The Application of Mass Spectrometry to Blood Gas Analysis

Abstract

This research project was concerned with applying the technique of mass spectrometry to the analysis of blood gases. A production model mass spectrometer was used for the experimental work. The performance of a commercially available blood gas catheter was investigated and found to be unsatisfactory. This led to a fundamental study of membrane systems used with mass spectrometers and blood. In the course of this it became apparent that the analysis of oxygen from blood by this method was affected by phenomena concerned with boundary layer depletion, in particular a complicated non-linearity between the oxygen flux measured by the mass spectrometer and the partial pressure of the oxygen in blood. Such phenomena, although observed by others in the past, had not been systematically studied or satisfactorily explained. A series of in vitro experiments was therefore devised to elucidate the situation. It was carried out using a number of membrane systems on whole blood, plasma, and haemolysed blood. A new theoretical model of oxyhaemoglobin dissociation in the depleted boundary level of blood was developed and found to explain the experimental observations qualitatively. An extension of this model yielded quantitative predictions that agreed with the results obtained by the experiments. The non-linearity effect was seen to be of significance for membrane systems with oxygen sampling rates of about 2.10-9 ml/s/torr and over...