Central venous oxygen saturation during cardiopulmonary bypass predicts 3-year survival

Abstract

Objectives: Long-term survival after cardiac surgery is determined by a number of different risk factors. Central venous oxygen saturation (S(v)O(2)) measures the balance between oxygen delivery and demand. S(v)O(2) levels in the intensive care situation are reported to be associated with patient outcome. The present report explores the connection between S(v)O(2) during cardiopulmonary bypass (CPB) and survival after cardiac surgery.

Methods: Retrospective analysis of one thousand consecutive cardiac surgical patients was undertaken. S(v)O(2) during CPB was monitored online. Registry data combining specific risk factors with S(v)O(2) were selected for Kaplan-Meier and Cox regression analysis to examine the influence on 30-day and 3-year survivals.

Results: Nine-hundred and thirty-two patient records were eligible for analysis. S(v)O(2) below 75% during CPB was associated with significantly shorter 30-day and 3-year survivals. Based on Kaplan-Meier statistics, the survival rate decreased by 3.1% (98.1-95.0), P = 0.011 and 6.1% (92.7-86.6), P = 0.003, respectively. The influence of S(v)O(2) on 3-year survival remained statistically significant after controlling for a series of risk factors in the Cox regression analysis. Patients with S(v)O(2) <75% carried a 2-fold (odds ratio 2.1) increased relative risk of shortened 3-year survival (P = 0.003). Other risk factors statistically significantly associated with 3-year survival were age, gender, duration of CPB, blood temperature, hypertension, haematocrit and type of surgical procedure.

Conclusions: We report decreased 30-day and 3-year survival expectancy for patients experiencing S(v)O(2) lower than 75% during CPB.

Figure 1:

S_vO₂ level in relation to specific physiological parameters. Depiction of systemic blood flow (A), body temperature (B), haematocrit (C) and mean arterial blood pressure (D) at S_vO₂ below or above 75% during cardiopulmonary bypass (CPB). P-values (ANOVA) represent group differences based on the S_vO₂ level and interaction effects of included time periods. S10–S30 denote commence and E30–E10 termination of CPB each with a time frame of 10 min (means ± SD).

Figure 2:

Three-year survival based on S_vO₂ during cardiopulmonary bypass (CPB). Three-year survival categorized on S_vO₂ below or above 75% during the last phase of CPB after controlling for possible confounders as defined in the Cox regression analysis.