Published in:
01-02-2013 | Physiological and Technical Notes
A new formula for determining arterial oxygen saturation during venovenous extracorporeal oxygenation
Published in: Intensive Care Medicine | Issue 2/2013
Login to get accessAbstract
Purpose
Venovenous extracorporeal membrane oxygenation (VV-ECMO) is used to treat severe forms of acute respiratory distress syndrome (ARDS). VV-ECMO management may be confusing due to the lack of information about the interplay between the determinant parameters and their impact on oxygenation. We found a relationship between arterial oxygen saturation (SaO2) and its relevant parameters. The aim of this study was to assess the validity of this model.
Methods
We report our experience in 17 patients under VV-ECMO for severe ARDS. We compared, at two different levels of pump flow, SaO2 and the oxygen saturation measured in the pulmonary artery (SpaO2) with the predicted saturation using the formula: SpaO2 = (EF/CO)SmO2 + (1 − EF/CO)SvO2 + 10−2PmO2, where PF is pump flow, R is recirculation, EF is effective flow [= (1 − R)PF], SmO2 is saturation of the oxygenator outgoing blood, CO is cardiac output, SvO2 is saturation of mixed venous blood, and PmO2 is oxygen partial pressure of the oxygenator outgoing blood.
Results
There was no significant difference between predicted and measured SpaO2: the mean predicted and measured SpaO2 values were 90.7 ± 2.8 % and 90.4 ± 2.7 % , respectively (p = 0.696, r = 0.966). Bland-Altman analysis showed good agreement between predicted and measured SpaO2. Predicted SpaO2 and SaO2 was well correlated (r = 0.80).
Conclusions
We have presented an explicit relationship between SaO2 and its direct determinants during VV-ECMO. Good agreement was found with the measured values of SaO2, but the model remains to be fully validated before its use in clinical practice.