Delirium is a common complication in elderly intensive care unit (ICU) patients and is associated with poor clinical outcomes. Circadian rhythm disruption is considered an important contributing factor in delirium development. Stellate ganglion block (SGB) may modulate autonomic nervous system activity and improve circadian rhythm regulation.

This prospective randomized placebo-controlled trial aims to evaluate the effects of ultrasound-guided stellate ganglion block on delirium incidence and circadian rhythm in ICU patients aged 65 years and older. Delirium will be assessed using validated clinical scales, and circadian rhythm will be evaluated through serial measurements of serum melatonin and plasma cortisol levels

Delirium is a common and serious complication among elderly intensive care unit (ICU) patients and is associated with increased morbidity, mortality, prolonged hospitalization, and poor long-term outcomes. Although the pathophysiology of delirium is multifactorial, growing evidence suggests that disruption of circadian rhythm and autonomic nervous system imbalance play an important role in its development. Current pharmacological and non-pharmacological treatment strategies remain limited, highlighting the need for novel preventive and therapeutic approaches.

Stellate ganglion block (SGB) is an ultrasound-guided autonomic modulation technique that has been shown to influence sympathetic activity, sleep regulation, and circadian rhythm. However, its potential role in reducing ICU delirium and modulating circadian biomarkers has not been clearly established.

This study is designed as a prospective, randomized, placebo-controlled to investigate the effects of ultrasound-guided stellate ganglion block on delirium and circadian rhythm in geriatric ICU patients. Eligible patients aged 65 years and older will be randomized in a 1:1 ratio to receive either stellate ganglion block with 0.5% bupivacaine or placebo saline injection. Randomization will be computer-generated, and outcome assessors will be blinded to group allocation.

Delirium will be assessed twice daily for seven days using validated clinical tools, including the Richmond Agitation-Sedation Scale (RASS) and Confusion Assessment Method for the ICU (CAM-ICU). Delirium severity will be evaluated using the Delirium Rating Scale-Revised-98, and motor subtypes (hyperactive, hypoactive, mixed) will be categorized according to RASS scores. Sleep quality will be assessed using the Richards-Campbell Sleep Questionnaire.

To evaluate circadian rhythm, serum melatonin and plasma cortisol levels will be measured at predefined circadian time points during the first three days following ICU admission. The study combines objective biomarker assessment with standardized delirium evaluation to explore potential mechanistic pathways linking autonomic modulation and neurocognitive outcomes.

The primary objective is to determine whether stellate ganglion block reduces delirium incidence in elderly ICU patients. Secondary objectives include evaluating delirium severity, motor subtype distribution, sleep quality, circadian biomarker changes, and ICU and hospital length of stay. This trial aims to provide mechanistic and clinical evidence regarding the potential role of stellate ganglion block in ICU delirium management.

Inclusion Criteria:

• Patients aged 65 years or older expected to remain in the intensive care unit for more than 48 hours
• RASS score > -4

Exclusion Criteria:

• History of neurodegenerative disease (e.g., Alzheimer's disease, dementia, vascular dementia)
• Uncontrolled psychiatric disorders
• Alcohol use disorder and/or substance abuse
• History of traumatic brain injury or ischemic/hemorrhagic cerebrovascular event
• Severe hearing and/or visual impairment
• Benzodiazepine use
• Renal failure (Acute Kidney Injury stage 2-3) and/or liver failure
• Beta-blocker use
• Contraindications to stellate ganglion block (e.g., coagulopathy, glaucoma, recent myocardial infarction)
• Sepsis
• Allergy to bupivacaine
• Inability to communicate in Turkish or English
• Severe hyponatremia
• Hemodynamic instability

Participants and outcome assessors will be blinded to group allocation. The anesthesiologist performing the procedure will assess block success based on the presence of Horner syndrome and will not participate in delirium assessments, sleep evaluations, biomarker measurements, or data analysis. All clinical outcome assessments will be performed by independent blinded investigators.