Intraoperative Anemia Mediates Sex Disparity in Operative Mortality After Coronary Artery Bypass Grafting

Area of Science:

• Cardiovascular Surgery
• Anesthesiology
• Medical Statistics

Background:

• Women experience higher operative mortality rates following coronary artery bypass grafting (CABG) compared to men.
• Understanding the factors contributing to this sex-based disparity is crucial for improving patient outcomes.

Purpose of the Study:

• To investigate the relationship between intraoperative anemia, defined by nadir intraoperative hematocrit, and operative mortality in CABG patients.
• To determine the extent to which intraoperative anemia mediates the increased mortality risk observed in women undergoing CABG.

Main Methods:

• A large cohort study of 1,434,225 isolated primary CABG patients (344,357 women) was conducted using data from the Society of Thoracic Surgeons Adult Cardiac Surgery Database (2011-2022).
• Operative mortality was the primary outcome. Causal mediation analysis was employed to assess the effect of female sex on mortality risk and the proportion mediated by intraoperative anemia.
• Attributable risk (AR) was calculated to quantify the association between female sex and CABG outcomes.

Main Results:

• Women exhibited lower median nadir intraoperative hematocrit (22.0%) compared to men (27.0%) and higher operative mortality (2.8% vs 1.7%).
• Intraoperative anemia was found to mediate 38.5% of the increased mortality risk associated with female sex.
• A stronger association between operative mortality and nadir intraoperative hematocrit was observed at values below 22.0%.

Conclusions:

• Intraoperative anemia is a significant mediator of the increased operative mortality risk in women undergoing CABG.
• Strategies aimed at avoiding nadir intraoperative hematocrit values below 22.0% could potentially reduce sex-based differences in CABG operative mortality.