Postoperative delirium is a common and serious complication in older adults undergoing total hip arthroplasty, associated with prolonged hospitalization, increased morbidity, delayed rehabilitation, and long-term cognitive decline. Modifiable perioperative risk factors include uncontrolled postoperative pain, opioid consumption, impaired early mobilization, and systemic inflammatory response.

The Pericapsular Nerve Group (PENG) block is a regional anesthesia technique targeting the sensory innervation of the anterior hip capsule and may provide effective analgesia while preserving motor function. Improved pain control and opioid reduction may decrease the incidence of postoperative delirium.

This prospective, randomized, parallel-group controlled trial aims to evaluate whether the addition of ultrasound-guided PENG block to spinal anesthesia reduces the incidence of postoperative delirium within 72 hours after primary total hip arthroplasty in patients aged 65 years or older. Delirium will be assessed using the Confusion Assessment Method (CAM) by blinded outcome assessors.

Secondary outcomes include postoperative opioid consumption, pain intensity (NRS), time to first rescue opioid, postoperative nausea and vomiting, time to mobilization, block-related adverse events, and perioperative inflammatory indices (neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, and monocyte-to-lymphocyte ratio).

The study will enroll 144 patients randomized 1:1 to spinal anesthesia alone or spinal anesthesia plus PENG block.

Postoperative delirium is a frequent and serious complication in older adults undergoing major orthopedic surgery, including total hip arthroplasty. Its incidence in this population ranges from 10% to 30% and is associated with prolonged hospital stay, increased healthcare costs, delayed functional recovery, long-term cognitive impairment, and increased mortality. Among modifiable perioperative risk factors, inadequate pain control, higher opioid consumption, postoperative nausea and vomiting, sleep disturbances, delayed mobilization, and systemic inflammatory response play an important role.

Regional anesthesia techniques may reduce delirium risk by improving analgesia, decreasing opioid requirements, and attenuating surgical stress and inflammatory response. The Pericapsular Nerve Group (PENG) block is an ultrasound-guided regional anesthesia technique targeting the articular branches supplying the anterior hip capsule. It has been shown to provide effective analgesia after hip surgery while largely preserving quadriceps motor function, potentially facilitating early mobilization.

This study is a prospective, randomized, parallel-group controlled trial designed to evaluate whether the addition of ultrasound-guided PENG block to spinal anesthesia reduces the incidence of postoperative delirium in patients aged 65 years or older undergoing primary elective total hip arthroplasty.

Eligible patients (ASA II-III) will be randomized in a 1:1 ratio to receive:

spinal anesthesia with standard multimodal postoperative analgesia (control group), or spinal anesthesia combined with ultrasound-guided PENG block plus standard multimodal postoperative analgesia (intervention group).

Randomization will be computer-generated with concealed allocation. Outcome assessors evaluating delirium and functional endpoints will be blinded to group assignment. The anesthesiologist performing the block cannot be blinded but will not participate in postoperative outcome assessment.

The primary endpoint is the incidence of postoperative delirium within 72 hours after surgery, assessed at least once daily using the Confusion Assessment Method (CAM) by trained, blinded personnel. Documentation review for delirium-related symptoms and use of antidelirium medications will complement, but not replace, structured CAM assessment.

Secondary endpoints include cumulative opioid consumption during the first 48 postoperative hours (expressed as morphine milligram equivalents), pain intensity at rest and during movement (Numeric Rating Scale), time to first rescue opioid administration, incidence of postoperative nausea and vomiting, time to first mobilization, and block-related adverse events.

Additionally, perioperative inflammatory response will be explored using routinely collected complete blood count parameters. Neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and monocyte-to-lymphocyte ratio (MLR) will be calculated at predefined time points (baseline, 24 hours, and 48 hours postoperatively). Exploratory analyses will assess associations between these inflammatory indices and postoperative delirium.

The planned sample size is 144 patients (72 per group), calculated to detect a clinically relevant reduction in delirium incidence with 80% power and a two-sided alpha of 0.05, accounting for potential dropouts.

The study will be conducted in accordance with the Declaration of Helsinki and Good Clinical Practice principles. Written informed consent will be obtained from all participants prior to enrollment.

Inclusion Criteria:

• Age ≥ 75 years
• Scheduled for elective primary total hip arthroplasty
• Planned spinal anesthesia
• ASA physical status II-III
• Ability to provide written informed consent
• Ability to communicate and reliably assess pain using the Numeric Rating Scale (NRS)
• Expected postoperative hospitalization ≥ 72 hours

Exclusion Criteria:

• Pre-existing delirium, acute psychosis, or active major psychiatric disorder
• Documented severe dementia or inability to provide informed consent
• Severe hearing or visual impairment preventing reliable CAM assessment
• Contraindications to regional anesthesia (e.g., coagulopathy according to institutional standards, infection at the injection site, allergy to local anesthetics)
• Pre-existing neurological deficits of the operative lower limb are interfering with assessment
• Chronic opioid use (>30 mg morphine milligram equivalents per day for >2 weeks prior to surgery)
• Severe renal impairment (eGFR <30 mL/min/1.73 m²)
• Severe hepatic insufficiency
• Participation in another interventional clinical trial within 30 days
• Any other condition that, in the investigator's judgment, may interfere with study participation or protocol adherence

De-identified individual participant data (IPD) underlying the results reported in publications (including demographic data, laboratory inflammatory indices such as SII, SIRI, AISI, CRP values, pain scores, opioid consumption, and time-to-event outcomes) will be made available to qualified researchers.

Data will be shared after removal of all direct identifiers in accordance with GDPR regulations and institutional data protection policies.

The study protocol, statistical analysis plan (SAP), and analytic code will also be available upon reasonable request.

Data will be provided for the purpose of secondary analyses, meta-analyses, or validation studies, subject to approval by the principal investigator and institutional review board, where applicable.

Data will become available 6 months after publication of the primary results and will remain available for 5 years.

A methodologically sound research proposal Institutional affiliation Ethical approval (if required) A signed data use agreement Requests should be directed to the principal investigator via institutional email.