Feeding the Critically Ill Obese Patient

Abstract

Obesity is increasing in prevalence. Supporting the critically ill obese patient will become an increasingly important skill in the intensivist’s armamentarium, and enteral nutritional therapy forms a cornerstone of this support. Despite this, neither an optimal total caloric goal nor the macronutrient components of a nutritional strategy for the critically ill obese patient has been established. The objective of the research described in this thesis was to systematically review the best available evidence describing nutritional strategies that target energy and protein delivery to reduce morbidity and mortality in the obese patient who is critically ill. A search for published and grey literature was conducted across a range of electronic databases including PubMed, Embase, CINAHL, ProQuest Dissertations and Theses and Conference Papers Index, Cochrane Central Trials Register, and the WHO Clinical Trials Register, and was supplemented by a hand search of the reference lists of study publications retrieved. Studies were selected for inclusion and subsequent assessment of methodological quality if they evaluated the clinical effect of targeting calorie and protein delivery in critically ill obese adult patients. In order to identify studies representative of critically ill patients, only studies conducted in intensive care units and in which ≥ 50% of recruited patients were receiving mechanical ventilation for ≥ 24 hours were eligible, while the World Health Organization definition (body mass Index ≥ 30 kg/m2) was used to classify obese patients. The search yielded 1000 unique records that were screened for eligibility. After removal of duplicates and screening of titles and abstracts, 18 studies were retrieved in full and underwent full text screening, of which six were excluded. Of the remaining 12 studies, only one recruited an obese population (albeit with an alternative definition of obesity). The remaining 11 studies identified recruited ICU patients without stratifying for, or targeting a particular weight, and therefore a proportion of whom would be expected to be obese. Contact was attempted with all corresponding authors to request access to the obese subgroup data for each study identified. Replies were received from eight authors representing 10 studies. Only two were able to provide raw data regarding the obese patients recruited to their studies; however, heterogeneity in research design of these two studies precluded meaningful data synthesis. The augmented versus routine approach to giving energy (TARGET) study compared two different enteral formulae with different caloric density, but with an identical protein component, the difference in caloric density being made up of fat and carbohydrate. The control arm targeted 19.9 kcal/kg/day, while the intervention arm targeted 29.3 kcal/kg/day. In the second study for which raw data were available, patients were randomised to either a eucaloric arm in which 100% of their estimated daily energy requirements were targeted (13 kcal/kg/day), or to a hypo- caloric arm in which 50% of their estimated daily energy requirements were targeted (8.8 kcal/kg/day). There was neither a signal for benefit nor for harm in the primary outcome of interest (mortality), nor in any of the secondary outcomes for which data were available (length of stay, nosocomial infection, duration of mechanical ventilation, gastro-intestinal intolerance or insulin requirement). In conclusion, there is a paucity of data supporting any approach to nutritional therapy for the critically ill obese patient. The optimal calorie and protein target remains elusive and further robust primary research is urgently required.