Baseline perfusion index as a predictor of hypotension following spinal anaesthesia in elderly patients undergoing lower limb orthopaedic surgery

Background and Aims: Hypotension is a frequent and clinically significant complication of spinal anaesthesia, with a heightened incidence in elderly patients due to diminished baroreceptor reflex compensation. Intermittent non-invasive blood pressure (NIBP) monitoring provides delayed detection. The Perfusion Index (PI), a non-invasive and continuous measure of peripheral perfusion, may serve as an early haemodynamic indicator and potential predictor of hypotension. This study aimed to evaluate the relationship between baseline PI and the incidence of hypotension in elderly patients undergoing lower limb orthopaedic surgery under spinal anaesthesia. Secondary objectives were to assess if intraoperative PI changes precede NIBP-defined hypotension and to observe the response of PI to vasopressor administration.Materials and Methods: In this prospective observational study, 64 patients aged ≥60 years scheduled for lower limb surgery under subarachnoid block were allocated into two groups based on their baseline PI: Group A (PI >3.5, n=32) and Group B (PI ≤3.5, n=32). The primary outcome was the incidence of hypotension, defined as a >20% decrease from pre-anaesthetic systolic blood pressure. Data were analyzed using the Mann-Whitney U test for non-normally distributed variables, independent t-test for normally distributed data, and Wilcoxon signed-rank test for intra-group comparisons over time. Diagnostic accuracy of a high baseline PI (>3.5) for predicting hypotension was calculated.Results: The incidence of hypotension was significantly higher in Group A (32/32, 100%) compared to Group B (7/32, 21.9%; p < 0.0001). Group A also experienced a greater number of hypotensive episodes. A baseline PI >3.5 predicted hypotension with a sensitivity of 82.1% (95% CI: 66.5–92.5%), specificity of 100% (95% CI: 86.3–100%), and an area under the curve (AUC) of 0.91 (95% CI: 0.81–0.97). The positive and negative predictive values were 100% and 78.1%, respectively.Conclusion: A baseline Perfusion Index >3.5 is a highly specific and sensitive non-invasive predictor for the development of hypotension in elderly patients under spinal anaesthesia. While intraoperative PI changes are associated with hypotension, they do not reliably precede its onset as measured by NIBP. Therefore, the clinical utility of PI lies in pre-operative risk assessment rather than in providing a pre-emptive intraoperative warning.