ORIGINAL ARTICLENegative impact of hypocaloric feeding and energy balance on clinical outcome in ICU patients
Introduction
Critically ill patients with prolonged and complicated evolution have intense metabolic responses, generally characterized by hypermetabolism and protein catabolism. During the acute phase of their illness, these patients are also exposed to underfeeding, and to negative energy balances resulting from insufficient feed delivery intake, which favor the development of progressive malnutrition. Enteral nutrition (EN), which is the recommended method of artificial feeding in intensive care units (ICU)1 is frequently associated with insufficient energy delivery.2 Moreover, compared with other ICU treatments, feeding continues to be considered lower priority, due to lack of specific education.3, 4 The deleterious effects of underfeeding on outcome have long been recognized,5 and the role of hospital in its development and worsening has newly been re-emphasized by the European Council.6
The optimal way to quantify malnutrition in the ICU is still a matter of debate, as the criteria are not unanimously accepted. Surgical scores, such as the prognostic nutritional index (PNI), have not been validated in ICU settings.7 The actual weight is a source of confusion as is not reliable for nutritional assessment due to the enormous fluid shifts observed in critically ill patients. Indeed non-nutritional factors such as fluid balance, and inflammatory status are more important determinants of body weight early on the clinical course: the actual body mass index (BMI) becomes unreliable. Protein indicators of malnutrition (plasma albumin<35 g/l, plasma transferrine <2 g/l), are altered by critical illness. Finally, anthropometric determinations such as the cutaneous skin-fold are rendered useless by edema. The patient's physical aspect, his nutritional history and the presence of acute disease on admission to the ICU appear as the best tool to assess nutritional status.8 Such a clinical assessment should be part of routines, particularly in the sickest ICU patients.
The difficulty of assessing “beginning” malnutrition prompts for search of other variables to detect malnutrition. Using indirect calorimetry, a few trials have shown that underfeeding is indeed frequent in the ICU,9, 10, 11 such patients may be hypo-, iso- or hypermetabolic, which is difficult to predict on a clinical basis.10, 12, 13 While energy intake can easily be recorded in the ICU setting, the measurement of total energy expenditure is problematic: 24-h indirect calorimetry, direct calorimetry or doubly labeled water techniques are not available in the ICU14; determining fat stores is only possible under strict investigation conditions. Even indirect calorimetry is not available in every ICU: it enables a fairly accurate estimation of the 24-h resting energy expenditure (REE)15 and its extrapolation to total energy expenditure. In addition, indirect calorimetry is not always possible to carry out, e.g. in a patient with an O2 inspiratory fraction >60%, or extubated and non-cooperative, or in those requiring fluidized beds for nursing (air leaks).
This present study aimed at testing the relationship between energy balance and clinical outcome in severely ill surgical patients with prolonged ICU stay, and to confront the results with the usual biological markers of malnutrition.
Section snippets
Material and methods
The study was designed as a prospective observational study in consecutive patients staying for more than 5 days in the surgical ICU of the tertiary University Hospital of Lausanne. Exclusion criteria were major burns, or short stay. The study was conducted with approval of our institutional Ethics Committee which delivered a ⪡waiver of consent⪢ provided for this observational study. Data were made anonymous for analysis.
Patient data: Age, sex, pre-event weight, height, and BMI were recorded;
Results
Fifty-five surgical ICU patients were enrolled out of 962 consecutive admissions (5.7%): 7 patients were excluded due to incomplete data, leaving 48 patients and 669 ICU days for analysis. The patients’ characteristics are reported in Table 1. The length of stay was variable with a mean length of stay of 15 days: 24 patients stayed for more than 2 weeks, 5 for more than 3 weeks, and 4 for 4 weeks or longer. Organ failure (single or multiple) was present in all the patients. The ICU mortality
Discussion
The hypothesis that persistent hypocaloric feeding and negative energy balances are associated with poor outcome in the sickest critically ill patients was verified. This study investigated the nutritional support over 669 ICU days in 48 very sick patients with prolonged ICU stay. It confirms the difficulty to keep a positive energy balance using the enteral route. Only 11 patients (23%) were in positive balance at the end of their stay, while 37 were in negative balance throughout. These
Conclusion
The study confirms that negative energy balances are very frequent during severe critical illness despite nutrition protocols. It shows that underfeeding is correlated with increasing number of complications, and particularly with infections. Analysis of timing shows that the energy debt is initiated during the first week after admission, and that delaying the initiation of nutritional support exposes the patients to energy deficits that cannot be compensated during the remaining ICU stay.
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