Safety of blood reinfusion after local infiltration analgesia with ropivacaine in total knee arthroplasty

Objective: The authors hypothesized that it is safe to combine local infiltration analgesia (LIA) in total knee arthroplasty (TKA) with a retransfusion drain since ropivacaine concentrations would not exceed the arterial toxicity threshold concentrations of 4.3 mg/L for total and 0.56 mg/L for unbound ropivacaine. Materials and methods: 22 patients scheduled for primary TKA were included. During surgery three peri-articular injections with ropivacaine (300 mg) were given. Plasma and shed blood samples were taken at 0, 1, 3, 6, 7, and 24 hours postoperatively. Results: At 6 hours postoperatively, the total ropivacaine plasma concentration ranged from 0.26 to 1.53 mg/L and unbound ropivacaine from 0.03 to 0.12 mg/L. At 7 hours, the total ropivacaine plasma concentration ranged from 0.19 to 1.71 mg/L and unbound ropivacaine from 0.02 to 0.09 mg/L. In the collected shed blood, a total of 0.27 to 12.8 mg (median 3.73 mg) unbound ropivacaine was present. Reinfusion would lead to an addition of 3.73 mg (median) unbound ropivacaine that would be reinfused into the patient. The calculated (modeled) estimation regarding the maximum unbound ropivacaine plasma concentration showed a median value of 0.114 mg/L (IQR: 0.09, 0.12 mg/L). All concentrations were well below reported toxicity thresholds. Conclusions: The combination of LIA and reinfusion presented herein are considered safe. However, differences in pain protocol lead to changes in the safety evaluation. Compared with previous studies, the technique of administration is of greater importance for the effect on unbound ropivacaine because of unknown mechanisms.