The Evaluation of a Noninvasive Respiratory Volume Monitor in Pediatric Patients Undergoing General Anesthesia

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Pediatric patients following surgery are at risk for respiratory compromise such as hypoventilation and hypoxemia depending on their age, comorbidities, and type of surgery. Quantitative measurement of ventilation in nonintubated infants/children is a difficult and inexact undertaking. Current respiratory assessment in nonintubated patients relies on oximetry data, respiratory rate (RR) monitors, and subjective clinical assessment, but there is no objective measure of respiratory parameters that could be utilized to predict early respiratory compromise. New advances in technology and digital signal processing have led to the development of an impedance-based respiratory volume monitor (RVM, ExSpiron, Respiratory Motion, Inc, Waltham, MA). The RVM has been shown to provide accurate real-time, continuous, noninvasive measurements of tidal volume (TV), minute ventilation (MV), and RR in adult patients.


In this prospective observational study, our primary aim was to determine whether the RVM accurately measures TV, RR, and MV in pediatric patients.


A total of 72 pediatric patients (27 females, 45 males), ASA I to III, undergoing general anesthesia with endotracheal intubation were enrolled. After endotracheal intubation, continuous data of MV, TV, and RR were recorded from the RVM and an in-line monitoring spirometer (NM3 monitor, Phillips Healthcare). RVM and NM3 measurements of MV, TV, and RR were compared during a 10-minute period prior to the incision (“Presurgery”) and a 10-minute period after the end of surgery (“Postsurgery”). Relative errors were calculated over 1-minute segment within each 10-minute period. Bias, precision, and accuracy were calculated using Bland-Altman analyses and paired-difference equivalence tests were performed.


Combined across the Presurgery and Postsurgery periods, the RVM’s mean measurement bias (RVM − NM3 measurement) for MV was −3.8% (95% limits of agreement) (±1.96 SD): (−19.9% to 12.2%), for TV it was −4.9 (−21.0% to 11.3%), and for RR it was 1.1% (−4.1% to 6.2%). The mean measurement accuracies for MV, TV, and RR were 11.9%, 12.0%, and 4.2% (0.6 breaths/min), respectively. Note that lower accuracy numbers correspond to more accurate RVM measurements. The equivalence tests rejected the null hypothesis that the RVM and NM3 have different mean values and conclude with 90% power that the measurements of MV, TV, and RR from the RVM and NM3 are equivalent within ±10%.


Our data indicate acceptable agreement between RVM and NM3 measurements in pediatric mechanically-ventilated patients. Future studies assessing the capability of the RVM to detect respiratory compromise in other clinical settings are needed.

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