Evaluation of Perfusion Index as a Predictor of Hypotension Following Spinal Anaesthesia in Lower Limb Orthopaedic Surgeries

Introduction: Subarachnoid block (SAB) is commonly used for lower limb and abdominal surgeries due to its benefits like reduced bleeding and good operative conditions. However, it can cause side effects like hypotension and bradycardia due to sympathetic blockade, reduced cardiac output, and peripheral blood pooling. Non-invasive blood pressure (NIBP) monitoring has limitations in detecting beat-to-beat perfusion variations. Perfusion index (PI), measured via pulse oximetry, assesses perfusion dynamics and may predict hypotension after subarachnoid block (SAB). This study aimed to determine if a baseline PI >3.5 predicts hypotension following spinal anesthesia. Perfusion index (PI), measured by pulse oximetry, reflects peripheral blood flow and vasomotor tone, influenced by factors like sympathetic tone, pain, and temperature. It indicates variations in blood volume and sympathetic vascular tone. PI changes with vasodilation and regional blocks, serving as a non-invasive marker of perfusion and sympathetic activity. Aims and Objectives: To evaluate the correlation between baseline perfusion index and incidence of hypotension following subarachnoid block in Lower limb orthopedic surgeries. Methodology: The study was conducted in Department of Anesthesiology, Gandhi Medical College Bhopal for a period of 1.5 years. This observational prospective cohort study involved 60 patients (aged 15-60, ASA grade I/II) undergoing lower limb orthopedic surgeries. Preoperative perfusion index (PI) was recorded, and various vital parameters were monitored during surgery. Subarachnoid block with 0.5% bupivacaine was administered, and blood pressure changes were compared to preoperative PI. Hypotension episodes were analyzed to assess PI's predictive value for intraoperative hypotension. Result: Demographic variables like age, weight, and surgery indication were similar across both groups and did not affect results. A significant difference in intraoperative blood pressure (SBP, DBP, MAP) was observed, with the PI >3.5 group showing a greater drop. Hypotension occurred in 73.3% of PI >3.5 patients versus 16.7% in PI <3.5 patients. Surgery duration and nausea/vomiting incidence were similar in both groups, with no respiratory distress or pruritus reported. Conclusion: The study found that a preoperative perfusion index (PI) >3.5 correlates with a higher incidence of intraoperative hypotension in lower limb orthopedic surgeries under spinal anesthesia compared to PI <3.5.