Continuous analgesia with a femoral catheter: plexus or femoral nerve blockade?

Objective: To evaluate the spread and quality of sensitive blockade produced by continuous and prolonged use of a femoral catheter inserted for postoperative analgesia. Study design: Prospective non comparative evaluation. Patients: The study included 20 consecutive patients undergoing major knee surgery with postoperative analgesia obtained with a femoral catheter, a technique commonly used in our department. Methods: Regional analgesia was induced after surgery with a bolus injection of 30 mt of 2% lidocaine with 1:200,000 epinephrine 1 in 200,000, maintained by continuous infusion of 1% lidocaine + morphine 0.03 mg.ml(-1) + clonidine 2 mu g ml(-1) for 48 h. The infusion rate was 0.1 mL.kg(-1).h(-1). The evaluation was based on: 1) the quality of analgesia at rest, at 30 min, hi, h3, h6, h12, h24 and h48; 2) the sensitive and motor blockade at the same time intervals. Results: A "3 in 1" block was only observed in 50% of patients after the initial bolus via the femoral catheter. During the maintenance of analgesia with a continuous infusion a blockade of the three main nerves of the lumbar plexus occurred in less than 20% of patients after 6 h and was limited to the territory of the femoral nerve in 45 to 50% of patients after 12 to 48 h. In all cases the median values of VAS were below 42 mm. Conclusion: In most patients, a local anaesthetic administered continuously via a femoral catheter produces a blockade limited to the femoral nerve. These data do not substantiate the conclusions by those who consider they are producing a continuous "3 in 1" block with this technique. However. it is obviously not essential to produce a sensitive blockade of the three main nerves of the lumbar plexus to obtain an effective analgesia after knee surgery. (C) 1998 Elsevier, Paris.