Modelling the distribution of the oxygen-haemoglobin dissociation curve in vivo: An observational study

Few studies have explored the variability of the oxygen-haemoglobin dissociation curve in vivo. 96,428 blood gas measurements were obtained (80,376 arterial, 6959 venous) from a cohort of 7656 patients who were admitted to a large UK teaching hospital between 1 February 2020 and 31 December 2021 for a Covid-19 related admission with a positive PCR. There was consistent variation of the distribution of the oxygen-haemoglobin curve across most oxygen saturation strata with typical values at 91-92 % saturation (mean 8.1kPa, standard deviation sd 0.6 kPa or 60.8 mmHg sd 4.5 mmHg), with the exception of the highest strata of oxygen saturation of 99-100 % (mean 17.7 kPa, sd 8.1kPa or 132 mmHg sd 60.8). The higher oxygen partial pressures at higher oxygen saturations are a concern in view of the increased mortality observed in RCTs of higher oxygen saturation targets. However, the observational study design precludes any attribution of causality.