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We read with interest the review article entitled “New endotracheal tubes designed to prevent ventilator-associated pneumonia: do they make a difference?” by Deem and Treggiari.1 In line with European experts,2 the American researchers state that “the high VAP rate in ventilated patients is probably due to factors associated with translaryngeal intubation rather than simply an effect of patient susceptibility from severity of illness.” We disagree with this expert opinion and we would argue that the severity of underlying disease is the major determinant of developing pneumonia in patients requiring treatment on the intensive care unit (ICU).3 Our statement that “the sicker the patients, the higher the pneumonia rate” is supported by the following quantitative data. The incidence of hospital-acquired pneumonia is approximately 5-10 per 1,000 admissions.3,4 The pneumonia rate is 7% in patients requiring treatment on ICU without endotracheal intubation, and increases to 12% in ICU patients requiring endotracheal intubation.3,4 The pneumonia rate is lower with noninvasive ventilation (1.58 per 1,000 ventilator days), compared with invasive ventilation (5.44 per 1,000 ventilator days).5 Remarkably, the patients receiving noninvasive ventilation were less ill than the ones who were endotracheally intubated. Finally, a recent epidemiological study on the prevalence and outcomes of infection in ICUs showed that the infection rate was related to disease severity assessed by the Simplified Acute Physiology Score II.6
Apart from illness severity, the abnormal oropharyngeal carrier state is a higher risk factor than the endotracheal tube. It is generally acknowledged that underlying disease promotes the abnormal oropharyngeal carrier state.7 Less known is that the presence of the nasogastric tube is another factor that promotes abnormal oropharyngeal carriage.8
Deem and Treggiari acknowledge that selective decontamination of the digestive tract (SDD) is an effective VAP prevention technique, referring to one of the first Italian meta-analyses in 1998.9 They fail to mention the most recent Cochrane meta-analysis of randomized controlled trials of SDD from 2009, demonstrating that SDD reduces VAP by 72% (odds ratio 0.28, 95% CI 0.20-0.38).10 As 2 of the originators of SDD, we would suggest that the efficacy of SDD is due to the control of gut overgrowth associated with critical illness.11 Gut overgrowth harms the critically ill in 4 main ways. Overgrowth of “abnormal” aerobic Gram-negative bacilli and/or endotoxin has been shown to cause inflammation, immunosuppression, infection, and antimicrobial resistance. SDD is a prophylactic measure using selected antimicrobials to control gut overgrowth, thereby reducing the 4 harmful side effects, including restoration of suppressed systemic immunity and reduction of severe infections of lower airways.
In conclusion, severity of underlying disease promoting oropharyngeal overgrowth and subsequent lower airway infection following migration is the major determinant factor for developing pneumonia, rather than factors associated with translaryngeal intubation.
- © 2012 by Daedalus Enterprises Inc.
The authors respond:330 331
We appreciate the interest that Zandstra and colleagues have shown in our review of “New endotracheal tubes designed to prevent ventilator-associated pneumonia.” We agree with Zandstra et al that severity of illness is an important risk factor for the development of ventilator-associated pneumonia (VAP). However, we stand by our original statement that VAP “is probably due to factors associated with translaryngeal intubation.” This is borne out by the nearly 50% reduction in VAP associated with subglottic secretion drainage,1 polyurethane-cuffed tracheal tubes,2 and a variety of other interventions designed to either reduce microaspiration or the bacterial burden of aspirated oropharyngeal secretions.3,4 The general decline in VAP rates over the past 5 years, as reported by the Center for Disease Control (CDC), and in association with widespread implementation of “VAP bundles” also supports the notion that VAP is a modifiable event. Zandstra and colleagues make this case very cogently in their argument for selective decontamination of the digestive track as a VAP-preventive measure.