A Long Axis Approach to the Femoral Artery Block (FAB) for Managing Tourniquet Pain and Hypertension in Below-the-Knee Fracture Surgery

Tourniquet application during lower limb orthopedic surgery is associated with significant hemodynamic responses, including pain and tourniquet-induced hypertension (TH), which may increase perioperative cardiovascular risk. Femoral artery block (FAB) is a novel ultrasound-guided regional anesthesia technique targeting the perivascular sympathetic plexus surrounding the femoral artery to attenuate these responses. Previous studies have described FAB using a short-axis in-plane ultrasound approach. This study proposes a novel long-axis in-plane ultrasound technique, hypothesizing that longitudinal visualization of the femoral artery may improve anatomical alignment with perivascular sympathetic structures, resulting in more effective sympathetic blockade, improved safety, and enhanced clinical efficacy. This is a prospective, randomized, double-blind controlled trial including adult patients (ASA I-III) scheduled for below-the-knee fracture surgery requiring tourniquet application for at least 45 minutes. After informed consent and baseline assessment, patients will be randomized into three groups: (1) short-axis FAB with ropivacaine, (2) long-axis FAB with ropivacaine, and (3) control group receiving normal saline injection. All patients will receive standardized anesthetic management including sciatic nerve block at the popliteal level and total intravenous anesthesia using propofol and remifentanil via Target-Controlled Infusion (TCI) under BIS monitoring. Hemodynamic variables (blood pressure and heart rate) will be recorded at predefined intraoperative and postoperative time points. Tourniquet-induced hypertension will be defined as a \>30% increase in systolic blood pressure from baseline. Secondary outcomes include intraoperative opioid and vasopressor requirements, incidence of femoral and saphenous nerve spread, procedural performance metrics (imaging and needling time), postoperative pain scores (VAS), and opioid consumption in the recovery unit. Data will be analyzed using repeated-measures and comparative statistical models to evaluate differences between groups over time and between interventions.