Mixed Venous Oxygen Saturation Has a Poor Association with Cardiac Index during Early Intensive Care Unit Stay after Cardiac Surgery

Abstract

Abstract

Objectives: Our aim was to assess the association between mixed venous oxygen saturation (SvO2) and cardiac index (CI) among cardiac surgical patients during the initial 4 hours in the intensive care unit (ICU).

Design: A single-center retrospective observational study.

Setting: A tertiary-level university hospital.

Participants: Adult cardiac surgical patients (N = 4,958) operated on during 2007 to 2020.

Interventions: Pulmonary artery catheter (PAC) measurements of SvO2 and CI were taken at ICU admission and 4 hours later. Linear regression was used to analyze the association between these variables.

Measurements and Main Results: Paired CI and SvO2 values were available from 4,958 patients. The median (interquartile range) SvO2 was 68% (63-72%) at ICU admission and 66% (61-71%) 4 hours later. CI was 2.34 L/min/m2 (2.03-2.79) at ICU admission and 2.48 L/min/m2 (2.15-2.86) 4 hours later. In the entire cohort, a 10% change of SvO2 coincided with a CI change of 0.36 L/min/m2 (95% confidence interval 0.34-0.38) at ICU admission and a change of 0.33 L/min/m2 (0.31-0.36) at 4 hours. In patients with SvO2 less than 60%, the association between CI and SvO2 weakened further.

Conclusions: Factors affecting oxygen consumption and demand weaken the association between SvO2 and CI values in the early ICU recovery phase after cardiac surgery. Therefore, SvO2 and CI values should not be relied upon in clinical decision-making as reliable predictors of one another.