Effect of a Liberal Fasting Regime (Sip-til-Send) on Preoperative Gastric Volume Measured Using Point of Care Ultrasound

Pulmonary aspiration of gastric contents during surgery is a rare but potentially catastrophic event. Current guidelines recommend that patients should fast for six hours for solid food and two hours for clear liquids. Despite this, many patients fast considerably longer than two hours for clear liquids, often as a result of logistical challenges. In response to this, the Sip-to-Send concept was developed where patients are permitted to drink small amounts of clear liquid (170-200 ml per hour) until they are called to the operating department. The introduction of Sip-to-Send has been well received by patients and has been associated with increased patient satisfaction. For planned general anaesthesia in the operating department, the incidence of pulmonary aspiration is estimated at approximately 1 per 4,500 anaesthetics. Because of this low incidence, it is in practice unrealistic to design studies using aspiration as the primary endpoint to demonstrate non-inferiority of new fasting regimens. For example, a study with a non-inferiority margin of 20%, power of 90% and a one-sided α of 0.025, based on an incidence of 1 per 4,500, would require approximately 2.6 million patients in each study arm. Gastric ultrasound represents a rapid, non-invasive technique for estimating gastric volume by measuring the cross-sectional area of the antrum and subsequently calculating volume. Several studies have shown that cross-sectional area correlates reliably with gastric volume, with good inter- and intra-observer reliability. Sip-to-Send has been established practice at the Day Surgery Department at Haukeland since October 2023. The purpose of this study is to investigate whether there is a clinically relevant change in gastric volume as a result of this liberal fasting regimen.