Spinal anesthesia is commonly used in transurethral prostate resection (TUR-P) surgeries; however, post-spinal hypotension remains a frequent and clinically significant complication, particularly in elderly patients. Early prediction of hypotension may allow timely interventions and improve patient safety.

This prospective observational study aims to evaluate the predictive value of preoperative ultrasound-based inferior vena cava collapsibility index (IVC-CI) and femoral vein collapsibility index (FVCI) for post-spinal hypotension in patients undergoing elective TUR-P under spinal anesthesia. Before spinal anesthesia, IVC and femoral vein measurements will be obtained using ultrasonography. Hemodynamic parameters will be recorded before and after spinal anesthesia, and the occurrence of hypotension will be assessed according to predefined criteria.

The study seeks to compare the diagnostic performance of IVC-CI and FVCI in predicting post-spinal hypotension and to identify potential clinical predictors associated with hypotension in this patient population.

This study is designed as a prospective observational study conducted at the University of Health Sciences, Antalya Training and Research Hospital. The study will include adult patients scheduled for elective transurethral prostate resection (TUR-P) under spinal anesthesia.

Spinal anesthesia is frequently preferred in TUR-P procedures; however, post-spinal hypotension is a common complication, particularly in elderly patients and those with limited physiological reserve. Hypotension following spinal anesthesia is primarily caused by sympathetic blockade, leading to reduced vascular tone and venous return. Early identification of patients at risk for hypotension may enable timely preventive and therapeutic interventions and reduce perioperative morbidity.

Prior to spinal anesthesia, all eligible patients will undergo ultrasonographic assessment of the inferior vena cava (IVC) and femoral vein while in the supine position. Measurements will be performed using a convex ultrasound probe in M-mode. The maximum and minimum diameters of the IVC and femoral vein during the same respiratory cycle will be recorded, and the collapsibility indices will be calculated using standardized formulas.

No fluid preload will be administered before spinal anesthesia. Standard monitoring, including electrocardiography, oxygen saturation, and noninvasive or invasive blood pressure monitoring when clinically indicated, will be applied. Baseline heart rate and blood pressure values will be recorded immediately before spinal anesthesia. Following spinal anesthesia, hemodynamic parameters will be recorded at two-minute intervals for a total duration of 15 minutes.

Post-spinal hypotension will be defined as a systolic blood pressure less than 90 mmHg, a decrease in systolic blood pressure greater than 30% from baseline, or a mean arterial pressure below 60 mmHg. Patients will be categorized into hypotension and non-hypotension groups based on these criteria. Severe or prolonged hypotension episodes will be treated according to standard clinical practice.

The primary objective of the study is to evaluate the predictive value of the inferior vena cava collapsibility index (IVC-CI) and femoral vein collapsibility index (FVCI) for post-spinal hypotension. Secondary objectives include comparing the diagnostic performance of these two indices and identifying additional clinical predictors associated with hypotension. The findings of this study may contribute to the identification of a practical and noninvasive method for predicting post-spinal hypotension in patients undergoing TUR-P.

Inclusion Criteria:

• Adult patients aged 18-75 years
• American Society of Anesthesiologists (ASA) physical status I-III
• Scheduled for elective transurethral resection of the prostate (TUR-P)
• Planned spinal anesthesia
• Ability to provide written informed consent

Exclusion Criteria:

• Refusal to participate in the study
• Body mass index (BMI) >30 kg/m²
• Use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers
• Emergency surgery
• Baseline systolic arterial blood pressure <90 mmHg or mean arterial pressure <70 mmHg
• Major peripheral vascular disease or severe cardiovascular disease
• Unstable angina or left ventricular ejection fraction <40%
• Chronic respiratory disease
• Increased intra-abdominal pressure
• Autonomic nervous system disorders
• Implanted pacemaker or implantable cardioverter-defibrillator
• Anticipated difficult airway
• Cognitive impairment or inability to cooperate

The study population consists of adult male patients aged 18-75 years with American Society of Anesthesiologists (ASA) physical status I-III who are scheduled to undergo elective transurethral resection of the prostate (TUR-P) under spinal anesthesia. All participants will be recruited from a single tertiary care center. Patients will be evaluated preoperatively, and eligible individuals who provide written informed consent will be included in the study.