Published Studies Used to Inform Recommendations
A literature search was performed to inform this guideline. Six studies published in English language were identified. All studies identified had small sample sizes, with primarily observational study designs, therefore the quality of the available evidence is low and should be interpreted with these limitations in mind. Where evidence is lacking the experience and usual practice of experienced critical care dietitians within the British Dietetic Association Critical Care Specialist Group was used to make recommendations.
Route of Delivery
Only one study was found which compared gastric and post-pyloric tube feeding. The study compared the incidence of microaspiration, defined by the presence of pepsin in endotracheal tube aspirates. No difference in microaspiration between those with post-pyloric and gastric feeding tubes were found4 however patients with overt feed intolerance were removed from the study thereby limiting conclusions in patients where this is present. All other studies found used gastric feeding tubes, and no increase in ventilator associated pneumonia was found in comparison to those in the supine position3,5.
Gastric Residual Volumes
Published studies have used a variety of gastric residual volume (GRV) cut offs, ranging from 150-500 ml every 3-6 hours6,7. Most commonly a GRV of 250 ml has been used3,5,8 however this appears to be an arbitrary choice likely related to local feeding practices. There were no published studies identified which compared the risk of aspiration based on different GRV thresholds. Most studies found no significant difference5-7 or a difference which was not clinically significant8 in GRVs in prone position compared to supine. Whilst one study reported higher GRVs in prone position3, this is likely related to the difference in care including head of the bed not elevated and a lower use of prokinetics compared to other studies. Four of the six studies stated that gastric aspirates were returned to the patient up to a maximum of 100 ml6 or 250 ml3,5,8, whilst other studies did not specify.
Enteral Feeding Regimens
All studies used feed delivery via pumps, however it is acknowledged that during the COVID-19 pandemic many hospitals are having to consider alternative feed administration options including gravity and bolus feeds.
The maximum feed rate used in the studies ranged from 65 ml/hr3 to 85 ml/hr5. The rate of feed increase was from 25 ml/hr, increasing by 25 ml/hr every six hours to target5, to 30 ml/hr and increase by 30 ml/hr every 24 hours3, to a 25% of target at day one increasing by 25% a day to reach target at day 47. This is reflective of the ranges in practice seen in enteral feeding in critical care, however it should be noted that one study found that an accelerated rate of enteral feed increase (increasing by 25 ml/hr every six hours) was well tolerated, and in conjunction with prophylactic prokinetics and a raised head of bed resulted in increased feed administration without increased tolerance issues5.
No studies compared different enteral feed types or energy densities on enteral feeding tolerance in the prone position.