The development of ventilator-associated pneumonia does not change aspectsof mechanical ventilation

Objective: To evaluate whether the development of ventilator-associated pne umonia (VAP) is associated with changes in ventilation parameters. Design: Matched case-control study. Setting: Mixed intensive care unit of a university hospital. Patients: From a large database we selected 33 patients with VAP, diagnosed with quantitative cultures of bronchoscopically obtained specimens. In add ition, 33 other mechanically ventilated patients who did not develop VAP we re selected (controls). Patients with VAT and controls were matched on seve n variables representing severity of illness: duration of ventilation until matching, diagnosis on admission, renal function, liver function, precedin g infection, preceding surgery and immunosuppressive therapy. Each patient with VAP was matched to a single control. Variables regarding; type and mod e of ventilation and interpretation of chest radiographs were not included in the matching procedure. Measurements and results. Characteristics of mechanical ventilation (mode o f ventilation, tidal volume, expired minute ventilation, peak airway pressu res, mean airway pressures, level of positive end-expiratory pressure, arte rial oxygen tension(PaO2)/fractional inspired oxygen (FIO2) ratio), were co mpared on the day of diagnosis of VAP (or matching for controls) and 2 and 4 days before. Although there was a significant difference in PaO2/FIO2 rat ios between cases and controls on the day of diagnosis of VAP, the change i n PaO2/FIO2, ratios during the days of study were not statistically differe nt between patients developing VAP and controls. No significant differences were found for any of the other variables of ventilation at any of the thr ee time points studied, nor were there significant differences in changes o f these parameters within individual patients. Conclusions: Characteristics and parameters of mechanical ventilation are n ot influenced by the development of VAP. It is, therefore, unlikely that th ese variables are useful in the diagnostic work-up of VAP.