Blood Pressure and Pleth Variability Index as Predictors of Tourniquet-Release Hypotension in Elderly Patients Undergoing Total Knee Arthroplasty: A Prospective Observational Study

Background: Tourniquet release during total knee arthroplasty (TKA) can cause abrupt hypotension in elderly patients, but simple intraoperative predictors remain unclear. We evaluated whether blood pressure and the pleth variability index (PVi) predict tourniquet-release hypotension. Methods: In this prospective observational study, 90 elderly patients undergoing TKA with a thigh tourniquet were analyzed. Noninvasive blood pressure and PVi were recorded at predefined perioperative time points. The primary endpoint was hypotension after deflation, defined as mean blood pressure < 65 mmHg. Secondary exploratory endpoints were systolic blood pressure < 90 mmHg and a ≥20% decrease in systolic blood pressure from pre-release values. Results: The primary endpoint occurred in 28.9% of patients and was more common in those with lower pre-release blood pressure. In multivariable analysis, pre-release mean blood pressure and PVi measured immediately after intubation independently predicted hypotension, with odds ratios of 0.95 per 1 mmHg increase and 1.12 per 1-point increase, respectively. The combined model showed moderate discrimination (AUC = 0.71). Similar patterns were observed for systolic definitions, without clear associations with early postoperative complications or hospital length of stay. Conclusions: Lower pre-release mean blood pressure and higher intubation PVi may help identify elderly TKA patients at risk of tourniquet-release hypotension.