Ropivacaine plasma levels following local infiltration analgesia for primary total hip arthroplasty

We measured total and free plasma concentrations of ropivacaine following high-volume, high-dose local infiltration analgesia in 19 patients aged 65 years or over undergoing unilateral total hip arthroplasty. The patients received 180 ml ropivacaine 0.2% (360 mg), which was injected into the deep and peri-capsular tissues, the gluteal muscles and fascia lata, and the subcutaneous tissues and skin. Patients were monitored for clinical symptoms and signs of systemic local anaesthetic toxicity. Total levels of plasma ropivacaine varied from 0.081 to 1.707 μg.ml ^-1 (mean (SD) 0.953 (0.323) μg.ml ^-1). Free levels of plasma ropivacaine varied from 0.000 to 0.053 μg.ml ^-1 (mean (SD) 0.024 (0.011) μg.ml ^-1). No samples reached the toxic threshold for venous ropivacaine concentration, although four patients exhibited mild symptoms consistent with local anaesthetic toxicity. One patient had episodes of complete heart block on ECG monitoring, but plasma ropivacaine levels were below toxic levels. We conclude that plasma levels for ropivacaine associated with toxicity in a volunteer population (total 2.2 μg.ml ^-1, free 0.15 μg.ml ^-1) are not reached during local infiltration analgesia for hip arthroplasty in elderly patients.