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Blood retransfusion following local analgesic for TKA may lead to toxic levels
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COPENHAGEN — Retransfusion of shed blood in patients following local infiltration analgesia during total knee arthroplasty may lead to toxic levels of analgesic, according to Dutch investigators.
“We used a postoperative drain system, as is traditional practice in our hospital, and we were wondering if with the use of local analgesia it was relatively safe to retransfuse the blood collected into the device,” Bregje Thomassen, MSc, said at the 12th EFORT Congress here.
Thomassen’s group studied 20 patients who had primary total knee arthroplasty and had undergone two intraoperative injections of ropivacaine (375 mg). Intra-articular retransfusion drains and wound catheters were used for continuous infusion of 8 mg/hr of ropivacaine for 24 hours. Any blood collected through the retransfusion device was used for laboratory analyses instead of being retransfused. Blood samples were taken immediately following surgery, and at 3-, 6- and 24-hours postoperatively.
The team used the 6-hour postoperative blood samples to predict cumulative ropivacaine concentrations, then used estimates of cumulative plasma concentrations to construct a model of instant retransfusion. Thomassen said the team used a safety threshold of 0.15 mg/L unbound ropivacaine per venous plasma sample.
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Total ropivacaine concentration was the highest at the 24-hour mark postoperatively, with unbound ropivacaine's maximal demonstration occurring at 6 hours postoperatively. Concentrations of ropivacaine ranged from 0.7 mg/L to 1.9 mg/L, Thomassen said, with unbound ropivacaine concentrations ranging between 0.03 mg/L and 0.11 mg/L. She also reported a 6-hour median shed blood volume of 600 mL, and a difference in free fraction ropivacaine amounts in shed blood (68.8%) and plasma (4.8%).
Thomassen said retransfusion would result in an average of 13 mg of unbound ropivacaine being intravenously administered – meaning instant retransfusion could lead to unbound venous plasma concentrations greater than 0.15 mg/L.
Thomassen said that local anesthetics in combination with infusion of ropivacaine is potentially safe, but noted that combining this process with shed blood retransfusion could lead to toxic levels. Therefore, formal testing would be required before the implementation of both modalities.
“We think that with the protocol utilized in our study, it is not safe to reintroduce shed blood in total knee arthroplasty,” Thomassen said.
Reference:
- Thomassen B, Pool L, van de Flier R, et al. Safety of retransfusing shed blood after local infiltration analgesia in total knee arthroplasty. Paper #2077. Presented at the 12th EFORT Congress 2011. June 1-4. Copenhagen.
- Disclosure: The authors received unrestricted grants from AstraZeneca and Baxter.
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