Introduction <p>Dexmedetomidine, a highly selective α₂-adrenergic receptor agonist, is widely utilized in clinical practice for its excellent sedative and analgesic effects, and is commonly employed as an adjuvant sedative during the perioperative period. Common adverse reactions associated with dexmedetomidine include bradycardia and hypotension, while respiratory depression is relatively rare.</p> Case presentation <p>A 69-year-old female patient of Han ethnicity was admitted due to a fracture of the middle and lower segment of the right femur. The patient underwent open reduction and internal fixation of the fracture under combined spinal-epidural anesthesia. During the surgery, to provide adjuvant sedation, dexmedetomidine was administered with a loading dose of 0.5&#xa0;μg/kg infused over 10&#xa0;min, followed by a maintenance infusion at a rate of 0.35&#xa0;μg/kg/h for 35&#xa0;min. At 50&#xa0;min after the completion of the infusion, the patient's oxygen saturation gradually decreased, while no significant changes were observed in heart rate or blood pressure. At this point, the patient was found to be unconscious, with cyanotic lips and no spontaneous respiratory effort, leading to a diagnosis of apnea. The medical staff immediately initiated continuous positive airway pressure via face mask, followed by endotracheal intubation under general anesthesia and conversion to mechanical ventilation. After the patient's vital signs stabilized, the general anesthetic agents were discontinued. The patient's consciousness and spontaneous breathing gradually recovered, with no residual sequelae.</p> Conclusions <p>Dexmedetomidine possesses favorable sedative, analgesic, and anxiolytic properties and is widely used in the perioperative period. This article reports a case of apnea occurring in a geriatric patient during dexmedetomidine sedation, which warrants attention from clinicians.</p>