Journal of Applied Physiology, Vol 51, Issue 6 1451-1456, Copyright © 1981 by American Physiological Society
Measurement of respiratory gas exchange during artificial respiration
I. H. Abdul-Rasool, J. H. Chamberlain, P. C. Swan and F. T. Mitchell
This paper reports a new system for the continuous measurements of
respiratory gas exchange in ventilated subjects. It involves mixing some of
the inspired gas with all of the expired gas and withdrawing the mixture at
a constant rate through a dry gas meter that measures the flow. The
inspired gas and expired gas mixtures are sampled and O2 and CO2
concentrations measured with a paramagnetic gas analyzer and a capnograph,
respectively, to an accuracy of 0.01%. Evidence is presented to confirm the
necessary stability and sensitivity of these instruments. It is possible to
use the system with high inspired O2 concentrations, with ventilators where
there is incomplete separation of inspired and expired gas, and in the
presence of intermittent mandatory ventilation, positive end-expiratory
pressure, and continuous airway pressure. The system was compared with the
N2-dilution method and with the collection of expired gas in a Douglas bag
in dog experiments and with patients in the intensive therapy unit.
Excellent correlation between these methods was found in all circumstances.
