| Frequently Asked Questions |
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| Category #8 - Femoral nerve block |
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Which way do you thread the catheter for a femoral block?
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We thread femoral catheters proximally, toward the lumbar plexus. In fact, it is not uncommon to be able to stimulate (and subsequently provide analgesia to) the obturator nerve from the femoral approach. We do, however, recommend advancing the catheter only 3-5 cm beyond the needle tip for all blocks. The femoral nerve splits into its seven branches distally and distal threading will cause the catheter to settle on one of these peripheral nerves.
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A number of my associates would prefer to use the continuous femoral nerve block for total knees, but are fearful of the subsequent occurrence of femoral neuropathy or femoral neuralgia. Is this concern a legitimate? I would appreciate your thoughts on this matter. Thank you.
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I have never tried to popularize psoas compartment blocks for knee surgery. As a matter of fact, I think it is a relatively dangerous block that requires very hard indications before it is done. I think it is done far too easy by inexperienced people, and from there the flurry of complications and medico-legal cases that we are seeing at present. The problem with the psoas compartment block is that it is so easy to do ad it works so well. Knee and primary hip replacements are very soft indications. Hard indications would be revision hip replacement, pelvic osteotomy, etc.
I am a big proponent of continuous femoral nerve block (CFNB) for anterior knee surgery and, in part, for major ankle surgery (For the latter it has to be done together with a continuous sciatic nerve block). The CFNB is excellent for this, the complications are almost non-existing, but the catheter HAS to be properly placed with a nerve stimulator. The old-fashioned 3-in-1 and "fascia iliaca" blocks or other "blind" catheter placement techniques are simply not good enough and a waste of time. Approximately 20% of patients with CFNB for TKR will complain of posterior knee pain, and this is usually short-lived pain and treatable with NSAID's. If it remains a problem and the surgeon is not nervous about a drop foot, a single injection sciatic nerve block takes care of this pain. The obturator nerve, however, has to be blocked with the femoral nerve. Our standard technique for TKR and ACL is CFNB followed by spinal anesthesia and intra-op sedation with Demerol and Midazolam depending on the patient's requirements. We also have Bosé noise cancellation earphones and iPods with the music of the patient's choice for the intra-op hammering. If time is a problem, we pace the spinal and then do the CFNB in the recovery room postoperative.
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What is your experience on the value of femoral nerve catheters for post-op pain management for patients undergoing anterior cruciate ligament repair?
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It is great and we do it all the time. Mostly, though, especially if a graft is taken from the hamstrings, a subgluteal single-injection sciatic block is also needed. This is the ideal situation to send a patient home with a catheter in place. See Tutorials # 10 - "CPNB at Home".
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Do you have any experience with PCRA for continuous femoral blocks?
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Yes, love it. We do it all the time. Use a background infusion of 5 ml/h (1/4 strength) and then patient controlled boluses of 10 ml every 60 minutes. It is good to limit the PCRA boluses to say 3 - 4 per 4 hr period. Another way to do this is to omit the background infusion and just use the boluses. Patients (or nurses or MD's) must use the boluses at least 30 minutes before PT sessions. I also like the continuous FNB combined with a single shot sciatic, which is normally long lasting. Our problem here is that our main surgeon is very hypertensive about checking for foot movements postop and he gets really nervous if we block the sciatic before he checked it. Most patients don't need the sciatic in any case, so we only place it prn postop (lateral approach).
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