This study aims to investigate the hypothesis that ultrasonographic optic nerve sheath diameter (ONSD) measurement can help predict the development and severity of postdural puncture headache (PDPH) in patients undergoing spinal anesthesia for total knee arthroplasty. PDPH is defined as a headache that worsens in an upright position and improves while lying down.

This prospective observational study aims to investigate the role of ultrasonographically measured optic nerve sheath diameter (ONSD) in predicting the development and severity of post-dural puncture headache (PDPH) in patients undergoing total knee arthroplasty (TKA) under spinal anesthesia.

The study will include patients aged 18 to 65 years, with American Society of Anesthesiologists (ASA) physical status I or II, who are scheduled to undergo total knee prosthesis (TKP) surgery under spinal anesthesia, with successful administration using a 27G Quincke spinal needle on the first attempt. Exclusion criteria will include a history of central nervous system disorders (e.g., cerebrovascular diseases, intracranial hemorrhage, brain tumors), ophthalmological disorders, hypertension, hepatic encephalopathy, renal failure, pregnancy, history of chronic headache or migraine, obesity (body mass index >35 kg/m²), alcohol or substance dependence, psychiatric disorders, local infection at the injection site, allergy to local anesthetics, bleeding diathesis, requirement for sedation during the procedure, conditions that may impair postoperative cooperation (e.g., mental retardation, language acquisition deficits), and inability to obtain reliable optic nerve sheath diameter (ONSD) measurements.

Ultrasonographic ONSD measurements will be performed using a 7.5 MHz linear ultrasound probe preoperatively (baseline) and at 6, 12, 24, 36, and 48 hours postoperatively. PDPH will be defined as a headache that worsens in the sitting or standing position and improves when lying down. Headache severity will be assessed using the Numerical Rating Scale (NRS), in which patients rate their pain from 0 (no pain) to 10 (the worst pain imaginable). Postoperative pain related to surgery will also be assessed using the NRS, and the need for rescue analgesics will be documented (NRS ≥ 4). Intraoperative vital parameters, including heart rate and arterial blood pressure, will also be monitored. In addition to the incidence and severity of PDPH, associated symptoms (nausea, vomiting, photophobia, diplopia, auditory symptoms, neck pain, and dizziness) will be recorded. Patients who develop PDPH will be assigned to Group H, while those who do not will be assigned to Group C.

The primary aim of this study is to determine the diagnostic and prognostic value of ONSD measurements in predicting PDPH following spinal anesthesia.

Inclusion Criteria:

• Age between 18 and 65 years
• ASA physical status I or II
• Scheduled for total knee arthroplasty under spinal anesthesia
• Successful spinal anesthesia with a single attempt using a 27G Quincke spinal needle
• Provided informed consent to participate in the study

Exclusion Criteria:

• History of neurological or central nervous system disorders (e.g., cerebrovascular disease, intracranial hemorrhage, brain tumor)
• Ophthalmological disorders
• Hypertension
• Hepatic encephalopathy
• Renal failure
• Pregnancy
• History of chronic headaches or migraine
• Obesity (BMI > 35 kg/m²)
• Alcohol or substance abuse
• Psychiatric disorders
• Local infection at the injection site
• Allergy to local anesthetics
• Bleeding diathesis
• Requirement for sedation during the procedure
• Inability to cooperate postoperatively (e.g., mental retardation, language deficits)
• Inability to obtain reliable ONSD measurements

Patients aged 18 to 65 years undergoing total knee arthroplasty under spinal anesthesia.