Diagnosing VAP: Less is More
Abstract & commentary
By Uday Nanavaty, MD, Assistant Director, AICU, St. Agnes Hospital, Baltimore, is Associate Editor for Critical Care Alert.
Dr. Nanavaty reports no financial relationship to this field of study.
Synopsis: In a randomized trial to evaluate two strategies for diagnosing VAP, authors found that endotracheal aspiration was as good as bronchoalveolar lavage fluid and quantitative culture in defining the pathogens and directing therapy.
Source: Canadian Critical Care Trials Group. A randomized trial of diagnostic techniques for ventilator-associated pneumonia. N Engl J Med. 2006 Dec 21;355(25):2619-30.
Ventilator-Associated Pneumonia (VAP) is a major nosocomial infection associated with increased morbidity and perhaps with some attributable mortality. There has been great controversy as to which is the best practical strategy to diagnose and treat VAP. Routine practice has been to evaluate endotracheal aspirates in suspected cases, and then to change the therapy based on culture results. Alternative strategies, including bronchoalveolar lavage (BAL) with quantitative cultures and protected brush specimens obtained via bronchoscopy with quantitative cultures, have been touted to be more specific and hence better than the routine practice.
In order to ascertain whether BAL with quantitative cultures is in fact a better strategy, the Canadian Critical Care Trials group performed a randomized controlled trial. Patients in 28 ICUs across Canada and the US were randomized to one of the two diagnostic strategies. The diagnosis of VAP was suspected in patients who were mechanically ventilated for at least 4 days who had new or persistent radiographic evidence of pneumonia without another obvious cause, and any two of the following features: temperature > 38° C, leukocytosis (defined as leukocyte count > 11.0 x 103 per mL) or neutropenia (neutrophil count less than 3500 per mL), purulent endotracheal secretions, potentially pathogenic bacteria isolated from the endotracheal aspirate, and increasing oxygen requirements. If patients were colonized or infected with MRSA or Pseudomonas species, or if they were immunocompromised, they were excluded from the study. The ICU physician or respirologist performed BAL from the area likely to be affected and also rated the pre-test likelihood of VAP as low, medium, or high. Two antibiotics with activity against pseudomonas, namely ciprofloxacin and meropenem, were administered in a randomized manner after either diagnostic strategy. One group received both agents and the other received meropenem alone. The antibiotics were continued until the culture results were available. If the culture was positive, antibiotics were narrowed according to the institutional practice. If cultures were negative, antibiotics were discontinued at the discretion of the attending physician except for the group with high likelihood of VAP. In the BAL group, if the quantitative culture had sub-threshold numbers of pathogenic organisms, the physician could elect to treat based on the clinical assessment.
The study was conducted under the auspices of the Canadian Critical Care Trials Group between May 2000 and February 2005. A total of 2531 patients were screened, and out of 1144 who were eligible, 740 patients were enrolled. Both groups were comparable including the number of patients receiving antibiotics within 24 hours prior to enrollment. The mean time between admission to the ICU and enrollment was 7.9±5.2 days. Significantly more patients in the BAL group had positive cultures (59.7% vs 51.9%). In the BAL group, study antibiotics were started approximately 8 hours after initial suspicion for VAP, as compared to 6.8 hours in the ET aspiration group (p < 0.001). The median duration of antibiotic treatment for VAP was 10 days. The adequacy of empirical treatment of antibiotics did not differ between the two groups in culture positive patients: 89% of the BAL group with positive cultures vs 89.5% of the ET aspirate group with positive cultures. The percentage of patients who were found not to have VAP was similar between the two groups: 13.7% in the BAL group, 17.1% in the ET aspiration group.
The 28-day mortality rate for the whole study population was 18.7% (95% confidence interval, 15.9% to 21.7%). The adjusted relative risk of death by 28 days in the BAL group as compared to the ET aspiration group was 1.01 (95% CI, 0.75 to 1.37; p= 0.94). In previously defined subgroups, there was no statistically significant difference in mortality with either strategy. Thus, BAL and quantitative cultures did not offer any advantage in patients who were considered highly likely to have VAP, in those with APACHE II scores more or less than 24, in patients who were in the ICU for less or more than 7 days at randomization, in those who had received antibiotics within 3 days before randomization, or in patients who were thought to have high-risk organisms (such as Acinetobacter, Methacillin-resistant Staphylococcus aureus (MRSA), Pseudomonas species, or S. maltophilia as well as multi-drug-resistant organisms). Overall, about 60% patients were considered cured of VAP, approximately 30% had clinical failure, and the remainder 10% or so had an indeterminate outcome. Again, both groups were similar in the outcome of VAP.
Commentary
VAP is unfortunately a common problem in most ICUs. One of the biggest problems in considering the incidence of VAP is the lack of a standard definition. With implementation of the "VAP bundle," many institutions have reported a VAP incidence rate of essentially 0%. I believe that although the goal rate of VAP should be 0%, it is a monumental task to achieve, and institutions that report these rates often use different definitions than that used in this study.
Once VAP is suspected, practice is highly variable. The variability exists in both the diagnostic method used and the therapies initiated for VAP. This study provides a practical starting ground for at least a fourth of the patients with suspected VAP (about 25% enrollment from the screened population).
One can use this study to standardize the diagnosis of VAP and to standardize the treatment of VAP once it is suspected. With further proof that endotracheal aspiration is as good as BAL in helping guide the management of VAP, the high cost of bronchoscopy can be avoided. In addition, because endotracheal aspiration is available at all settings that provide mechanical ventilation, one can presumably shorten the interval between the time of suspected VAP and the start of antibiotic therapy. Once the strategy to identify those patients at high risk of staphylococcal infection, especially MRSA infection, is identified, appropriate antibiotics can be started for the majority of patients with suspected VAP. Between appropriate diagnostic strategy and guidelines based appropriate antibiotic therapy, true reduction in morbidity and mortality of VAP is achievable.
Ventilator-Associated Pneumonia (VAP) is a major nosocomial infection associated with increased morbidity and perhaps with some attributable mortality. There has been great controversy as to which is the best practical strategy to diagnose and treat VAP.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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