To explore the correlation between preoperative sleep parameter clustering and postoperative brain and renal dysfunction.

Postoperative delirium (POD) and acute kidney injury (AKI) are common and serious complications following cardiac surgery. They often occur concurrently and interact with each other, significantly prolonging hospital stay, increasing medical costs, and correlating with long-term cognitive decline, renal function deterioration, and elevated mortality risk. The recently proposed brain-kidney axis theory suggests that the central nervous system and the kidney communicate bidirectionally through pathways including inflammation, oxidative stress, sympathetic overactivation, and hemodynamic instability, amplifying damage in a cascade manner. This provides an important theoretical framework for understanding the comorbidity mechanism of postoperative delirium and renal injury. Early identification of modifiable preoperative risk factors and blocking abnormal activation of the brain-kidney axis are critical to improving outcomes in cardiac surgery patients.

A growing body of evidence indicates that preoperative sleep disturbance is highly prevalent in surgical patients and represents an independent risk factor for adverse perioperative outcomes. Sleep disruption can disrupt circadian rhythms, exacerbate systemic inflammation, impair neurocognitive function, disturb renal hemodynamic homeostasis, and simultaneously aggravate secondary damage to both the central nervous system and the kidney via the brain-kidney axis, thereby significantly increasing the risk of comorbid postoperative delirium and acute kidney injury. However, most previous studies evaluated sleep using a single total scale score or one-dimensional indicators, which cannot fully capture the complexity and heterogeneity of preoperative sleep architecture.

To date, few studies have explored the associations between preoperative sleep phenotypes and postoperative POD, AKI, or their comorbidity in cardiac surgery based on objective sleep monitoring data and combined with the brain-kidney axis theory. Furthermore, the potential mediating role of postoperative sleep disturbance in these pathways remains unclear.

Therefore, this study aims to identify preoperative sleep phenotypes in cardiac surgery patients using cardiopulmonary coupling-derived objective sleep parameters; to investigate the associations of different sleep phenotypes with postoperative POD, AKI, and their comorbidity; and to further conduct subgroup analyses and mediation analyses to explore effect modifiers and underlying mechanisms, with a particular focus on the pathways through which abnormal sleep affects adverse postoperative outcomes via the brain-kidney axis.

Inclusion Criteria:

Aged 18 years or above who were scheduled for elective cardiac surgery with cardiopulmonary bypass

Exclusion Criteria:

Patients undergoing congenital heart disease repair surgery or surgeries necessitating deep hypothermic circulatory arrest were excluded.

Patients with a history of schizophrenia, epilepsy, Parkinson's disease, myasthenia gravis, or neurosurgery were also excluded.

Patients with a preoperative Mini - Mental State Examination (MMSE) score less than 24 , or those unable to communicate due to coma, severe dementia, or language barriers were excluded.

Adults scheduled for elective cardiac surgery with cardiopulmonary bypass