Diagnostic value of sputum smear and simplified clinical pulmonary infection score of ventilator associated pneumonia in the early stage

Abstract

Objective To explore the diagnostic value of sputum smear coupled with simplified clinical pulmonary infection score (CPIS) of ventilator associated pneumonia (VAP) in the early stage. Methods A cohort of 59 consecutive patients with VAP admitted in Intensive Care Unit from June, 2014 to June, 2016 were enrolled for a prospective and observational study. Concurrently, another 59 patients without pulmonary infection undergone mechanical ventilation over 48 hrs, were assigned into the control group. The criteria of exclusion were patients with pulmonary malignancies, autoimmune diseases and immunodeficiency. APACHEⅡscores of all patients were recorded. All patients’ inferior airway sputum which met the criteria was taken to make a validated sputum smear(i.e. polymorphonuclear leukocyte >25 and squamous epithelial cell <10 per low-power field) for Gram stain and culture on the admission day. Meanwhile, simplified CPIS were calculated. Data were statistically processed by SPSS 15.0, enumeration data were statistically analyzed by Chi-Square test, and measurement data were represented as Mean±SD. The significant differences in characteristics between two groups were analyzed by independent t test, and P<0.05 was considered statistically significant. As positive sputum smear and simplified CPIS≥5 were set respectively as a positive screening criterion, sensitivity, specificity, positive predictive value and negative predictive value of each marker and combined markers were calculated. Results There were no significant differences in demographics and clinical features (including age, sex, APACHEⅡscores) of patients in VAP and non-VAP patients (P>0.05). The rates of bacteria detected were Gram-negative [44.1% (26/59)], Gram-positive [40.6% (24/59)], none [10.2% (6/59)] and both [5.1% (3/59)] bacteria in VAP group, while [39.0% (23/59)], [30.5% (18/59)], [27.1% (16/59)] and [3.4% (2/59)] were found in non-VAP group correspondingly. There were no significant differences in the percentages of different bacteria in sputum smear between two groups(P>0.05). The values of diagnostic sensitivity of sputum smear and sputum smear coupled with simplified CPIS were 89.8% and 84.7%; the specificity were 27.1% and 79.7%; the positive predictive values were 55.2% and 80.6%; and the negative predictive values were 72.7% and 83.9%, respectively. Conclusions No matter the ventilated patients suffered VAP or not, bacteria might be detected from their lower respiratory tracts. Sputum smear could not be taken as an exclusively diagnostic evidence. While sputum smear coupled with simplified CPIS might improve the diagnostic efficacy of VAP, and provide the guildlines of appropriate choice of antibiotics employed in the early stage. Key words: Sputum smear and gram stain; Clinical pulmonary infection score; Ventilator associated pneumonia