Non-Ventilator ICU-Acquired Pneumonia After Cardiothoracic Surgery: Accuracy of Diagnostic Tools and Outcomes

Abstract

Background: Non-ventilator ICU-acquired pneumonia after cardiothoracic surgery is challenging to diagnose, and little is known about its impact on patient outcomes. Here, our primary objective was to compare the sensitivity and specificity of cultures of 2 types of fiberoptic bronchoscopy (FOB) specimens: endotracheal aspirates (FOB-EA) and bronchoalveolar lavage fluid (FOB-BAL). The secondary objectives were to evaluate the sensitivity and specificity of spontaneous sputum cultures and of the modified Clinical Pulmonary Infection Score (CPIS) and to describe patient outcomes.

Methods: We conducted a prospective observational study of consecutive cardiothoracic surgery subjects with suspected non-ventilator ICU-acquired pneumonia. Using FOB-BAL cultures ≥10(4) cfu/mL as the reference standard, we evaluated the accuracy of FOB-EA ≥10(5) cfu/mL and spontaneous sputum ≥10(7) cfu/mL. On the day of FOB, we determined the modified CPIS. Mortality and antibiotic treatments were recorded.

Results: Of 105 subjects, 57 (54.3%) received a diagnosis of non-ventilator ICU-acquired pneumonia. FOB-EA cultures had 82% (95% CI 69-91%) sensitivity and 100% (95% CI 89-100%) specificity and were significantly less sensitive than FOB-BAL cultures (P < .004). Spontaneous sputum was obtained from one-third of subjects. Spontaneous sputum cultures had 82% (95% CI 56-95%) sensitivity and 94% (95% CI 68-100%) specificity and were non-significantly less sensitive than FOB-BAL (P = .061). A modified CPIS >6 had 42% (95% CI 29-56%) sensitivity and 87% (95% CI 74-95%) specificity for non-ventilator ICU-acquired pneumonia. Antibiotic therapy was stopped in all subjects without non-ventilator ICU-acquired pneumonia, after 1.6 ± 1.2 d, without deleterious effects.

Conclusions: The modified CPIS has low diagnostic accuracy for non-ventilator ICU-acquired pneumonia. FOB-EA cultures perform less well than do FOB-BAL cultures for diagnosing non-ventilator ICU-acquired pneumonia. Spontaneous sputum is valuable when FOB cannot be performed but could be obtained in only a minority of subjects. When cultures are negative, antibiotic discontinuation is safe.

Keywords: antibiotics; bronchoalveolar lavage; cardiothoracic surgery; endotracheal aspirates; fiberoptic bronchoscopy; mortality; postoperative pneumonia; sensitivity; specificity; spontaneous sputum.