Significance of Mini Bronchoalveolar Lavage Fluid Amylase Level in Ventilator-Associated Pneumonia: A Prospective Observational Study

Abstract

Objectives: Aspiration of oropharyngeal or gastric contents in intubated patients can lead to ventilator-associated pneumonia. Amylase in respiratory secretion has been reported as a possible marker of aspiration. We studied whether elevated α-amylase in mini bronchoalveolar lavage specimens can be suggestive of ventilator-associated pneumonia in intubated patients with high clinical suspicion.

Design: Prospective single-center observational study.

Setting: Department of Critical Care Medicine, tertiary care academic institute.

Patients: Adult patients on mechanical ventilation for more than 48 hours with with clinically suspected ventilator-associated pneumonia as per defined criteria, admitted between December 2014 and May 2016.

Methods: Mini bronchoalveolar lavage samples were collected within 72 hours of endotracheal intubation. Samples were sent for α-amylase level assay and quantitative culture. Ventilator-associated pneumonia was confirmed from mini bronchoalveolar lavage microbial culture of greater than or equal to 10 cfu/mL, and patients were divided into ventilator-associated pneumonia and no ventilator-associated pneumonia groups. Pre- and postintubation risk factors for aspiration were also noted.

Results: The prevalence of ventilator-associated pneumonia was 64.9% among 151 patients in whom it was clinically suspected. Median (interquartile range) mini bronchoalveolar lavage α-amylase levels in ventilator-associated pneumonia and no ventilator-associated pneumonia groups on the day of study inclusion were 287 U/L (164-860 U/L) and 94 U/L (59-236 U/L), respectively (p < 0.001). Median (interquartile range) α-amylase levels in patients with 0, 1, 2, and 3 preintubation risk factors were 65 U/L (35-106 U/L), 200 U/L (113-349 U/L), 867 U/L (353-1,425 U/L), and 3,453 U/L (1,865-4,304 U/L), respectively (p < 0.001) and 472 U/L (164-1,452 U/L) and 731 U/L (203-1,403 U/L) in patients with 1 and 2 postintubation risk factors, respectively (p < 0.001). A mini bronchoalveolar lavage α-amylase of 163 U/L or more yielded sensitivity and specificity of 73% and 68.6%, respectively, with area under the receiver operating characteristic curve of 0.746 (95% CI, 0.66-0.83).

Conclusions: Patients with ventilator-associated pneumonia within 72 hours from intubation have significantly elevated α-amylase concentrations in mini bronchoalveolar lavage fluid. Mini bronchoalveolar lavage α-amylase concentrations increase with increasing number of aspiration risk factors.