Abstract

Postoperative respiratory complications are common in patients after surgery. Respiratory depression and subsequent adverse outcomes can arise from pain, residual effects of drugs given during anaesthesia and administration of opioids for pain management. There is an urgent need for a continuous, real-time and non-invasive respiratory monitoring of spontaneously breathing postoperative patients. For this purpose, we used rib cage and abdominal respiratory effort belts for the respiratory monitoring pre- and postoperatively, with a new calibration method that enables accurate estimates of the respiratory airflow waveforms even when breathing style changes. Five patients were measured with respiratory effort belts and mask spirometer. Preoperative measurements were done in the operating room, whereas postoperative measurements were done in the recovery room. We compared five calibration models with pre- and postoperative training data. The postoperative calibration approach with two respiratory effort belts produced the most accurate respiratory airflow waveforms and tidal volume, minute volume and respiratory rate estimates. Average results for the best model were: coefficient of determination R² was 0.91, tidal volume error 5.8%, minute volume error 8.5% and BPM (Breaths per Minute) error 0.21. The method performed well even in the following challenging respiratory cases: low airflows, thoracoabdominal asynchrony and hypopneic events. It was shown that a single belt measurement can be sufficient in some cases. The proposed method is able to produce estimates of postoperative respiratory airflow waveforms to enable accurate, continuous, real-time and non-invasive respiratory monitoring postoperatively. It provides also potential to optimize postoperative pain management and enables timely interventions.