Intra-operative gas exchange and post-operative hypoxaemia

Abstract

The relation between intra-operative gas exchange and post-operative oxygen saturation was examined using pulse oximetry (SpO₂) 30 h after anaesthesia for upper abdominal surgery. The inspired oxygen partial pressure (PIO₂) was varied during anaesthesia to produce a plot of PIO₂ vs. SpO₂. Gas exchange during anaesthesia was inferred from the relation between PIO₂ and SpO₂ which was described by its lateral and vertical displacement away from the position of a standard oxygen dissociation curve. With patients breathing air, the SpO₂ was measured over a 10-min period at 30 h after surgery. The correlation coefficient of the lateral displacement with post-operative SpO₂ was 0.7, and that of the vertical displacement with post-operative SpO₂ was 0.66. The correlation coefficient of intra-operative SpO₂ at PIO₂ = 21 kPa with post-operative SpO₂ was 0.69. It can be concluded that gas exchange abnormalities during anaesthesia deduced from the displacement of the PIO₂ vs. SpO₂ curve correlate with SpO₂ 30 h post-operatively and may help to identify patients at risk of post-operative hypoxaemia.