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Dr. Balk is Professor of Medicine, Rush Medical College and Director of Pulmonary and Critical Care Medicine, Rush-Presbyterian-St. Luke’s Medical Center, and Cook County Hospital.
Correspondence to: Robert A. Balk, MD, FCCP, Section of Pulmonary and Critical Care Medicine, 1753 West Congress Pkwy, Chicago, IL; e-mail: rbalk{at}rush.edu
Infection and its major consequence, sepsis, are ever-increasing problems in the ICU environment. A recent study1 by Angus and coworkers suggest that there are > 750,000 episodes of severe sepsis each year in the United States. Their projections suggest that the incidence will continue to increase at a rate of 1.5%/yr.1 One of the most common ICU infections and the nosocomial infection associated with the highest mortality rate is hospital-acquired pneumonia.2 3 4 5 6 Ventilator-associated pneumonia (VAP) is the term for hospital-acquired pneumonia that develops in an intubated patient receiving mechanical ventilatory support.3 4 5 VAP presents multiple diagnostic and therapeutic challenges for the clinician.3 4 5 One of the most controversial areas concerns the benefits of an aggressive diagnostic approach vs empiric treatment for VAP.7 8 9 10 11 The aggressive diagnostic approach utilizes fiberoptic bronchoscopy along with a protected specimen brush or BAL coupled with quantitative cultures to ensure that sufficient thresholds of microorganisms are present.7 8 Advocates of this approach point out the poor specificity of the clinical diagnosis of VAP and our need to use antibiotics judiciously in this time of increasing antibiotic resistance.8 9 11 12 However, the supporters of empiric treatment contend that the aggressive invasive approach is more costly, and only defines treatment failure, and emphasize the need for additional randomized, prospective, multicentered controlled clinical trials to determine if either strategy is associated with a survival benefit.7 10 Another controversial area surrounds the determination of the attributable mortality of VAP that typically develops in patients with comorbid conditions that are associated with significant mortality.3 5
Given the current difficulties with the clinical diagnosis, treatment, and assessment of attributable mortality of VAP, perhaps, the most prudent goal would be to channel our efforts toward prevention. Current prevention strategies include positioning patients with their heads elevated > 30°, selective digestive decontamination, rotational therapy, and continuous subglottic aspiration/suctioning, and early extubation with liberation from mechanical ventilatory support.6 13 14 15 16 17 Indwelling catheters, such as Foley and central venous catheters, invade the normal body barriers and subsequently become coated with a "biofilm."18 This biofilm is an excellent growth medium for bacteria and ultimately gives rise to infection. Specialized coatings have been used to retard the growth of the biofilm and to decrease the likelihood of subsequent colonization of the catheter surface with microorganisms.18 19 Some common nosocomial infections, such as blood stream and urinary tract infections, have been prevented by the use of special coatings on the indwelling catheter.19 20 21 A natural extension of this technology would be to coat the endotracheal tube in an attempt to decrease the development of VAP.
The report by Olson and coworkers in this issue of CHEST (see page 863) evaluated silver coated endotracheal tubes in an experimental animal model of VAP. The investigators evaluated the special coated endotracheal tube compared to a standard endotracheal tube in a prospective, randomized, double-blind, controlled trial in dogs receiving mechanical ventilation with Pseudomonas placed in the oropharynx. Serial swabs were obtained from the endotracheal tubes; at death, the endotracheal tube, tracheal, and lung parenchymal bacterial burdens were assessed. The silver coating was found to delay the appearance of bacteria on the inner surface of the endotracheal tube. In addition, there were significantly less aerobic bacteria in the lung parenchyma and less parenchymal inflammatory changes on histologic assessment.
While this was a small study of relatively short duration, the results suggest that silver coating endotracheal tubes may offer some help in the battle to prevent VAP. The investigators attempted to recreate "life in the ICU," where all too frequently patients are managed in a sedated, supine, flat position. The dogs involved in this trial were kept in this same state, which would tend to promote aspiration of the deposited oropharyngeal bacteria and potentiate the subsequent colonization of the lower airway and endotracheal tube. However, at present, there is little to no data to help us understand the significance of decreased numbers of colonizing bacteria on an endotracheal tube. It might be assumed that less is better, but it may be an all-or-none phenomenon. The same issues surround the implications of a decreased aerobic bacterial burden on the eventual development of pneumonia or, more importantly, on ultimate survival. Future trials will need to compare the coated endotracheal tube to our current preventive strategies (ie, elevated head of the bed, rotational/kinetic therapy, continuous subglottic suction, etc.) to see if there is continued or additional benefit. Nonetheless, VAP is an important cause of morbidity, mortality, and increased length and cost of care for the critically ill. If a strategy as simple and likely inexpensive as silver coating the endotracheal tube can prevent VAP, it is indeed the silver lining that we have been searching for. At this time, however, the data are far from complete, and further trials are both needed and warranted.
References
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