Clinical diagnosis of ventilator associated pneumonia revisited: comparative validation using immediate post-mortem lung biopsies

Background-A study was undertaken to assess the diagnostic value of differe nt clinical criteria and the impact of microbiological testing on the accur acy of clinical diagnosis of suspected ventilator associated pneumonia (VAP ). Methods-Twenty five deceased mechanically ventilated patients were studied prospectively. Immediately after death, multiple bilateral lung biopsy spec imens (16 specimens/patient) were obtained for histological examination and quantitative lung cultures. The presence of both histological pneumonia an d positive lung cultures was used as a reference test. Results-The presence of infiltrates on the chest radiograph and two of thre e clinical criteria (leucocytosis, purulent secretions, fever) had a sensit ivity of 69% and a specificity of 75%; the corresponding numbers for the cl inical pulmonary infection score (CPIS) were 77% and 42%. Non-invasive as w ell as invasive sampling techniques had comparable values. The combination of all techniques achieved a sensitivity of 85% and a specificity of 50%, a nd these values remained virtually unchanged despite the presence of previo us treatment with antibiotics. When microbiological results were added to c linical criteria, adequate diagnoses originating from microbiological resul ts which might have corrected false positive and false negative clinical ju dgements (n = 5) were countered by a similar proportion of inadequate diagn oses (n = 6). Conclusions-Clinical criteria had reasonable diagnostic values. CPIS was no t superior to conventional clinical criteria. Non-invasive and invasive sam pling techniques had diagnostic values comparable to clinical criteria. An algorithm guiding antibiotic treatment exclusively by microbiological resul ts does not increase the overall diagnostic accuracy and carries the risk o f undertreatment.