Effect of Premedicant Oral Paracetamol on Gastric Volume and pH

Overview

Patients are asked to fast before general anaesthesia to reduce the risk that any gastric contents could be regurgitated and aspirated into the lungs once anaesthetised. If aspiration does occur, the volume and acidity of the fluid aspirated are thought to determine the extent of any harm caused. Recent guidelines have reduced the required fasting time for children for clear fluids from 2 hours to 1 hour before induction of anaesthesia, as it is understood that this does not adversely affect the gastric residual volume or increase its acidity. Paracetamol is commonly used to relieve pain during and after surgery. Paracetamol syrup preparations used in children are viscous and not classified as clear fluid. This study seeks to establish whether there is non-inferiority in gastric residual volume (GRV) and pH in children receiving oral paracetamol one hour before induction of anaesthesia and those who do not, when both groups have received a set volume of diluted orange cordial to drink. It is anticipated that if shown to have little or no impact on GRV and pH, oral paracetamol syrup can be given to children before surgery. This will omit the need for IV paracetamol to be given in theatre, potentially reducing cost and the risk of drug errors.

Patients are asked to fast before anaesthesia to reduce the risk that residual gastric contents could be regurgitated and aspirated into the lungs once anaesthetised. In animal studies, gastric contents that are less acidic (with a pH \>1.8) have been shown to be less harmful when aspirated than those that are more acidic, even at higher gastric residual volumes. Recent European and UK guidelines have reduced the length of the recommended clear fluid fast to 1 hour for children, as there is no significant difference in GRV or pH in children fasted for 1 hour compared to 2 hours. It is therefore believed to present no additional risk of harm. Some anaesthetists administer oral paracetamol syrup to children pre-operatively as an alternative to intravenous administration of paracetamol during their surgery. The oral route has been suggested to be pleasant for children, cheaper, more convenient, and reduce the risk of drug errors associated with the IV preparation. Anderson et al found no significant difference in gastric volume or pH in children with a mean age of 8.5 years given paracetamol orally 90 minutes before surgery compared to children given paracetamol rectally. Burke et al. demonstrated that giving paracetamol orally up to 8 minutes before induction of anaesthesia was not associated with an increase in the volume of stomach contents, and that the pH of stomach contents was higher than in control subjects who did not receive paracetamol. This suggests that giving oral paracetamol before induction of anaesthesia may not present any increased risk of harm from aspiration. This was in the context of a mean fluid fast of 5 hours and a mean age of 5.1 years. To our knowledge, no studies have assessed the effect of oral paracetamol syrup on gastric residual volume (GRV) and pH in the context of the newly recommended reduced clear fluid fasting time of 1 hour. Neither has this been studied in children as young as 44 weeks post-conceptual age.