The relevance of early continuous or intermittent enteral feeding of critically ill
patients has been discussed controversially in the last years. Today, continuous feeding
is still the standard for enteral nutrition in the ICU. The continuous nutrition can
prevent abdominal intolerance like vomiting, diarrhoea and aspiration. Pulmonary
aspiration is the most dramatic consequence of enteral nutrition and can be limited by a
continuous feeding as shown by a study in 2003. However, nutrition was started with a
bolus of 125ml as baseline by force of gravity over 15 minutes. Compared to the
continuous nutrition, this is considered much volume in a short time. Naturally, risk of
gastric intolerance in this scenario is very high.
In other studies, a similar amount of nutrition was given over a longer period of time
(30 - 60 minutes) every 4 hours. In each cohort (continuous and bolus), only one case of
pulmonary aspiration or tube obstruction was detected. After this study, other trials
with a similar result followed. In 2007 a trial of Georgia et al. showed no statistical
differences in complications regarding tube feeding, no differences of diarrhoea, emesis
or pneumonias between continuous and bolus nutrition. The feeding time for bolus
nutrition is also a critical influential factor. When an intermittent feeding is given
over a longer period of time (20-40 minutes), the incidence of nausea and vomiting has
not increased.
Intermittent feeding is not only a good alternative to continuous feeding, but also more
natural, as long-term intake of nutrition over 20 hours is not common in any mammal. The
alimentary tract and metabolic pathways of humans seem designed for intermittent
ingestion of essential nutrients reduced to a few times a day. Different hormones of the
endocrine cells affect complex roles of gastrointestinal motility, gall bladder
contraction and nutrient absorption. The level of these hormones depends on the amount of
nutrient ingestion. This response of the hormones is almost completely abolished in
continuous feeding. But in intermittent nutrition, hormones like incretin,
glucose-dependent insulinotropic polypeptide (GLP-1) and glucose-dependent insulinotropic
polypeptide (GIP) boost the level of insulin and the resulting carbohydrate load and
therefore influence the muscle protein synthesis and breakdown.
In healthy individuals, the anabolic effects of feeding occur due to an increase on the
synthetic rate of muscle protein synthesis of approximately 300% with a simultaneous 50%
decrease in the rate of protein breakdown. Two studies of 2009 and 2011 compared the
intermittent bolus and continuous feeding and the effect of protein synthesis in skeletal
muscle in neonatal pigs. They analysed the fractional rates of protein synthesis in
muscle samples of continuous and intermittent bolus feeding groups. They could show that
although both groups, continuous and intermittent bolus feeding, stimulate muscle protein
synthesis, but in the bolus-fed, in the fractional rates of protein synthesis called K's
was greater after a meal.
An ongoing study wants to show the effect of bolus vs. continuous feeding in ICU patients
related to muscle wasting by measurements of ultrasound and blood samples. In this trial,
the investigators would like to have a similar approach but with different measurements.
Using ultrasound and muscle biopsies, the investigators aim to determine whether
intermittent enteral feeding could preserve muscle mass better or more than standard
continuous enteral feeding in the critically ill patients. In addition, the investigators
would like to assess if intermittent bolus feeding optimizes protein intake in the first
7 days of critical illness since the intermittent route is less affected by interruptions
following treatment and diagnostic procedures.