Association of Low Oxygen Delivery on Cardiopulmonary Bypass and Increased Long-Term Mortality.

BACKGROUND

Although delivering less oxygen is associated with acute kidney injury, little is known about its association with long-term mortality and how the association may be modified by transfusion.

METHODS

Minute-by-minute pump flow and hemoglobin were used to estimate oxygen delivery indexed to body surface area (DO2I) during cardiopulmonary bypass. In this retrospective study, the associations between mean DO2I and cumulative DO2I deficit <300 mL/min/m2 threshold and long-term mortality were estimated using Cox proportional and nonproportional hazard models.

RESULTS

At a mean follow-up of 5.00 (SD, 1.86) years (range, 3.10-8.12 year), 698 of 4203 patients (17%) had died. Patients who died had lower mean DO2I (230 [SD, 40] mL/min/m2 vs 251 [SD, 47] mL/min/m2) and greater cumulative DO2I deficit (9.94 [SD, 8.64] mL/min/m2 vs 7.01 [SD, 7.07] L/min/m2). After adjusting for demographics, comorbidities, laboratory values, type and status of the operations, blood pressure, and red blood cell transfusion during bypass, we found that mean DO2I was associated with mortality (hazard ratio [HR], 0.997; 95% CI, 0.995-0.999; P = .001). When cumulative DO2I deficit was added to the model, it replaced mean DO2I (HR, 1.031; 95% CI, 1.018-1.045; P < .001) of dying for each liter of O2/m2 deficit, with a small time-varying component (HR, 0.994; 95% CI, 0.990-0.999) per year of follow-up (P = .010). After adjustment, red blood cell transfusion did not remain in the models.

CONCLUSIONS

There is an inverse relationship between decreased DO2I (measured as mean or cumulative deficit) and long-term mortality. Red blood cell transfusion did not significantly modify the relationship between DO2I and mortality.