Computerized lung sound monitoring to assess effectiveness of physiotherapy and secretion removal: a feasibility study

Introduction

Intubation and mechanical ventilation impair secretion clearance and can lead to lung collapse, consolidation and ventilator-associated pneumonia [1]. There is, however, no valid diagnosis of secretion retention in the intubated and ventilated patient. Vibration response imaging (VRI) is a commercially developed acoustic lung imaging system that displays breath sound distribution [2]. VRI should be able to identify relationships between specific breath sound distributions and secretion retention. This preliminary study investigated the changes in VRI measurements before and after chest physiotherapy in adult intubated and mechanically ventilated patients.

Methods

Intubated and ventilated adult patients who were receiving chest physiotherapy were investigated. Lung sound amplitude at peak inspiration was measured immediately before and after chest physiotherapy using two arrays of sensors attached to the patient's back in a supine position. Chest physiotherapy included combinations of closed airway suctioning, saline lavage, postural drainage, manual techniques and/or lung hyperinflation, dependent upon clinical indications. Means are compared with the Wilcoxon matched-pairs signed-ranks test.

Results

A total of 16 patients were included in the study (12 males, four females, age 65 ± 14). Patients were predominantly ventilated with continuous positive airway pressure and pressure support. Following physiotherapy, total lung sound amplitude at peak inspiration decreased twofold from 37 ± 58.10⁶ to 18 ± 23.10⁶ arbitrary units (AU), with significant reduction in the left lung (P = 0.03). Furthermore, the difference in sound amplitude between right and left lungs significantly decreased post-treatment compared with pretreatment (P = 0.03).

Conclusions

Computerized lung sound monitoring may be useful to assess secretion retention and the effectiveness of secretion removal in mechanically ventilated patients. Further investigation is, however, necessary in order to distinguish between secretion-related effects and changes due to other factors such as airflow rate and pattern.