Nosocomial pneumonia is an important cause of morbidity and mortality in hospitalized patients. Diagnosis and treatment continues to challenge clinicians and stimulate investigators. Prevention of this serious infection has been the focus of numerous studies, conferences and professional documents. Nosocomial pneumonia prevention strategies may be directed at the ventilator circuit (frequency of tubing circuit changes and gas humidification strategies), the endotracheal tube (intubation orifice, secretion drainage and suctioning) or body position (kinetic bed therapy and semirecumbancy). Other nonpulmonary approaches are pharmacologic (selective digestive decontamination and stress ulcer prophylaxis) or nutritional (the type, site and timing of enteral feeds).
The largest number of published randomized trials in intensive care medicine have evaluated selective digestive decontamination and stress ulcer prophylaxis. Five meta-analyses [1
] suggest that selective digestive decontamination confers a large, clinically important and statistically significant reduction in nosocomial pneumonia rates (common odds ratio approximately 0.30, 95% CI 0.28–0.48). Nevertheless, selective digestive decontamination is not widely used, in part due to concern about long-term microbial resistance patterns and antibiotic costs [6
]. Stress ulcer prophylaxis trials have been recently summarized in a meta-analysis suggesting that sucralfate, as compared with histamine-2-receptor antagonists or antacids, is associated with a trend toward a lower rate of nosocomial pneumonia (common odds ratio 0.78, 95% CI 0.60–1.01) [7
]. Other experiments show that modifying gastric pH with acidified enteral feeds decreases gastric colonization, thereby supporting this underlying biologic rationale [8
]. However, sucralfate is not considered of proven benefit due to the possibility that sucralfate confers a protective effect only when compared with gastric pH-altering drugs (which themselves are associated with a modest increase in nosocomial pneumonia compared to control) [7
Kinetic bed therapy has been reviewed in a meta-analysis of six trials in seriously and critically ill patients, which indicated a significantly lower rate of pneumonia and atelectasis in patients receiving continuous postural oscillation [9
]. A less expensive and adaptable pneumonia prevention strategy focussing on body position has been studied in three randomized trials [10
]. Torres et al
] found that after instillation of radioactive technetium sulfur colloid into the stomach, radioactive counts in endobronchial secretions were significantly higher in samples obtained while patients were supine than when they were semirecumbent. In another study, scintigraphic evidence of esophageal reflux was found in 81% of patients in the supine position compared to 64% in the semirecumbent position [11
]. Orozco-Levi et al
administered nasogastric technetium sulfur colloid and found that radioactive counts in endobronchial secretions increased over time, but were higher in the supine than the semirecumbent position [12
]. Although a causal relationship between pneumonia and this secondary endpoint of aspiration of gastric contents has not been convincingly demonstrated, these trials are in keeping with the gastropulmonary route of infection.
The gastropulmonary route of infection is a concept at least two decades old [13
], support for which is derived from multiple human observational studies and experimental evidence [14
]. Enteral nutrition, compared to parenteral nutrition, is associated with decreased translocation in animals and decreased infectious morbidity in critical illness in humans [16
]. Accordingly, it holds the promise of affording protection against nosocomial pneumonia. However, enterally feeding critically ill patients is often associated with intolerance, thereby predisposing them to aspiration pneumonia. The goal of this systematic review is to critically appraise and summarize the randomized trials of nutritional strategies and their influence on nosocomial pneumonia in critically ill patients.