Obesity is suggested to reduce postoperative bleeding in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) but perioperative hemostasis variations have not been studied. Therefore, we investigated the effects of severe obesity (body mass index [BMI] ≥ 35 kg/m ²) on chest tube output (CTO) and hemostasis in patients undergoing cardiac surgery with CPB.

We prospectively investigated 2799 consecutive patients who underwent coronary and/or valve surgery using CPB between 2008 and 2012. 204 patients (7.3%) presented a severe obesity.

In the severe obesity group, the 6-h and 24-h CTO were significantly reduced by -21.8% and -14.8% respectively (P < 0.0001) compared with the control group. A significant reduction of the mean number of red blood cell units transfused at 24 h was observed in the severe obesity groups (P = 0.01). On admission to the intensive care unit, a significant increase of platelet count (+ 9.2%; P < 0.0001), fibrinogen level (+ 12.2%; P < 0.0001) and prothrombin time (+ 4.1%; P < 0.01) and a significant decrease of the activated partial thromboplastin time (-4.2%; P < 0.01) were observed in the severe obesity group compared with the control group.

In multivariate analysis, severe obesity was significantly associated to a decreased risk of excessive bleeding (24-h CTO > 90th percentile; Odds ratio: 0.37, 95% CI: 0.17 to 0.82). No significant differences were observed regarding postoperative thromboembolic events between the two groups.

Severe obesity is associated with a prothrombotic postoperative state that leads to a reduction of postoperative blood loss in patients undergoing cardiac surgery with CPB.