The evaluation of a non-invasive respiratory volume monitor in surgical patients undergoing elective surgery with general anesthesia

Continuous respiratory assessment is especially important during post-operative care following extubation. Respiratory depression and subsequent adverse outcomes can arise due to opioid administration and/or residual anesthetics. A non-invasive respiratory volume monitor (RVM) has been developed that provides continuous, real-time, measurements of minute ventilation (MV), tidal volume (TV), and respiratory rate (RR) via a standardized set of thoracic electrodes. Previous work demonstrated accuracy of the RVM versus standard spirometry and its utility in demonstrating response to opioids in postoperative patients. This study evaluated the correlation between RVM measurements of MV, TV and RR to ventilator measurements during general anesthesia (GA). Continuous digital RVM and ventilator traces, as well as RVM measurements of MV, TV and RR, were analyzed from ten patients (mean 62.6 ± 7.4 years; body mass index 28.6 ± 5.2 kg/m²) undergoing surgery with GA. RVM data were compared to ventilator data and bias, precision and accuracy were calculated. The average MV difference between the RVM and ventilator was −0.10 L/min (bias: −1.3 %, precision: 6.6 %, accuracy: 9.0 %. The average TV difference was 40 mL (bias: 0.4 %, precision: 7.3 %, accuracy: 9.1 %). The average RR difference was −0.22 breaths/minute (bias: −1.8 %, precision: 3.7 % accuracy: 4.1 %). Correlations between the RVM traces and the ventilator were compared at various points with correlations >0.90 throughout. Pairing the close correlation to ventilator measurements in intubated patients demonstrated by this study with previously described accuracy compared to spirometry in non-intubated patients, the RVM can be considered to have the capability to provide continuity of ventilation monitoring post-extubation This supports the use of real-time continuous RVM measurements to drive post-operative and post-extubation protocols, initiate therapeutic interventions and improve patient safety.