to the evolving nature of the literature, several societies continue to publish updated versions of their own fasting guidelines, and recommendations continue to vary [1, 2]. For example, while the American Society of Anesthesiologists (ASA) recommend a fasting time of 8 h for a meal that includes fried or fatty foods, the Scandinavian Society of Anesthesiologists make no such exemptions, and recommend a 6 h fast for all solid food [2, 3]. A recent systematic review of fasting guidelines concluded that in the absence of obvious contraindications, preoperative fasting should be minimized and fasting from midnight is unnecessary in most patients. The review also concluded that patients can consume solids up to 6 h before anesthesia and drink clear fluids or an unlimited amount of water up to 2 h before anesthesia . Despite the available evidence, studies show that patients continue to experience prolonged fasting times and that the majority of fasting guidelines are non-compliant with recommended fasting standards [5, 6].
The following chapter will describe some of the unintended consequences of prolonged preoperative fasting and attempt to explain why patients may be better served if fasting guidelines were patient and/or procedure specific.
Metabolic Consequences of Preoperative Fasting
Fasting for greater than 10 h has been associated with a greater increase in basal metabolic rate .
This increased metabolic rate has been shown to be associated with a catabolic state and the depletion of glycogen storage before the start of surgery.
The preoperative stress response, as measured by serum levels of cortisol and C-reactive protein are higher in patients who have fasted for 8 h or more .
In a prospective clinical observational study of children undergoing elective surgery, prolonged fasting times were associated a higher concentration of ketone bodies, a higher serum osmolality and anion gap, and a significantly lower base excess .
Patients requiring repeat procedures over a prolonged duration of time may experience malnutrition as a consequence of the observation of strict fasting guidelines.
Malnutrition has been associated with poorer outcomes especially in cancer patients .
Psychological Consequences of Preoperative Fasting
Prolonged preoperative fasting may be associated with increased preoperative anxiety .
Patient comfort and satisfaction is negatively impacted by prolonged fasting times.
In a single center prospective randomized control trial of patients undergoing ophthalmologic surgery, patients drinking 200 ml of a carbohydrate drink before surgery had better postoperative satisfaction scores than patients who fasted for at least 8 h .
Current Evidence Suggests the Following
Solid food intake may be safe for up to 6 h before surgery .
Clear liquids may be safe for up to 2 h before surgery .
Obese adults have been shown to have acceptably low gastric fluid volume 2 h after the ingestion of clear liquids .
Two hours after the ingestion of clear liquids, gastric fluid volumes of obese children were identical to that of children with lower body mass indices .
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