Ventilator associated pneumonia: asking the right question
Everything about ventilator associated pneumonia is contentious. What is the microbial pathogenesis? How can it be prevented? How should it be treated? One strongly advocated preventive strategy consists of intensive topical and systemic antimicrobial prophylaxis. An opposing but equally strongly advocated approach is the use of conventional but firmly applied infection control measures together with limitation of antibiotic use. For treatment, questions abound. One drug or two? Which drug? For how long?
There are two main reasons which underlie our failure to move toward consensus on many of these questions. Firstly, the magnitude and nature of the problem varies widely between intensive care units. The incidence of pneumonia in mechanically ventilated patients ranges from as little as 5% in some units to more than 50% in others.1-4 This may represent, in part, differences in diagnostic approach, but most of the difference in incidence is probably real, reflecting differences in patient population, medical and nursing practice, and infection control practices. Because many studies of pneumonia are generated by intensive care units with high pneumonia rates, questions naturally arise about whether their conclusions are necessarily applicable to units with lower rates.
The second main cause of contention is the problem of definition. How is the diagnosis of ventilator associated pneumonia made? One point of view is that reliable diagnosis must rely on bronchoscopy combined with quantitative bacteriology of the specimens so obtained. An alternative view is that clinical and radiological evidence of infection combined with conventional semi-quantitative bacteriology is sufficient for diagnosis in most cases, and reduces morbidity caused by delay in treatment while waiting for quantitative bacteriological results.
Advocates of bronchoscopy point out that at least half of ventilated patients who might be diagnosed with pneumonia using a standard infection control definition (radiological pulmonary infiltrate, a fever, raised white blood …
