The effect of oxygen utilisation on PaO2.
The relationship between oxygen utilisation in the steady state and the arterial PO2 is shown in this graph.
The data were obtained from a 'virtual' patient (at 36.9 C) who had been placed on full cardio-pulmonary bypass (VA-ECMO) by the supervisor. The pump output and gas flow through the oxygenator were both held steady at 4.5 lpm throughout the experiment.
Starting with a metabolic rate (oxygen utilisation) of 100 mls/min, the supervisor has progressively increased the oxygen utilisation to 500 mls/minute in increments of 100 mls/min. After a period of stabilsation of 10 minutes at each utilisation level, the arterial PO2 has been recorded.
As the oxygenator is required to transfer more and more oxygen (in order to maintain the steady state), so the oxygenator becomes progressively less efficient and the PaO2 falls.
This illustrates one of the central tenets of ECMO - That when oxygen utilisation increases, arterial PO2 (and saturation) falls.