Plasma bupivacaine levels following single dose intraarticular instillation for arthroscopy

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Abstract
Arthroscopy of the knee was performed using 30 ml single dose intraarticular instillations of 0.5% or 0.25% solutions of bupivacaine (Marcaine). A total of 18 pa tients (mean age, 34 years), divided into two groups, participated in this study. Venous plasma levels were measured at 0, 10, 20, 30, 45, 60, 90, 120, and 240 minute intervals following a single instillation into the knee joint. All patients had suspected traumatic internal derangement of the knee. Electrocardiogram tracings, blood pressure, and neu rologic assessment were monitored at each venous sampling interval or more often if clinically indicated. The type and amount of supplemental anesthesia were also recorded. None of our 18 patients required a general anesthetic because of pain although the follow ing procedures were performed: meniscectomy, plica release, abrasion chondroplasty, loose body retrieval, and limited meniscal repair. A new methodology for the measurement of plasma bupivacaine using the gas chromatograph mass spectrometer is described. Mon itoring specific molecular mass fragments allows the measurement of picogram per milliliter levels of bupi vacaine. The highest peak plasma concentration occurred 20 minutes after instillation of 30 ml of 0.5% bupivacaine. The 625 ± 225 ng/ml level was well below the 2,500 to 4,000 ng/ml reported to elicit early subjective CNS symptoms of bupivacaine toxicity. Thus, a single dose intraarticular instillation of 30 ml 0.5% or 0.25% bupi vacaine is convenient, efficacious, and pharmacologi cally safe for routine clinical arthroscopy.