Physiologic and Clinical Sequelae After Pneumatic Tourniquet Release in Frail Patients Undergoing Total Knee Arthroplasty Under Regional Anesthesia: A Prospective Observational Study.

BACKGROUND

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.

METHODS

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, predeflation, and 1- to 30-minute postdeflation. 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, postanesthesia care unit (PACU) interventions, acute kidney injury, and hospital lengths of stay.

RESULTS

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 (MAP) decreased by 18% at three minutes postdeflation, 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. Acute kidney injury 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, 90 to 150), and the median hospital length of stay was five days (interquartile range, four to seven).

CONCLUSIONS

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 nonfrail cohorts. Proactive monitoring and early hemodynamic management are warranted to mitigate risk in this vulnerable population.