The safety implications of prolonged fasting in young children prior to general anaesthesia are well described. Current UK guidance recommends a fasting time of 6 hours for formula milk prior to general anaesthesia. European guidance published in 2022 recommended a reduced fast of 4 hours for infants taking formula milk, albeit with a downgraded level 2B of evidence given the paucity of high quality research in this area. Although pulmonary aspiration of gastric contents under anaesthesia in children is a rare event, animal studies suggest that aspiration of particulate matter at volumes greater than 0.8 ml/kg gastric volume are associated with demonstrable lung injury and mortality. Although rate of gastric emptying of formula preparations has been extensively studied in neonatal intensive care settings for preterm babies using ultrasound, few studies have measured gastric volume directly in healthy term infants undergoing anaesthesia.

Traditional fasting guidelines of 6 hours for formula milk may be unnecessarily long. In practice, children also tend to be fasted for longer than the guidelines advise, as they may not always feed on cue, and delays in the hospital can occur on the day of surgery. Prolonged fasting in young children and infants is less well tolerated than in adults and can lead to hunger, dehydration and low blood sugar, as well as distress for the child and parents. We know from previous research in smaller babies that after a formula feed, the stomach empties by half in around 80 minutes, and empties completely by around 3 hours.

The investigators want to find out if young children and infants who are fed with formula milk 4 hours prior to an anaesthetic have similar levels of stomach contents at the time of their anaesthetic as those who are fed at 6 hours.

The investigators will carry out a clinical trial where children are randomised into 2 groups. Parents of children in Group 1 will be asked to offer a formula feed to their child 6 hours prior to the planned start time of their anaesthetic. Parents of children in Group 2 will be asked to offer a formula feed to their child 4 hours prior to the planned start time of their anaesthetic. Prior to having their anaesthetic a study team member will perform an abdominal ultrasound scan to check and record antral cross sectional area. Once asleep, gastric aspiration will be performed via naso-gastric tube. Volume, colour and pH of the fluid will be measure

The volume and acidity of any stomach contents will be compared between group 1 and group 2.

Inclusion Criteria:

Term or term corrected (> 37 weeks) upto 12 months Formula fed ASA 1-3

Exclusion Criteria:

Significant reflux Co-administration of drugs known to impact gastric motility or PH of gastric contents Significant respiratory comorbidity including chronic lung disease on home oxygen Significant cardiac comorbidity