Surveillance tracheal aspirate in ventilator associated pneumonia (VAP)
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KeywordsBlood Culture Clinical Suspicion Ventilator Associate Pneumonia Pleural Fluid Concordance Rate
VAP is associated with increased ICU stay and mortality, particularly when treatment is delayed or inappropriate . When a clinical suspicion of VAP is justified, specific diagnostic tests are usually conducted: bronchoalveolar lavage (BAL), protected specimen brushing (PSB), diagnostic tracheal aspirate (dTA), blood cultures and pleural fluid. We evaluated the concordance between specific diagnostic tests and the surveillance tracheal aspirates (sTA).
In our ICU routine sTA are performed weekly. The sTA and the specific diagnostic tests were considered concordant if the isolated bacteria were of the same strain and species, with identical sensitivity.
From January 1999 to June 2000, 256 patients were intubated longer than 48 h. 150 clinical episodes of VAP were identified and in 139 a diagnostic test was performed (80 BAL, 3 PSB, 50 dTA, 3 blood cultures and 3 pleural fluid). Eighty-two resulted in a positive culture. In 56 of these microbiologically confirmed VAP, at least one sTA less than 8 days old was available, for a total of 65 sTA. The specific diagnostic specimen and sTA were concordant in 35/65 cases (54%). When negative or contaminated sTA were omitted concordance reached 78% (in order to consider the value of sTA to target therapy). In sTA taken = 4 days before the clinical suspicion of VAP, concordance was better than for sTA taken more than 4 days before the specific tests (83% vs 55.6%; P = 0.07). In addition, mean colony counts = 106 cfu/ml (96%) were more frequently concordant than colony counts < 106 cfu/ml (50%) (P = 0.0003). Concordance rate was not significantly different in Early Onset Pneumonia (within 4 days after intubation-EOP) and Late Onset Pneumonia (that occurs more than 4 days after intubation-LOP). In EOP, a mean colony counts = 106 was associated with high rate of concordance. In LOP, even low colony counts specimens identified the correct pathogen in 56% of cases.
The concordance between sTA and diagnostic test was function of mean colony count and of time interval between the sTA and VAP onset. In LOP concordance was acceptable (56%) even with a low bacterial count. Surveillance TA may be a useful guide to improve early empiric therapy in suspected VAP.