Technique for accurate determination of the blood nitrogen tension by mass spectrometer

Heretofore, the technical difficulties encountered in the measurement of blood nitrogen tension (PN2) by gas chromatographic techniques effectively prevented the utilization of PN2 as a clinical tool to characterize mismatching of pulmonary ventilation and perfusion. The development of mass spectrometric techniques allows for the accurate measurement of blood gas tensions; however, due to the dependency of the measurement upon flow, this technique has proven to be inaccurate for determinations of blood PN2. This technical impediment has been effectively circumvented by the development of commercially available attachment (Searle in vitro module) to a mass spectrometer. Tonometrically analyzed water was used to evaluate the validity of the measurement and the error inherent in the technique. A significant difference between the values for tonometrically analyzed water and tonometrically analyzed blood was not detected. Since the blood PN2 is a measure of the nitrogen dissolved in the water of the plasma, these studies show that tonometrically analyzed water is a valid standard of calibration for this mass-spectrometric method of determining the blood PN2.