This prospective observational study aims to investigate the role of the baseline perfusion index (PI) in predicting spinal anesthesia-induced hypotension (SAIH) in ASA I-II patients undergoing day-case knee arthroscopy.

Spinal anesthesia is a widely preferred technique for lower extremity surgeries, including knee arthroscopy. However, sympathetic blockade during spinal anesthesia frequently leads to significant hemodynamic instability, particularly hypotension, which can result in adverse perioperative outcomes. While age and baseline blood pressure are traditional risk factors, they often fail to accurately predict the onset of hypotension in healthy populations. The perfusion index (PI), a non-invasive parameter measured via pulse oximetry, reflects peripheral vascular tone and baseline sympathetic activity. An elevated baseline PI indicates baseline vasodilation and a higher susceptibility to sympathectomy, potentially offering an early and non-invasive prediction of SAIH before the hemodynamic collapse occurs.

The primary outcome of the study is the incidence of spinal anesthesia-induced hypotension (defined as a mean arterial pressure < 65 mmHg or a decrease in systolic blood pressure > 25% from baseline). Secondary outcomes include the onset time of sensory block, and intraoperative ephedrine and fluid requirements.