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Paper text:
in their article in the present issue of critical care , wierdsma and colleagues validated a novel and feasible method to measure the degree to which enteral nutrition ( en ) is absorbed by the gastrointestinal tract .
the accuracy of simply weighing daily faecal production to identify gastrointestinal dysfunction was validated against three reference methods .
the contribution of protein and fat to the faecal nutritional losses were estimated by labour - intensive chemical analyses .
the authors identified a daily faecal weight above > 350 g as a reliable indicator for gastrointestinal malabsorption .
of course , these results need to be confirmed in a larger study population , including the most critically ill and those with known gastrointestinal problems .
the present study is of methodological and conceptual importance to nutritional research and clinical nutrition management .
first , the validation of this new assessment technique has been done in a very accurate and complete way and thereby provides a new reliable tool .
secondly , these results focus on a rarely addressed problem in the critically ill : is the en administered to a patient truly absorbed ? in 9 out of the 48 stable patients in this trial , the nutrition was only partially absorbed .
this 19% represents a high incidence of gastrointestinal dysfunction since patients with known gastrointestinal problems were not included .
previous studies assessed and treated diarrhoea in critically ill patients , measuring the frequency , liquidity and volume of stools but not the proportion of en energy , proteins and fat lost by the patient . whether studying the effect of nutritional interventions or managing nutrition in clinical practice , we will have to take into account these data on gastrointestinal energy losses .
the discrepancy between prescribed and effectively infused en doses in critically ill patients is relevant .
interruptions of en for procedures , emesis , high gastric residual volumes ( grvs ) , diarrhoea and feeding tube replacement are important culprits .
en lost in grvs being discarded after grv assessment can be measured using a refractometer .
an alternative is to reinject grvs after measuring or to refrain from measuring grvs , since evidence supporting this practice is limited .
briefly , we should be aware that the amount of en effectively taken up by the patient is the prescribed volume minus the volume not administered to the patients , minus the en discarded with grv minus the en lost in faeces .
indirect calorimetry , however , does not measure energy needs but energy consumption , and indirect calorimetry is less reliable in patients on renal replacement therapy , aggressive ventilation and other conditions often present in the critically ill .
a recent randomised trial showed more morbidity in the icu , but an unexplained reduction in hospital mortality in the per - protocol analysis , when feeding was guided by indirect calorimetry .
recent trials found no benefit in early en administration up to the calculated target as compared with low en intake .
finally , what should be done if en uptake is insufficient ? probiotics or fibre - rich en reduced the volume or frequency of diarrhoea in critically ill patients in some of the few randomised controlled trials on this topic .
absorption of en by dysfunctional gut could be facilitated by the absence of proteins or even peptides in , respectively , semi - elemental en or elemental en ; however , trials in critically ill patients failed to provide convincing evidence . the best controlled method to effectively complete insufficient en would be the intravenous administration of nutrition : parenteral nutrition . supplementing insufficient en with parenteral nutrition during the first week of critical illness , however , resulted in more infections and delayed recovery in a large randomised controlled trial . in conclusion , the optimal en dose during different stages of critical illness is not yet known .
stool weight measurements could improve our knowledge of true en absorption , however , and could thus lead to more accurate research and clinical practice .
ku leuven received an institutional partial ( < 30% ) , unconditional and nonrestrictive research grant for the epanic trial from baxter healthcare ( maurepas , france ) .
mpc receives funding from the research foundation flanders , belgium ( fwo doctoral fellowship ) , and dm from the clinical research fund of the university hospitals leuven , belgium ( postdoctoral fellowship ) .
the nutrition dose truly absorbed by a patient is crucial information in the management or the investigation of nutrition during critical illness . in the present issue of critical care , assessment of nutritional losses in stools 
 was studied . 
 these losses together with enteral nutrition lost in gastric fluids and enteral nutrition prescribed but never infused make up the difference between the dose supposedly given to a patient and the amount effectively taken up . 
 additionally , the optimal dosing and timing of nutrition during critical illness are still debated . when enteral nutrition is insufficient , the options are limited .