Safety of retransfusing shed blood after local infiltration analgesia in total knee arthroplasty.

We investigated the safety of LIA (local infiltration analgesia) combined with retransfusion of drained blood. Total knee arthroplasty patients received two peri-articular injections during surgery followed by continuous infusion, both with ropivacaine (567 mg). Ropivacaine plasma concentrations were determined in blood samples taken at 0, 3, 6 and 24 hours postoperatively. The collected shed blood was not retransfused, instead retransfusion was modelled by estimating the cumulative plasma concentrations at 6 hours postoperative. Total and unbound ropivacaine plasma concentrations ranged respectively from 0.08 to 1.9 mg/L and 0.003 to 0.11 mg/L. An average of 13.1 +/- 3.7 mg unbound ropivacaine would have been returned to the patient. The estimated cumulative ropivacaine plasma levels showed that instant retransfusion would have led to plasma levels below 0.26 mg/L. It appears to be safe to transfuse autologous blood in combination with LIA. However, before drawing definite conclusions formal measurement of actual concentrations is required.