Anesthesia alters microcirculation and tissue oxygen saturation (StO2). We sought to examine changes in StO2 using near-infrared spectroscopy and a vascular occlusion test (VOT) during spinal anesthesia. This prospective observational study was included 51 patients without comorbidities who underwent elective surgery under spinal anesthesia. We measured the StO2 in the lower extremity during VOT before and after intrathecal injection.

The vascular occlusion test (VOT) procedure was conducted twice in each patient, before and 15 min after intrathecal injection. An near-infrared spectroscopy (NIRS) sensor (INVOSTM 5100C Cerebral/Somatic Oximeter; Medtronic, Minneapolis, MN, USA) was attached to the patient's gastrocnemius muscle. A tourniquet (A.T.S ® 3000 Automatic Tourniquet System; Zimmer Inc., Warsaw, IL, USA) was applied to the thigh and inflated to a pressure value 50 mmHg over the patient's baseline systolic blood pressure in the leg and maintained for 5 min. After a 5-min ischemic period, the tourniquet was rapidly deflated to 0 mmHg. The tissue oxygen saturation (StO2) data was continuously recorded during the VOT procedure. After confirmation of spinal anesthesia using cold sensitivity, the VOT procedure was repeated in the same manner as mentioned above. The occlusion slope and recovery slope were calculated based on the measured StO2 data. The occlusion slope was defined as the descending slope of StO2 value until it reached the minimum value. The recovery slope was calculated from the deflation of the tourniquet until the recovery of StO2 to the maximum value.

Inclusion Criteria:

• The patients who were scheduled for spinal anesthesia
• 18< age < 60 years old

Exclusion Criteria:

• American Society of Anesthesiologists physical status class > III,
• allergy or sensitivity to study medications,
• alcohol or drug abuse history,
• body mass index > 35 kg/ m2 or < 15 kg/m2,
• p regnancy or breastfeeding status,
• diabetes and on insulin treatment,
• untreated or uncontrolled arterial hypertension,
• peripheral arterial disease,
• corticosteroid treatment, coagulopathy, and lower limb deformities or burns
• patients who may not tolerate VOT

adult patients, 18\