Plasma Concentration of Ropivacaine following Peri- and Intraarticular Injection

Introduction

Local infiltration analgesia (LIA) in total knee arthroplasty (TKA) often involves high doses of local anesthetics (LA), e.g. ropivacaine 400 mg periarticularly and 200 mg intraarticularly (1). The purpose of this study was to investigate the free (unbound) and total plasma concentrations of ropivacaine and possible systemic effects.

Fig 1

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Methods

In 8 ASA I – II patients aged 73 (55-85) yrs, weight 78 (55-97) kg undergoing TKA the LIA technique was performed in the following way: 400 mg ropivacaine, 30 mg ketorolac and 0.5 mg epinephrine were infiltrated by the surgeon into the soft tissues periarticularly during the operation (Fig 1). At 21 hours postoperatively, 200 mg ropivacaine, 30 mg ketorolac and 0.1 mg epinephrine were injected intraarticularly (Fig 2). Total and free concentrations of ropivacaine were analyzed using chromatography with a Zorbax SB-C18 column postoperatively after 15, 30, 60, 90, 120 and 180 minutes and just before and after the catheter injection at 15, 30, 60, 90, 120 and 180 minutes.

Results

The individual maximum free venous plasma concentration of ropivacaine varied between 0.032-0.121 µg/mL (Fig 3), which was far below those shown to be associated with mild CNS toxicity (2). The total plasma concentration showed increasing values (Fig 4), but the free concentration remained low (Fig 3). The free fraction expressed in percent was 4.4 ±1 (3.3–5.6), mean ±SD (range) % and decreased with time. Two patients had blood pressure fall during the first 12 postoperative hours (21% and 30% respectively). No bradycardia occurred in any patient. No patient had clinical symptoms of systemic LA toxicity.

Fig 3

Fig 4

1) Essving P. Reduced morphine consumption and pain intensity with local infiltration analgesia (LIA) following total knee arthroplasty. Acta orthop 2010;81 (3): 354-60.
2) K Knudsen. Central nervous and cardiovascular effects of iv infusions of ropivacaine, bupivacaine and placebo in volunteers. BJA 1997;78:507-514.