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.
Able to give written consent
Adult patient (> 18 years of age)
Planned general anaesthesia or deep sedation
Fasted for at least six hours for food and two hours for clear fluids upon arrival
Unable to give written consent
Active gastrointestinal obstruction
Pregnancy
Ongoing opioid use
Study population includes all adult patients for planned general anaesthesia or deep sedation at the day surgery unit at Haukeland University Hospital
Cohort
Prospective
Not listed
Difference in gastric volume
Gastric volume will be calculated using gastric ultrasound and the difference between fasting two hours for fluids and permitted drinking evaluated.
Time to first usable ultrasound image
Assess the ease of acquiring a usable ultrasound image by documenting the time to first usable image in seconds.
Inter-rater reliability of gastric ultrasound
Assess inter-oberserver reliability by blinded observers measuring gastric volume from a 120 second recorded ultrasoud video of the examination
Establish how much patients drink during the one hour on the liberal fasting regime
The volume of fluid actually consumed by the patient will be measured whilst the patients wait on the liberal fasting regime for their operation
Develop a machine-learning algorith to enable automatic and real-time calculation of gastric volume
Video sequences that were saved as part of the inter-rater reliability component of the study will be used to develop a machine-learning algorithm that will aim to automate the process of calculating the gastric volume.
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