Emergence delirium (ED) is a prevalent and severe postoperative complication in elderly surgical patients. It can occur at any perioperative stage but most frequently develops during or immediately after emergence from general anesthesia. Characterized by acute agitation and confusion, ED manifests as sharp declines in attention and cognitive function, accompanied by impaired consciousness and disorganized thinking. As a common adverse event in the early postoperative period, ED occurs in up to 87% of critically ill patients, 10%-24% of adult general medical patients, 37%-46% of anesthetized general surgical patients, with the highest incidence of 50% observed in elderly surgical patients during early recovery in the Post-Anesthesia Care Unit (PACU). Anesthesiologists have long attached great importance to the harmful effects of ED on clinical outcomes, as ED elevates risks of postoperative hemorrhage and physical trauma, extends PACU monitoring duration and hospital length of stay, and increases postoperative complications, mortality and medical resource consumption.

Chronotype describes the behavioral manifestation of the endogenous 24-hour circadian timing system. In mammals, circadian rhythms are maintained and regulated by a complete clock system: the central master clock resides in the suprachiasmatic nucleus (SCN) of the hypothalamus, while peripheral clocks exist in organs such as the liver, lungs and skeletal muscle. Patients with delirium commonly suffer severe circadian disturbances, which are embodied in disordered sleep-wake cycles, abnormal secretion rhythms of melatonin and cortisol, and altered expression of clock genes. Chronotypes are conventionally divided into morning, evening and intermediate types. Previous observational studies have proven that chronotype correlates with numerous disorders including metabolic diseases, psychiatric illnesses, brain function, delirium and cognitive performance. Accumulated evidence supports an association between delirium and circadian rhythms, and suggests that circadian dysfunction contributes to the pathological development of delirium.

Nevertheless, few studies have investigated how chronotype affects ED in elderly patients. This study intends to explore the correlation between chronotype and postoperative ED in elderly surgical patients and compare ED incidence among patients with distinct chronotypes. The results of this research will offer scientific references for formulating targeted preventive measures against ED in elderly populations, lower postoperative ED rates, alleviate adverse postoperative events, and optimize long-term clinical prognosis.