21 Apr 2020
Within the UK intensive care environment, enteral nutrition is predominantly provided via a feeding pump. However due to the rapid expansion of existing intensive care units (ICU) and the creation of entirely new ICU capacity in Critical Care Field Hospitals throughout the UK to manage COVID-19 patients, it is expected that there will be a shortfall in the number of feeding pumps required. In this instance it may become necessary to consider bolus feeding in a select cohort of ICU patients.
Summary of published studies used to inform recommendations.
A literature search was performed to inform this guideline from 2016-April 2020. Four studies published in the English language pertaining to bolus feeding were identified. Of the four 1-4 studies, three1-3 were in intensive care patients of which two were randomised control trails1-2 and one an observation study3, none of the studies specifically considered patients with severe respiratory failure as characterised by the COVID-19 patients and therefore the extrapolation of their results to the COVID-19 patient group should be made cautiously. The recommendations on bolus feeding from the ESPEN guideline on clinical nutrition in the intensive care unit 2019 were also included 5 Where evidence was lacking recommendations were made based on the consensus of best practice established amongst the working group which contained experienced critical care dietitians from within the British Dietetic Association Critical Care Specialist Group. When ICU specific evidence was lacking descriptive evidence presented in the fourth study which was a cross section survey of bolus tube feeding in home enterally fed patients4 was considered to help inform guidance.
Definition of feeding methods
Continuous or cyclical feeding, is defined as feeding via a feeding pump for several hours during a 24hour period. Usually in the ICU setting patients are continuously fed over 20-24hrs.
Bolus feeding, is used to describe a method of feeding where either a syringe or gravity is used to deliver feed over a 5-10 minute period, 4-6 times a day6.
The safety of bolus vs continuous feeding in the ICU.
Since the introduction of enteral feeding pumps in the UK they have become the mainstay method of delivering feed on ICU. Although the evidence base is limited continuous feeding is expected to improve feed tolerance thereby helping to manage the risk associated with poor feed tolerance. It is also considered to cause less variability in blood glucose levels.
Of the literature reviewed, two studies1,2 recorded no difference in gastric tolerance between the groups of patients fed continuously or via bolus in the ICU setting. Both studies monitored gastric tolerance through a combination of gastric residual volumes (GRVs), symptoms of diarrhoea, nausea and abdominal distention. GRVs were monitored 3hourly2 with a tolerance of 200-300mls.
It is however noted that the ESPEN guideline 5recommends using continuous rather than bolus, as a meta-analysis found a significant difference in rates of diarrhoea in bolus feeding compared to continuous feeding.
Blood sugar control
Blood sugar control on the ICU focuses on the avoidance of glucose variability, whilst recognising that hypoglycaemia is independently linked to a poorer outcome.
One study of 50 ICU patients randomised to continuous or bolus feeding via a percutaneous endoscopic gastrostomy tube3 (PEG) recorded no difference between glucose variability or insulin utilisation seen between the two groups. It is however acknowledged that as the study population were feeding via a PEG tube they were likely to represent a more stable ICU patient. The study also provided no detail on the type of feed used, how the feed bolus was administered or if any of the study population had pre-existing diabetes.
In a study by McNelly et al 20201 those that were bolus fed were observed to have a greater number of days with hyperglycaemia but there was no difference in cumulative insulin received between the continuous and bolus feeding groups. There was also no difference in hypoglycaemic events between the two groups, but of the seven adverse events recorded in the bolus group two were related to erratic glucose levels in patients with pre-existing diabetes. The author therefore concluded that the increased blood glucose variability seen in the bolus feeding may require more bespoke insulin protocols for patients with greater insulin resistance.
Enteral feeding regimes
Of the 2 studies1,2 that described their bolus feeding method, bolus feeds were administered 3-4 hourly up to 6 times a day. Feeding was initiated at 50-80ml boluses which were increased as gastric tolerance was established, to a maximum of 200mls/feed bolus2 (1200ml/day).
The type of feed varied in nutritional composition from 1kcal/ml2 using a reconstituted feed to 2.4kcal/ml1 using a compact style oral nutritional supplement.