Quantitative continuous measurement of pO2 and pCO2 in artery and vein

A technique using a quadrupole mass spectrometer has been developed for the continuous measurement of partial pressures of physiological blood gases. The depletion phenomenon is eliminated with a new sampling cannula equiped with a polyethylene membrane for velocities greater than 1 cm per second. The importance of this development resides in the fact that this phenomenon, which is due to a sampling rate around the cannula in excess of the remplacement by the medium of the molecules withdrawn, leads to an under-estimation of the real partial pressure which increases as the blood velocity falls. Thanks to the new cannula, accurate measurements can now be made in both arteries and veins; moreover, continuous observation of physiological phenomena can be carried out with a time constant of under 1 minute resulting from the thinness of the membrane.