Prevention of Ventilator-Associated Pneumonia

Selecting Interventions That Make a Difference

In this issue of CHEST (see page 858), Smulders et al describe the results from their randomized trial of intermittent subglottic drainage for the prevention of ventilator-associated pneumonia (VAP). They found that general ICU patients receiving intermittent subglottic drainage had a significantly lower incidence of VAP compared to patients in their control group (4% vs 16%; p = 0.014). The duration of mechanical ventilation, length of stay in the ICU and hospital, and mortality were similar for both groups.

The results of this study are in agreement with those of three previous randomized trials of subglottic drainage using specially designed endotracheal tubes.¹²³ Taken together, these studies all support the utilization of subglottic drainage to reduce the incidence of VAP. Unfortunately, other important clinical and economic outcomes, such as mortality and lengths of stay, did not appear to be significantly influenced by the use of this intervention. This may be explained, in part, by the design of the four randomized studies performed to date, which focused on the prevention of VAP during the first 5 to 7 days of mechanical ventilation. VAP occurring later during mechanical ventilation may be more important to prevent, as it is more likely to be due to “high-risk” antibiotic-resistant bacteria such as Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus.⁴ VAP attributed to antibiotic-resistant pathogens has been associated with greater hospital mortality and longer lengths of stay compared to VAP attributed to antibiotic-sensitive bacteria such as methicillin-sensitive S aureus and Haemophilus influenzae.⁵⁶ Therefore, additional larger studies focusing on the prevention of VAP due to antibiotic-resistant bacteria may be needed to demonstrate a mortality advantage for subglottic aspiration, as has been done for selective digestive decontamination.⁷⁸

An important omission from the studies examining subglottic drainage has been the influence of this intervention on antibiotic utilization in the ICU setting. The findings of these trials suggest that reductions in the occurrence of VAP in patients receiving subglottic aspiration should be associated with fewer antibiotic days. Reducing the use of antibiotics in the ICU setting may result in a lower incidence of hospital-acquired infections due to antibiotic-resistant bacteria, as has been demonstrated by other strategies that have successfully decreased the use of empiric antibiotic therapy for VAP.⁹ Noninvasive ventilation for acute respiratory failure is another example of an intervention associated with reductions in the incidence of VAP and antibiotic use.¹⁰ In addition to reducing the use of antibiotics and the occurrence of antibiotic-resistant bacterial infections, pharmacy drug costs are decreased with implementation of antibiotic-sparing strategies.⁹

Interventions aimed at the prevention of VAP can be segregated into two broad categories (Table 1 ). The first category includes pharmacologic strategies that aim to reduce colonization of the aerodigestive tract with pathogenic bacteria. The second category includes nonpharmacologic strategies attempting to decrease the occurrences of aspiration. Both of these approaches to VAP prevention appear to be important given our current understanding of the pathophysiology of VAP, which is thought to result from aspiration of contaminated secretions originating from the aerodigestive tract and ventilator circuit.¹¹ Additionally, infection control programs employing combinations of interventions aimed at preventing both colonization of the aerodigestive tract with pathogenic bacteria and aspiration have been shown¹²¹³ to be successful and cost-effective. These quality improvement studies further support the use of prevention strategies aimed at both processes involved in the pathogenesis of VAP.

There are a number of effective pharmacologic and nonpharmacologic interventions available to clinicians for the prevention of VAP.¹⁴ Developing a VAP prevention program for use in a specific ICU should be based on careful consideration of the following factors. Focused infection control efforts with buy-in from all patient-care providers (physicians, nurses, respiratory therapists) are most likely to be successful.¹⁵ The selection of interventions for a VAP prevention program depends on the available patient staffing, administrative resources, and the ability of the unit or infection control group to tract compliance with the program over time. Several studies¹⁶¹⁷¹⁸ have shown the importance of unit staffing on compliance with interventions, such as hand washing and ventilator weaning, which should decrease the incidence of nosocomial infections. In units with suboptimal staffing, interventions requiring minimal effort from bedside nurses and respiratory therapists may be most applicable (eg, semirecumbent patient positioning, alcohol foam and gels for hand disinfection, subglottic drainage). Additionally, the influence of interventions on patient outcomes should be tracked over time to determine their success and cost-effectiveness.¹²¹³ This will help to determine whether these interventions should be continued and whether erosion in compliance with the VAP prevention program has occurred. The latter may necessitate further education and training of unit staff or implementation of alternative interventions to improve the effectiveness of the infection control program.

No simple, low-cost interventions currently exist that effectively prevent both colonization of the aerodigestive tract with pathogenic bacteria and aspiration. The intervention that comes closest to accomplishing this goal is the use of noninvasive positive-pressure ventilation administered via a face mask as an alternative to tracheal intubation and mechanical ventilation.¹⁰ Clinical studies¹⁰¹⁹²⁰ have demonstrated the ability of noninvasive ventilation to reduce the occurrence of nosocomial infections, including VAP, compared to the use of conventional mechanical ventilation. Unfortunately, the use of noninvasive ventilation may initially require more support from trained respiratory therapists that may impede its utilization locally.²¹ Therefore, additional simple interventions for the prevention of VAP in patients requiring tracheal intubation are required.

Biofilm formation routinely occurs on endotracheal tubes and is considered an important factor promoting the occurrence of VAP.²² Unfortunately, there are no current interventions that have the ability to prevent biofilm development on the endotracheal tube as well as within the airways of patients receiving mechanical ventilation. Chemicals aimed at blocking gene products from bacteria that form biofilms, antibodies that block fibronectin-binding protein adhesion of bacteria, and the use of specialized coatings that block bacterial adherence and communication offer the future possibility to block biofilm formation in patients receiving mechanical ventilation to further reduce the incidence of VAP.²³²⁴ One exciting approach would be to have a specially designed endotracheal tube that helps to prevent both colonization of the aerodigestive tract with pathogenic bacteria and aspiration. Until such devices are developed and shown to be clinically useful, clinicians should employ currently available measures for their patients receiving mechanical ventilation that have been shown to be safe and cost-effective.