Nutrition and Lung Disease
* Division of Allergy, Pulmonary, and Critical
Care Medicine, Vanderbilt University, Nashville, Tennessee; and Correspondence: James P. Maloney, MD, Medical College of Wisconsin, 9200 West Wisconsin, Milwaukee, WI 53226. Electronic mail may be sent to jmaloney{at}mail.mcw.edu.
"Let thy food be thy medicine and thy medicine be thy food." Hippocrates (460–377 B.C.) Like Hippocrates, we realize that the nutrition we give patients is more than a source of calories. Unlike Hippocrates, we can consult an increasing body of literature that helps us address those areas where disease and nutrition intersect. This issue of Nutrition in Clinical Practice focuses on the delivery of nutrition to improve outcomes in patients with acute and chronic pulmonary illnesses. The reviews here examine many different strategies and outline the strengths and weaknesses of the supporting science. Like Hippocrates, we have yet much to learn and we must realize that his "primum non nocere" dictum also applies to nutrition science. For instance, immunonutrition appears to lower infectious complications in surgical patients, but may increase mortality in patients with sepsis.1,2 The blue dye practice for aspiration detection during enteral feeding was widely embraced before its poor specificity and potential for harm were appreciated, leading to an FDA Public Health Advisory.3 The discovery of such unexpected findings highlights the continued importance of randomized controlled trials to evaluate the efficacy and safety of nutritional interventions before we accept them as general practice. The safe and optimal provision of nutrition to patients with lung disease remains a challenge, and it is often unclear what nutritional approach is best. Optimizing nutrition in chronic lung diseases has mostly focused on preventing and treating malnourishment common to diseases such as emphysema and cystic fibrosis. Common diseases such as asthma are not often associated with malnutrition; we don't have evidence that they benefit from specific dietary approaches. Chronic obstructive pulmonary disease (COPD) is the fourth largest cause of death in the United States, and a large subset of patients with moderate-to-severe COPD are underweight and malnourished, as Mallampalli points out in her review.4 No specific hormonal or nutritional regimen has been successful enough in these patients to be of routine use. The severity of underlying disease in COPD and the high metabolic rate needed to respire with diseased lungs currently precludes substantial benefit from dietary intervention in most patients. Yet the importance of the disease mandates continued investigation. The utility of specific formulas to minimize carbon dioxide production and thereby aid weaning in mechanically ventilated COPD patients also is poor. Such formulas should be used selectively. Olson and Schwenk5 show how an organized approach, advocacy, and clinical experience can minimize the malnutrition associated with cystic fibrosis, even in the absence of large trials. Yet it is difficult to control the diet of chronically ill patients. The potential benefit of dietary strategies is often negated by what patients will (or won't) eat in their own homes. The provision of nutrition to acutely ill patients, many of whom are in intensive care units, creates unique challenges and is an area where the most impact may occur from specific nutritional strategies. Studies have shown that enteral nutrition is better than the parenteral route in acutely ill patients. However, scientific investigations have not always clarified the optimal timing, composition, delivery location, and means of avoiding complications when administering enteral nutrition, thus resulting in a wide variation in delivery practices. Most of this work has been done in adults and, as Carlson points out, the nutritional care of infants with lung disease has yet to be guided by large clinical trials.6 Once the decision is made to provide enteral nutrition, the first questions encountered are what type of tube should be used. Guidroz and Chaudhary7 discuss the advantages and disadvantages of many of the different tube types used for maintaining enteral access. Historically, placement of these tubes was preferentially trans-nasal, but appreciation of nasal tubes as risk factors for sinusitis now results in many trans-oral insertions, at least in intubated patients.8,9 Guidroz and Chaudry point out the many ways to initiate and maintain enteral access. Tolerance of enteral feedings and aspiration prevention remain as problems. Endotracheal intubation and enteral feeding are probably the biggest risk factors for aspiration and the development of nosocomial pneumonia, which is often ventilator-associated pneumonia (VAP). Parker and Heyland10 outline some of the practices that have been utilized in an attempt to minimize these complications. One of the most effective prophylactic measures demonstrated in randomized clinical trials for aspiration and NP prevention in ventilated patients is raising the head of the bed. In addition to being effective, this measure is easy and incurs no cost. Some aspects of patient care make it difficult to maintain the head of the bed at 45°. As Parker and Heyland conclude, raising the head of the bed for any intubated patient receiving enteral feedings is evidence-based, easy, and is usually safe. Two other easy practices also help prevent VAP: draining the condensate from ventilator tubing and minimizing tubing changes.11,12 Subglottic suctioning represents another appealing measure for preventing VAP. However, as Parker and Heyland describe, data on the effectiveness of this technique are conflicting and it may not be free of harm. Subglottic suctioning requires the placement of a special endotracheal tube and thus one must either have the foresight to predict which patients may benefit, or accept the additional risk of pneumonia from the extubation and re-intubation necessary to place this specialized and more expensive tube. Because aspiration is believed to contribute to VAP, numerous practices have been implemented to prevent it. Many clinicians continue to utilize specific gastric residual volume (GRV) cut-offs as a measure of tolerance and safety, resulting in frequent feeding interruptions. However, using GRV as the sole determination for altering enteral feeding rates lacks supportive evidence. As Parker and Heyland emphasize, numerous studies have demonstrated that GRV do not correlate with gastric emptying and are poor predictors of feeding complications. Armed with such data, in one of our intensive care units (TR) we have abolished the checking of gastric residual volumes in our enterally fed, mechanically ventilated patients. Most critically ill patients tolerate gastric feedings without difficulty, and given the data as reviewed in this issue, we utilize postpyloric feeding in a minority of patients. Whether to pursue postpyloric feedings as a means to decrease nosocomial pneumonia is less clear, as studies have been contradictory regarding such benefit. The benefits of guiding nutrition support to patients with severe lung disease by adjusting caloric needs based on measurements of energy expenditure has always been appealing, but remains of unproven benefit. It is fraught with technical confounders, as Branson and Johannigham13 point out, and it requires a metabolic cart. It should only be done in centers that are both expert with the technique and perform it often, as bad information is never helpful.
In addition to providing protein and caloric support, components of enteral
nutrition have also been shown to alter human physiology and the response to
acute illness. Clinician beliefs about the ability of nutrition to alter the
immune response, or "immunonutrition," vary widely. Mizock and
DeMichele14 examine
the role of modulating inflammation via dietary lipids in patients with the
acute respiratory distress syndrome (ARDS). The concept of altering the immune
response by providing As recent data on immunonutrition and aspiration prevention point out, we are beginning to make headway in our search to find the best nutritional approach to patients with pulmonary disease. Challenging conventional approaches is important in patient nutrition, as in all areas of medicine. Carrying those initial challenges forward into large randomized trials rather than relying on experience and dogma is crucial, and in the next decade should help us build on the knowledge summarized in these reviews. Food is medicine, and we need better medicine.
Nutrition in Clinical Practice, Vol. 19, No. 6,
547-549 (2004)
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-3 fatty acids and antioxidants makes physiologic
sense. The data in animal models of ARDS and from human trials are
exciting—leukocyte and cell membranes are fluid and can be influenced by
diet (for the better) and inflammation can be modulated. Unfortunately,
although these studies demonstrated decreased lung inflammation and reduced
dependence on mechanical ventilation, they had limitations that prevented a
conclusion of proof of benefit. Many of the analyses were not done on an
intention-to-treat basis, a notorious cause of bias. One-third of the 146
enrolled patients in the multicenter trial were removed from the final
analysis because of protocol violations; this is quite high for any
interventional trial. Furthermore, the control diet may not have represented
standard formulas and the gender composition of groups were different. For all
of these reasons, the trial, although exciting, should be considered as a
Phase II "proof of principle"
trial.