To analyze the relationship between tourniquet pressure and intraoperative blood loss, systolic pressure, body mass index (BMI) and other factors during total knee arthroplasty (TKA), and to provide reference for improving the safety of tourniquet use.

A retrospective study was conducted on consecutive series of primary TKA in the Second Affiliated Hospital of Guangzhou University of Traditional Chinese Medicine from January 2019 to December 2019.The patients who had undergone primary total knee replacement were included, those with unicondylar knee replacement and complex secondary knee revision were excluded. Demographic data, tourniquet pressure, tourniquet time, operation time, and intraoperative blood loss were collected. (±s)or M(P₂₅, P₇₅)were used for data description, and Spearman's correlation analysis was used. Rank sum test (Kruskal-Wallis H test) was used for comparison of blood pressure at eight observation time points: blood pressure measured one day before surgery (T1), before anesthesia (the first time in the operating room) (T2), after anesthesia (T3), before tourniquet inflation (T4), tourniquet inflation two minutes (T5), tourniquet inflation 10 min (T6), before tourniquet deflation (T7), tourniquet deflation 10 min (T8).

A total of 475 patients were enrolled. The tourniquet time was 52 (41, 62) min, the operation time was 96 (85, 115) min, and the intraoperative blood loss was 50 (50, 50) ml. There was a positive correlation between tourniquet pressure and body mass index (BMI) (r_s=0.283, P<0.01). The systolic pressure differences among different tourniquet pressure groups were statistically significant at T2, T4, T5 and T7 (H=11.077, P=0.004; H=19.688, P<0.001; H=10.326, P=0.006; H=9.103, P<0.01). There was no intraoperative blood transfusion, no skin or tissue compression injury, deep vein thrombosis, nor other complication occurred after the surgery.

There is a positive correlation between BMI and tourniquet pressure, suggesting that patients' BMI should be considered in setting tourniquet pressure. Tourniquet pressure changed the distribution of blood volume in the circulatory system after the tourniquet blocked lower extremity blood flow, the level of tourniquet pressure is related to the change of systolic pressure during the operation, and attention should be paid to the changes of systolic pressure.