Tracheal Sound Analysis for Automatic Detection of Respiratory Depression in Adult Patients during Cataract Surgery under Sedation

Neda Esmaeili, Hossein Rabbani, Soheila Makaremi, Marzieh Golabbakhsh, Mahmoud Saghaei, Mehdi Parviz, Khosro Naghibi


Background: Tracheal sound analysis is a simple way to study the abnormalities of upper airway like
airway obstruction. Hence, it may be an effective method for detection of alveolar hypoventilation
and respiratory depression. This study was designed to investigate the importance of tracheal sound
analysis to detect respiratory depression during cataract surgery under sedation. Methods: After
Institutional Ethical Committee approval and informed patients’ consent, we studied thirty adults
American Society of Anesthesiologists I and II patients scheduled for cataract surgery under sedation
anesthesia. Recording of tracheal sounds started 1 min before administration of sedative drugs using a
microphone. Recorded sounds were examined by the anesthesiologist to detect periods of respiratory
depression longer than 10 s. Then, tracheal sound signals converted to spectrogram images, and
image processing was done to detect respiratory depression. Finally, depression periods detected from
tracheal sound analysis were compared to the depression periods detected by the anesthesiologist.
Results: We extracted fve features from spectrogram images of tracheal sounds for the detection
of respiratory depression. Then, decision tree and support vector machine (SVM) with Radial Basis
Function (RBF) kernel were used to classify the data using these features, where the designed
decision tree outperforms the SVM with a sensitivity of 89% and specifcity of 97%. Conclusions:
The results of this study show that morphological processing of spectrogram images of tracheal sound
signals from a microphone placed over suprasternal notch may reliably provide an early warning of
respiratory depression and the onset of airway obstruction in patients under sedation.

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