1997 OPEN FORUM Abstracts
EVALUATION OF A RESPIRATORY FLOW SENSOR
Katie Kinninger RCP, Wayne Johnson RCP, Kathy Jacobson, Elzbieta Bak MS, David Burns M.D. UCSD Medical Center, San Diego, CA
Introduction Respiratory monitoring of neonate, pediatric and adult patients in the ICU requires accurate flow and volume measurements. The purpose of our study was to evaluate a new device designed for use during mechanical ventilation. We used a laboratory bench test to determine whether influences caused by flow, pressure, and patient tubing configurations effect the performance characteristics of the neonatal and pediatric/adult sensors of the Ventrak 1550 Respiratory Monitor (Novametrix Medical Systems, Walliford, Conn.). Methods We tested the accuracy of 3 Neonatal sensors (Model 7224) and 3 Pediatric/Adult sensors (Model 7222). Flow was generated with wall air as source and controlled with precision rotometers. The volume measurements were made with calibration syringes. Each sensor is intended for single patient use and contains its own calibration data that communicates with the Ventrak. All test conditions were conducted at ambient temperature. The Neonatal sensors were tested across a flow range of 4.0 to 30.0 L/min and volumes of 50mls and 500mls. The Pediatric/Adult sensors were tested across a flow of 20.0 to 180.0L/min and volumes of 50mls, 500mls and 1000mls. Inspiratory flow was evaluated with and without an endotrachael tube (ET) inline and a smooth bore 22 ID tube delivering flow. A 4.0 ID ET was in line (Hudson) with neonatal sensors and a 7.0 ID ET was inline (Mallinckrodt) with the pediatric/adult sensors while flow was measured. The resistive backpressure was measured at each flow rate. Backpressure is measured as the difference between pressure at the sensor inlet and atmosphere pressure using a manometer (Dwyer Instr. Inc. Michigan City IN.). Results There was no significant difference in flow measurements with or without the ET inline. Values in table reflect flow measured without an ET tube.
Average of 3 sensors % Error
Set Flow L/min. 4.0 10. 20. 30. 60. 120. 150. 174.*
Neonatal Sensor 5.8 7.0 3.17 1.78
Pedi/Adult Sensor 4.33 2.11 .44 3.47 1.53 -.34
Average of 3 sensors %Error
Volume Measurement 50mls 500mls 1000mls
Neonatal Sensor .667 -.21
Pedi/Adult Sensor -3.0 -1.39 1.77
The resistive backpressure for the Pediatric/Adult sensor was 2cmH2O/L/sec. The backpressure for Neonatal sensor was 11.6 cmH20 at .5L/second.
Conclusion Flow and volume measurement were acceptable for both sensors. The high backpressure measured on the Neonatal sensor was of concern, as was the fact that the *Ventrak displayed measurements were limited at 180L/min. A future performance evaluation of the total system is needed.