Comparison of the Effects of General Anesthesia and Spinal Anesthesia on Tissue Perfusion in Patients Undergoing Lower Extremity Surgery

Comparison of the Effects of Anesthesia Techniques on Tissue Perfusion in Patients Undergoing Lower Extremity Surgery With Tourniquet Use

This prospective, single-center observational study compares the effects of general anesthesia and spinal anesthesia on tissue perfusion in patients undergoing lower extremity surgery with tourniquet use. Tissue oxygenation in the limb distal to the tourniquet is monitored noninvasively using near-infrared spectroscopy (NIRS), and perfusion loss is quantified using an area-under-the-curve (AUC) approach. The primary objective is to evaluate whether spinal anesthesia better preserves distal tissue oxygenation during tourniquet inflation compared with general anesthesia. Secondary objectives are to assess reperfusion response after tourniquet release using changes in NIRS values at 20 minutes relative to baseline, the presence of early hyperemia (rSO₂ overshoot), and the association between tourniquet duration and perfusion loss. Additional exploratory analyses evaluate selected metabolic and inflammatory markers, including pH, lactate, and potassium.

Inclusion Criteria:

• Age 18 to 65 years
• Scheduled for elective lower extremity orthopedic surgery
• ASA physical status I or II
• Expected operation duration 30 to 120 minutes
• Expected tourniquet duration 30 to 90 minutes
• Informed about the anesthesia method and agreed to participate voluntarily
• No contraindication to neuraxial block

Exclusion Criteria:

• Refusal to participate
• History of peripheral arterial disease, diabetic neuropathy, or advanced vascular insufficiency
• Severe or uncontrolled systemic disease, including ASA III or higher
• Coagulopathy, local infection, or contraindication to spinal anesthesia
• Body mass index greater than 35 kg/m²
• Pregnancy or impaired consciousness
• Intraoperative hemodynamic instability or anticipated instability
• Need for additional intraoperative sedative or analgesic medication
• Inability to obtain adequate and reliable NIRS signal for technical reasons