Detection of intratracheal accumulation of thick secretions by using continuous monitoring of respiratory acoustic spectrum: a preliminary analysis

Abstract

The accumulation of tracheobronchial secretions may contribute to a deterioration in pulmonary function and its early detection is important. In this study, we analyzed the respiratory sound spectrum in patients with intratracheal secretion, and compared acoustic characteristics before and after therapeutic endotracheal suctioning. After review of anesthetic records of liver transplant recipients, we included recipients with identified intratracheal secretion during surgery. Intraoperative breath sounds recorded through esophageal stethoscope were sampled in 20 s-period before and after suctioning of secretion and analyzed using fast Fourier transform. We also analyzed normal breath sounds from recipients without any respiratory problem as control group. The maximal power (dBm_Max), total power from whole frequency range of 80-500 Hz (P_t), total power of each frequency range (80-200 Hz, P_80-200; 200-300 Hz, P_200-300; 300-400 Hz, P_300-400; 400-500 Hz, P_400-500), and their ratio (P_80-200/P_t, P_200-300/P_t, P_300-400/P_t, P_400-500/P_t) were compared. Breath sounds were obtained from 20 recipients; 9 pairs of breath sound before and after suctioning of secretion and 11 normal breath sounds. Patients with intratracheal secretion showed significantly higher P_80-200, P_200-300, P_300-400, P_400-500 when compared to the those of normal control patients (P = 0.003, P = 0.002, and P = 0.009, respectively), while dBm_Max did not differ. Elimination of secretions attenuated P_80-200, P_200-300, P_300-400, and P_400-500 by 22.4%, 25.7%, 48.5%, and 15.3%, respectively (P = 0.002, 0.024, 0.009, and 0.016, respectively). Identifying the presence of intratracheal secretions with power ratio at 80-200 Hz and 300-400 Hz showed the highest area under the curve of 0.955 in receiver operating characteristic curve analysis. We suggest that spectral analysis of breath sounds obtained from the esophageal stethoscope might be a useful non-invasive respiratory monitor for accumulation of intratracheal secretion. Further prospective studies to evaluate the utility of acoustic analysis in surgical patients are warranted.

Keywords: Acoustic; Critical care; Respiratory monitoring; Stethoscope.