Perioperative hypothermia is a common complication during total knee arthroplasty (TKA) and may increase the risk of shivering, delayed anesthetic recovery, and postoperative complications. This historical control study aims to evaluate the effectiveness and safety of intraoperative forced-air warming in preventing perioperative hypothermia in patients undergoing primary unilateral TKA.

A total of 240 patients were included. Patients in the historical control group received routine passive warming measures, while patients in the intervention group received additional forced-air warming during the perioperative period. Core body temperature, incidence of inadvertent perioperative hypothermia, anesthetic recovery outcomes, postoperative complications, and safety outcomes were evaluated.

This single-center historical control study was conducted at Shanghai 6th People's Hospital between May 2018 and December 2018 to evaluate the effectiveness of intraoperative forced-air warming for preventing perioperative hypothermia in patients undergoing total knee arthroplasty (TKA).

A total of 240 patients undergoing primary unilateral TKA were enrolled and divided into two groups according to the study period. Patients enrolled between May 2018 and August 2018 were assigned to the historical control group and received routine passive warming measures, including warmed intravenous fluids, warmed irrigation fluids, operating room temperature control, and cotton blanket coverage. Patients enrolled between September 2018 and December 2018 were assigned to the intervention group and received additional active warming using a forced-air warming system during the perioperative period.

The forced-air warming system was initiated 30 minutes before anesthesia induction and continued until transfer to the post-anesthesia care unit (PACU). Core temperature was continuously monitored using a temperature-sensing urinary catheter.

The primary outcomes included perioperative core temperature changes and the incidence of inadvertent perioperative hypothermia, defined as core temperature below 36°C at any perioperative time point. Secondary outcomes included postoperative shivering, emergence agitation, anesthetic recovery time, blood loss, postoperative complications, and safety outcomes including skin burns and surgical site infection.

This study was approved by the Ethics Committee of Shanghai 6th People's Hospital (Approval No. 05.12.19035). Written informed consent was obtained from all participants before enrollment.

Inclusion Criteria:

• Age between 60 and 85 years
• ASA physical status I or II
• Diagnosed with knee osteoarthritis
• Undergoing first unilateral primary total knee arthroplasty
• Able to provide written informed consent

Exclusion Criteria:

• Abnormal coagulation function (international normalized ratio >1.2)
• Preoperative body temperature >37.5°C or <36°C
• Cognitive or psychiatric disorders affecting communication
• Moderate or severe anemia
• Body mass index >30 kg/m² or <18.5 kg/m²
• Moderate or severe malnutrition
• Surgery duration longer than 4 hours
• Intraoperative blood loss greater than 500 mL
• Transfer to surgical intensive care unit after surgery

Individual participant data will not be publicly shared because the study involves retrospective clinical data and institutional privacy restrictions.

No masking was used because the forced-air warming intervention was visible to participants and care providers.