Delirium is a common, distressing, and dangerous complication after cardiac surgery with cardiopulmonary bypass (CPB) with few modifiable risk factors. This study aims to determine the association between post-operative oxygen delivery (DO2i) and the risk of delirium and assess the critical threshold for DO2i associated with delirium risk after surgery.

This study is a multi-site retrospective cohort study with 1690 patients undergoing elective cardiac surgery with CPB who had multiple cardiac output measurements with a pulmonary artery catheter and arterial blood gas analyses.

The cohort of 1690 patients analyzed included 185 patients diagnosed with delirium within 7 days of surgery (11%). Patients with delirium had a lower post-operative DO2i (mean difference of 26 ml/min/m², 95% CI 14 to 36, p < 0.0001) compared to the 1505 patients without delirium. In a multivariable analysis controlling for age, sex, race, heart failure, diabetes, obstructive sleep apnea, body mass index, CPB time, circulatory arrest time, aortic cross clamp time, carotid stenosis, and cognitive impairment the post-operative mean DO2i was not independently associated with delirium. Post-operative DO2i was inversely correlated with CPB time with a decrease of 0.27 ml/min/m² per minute of CPB exposure (p < 0.0001). The critical threshold of DO2i after cardiac surgery is lower with increased age and female sex.

Post-operative DO2i over 7 days is not independently associated with the risk of delirium but significantly correlated with CPB time. Older patients may have a lower DO2i critical threshold for risk of delirium.