Prediction of gastric fluid volume by ultrasonography in infants undergoing general anaesthesia

This prospective observational study from South Korea used point-of-care ultrasonography and developed a predictive model for estimating gastric content volume in infants.

200 infants, 12 months of age or younger having a general anaesthetic needing intubation were included in the study. Gastric ultrasound assessment was done post anaesthetic induction, whilst maintaining spontaneous ventilation in order to avoid erroneous results with gastric insufflation due to positive pressure ventilation. Gastric cross-sectional area (CSA) was measured in both supine and right lateral decubitus (RLD) positions. Gastric fluid visualised was quantitatively graded from Grade 0-2 depending on visibility in one or both positions.

Post intubation with muscle relaxant, a nasogastric tube was inserted to carefully aspirate the gastric fluid contents. Suctioned gastric volume was measurable in only 48 of the 192 infants. No pulmonary aspirations were reported in any of the studied cases.

The authors derived a predictive model to assess gastric fluid volume based on the CSA measurements, quantitative grading score, age & weight. Supine CSA, RLD CSA and the quantitative grading system were all found to be independent predictors for suctioned gastric volume but age or weight were not. They also used two pre-existing predictive models for comparison and found a lower degree of co-relation than their model when applied to infants.

When they statistically compared the agreement between predicted volume and the suctioned gastric fluid, they found a difference of 0.58-0.62 ml/kg (less than the expected 1.25 ml/kg) and this was deemed clinically acceptable.

Take home message:

Prolonged pre-operative fasting in paediatric patients can lead to undesirable effects and most recent studies support clear fluid consumption in the paediatric population until 1 hr before surgery. The authors have opined that this approach still lacks sufficient clinical evidence in terms of the risk of aspiration. A point of care approach with gastric ultrasound can detect residual gastric volumes and increase the safety margin in the infants. The existing predictive models are not validated for the infant age group and hence this study provides some inroads in that aspect.

However, the authors admit that the blind aspiration of residual gastric fluid via nasogastric tube has not been found to be an accurate technique in adults to reflect actual gastric volume and therefore its validity in infants could be questioned. Only fasted kids for elective surgery were included in this study. The question remains whether this study can be extrapolated to unfasted infants for emergency surgery, where the risk of aspiration would be deemed much higher.

Reviewed by Dr Priya Sreedharan