John E. Mazuski, MD, PhD, FCCM
Washington School of Medicine
St. Louis, Missouri, USA
Beth Taylor, MS, RD, FCCM
Barnes-Jewish Hospital
St. Louis, Missouri, USA
Gastric Versus Intestinal Feedings: Does it Make a Difference?
Generally, healthcare professionals have accepted enteral nutrition as the optimal form of specialized nutritional support for critically ill patients. For most of these patients, this will be temporary, used until the critical illness abates. Considerable debate exists on how to provide the best enteral support to critically ill patients. The timing, amount and type of enteral feedings are all areas of controversy. Additional questions relate to whether nutrients should be delivered into the stomach, into the small bowel or through other modes of delivery. More specifically, the discussion centers on whether to feed a critically ill patient enterally through a feeding tube positioned pre-pylorically or post-pylorically.1,2 Advocates of post-pyloric feeding have cited more reliable delivery of nutrients and decreased risk of aspiration and pneumonia as advantages of this approach. However, advocates of pre-pyloric feeding question these benefits, noting that placement of post-pyloric feeding tubes requires trained personnel and intensive care unit (ICU) resources that could be used for other purposes.
What is the Evidence Regarding the Benefits and Risks of Prepyloric and Post-pyloric Feeding?
A number of prospective randomized controlled clinical trials compared these modalities in critically ill patients. Most of these trials have been small, so they haven’t been powered to detect relatively small changes in outcome parameters. The results of these trials have been combined in meta-analyses performed by Heyland et al,3 Marik and Zaloga,4 and Ho et al,5 none of which identified differences in mortality related to pre-pyloric versus post-pyloric feedings. However, the results differed with regard to outcomes related to adequacy of nutrient delivery and association of feeding site with risk of pneumonia.
In the meta-analysis by Heyland et al, nutrient delivery was superior in patients randomized to receive post-pyloric feedings compared to those receiving pre-pyloric feedings.3 Significance was dependent on the inclusion of a single study, in which an intervention designed to enhance the delivery of enteral nutrients to patients with head injuries was compared to a standard approach. Placement of an intestinal feeding tube was a component of the intervention in the patients randomized to receive enhanced enteral nutrition; however, this placement was successful in only 34% of patients.6 When the authors excluded this study from their meta-analysis, the significant difference in nutrient delivery was lost. No significant differences in nutrient delivery were observed in the other two meta-analyses.4,5
Nutrient delivery represents a surrogate endpoint. Except in cases of profound, prolonged macronutrient deficiency, inadequate nutrient delivery has been difficult to correlate with other measures of ICU morbidity. The risk of aspiration and development of pneumonia may be an endpoint of greater interest to critical care practitioners. The meta-analysis by Heyland et al identified a significant decrease in the incidence of pneumonia in patients randomized to post-pyloric feedings,3 a finding that was not echoed in the other meta-analyses.4,5 This difference was again dependent on the inclusion of the trial of enhanced enteral nutrition,6 and significance was lost when that trial was excluded. It is notable, though, that all three meta-analyses showed a trend toward a decreased incidence of pneumonia in patients randomized to receive post-pyloric feedings; this difference was probably in the range of 20%. Ho et al calculated that a sample size of 2,600 patients would have been needed to reliably detect a 20% difference in pneumonia rates.5 The actual sample size in their meta-analysis was 500 patients, indicating that lack of significance could have been due to a type II error.
Recent evidence also suggests that the position of the feeding tube has an influence on gastric aspiration. Metheny et al used a highly sensitive assay of pepsin in tracheal secretions to determine the frequency of gastric aspiration in a large cohort of critically ill patients.7 There was a significant increase in the number of gastric aspiration events in patients receiving pre-pyloric feedings compared to those receiving post-pyloric feedings, a difference that remained significant in a multivariate analysis (N. Metheny, personal communication). In the overall analysis, the percentage of positive pepsin samples in a given patient was a highly significant risk factor for the development of pneumonia.
How Should These Data Affect Our Use of Post-pyloric Enteral Feeding in Critically Ill Patients?
It probably is premature to conclude that post-pyloric feeding has no benefit at all or that it should be used in every critically ill patient given enteral nutrition. Ultimately, the use of postpyloric feeding depends in large part on the capabilities of the specific institution. Bedside placement of post-pyloric feeding tubes can be achieved in high numbers of patients if trained personnel carry out the procedure on a frequent basis.8,9 If that capacity is available, use of post-pyloric feeding seems reasonable.
If it is not, however, pre-pyloric enteral feeding is still a reasonable option for many, if not most, critically ill patients. The perceived risks of aspiration and pneumonia secondary to pre-pyloric enteral nutrition probably are overemphasized.1,2 Enteral nutrition often is withheld or discontinued on the basis of supposed aspiration events, the clinical diagnosis of which has been shown to be extremely inaccurate,10 or because physiologically insignificant amounts of residual fluid are present in the stomach. In the end, careful attention to the overall nutritional regimen of our critically ill patients, based on current guidelines and the clinical expertise of nutritional support practitioners, is likely more important than a narrow focus on the specific technique by which nutrients are delivered.
