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| Frequently Asked Questions |
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| Category #17 - The knee joint |
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| TKR and Enoxaparin |
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What is your current protocol for use of Lovenox post-operatively for total knee replacement with a femoral catheter in place? Also, how do you achieve ambulation with a femoral catheter in place?
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Thank you for asking these interesting questions.
There are no data available in the literature to answer these questions so I will resort to giving you my personal opinion. Please note that this is a personal opinion.
The very reason for the development of continuous peripheral nerve blocks, especially for the lower extremity, was because the use of Lovenox increased worldwide and that limited our potential use of epidural catheters. The task force at the American Society of Regional Anesthesiologists recommended that continuous peripheral nerve blocks should be managed like neuraxial blocks and addressed the controversy around continuous nerve blocks. This is probably too cautious and even they admit that there is absolutely no data to support their views and statement (nor mine for that matter!!) and there are absolutely no case reports in this regard. There will also be no data in the foreseeable future, since problems due to anticoagulation is such a rare event, that it will require massive studies to evaluate.
It is therefore my contention that this is probably not too wise a statement by ASRA, but we are going to have to live with it, (at least for a while). My approach to this problem has served me very well and has always been to manage each and every patient as an individual by carefully balance the risks and benefits. If you balanced the risks and benefits for femoral nerve catheters, you will find that the risks are minuet and the benefits are huge for normal cases especially total knee replacement and ACL and therefore I do not have any problems placing a femoral catheter for total knee replacement patients, even if the patient were to receive Lovenox. I do, however, time the removal of the catheter as if it were a neuraxial catheter, although even this practice does not make much sense. My personal strategy and recommendation is therefore to carefully balance the risks and benefits of continuous peripheral nerve block for patients with total knee replacement; to be very aware that the patient understands the issues and gives me informed consent; to be sure that the surgeon understands the issues; and to remove the catheter at least 12 hours after the last injection of Lovenox or two hours before the next injection.
As a general principle regarding continuous peripheral nerve blocks and anticoagulation, I assume the strategy that the more peripheral the catheter the least the risk and visa versa. In other words, the more central the block, the less keen I am on placing catheters in the presence of anticoagulation. For example, a lumbar paravertebral block in my hands in an anticoagulated patient would need very specific, hard and clear benefits. On the other hand, popliteal catheter has a much lower risk and it would be easier to balance these risks against the benefits.
As a general rule, if I could get to a potential bleeding by applying external pressure such as in a peripheral nerve block, (femoral nerve block, sciatic nerve block, subgluteal block, axillary block, popliteal block), I would not hesitate to place catheters in the presence of anticoagulation if the indications are good. On the other hand, if I cannot get to the potential site of bleeding, (such as for cervical, thoracic or lumbar paravertebral blocks, supra or infraclavicular blocks, and even interscalene block) I would be much more hesitant to place peripheral nerve block catheters.
The second part of your question - how to achieve ambulation with femoral catheters in place is an interesting question for which there is no answer at present, but we are looking at different strategies. These unfortunately vary from patient to patient and again, like any other continuous peripheral nerve block, this has to be tailored to suite the needs of every individual patients. It will definitely be the same strategy for all patients, but a "default strategy" is a good place to start working from.
At the current state of our knowledge, we are not sure if preserving quadriceps muscle function is at all beneficial, there is absolutely no data on this matter but if one assumes that maintaining quadriceps muscle function in the post-operative period is advantageous for the rehabilitation of the patient, one could try to use lower concentrations of local anesthetic agents at lower infusion rates. For instance, we use 0.1% ropivacaine at an infusion rate of 0-3 mL per hour and a patient controlled regional anesthesia (PCRA) of 10 mL and a lockout time of one hour. This gives us almost no infusion when the patient needs to be ambulating but the patient has the opportunity to administer a bolus when ever he or she needs to be free of pain or does not need to ambulate, for example at night when he or she needs to sleep.
There is some ongoing work at the moment to evaluate the necessity of quadriceps muscle function preservation in our institution and we are also evaluating the effect of adding oral low dose gabapentin to the multimodal regimen combined with very low concentrations and infusion rates of local anesthetic agent.
I trust that you find these answers satisfactory and I invite to ask further questions to any of your preferred consultants on the website.
Yours sincerely,
André Boezaart
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Which catheter combination do you use for a knee scope?
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The knee receives most of its anterior innervation from the femoral nerve. The femoral nerve innervates the medial side of the tibia, while the lateral part of the tibia is innervated by the sciatic nerve. It also has contributions medially from the obturator nerve, and posteriorly from the sciatic nerve and laterally from the lateral cutaneous nerve of the thigh. If the proposed surgery is only a diagnostic knee arthroscopy, single injection femoral nerve block will likely be adequate, but the portal sites will most probably require infiltration. However, in the case of ligament or meniscus surgery, the contributions of the other nerves must be considered. In the case of ligament repair surgery, it is important to note that the ligament harvest site is often painful. We have had good success with sciatic nerve blocks, usually carried out from a subgluteal approach, in these cases.
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Can you tell me if there is more of a chance of nerve damage to do femoral nerve blocks post total knee replacement under spinal in the recovery room?
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There are only theoretical problems of nerve damage with doing blocks in the PACU after spinal, and these will always remain theoretical, since nobody will be able to do a large enough study to conclusively show a higher incidence of a complication that is so very rare. So, the practitioners must follow their beliefs and both scenarios can easily be defended. There are some theoretical objections against doing blocks in insensitive limbs. I, for one, don't believe these are valid objections, but you will here as many different opinions as you ask opinions.
A practical problem though, is that there are bandages on the leg and patella movements are not readily visible. This does make femoral nerve block a bit more difficult, although not impossible if you understand the implantation of the sartorius muscle is on the ASIS.
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The surgeons that I work with insist that quadriceps function is important for the rehabilitation of total knee replacement patients. What shall I tell them?
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We get literally hundreds of questions regarding quad function. The problem is that most orthopaedic surgeons and physical therapists believe (note "believe" and not "know") that quad function is important for rehab after knee replacement and ACL repair. There are studies ongoing to evaluate this belief, but in the meantime, while this is the prevailing wisdom, the challenge is to provide analgesia without causing a motor block to the quads. The other issue is also that it does not have to be an "all or nothing" situation. There are times when he patient does not need to ambulate and does not want to have pain, like at night while asleep for example. Other times, ambulation is important. Problem is that most of these old folks have to get up 2 AM to pee and they do not want to wake their partners and this is when they fall and break their hips or new knee prostheses. So, we have to juggle between these, and my preference is to either run a very small infusion of 0.1% ropivacaine (say 3 mL per hour) or no infusion at all and use only PCRA at boluses of say 10 mL and 60 minutes lockout times. If they then do wake at 2 AM with pain, they can ambulate to go for a pee and bolus the catheter again. That puts the patient in charge and he/she can ambulate when the need is there and rest when the need is there.
Furthermore, I think we should move away from long-acting drugs like ropivacaine and bupivacaine. We should use shorter acting drugs like lidocaine and mepivacaine for continuous infusions. The longer-acting drugs are remnants of the days when we did not yet know how to place catheters accurately. Now we know how to do that and short-acting drugs should be used. The ropivacaine manufacturers scared the living daylights out of us with this nerve damage story of lidocaine as the sevoflurane guys scared us with halothane hepatitis to sell their drugs. I think we should play around with various concentrations and infusion rates and PCRA doses of mepivacaine and lidocaine now.
There is no question that bupivacaine is about 8 times less expensive that ropivacaine, and frankly, at the very low concentrations and infusions that we now use, it does not really make a clinical difference which drug we use. The ropivacaine guys also scared us with this bupivacaine toxicity, but again, at the dosages and concentrations that we are using it, it should not be a factor. But, and that's the BIG BUT, your catheters have to be perfectly placed.
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