2004 OPEN FORUM Abstracts
Accuracy of Tidal Volume Measurements in the Presence of Helium/Oxygen Mixtures
James
Bement, RRT, Dinesh G. Haryadi, Ph.D.Clinical
Research Department, Respironics Hospital Division, Wallingford, CT
06492
Introduction:
Helium/oxygen mixtures are used to improve gas exchange in anesthesia
and critical care. Respiratory flow and volume measurements needs to
be adequately compensated when using helium since it has a lower
density when compared with air. The objective of this study was to
evaluate the performance of the NICO (Model 7300) Cardiopulmonary
Management System while measuring volume of gas mixtures containing
heliox in concentrations of 70% helium/30% oxygen and 60% helium/40%
oxygen.
Methods:
For each concentration of Heliox, a 30-liter non-diffusing gas bag
(Hans Rudolf, Inc.) was filled with the gas mixture. The NICO
flow/CO2 sensor was connected between a one-liter
calibration syringe and the gas bag. The valve of the gas bag was
additionally connected to a one-liter test lung (Siemens, Inc.) so
that testing could be performed with and without pressure to
determine if airway pressure has an effect on gas measurement. The
calibration syringe was set to the full one liter, and pumped back
and forth on the gas bag, and measurements were recorded using data
collection software. The concentration of Heliox was entered into
the NICO monitor. The valve was then switched, and the measurements
repeated cycling the gas back and forth through the one-liter test
lung. The volume of the calibration syringe was decreased in
increments of 100 ml and the test repeated until the volume of 100 ml
was reached. Average bias was calculated as the difference between
the syringe volume and measured volume. Data was analyzed using
Bland-Altman Statistics.
Results:
The average difference between the tidal volume measurements of the
calibrated syringe and the NICO measurements were -0.65% (Bias) ±
1.79% (1 STDEV).
| Gas Mixture | Bias ± 1 STDEV |
| 60/40 (No pressure) | +0.71% ± 0.26% |
| 70/30 (No pressure) | -1.83% ± 1.67% |
| 60/40 (With pressure) | +0.32% ± 0.63% |
| 70/30 (With pressure) | -1.81% ± 2.10% |
Conclusions:
Based
on the above results, the accuracy of the tidal volume measurements
using the NICO in the presence of heliox mixtures typically used in
clinical settings is within specification.
Reference:
Sondergaard S, Karason S, Lundin S, Stenqvist O. Evaluation of a
Pitot type spirometer in helium/oxygen mixtures. J Clin Monit Comput.
1998 Aug;14(6):425-31.