Evaluation of two electronic respiratory rate monitoring systems

Two electronic systems for monitoring respiratory rates in critical care patients were evaluated--one a system using impedance sensors and the other a system using thermistor sensors. The thermistor sensor, attached to a nasal cannula or air-entrainment mask, was connected to a sensitivity calibrating control and a digital display module. The impedance system consisted of three electrocardiogram chest leads connected to an identical digital display module. Each of 10 patients was simultaneously monitored by both systems; indicated rates from the two systems were then compared to a counted control rate to determine accuracy. Data were collected at 17 successive half-hour intervals. Analysis of variance of the data gave a significant F ratio for differences among the three methods of rate monitoring. The impedance system gave readings progressively higher and the thermistor system gave readings progressively lower than the counted control rates. This study indicates that this configuration for both impedance and thermistor sensing lacks the desired accuracy for respiratory rate monitoring but may be suitable for apnea alarms.