Physiologic and clinical sequelae after pneumatic tourniquet release in frail patients undergoing total knee arthroplasty under regional anesthesia: a prospective observational study.

Abstract

Tourniquet deflation during total knee arthroplasty (TKA) produces abrupt reperfusion physiology, including hyperkalemia, acidosis, and hemodynamic instability. Frail patients are particularly vulnerable; however, this population has not been prospectively studied. We conducted a prospective, observational study of frail adults (Clinical Frailty Scale ≥ 4) undergoing elective, unilateral, cemented TKA under spinal anesthesia with a pneumatic thigh tourniquet. There were 40 frail patients (mean age, 76 years [range, 65 to 88]; 65% women) included. Tourniquet duration averaged 84 minutes (range, 70 to 96). Patients with baseline hyperkalemia, severe renal dysfunction, significant arrhythmias, or planned revision or bilateral arthroplasty were excluded. Hemodynamics and arterial blood gases (pH, PaCO₂, lactate, potassium, and electrolytes) were recorded at baseline, pre-deflation, and one to 30 minutes post-deflation. The primary endpoint was the change in serum potassium after tourniquet release, and hemodynamic instability was analyzed as a key clinical outcome. The secondary outcomes included the incidence of hyperkalemia (≥ 5.5 mmol/L), acidosis (pH less than 7.30), hypotension, arrhythmias, post-anesthesia care unit (PACU) interventions, acute kidney injury (AKI), and hospital lengths of stay (LOS). After deflation, serum potassium rose from 4.3 ± 0.3 to 4.8 ± 0.4 mmol/L at five minutes (P < 0.001), peaking at 4.9 ± 0.4 mmol/L at 10 minutes (mean change, +0.5 mmol/L). Lactate increased from 1.2 ± 0.5 to 2.8 ± 0.9 mmol/L (P < 0.001). The mean arterial pressure decreased by 18% at three minutes post-deflation, with hypotension requiring vasopressors in 30% of patients. Hyperkalemia (≥ 5.5 mmol/L) occurred in three of 40 patients (7.5%), all within 10 minutes of deflation. Acidosis (pH < 7.30) was seen in four of 40 (10%). There were no sustained arrhythmias or cardiac arrests. In the PACU, 28% required vasopressor boluses, 15% received antiemetic treatment, and 10% required prolonged oxygen supplementation. AKI developed in two of 40 patients (5%) within 48 hours. Tourniquet duration was not significantly correlated with potassium change or hypotension (P > 0.05). The median PACU stay was 115 minutes (interquartile range [IQR], 90 to 150), and the median hospital LOS was five days (IQR, four to seven). In frail patients undergoing TKA, tourniquet release caused significant, but transient increases in potassium and lactate, accompanied by frequent hypotension requiring intervention. Although severe complications were uncommon, physiologic derangements were more pronounced than those observed in non-frail cohorts. Proactive monitoring and early hemodynamic management are warranted to mitigate risk in this vulnerable population.