Does Early Enteral Feeding Improve Outcomes in Medical ICU Patients?
Abstract & Commentary
By David J. Pierson, MD, Editor, Professor, Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, Seattle, is Editor for Critical Care Alert.
Synopsis: In a retrospective analysis, medical ICU patients requiring mechanical ventilation for 2 days or more had lower ICU and hospital mortality (but more ventilator-associated pneumonia) if they were begun on enteral feeding during that time than if they were not.
Source: Artinian V, et al. Chest. 2006;129:960-967.
Artinian and colleagues performed a retrospective analysis on a large prospectively acquired database from ICUs across the United States to examine the effect of initiating early enteral feeding on outcomes in non-surgical, mechanically ventilated ICU patients. They used patient data from Project IMPACT CCM, Inc (www.cerner.com/piccm/about.html), a proprietary ICU data collection and management system. After exclusion of patients who were weaned or died within 48 hours, or were predicted to have a contraindication to enteral feeding (such as those with gastrointestinal bleeding, ileus, or pancreatitis), data from 4,049 patients who were ventilated for at least 2 days were used in the study. Patients in whom the records showed that enteral feeding was begun within the first 48 h of commencement of ventilatory support (n = 2,537) were compared to those without such documentation (n = 1,512). The investigators determined associations between early feeding status and ICU and hospital mortality, ventilator-free days, ICU length of stay, and the incidence of ventilator-associated pneumonia (VAP), using a standardized definition. They also attempted to adjust for imbalances in the patient groups by matching a subset of 1,264 of the early feeding patients with an equal number of non-fed patients by means of a propensity score.
The 63% of patients who received early feeding were significantly older, more likely to be white, and to have been admitted to the ICU for respiratory reasons. Early feeding patients were also less seriously ill as measured by MPM-0 and SAPS II scores. ICU and hospital mortality were lower in the early feeding patients (18% vs 21%; P = 0.01, and 29% vs 34%; P = 0.001, respectively). The mortality differences were primarily among the most seriously ill quartile of the early feeding group, and these persisted in the secondary analysis using propensity score. Early feeding patients had longer ICU lengths of stay (10.9 vs 10.2 days; P = 0.01), and also had an increased risk of VAP in all adjusted analysis, but there was no difference in 28-day ventilator-free days. In the several prediction models used, early enteral feeding was associated with an approximately 20% decrease in ICU mortality and a 25% decrease in hospital mortality. The authors recommend early enteral feeding for medical ICU patients, based on their conclusion that such an approach to nutritional support reduces ICU and hospital mortality primarily because of improvements in the sickest patients.
The clinical importance of early nutritional support in the ICU remains controversial. Food is good, and it would seem to be self-evident that feeding critically ill patients would be good for them, yet this has been surprisingly difficult to establish convincingly. Poorly nourished patients do less well than those with better nutritional status, but this is not the same as saying that early, aggressive feeding across the board will improve outcomes. A systematic review of studies in critically ill patients with abdominal surgery, hip fracture, trauma, and burns concluded that early enteral feeding was beneficial in those groups.1 However, the only previous study2 in mechanically ventilated medical ICU patients—a single-center randomized controlled trial—found that early institution of full enteral nutritional support was associated with increases in the rates of VAP and Clostridium difficile-associated diarrhea, longer stays in the ICU and in the hospital, and no differences in mortality. The results of this study differ strikingly from those of the latter.
In the hierarchy of evidence-based medicine, the findings of appropriately powered randomized clinical trials—or better yet, of meta-analysis of several such trials—carried out with patients similar to those of present interest and using clinically relevant end points, are at the top of the list. The results of smaller clinical trials and prospective studies with surrogate end points, data from retrospective studies, and the findings of studies on animals are placed progressively lower on the list. This is not to say that a retrospective study can't get it right or that the results of such a study should not be taken seriously. A retrospective analysis with findings at variance with those of a randomized clinical trial does present the clinician with a dilemma, however,
As the authors acknowledge, the present study has several limitations. The only thing in the database about the nutritional management of the patients is whether enteral feeding was initiated in the first 48 hours of mechanical ventilation; how much was given or whether it was tolerated is unknown, as are the nutritional formula used and whether the tube was gastric or postpyloric. Perhaps more importantly, as in any retrospective analysis it is not possible to know for sure why early enteral feeding was done in some patients and not others. Although the authors went to great lengths to eliminate confounding by indication, the possibility remains that something important about the early feeding patients that was not included in the database was different. As one of my colleagues likes to remind me, sicker patients don't do as well as patients who are less sick. Or perhaps there was something different about the medical ICU physicians who started their patients on early enteral feeding as compared with those who did not.
These issues notwithstanding, this study provides evidence for improved outcomes among medical ICU patients who require mechanical ventilation for 2 days or more—especially those who are more seriously ill—if they are begun on enteral feeding during that time. In the absence of contraindications, it would be reasonable to attempt enteral feeding under such circumstances, although the state of the evidence at present is that we do not know for sure whether this is really in our patients' best interests.
- Marik PE, Zaloga GP. Crit Care Med. 2001;29:2264-2270; Erratum in: Crit Care Med. 2002;30:725
- Ibrahim EH, et al. JPEN J Parenter Enteral Nutr. 2002;26:174-181.