CPNB for AKA
I have done continuous blocks in the past for post-operative analgesia (and to mitigate the risks of persistent pain and phantom pain and a multitude of other potential benefits) for amputations and as the primary anesthetic for foot amputations and BKA’s many times in the past. I have more consistently been performing CPNB’s for AKA’s recently as the primary anesthetic and would like to pass on a few of the points that I have gathered along the way. [nonmember]…
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I will typically select a site for both the sciatic and femoral nerve block depending on the level of amputation. I usually attempt to go as distal as possible. One reason to go distally is that, many times, patients have severe peripheral vascular disease with a non-healing wound, and they are often anti-coagulated to various degrees. This precludes doing a spinal or epidural many times, and distal sites are generally less likely to run into bleeding issues. Again, this tip could highlight the same topic addressed in ‘Another Arrow in the Quiver’, but that is not where I want to take this one. Further, if a hematoma were to develop, I would prefer it to be in a more easily noticed location and easier to compress. Let me mention here again that I am not endorsing a more liberal stance than has been recently outlined by the ARSA Guidelines on Anti-coagulated Patients, and I am not recommending that you should perform nerve blocks in circumstances in which you are not experienced or familiar.
Beyond potential coagulation issues, more distal sites (such as saphenous over femoral) provide more targeted analgesia, possibly requiring less local anesthetic. When formulating your plan, however, do not forget to consider the possible use and position of a tourniquet. If the block is too far distal, tourniquet pain may become unbearable for a lengthy procedure. It may become more of a factor if the nerve block is also the primary anesthetic for the case.
I did not recognize how proximal the incisions in the soft tissue were going to be the first time I chose to do an AKA for a very frail and elderly patient utilizing continuous nerve blocks as the primary anesthetic. All was wonderful until the surgeon contacted an area in the distribution of the lateral femoral cutaneous nerve. The surgeon infiltrated a small area with local anesthetic, and we got through the rest of the case without incident. The patient did, however, have an elevated heart rate and blood pressure in response to the surgical stimulation, and that was one thing that I was trying hard to avoid.
Since that time, I have adjusted my technique to include a continuous fascia iliaca nerve block and sciatic nerve block that I place somewhere between a subgluteal and a mid-thigh (or a ‘very high’ popliteal) depending on the situation. Since the fascia iliaca block covers the obturator and lateral femoral cutaneous nerves along with the femoral nerve, I have been able to perform these cases with the patient somewhere between awake and sedated (or for various reasons with an airway in place) with little, if any, hemodynamic change. I feel much more comfortable placing a fascia iliaca block than I would with a lumbar plexus block in this patient population.
Since the nerve blocks are continuous, patients commonly bolus their catheters or take a few pain pills through the next few days…that is, if they do not have other sites that cause them pain. I did have a nurse tell me recently that one of my patients had significant trouble with foot pain overnight after his AKA that required significant intervention. As it turns out, the patient had claudication from severe blockages in the non-operative leg as well, and that was the cause of his pain. The patient had zero operative site pain. Certainly, his other leg needed to be addressed and treated as well, but that initial report (without further evaluation) could have led to inappropriate treatment (or just concern on my part about my skills). There are a few Tip of the Week topics that include some subtle points on this subject under ‘Block Evaluation’, but don’t forget the obvious. Remember to ask where the patient is hurting before you decide how well your block is working! More on that in a future Tip of the Week!
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