Comparison of Mixed Venous Oxygen Saturation and Premembranous Venous Oxygen Saturation in Patients on Peripheral Venous-Arterial Extracorporeal Membrane Oxygenation

In patients on veno-arterial extracorporeal membrane oxygenation (ECMO) premembranous venous oxygen saturation (S pm-v O 2 ) is continuously displayed on the ECMO console. However, the concordance between S pm-v O 2 and mixed venous oxygen saturation (S v O 2 ) remains largely unexplored. Our single-center retrospective study included adult patients who had paired S v O 2 and S pm-v O 2 readings within 15 minutes of each other, on peripherally cannulated V f ivc -A ECMO and a pulmonary artery using catheter (PAC). The 82 pairs of observations showed a mean difference of 11.37% (95% limits of agreement −6.0 to 28.74, p < 0.001) between S pm-v O 2 and S v O 2 . Although the two values correlated with each other ( r = 0.51, p < 0.01), the difference between the paired measurements was larger at lower values of S v O 2 (3.72 ± 6.38% when S v O 2 >80%, 11.79 ± 7.46% when S v O 2 between 60% and 80%, and 18.81 ± 12.09% when S v O 2 <60%). The equation S v O 2 = 1.2* S pm-v O 2 – 28.03 was obtained by Passing Bablok regression. Cardiac index calculated by S pm-v O 2 and S v O 2 differed by 0.8 L/minute/m 2 (95% limits of agreement −0.52 to 2.17, p < 0.001). In peripheral VA-ECMO, S pm-v O 2 is consistently higher than S v O 2 , with more discordance at lower saturation levels. Using S pm-v O 2 to estimate cardiac output using Fick method yields inaccurate results.