Use of a Respiratory Volume Monitor to Assess Respiratory Competence in Cardiac Surgery Patients After Extubation

Abstract

Background: Patients who have cardiac surgery are mechanically ventilated postoperatively. Early postoperative extubation is currently recommended in anesthesia guidelines. No current technology can accurately, non-invasively, measure respiratory competence after extubation. Pulse oximetry has been helpful, but this is a late indicator of respiratory compromise. A novel, non-invasive, Respiratory Volume Monitor (RVM) has been shown to deliver accurate continuous, real-time minute ventilation (MV), tidal volume (TV) and respiratory rate (RR) measurements and provide an objective measure of respiratory competence. Objective: The RVM will accurately reflect MV, TV and RR in cardiac surgery patients before and after extubation. Methods: RVM traces were recorded from patients before and after cardiac surgery. Continuous monitoring began on admission to the unit and was ended at 24 hours after extubation. RVM based MV, TV & RR were calculated from 30-second segments. MV, TV & RR were also continuously recorded from the ventilator prior to extubation. The RVM was calibrated to each patient using the readings from the ventilator. Results: During mechanical ventilation, the RVM measured TVs strongly correlated with the ventilator TVs (r=0.97). Following extubation the patient's breathing became more erratic and TVs and MVs decreased. Within one hour all patients studied showed a marked recovery of MV and TV. Conclusions: RVM based MV, TV and RR correlated well with similar data collected from ventilators. After extubation, RVM shows promise as a means to monitor respiratory competence of intubated and non-intubated patients, and has implications for improving patient safety.