Patients with cognitive decline are frequently comorbid with sleep disorders which may in turn aggravate cognitive decline. Sedative dose dexmedetomidine improved sleep quality but incresed bradycardia and hypotension; low dose dexmedetomidine produce less side effects, but the sleep promoting effects are relatively weak. Low dose esketamine also has sleep-promoting effects but may produce neuropsychiatric side effects. Both dexmedetomidine and esketamine are approved for intranasal administration. We suppose that intranasal administration of dexmedetomidine-esketamine combination may improve sleep quality and therefore cognitive function in older ptients with Alzheimer's disease cognitive impairment and sleep disorders.

Along with aging population, the number of older adults with cognitive decline (such as Alzheimer's disease) is also increasing and constitutes a great challenge to public health. Normal sleep is important for maintaining both physical and mental health. However, patients with cognitive decline are frequently comorbid with sleep disorders which are associated with increased need of health care; sleep disorders may in turn aggravate cognitive decline in these patients.

Dexmedetomidine is a highly selective alpha 2-adrenoceptor agonist with sedative, anxiolytic, and analgesic effects. In previous studies, infusion of sedative dose dexmedetomidine improved sleep quality but incresed bradycardia and hypotension. Infusion of low dose dexmedetomidine is also effective in improving sleep quality with less side effects; however, the sleep promoting effects are relatively weak. Intranasal dexmedetomidine provides a non-invasive intervention and is used for sleep promotion in preoperative patients, but requires hemodynaamic monitoring due to potential side effects.

Ketamine is a noncompetitive N-Methyl-D-aspartic acid (NMDA) receptor antagonist and has been used as a dissociative anesthetic for decades. Esketamine is the S-enantiomer and has approximately twice the potency of ketamine. Recent studies showed that low dose esketamine also has anti-depressive and sleep-promoting effects. Intranasal esketamine has been approved for treatment-resistant depression, and is also used as premedication in children and to relieve postoperative pain in adults.

Even low dose ketamine/esketamine may produce neuropsychiatric side effects, which can be relieved by dexmedetomidine. A study in pediatric patients reported that intranasal co-administration of dexmedetomidine and esketamine produced synergetic effects on sedation. A study in adults showed that dexmedetomidine-esketamine combination as a supplement to patient-controlled opioid analgesia improved both analgesia and sleep quality without increasing side effects. A recent trial in older adults indicated that intranasal dexmedetomidine-esketamine improved neurocognitive recovery after surgery.

We suppose that intranasal administration of dexmedetomidine-esketamine combination may improve sleep quality and therefore cognitive function in older ptients with Alzheimer's disease cognitive impairment and sleep disorders.

Inclusion Criteria:

1. Aged ≥ 60 years.
2. Meeting the clinical diagnostic criteria for Alzheimer's disease, with mild cognitive impairment (MoCA score 18-25) or moderate cognitive impairment (MoCA score 10-17) due to Alzheimer's disease.
3. Comorbid with sleep disorders (Pittsburgh Sleep Quality Index [PSQI] score ≥ 7).
4. Signed informed consent.

Exclusion Criteria:

1. Cognitive impairment/dementia due to other causes (e.g., vascular dementia, frontotemporal dementia, Parkinson's disease dementia).
2. Unsuitable for intranasal administration due to nasal cavity diseases (e.g., rhinitis, nasal polyps, or nasal congestion of any cause).
3. Inability to communicate due to visual, auditory, language, or other reasons, or Mini-Mental State Examination (MMSE) score ≤ 9 or MoCA score ≤ 9.
4. History of schizophrenia, epilepsy, or Parkinson's disease, or confirmed diagnosis of glaucoma, hyperthyroidism, pheochromocytoma, or myasthenia gravis.
5. Confirmed diagnosis of restless legs syndrome or sleep apnea, or judged to be at high risk of moderate-to-severe sleep apnea according to STOP-Bang score, or Body Mass Index (BMI) > 30 kg/m2.
6. History of stroke or transient ischemic attack within 12 months prior to enrollment, confirmed intracranial aneurysm, or elevated intracranial pressure from any cause.
7. Uncontrolled hypertension (e.g., hypertensive crisis or systolic blood pressure > 160 mmHg and/or diastolic blood pressure > 100 mmHg prior to enrollment), myocardial infarction, unstable angina, revascularization surgery within 12 months prior to enrollment, or NYHA class III.
8. Sick sinus syndrome, severe sinus bradycardia (heart rate < 50 beats/min), atrioventricular block above degree II without a pacemaker, corrected QT interval (Fridericia-corrected QTcF) ≥ 450 ms, or other severe arrhythmias (e.g., frequent premature ventricular contractions).
9. Uncontrolled diabetes (e.g., HbA1c > 9%, diabetic ketosis, hyperglycemic coma, or hypoglycemia).
10. Severe hepatic dysfunction (Child-Pugh Class C), renal dysfunction (eGFR ≤ 30 ml/min/1.73m2), respiratory insufficiency (SpO2 < 93% on room air), or other severe diseases (e.g., frailty with inability to walk independently, advanced-stage tumors).
11. Alcohol or drug dependence (manifested as strong cravings, uncontrolled use, and withdrawal symptoms upon cessation), or use of contraindicated medications.
12. Major surgery under general anesthesia within 12 weeks prior to enrollment, or planned surgery within 12 weeks.
13. Allergy to dexmedetomidine and/or esketamine.
14. Participation in other interventional clinical studies.
15. Any other conditions deemed unsuitable for study inclusion by the investigator.