Location

Utah State University

Start Date

11-5-2011 1:30 PM

Description

There is a need for an automated bedside functional residual capacity (FRC) measurement method that can continually monitor both the size and a change in size of a patient’s lung volume during mechanical ventilation without the use of bulky equipment, expensive tracer gases or step increases in inspired oxygen fraction. We developed a CO2 rebreathing method for FRC measurement that simply requires data from a volumetric capnometer (partial pressure of end-tidal carbon dioxide (PetCO2) and volume of CO2 eliminated (VCO2) for the measurement. This study was designed to assess the accuracy, precision and repeatability of the proposed FRC measurement system during stable ventilation. Methods: Accuracy and precision of measurements were assessed by comparing the CO2 rebreathing FRC values to the gold standard, body plethysmography, in nine spontaneously breathing volunteers. Repeatability was assessed by comparing subsequent measurements in nine intensive care patients whose lungs were under mechanical ventilation. The accuracy and precision of the CO2 FRC measurement during mechanical ventilation were then compared to the reference method, modified multiple breath nitrogen washout, in the same ICU patients. Results: Compared to body plethysmography, the accuracy (mean bias) of the CO2 method was -0.085 L and precision (1 standard deviation) was 0.033 L (-2.3 ± 9.2% of body plethysmography). The accuracy in the mechanically ventilated patients was -0.055 L and precision was 0.336 L (-2.6% ± 17.5% of nitrogen washout). The difference between repeated FRC measurements in the ICU patients was 0.020 ± 0.42 L (mean ± standard deviation) (1.1 ± 23.4 %). Conclusions: The CO2 rebreathing method for FRC measurement provides acceptable accuracy and repeatability compared to existing methods during ventilation with mechanical ventilation. Further study of the CO2 rebreathing method is needed.

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May 11th, 1:30 PM

Evaluation of a CO2 Partial Rebreathing-Based Functional Residual Capacity Measurement Method for Mechanically Ventilated Patients

Utah State University

There is a need for an automated bedside functional residual capacity (FRC) measurement method that can continually monitor both the size and a change in size of a patient’s lung volume during mechanical ventilation without the use of bulky equipment, expensive tracer gases or step increases in inspired oxygen fraction. We developed a CO2 rebreathing method for FRC measurement that simply requires data from a volumetric capnometer (partial pressure of end-tidal carbon dioxide (PetCO2) and volume of CO2 eliminated (VCO2) for the measurement. This study was designed to assess the accuracy, precision and repeatability of the proposed FRC measurement system during stable ventilation. Methods: Accuracy and precision of measurements were assessed by comparing the CO2 rebreathing FRC values to the gold standard, body plethysmography, in nine spontaneously breathing volunteers. Repeatability was assessed by comparing subsequent measurements in nine intensive care patients whose lungs were under mechanical ventilation. The accuracy and precision of the CO2 FRC measurement during mechanical ventilation were then compared to the reference method, modified multiple breath nitrogen washout, in the same ICU patients. Results: Compared to body plethysmography, the accuracy (mean bias) of the CO2 method was -0.085 L and precision (1 standard deviation) was 0.033 L (-2.3 ± 9.2% of body plethysmography). The accuracy in the mechanically ventilated patients was -0.055 L and precision was 0.336 L (-2.6% ± 17.5% of nitrogen washout). The difference between repeated FRC measurements in the ICU patients was 0.020 ± 0.42 L (mean ± standard deviation) (1.1 ± 23.4 %). Conclusions: The CO2 rebreathing method for FRC measurement provides acceptable accuracy and repeatability compared to existing methods during ventilation with mechanical ventilation. Further study of the CO2 rebreathing method is needed.