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Blocks under General Anesthesia

Question:
“I am an experienced regional anesthesiologist living in New Zealand with about 600 interscalene catheters to my credit. I lately do these in the operating room under general anesthesia. But I still use the B Braun Tuohy Contiplex kit. I recite the catheter in the PACU if it has failed and of my last 50, I had five failures in the PACU of which three were uneventfully recited.

My question is that I am reluctant to change what I am doing in terms of sedation versus general anesthesia when I’ve gotten to the point of a pretty good success rate. What are your thoughts on this?”

Answer:

Thank you asking this interesting question. This topic has been debated in the literature, especially the British literature, and the bottom line is that there is no specific answer, (and in my humble opinion, it does not matter!)  since it will not be possible to research such a extremely infrequent event as nerve damage due to nerve block. Nerve damage due to continuous nerve block has never been seen, although it has been suggested.

If we have learned one thing from ultrasound and regional anesthesia it is that, unless the nerve is transfixed like the ulnar nerve in the sulcus ulnaris, it is extremely hard to place a needle inside a nerve. It is even more impossible to place a Tuohy needle inside a nerve not to even mention a bullet-tipped catheter. We have tried in pigs to place these needles and catheters inside nerves under direct vision without any success.

Having said that, as you well know, the nerves as they come out of the neuroforamens of the vertebrae are surrounded by dura and penetration of the dura is possible and even likely if a sharp thin needle is used. This is the reason why we advocate and use the thickest and bluntest needles that are available.

Your comments about the B Braun Contiplex needles need no further discussion. What you need to decide is if you want the block to work or not. If the answer is that you would like the block to work, then obviously the best approach would be to use either ultrasound or a stimulating catheter. Considering all the mishaps out there, I am rigidly oposed to doing blocks that do not have to work.  If a block does not HAVE to work, for Goodness sake, don’t do the block.  If it HAS to work, do it properly.  In YOUR hands 5 of 50 (6%) might sound like a small number, but in your introductory sentence you say you are an experience practitioner.  Can you imagine what this number would look like in less experienced hand?  Does 60% sound far fetched?  I don’t think so.

I personally do not have much experience or faith in the ultrasound technique for placing catheters at present.  I have to rely on what experts like Vincent Chan and Su Ganapathy tell me.  They place the needle with ultrasound and the catheter with stimulation.  I think at this current (2009) stage of our knowledge that is the best practice.  As far as ultrasound in general goes, the high frequency probes that we currently have readily available do not have deep tissue penetration, and give us great assistance in the superficial nerve where you do not need assistance, but when it comes to the deeper nerve, this is where it handsomely fails you. The resolution of the low frequency probes are just not good enough yet.

I personally do not use non-stimulating catheters. When we started off in the Cape Shoulder Institute with continuous nerve blocks, we also used the Contiplex system and we were disgusted (bordering on apauled) by our failure rate, which was even worse than your 10%. We approached 40%, and that is the experience of most people that honestly measure their secondary failure rate. Your 10% should be approaching zero if you, like we did, changed to a stimulating catheter technique. All 16 of the nerve blocks described on the movies and tutorials on this website and the RAEducation.com website are done with stimulating catheters and that should give you a good idea of where I stand in this matter.

To answer your question regarding placing blocks under general anesthesia, this is purely a question of semantics. All blocks are done under some form of anesthesia; some under general anesthesia, some under regional anesthesia, some under local anesthesia, and some even under topical anesthesia (eye blocks). You know examples of each, but retrobulbar blocks, for example, are done under topical anesthesia while I do interscalene blocks under regional anesthesia after blocking the superficial cervical plexus. There are good arguments for doing blocks awake or asleep, and all these arguments are based on opinions and emotions and not on scientific facts.

I am of the opinion that every single patient should be managed as an individual and the anesthetic appropriate for that patient should be used to place a block – being that general anesthesia or topical anesthesia or anything in-between. I personally do not think it is at all necessary to put patients under general anesthesia for routine blocks and if you view the movies on the website, all these blocks have been done on volunteers that are totally un-sedated and un-anesthetized. That certainly represents the bulk of our routine practice. I, however, have absolutely no problems placing a block in an anesthetized patient if it is necessary. Conditions that make this necessary include: children, severe anxiety, severe pain with movement of the limbs such as following fractures, etc. I do, however, explain to the patient that there is a notion, which is unproven and scientifically unjustified that there might be a higher complication rate if you did the blocks after induction of anesthesia (and which I personally do not believe is true). I make sure that the patient gives me his or her consent to continue with the block under general anesthesia. The most common reason for pain experienced by nerve blocks is anxiety, and I therefore make liberal use of short-acting anxiolytic agents like midazolam.

Another indication for performing blocks under general anesthesia, is the nature of your practice and it was my practice with the first 4,700 interscalene catheters to place blocks under GA simply because it suited the high turnover nature of our shoulder practice at that stage and we had one surgeon working in two operating rooms. At the moment, where I work, we have residents and nurses to help us and time in our academic institution is not of too much concern.

Your referred to the paper that I published on cervical paravertebral approach where I offered the patient a choice for block under general anesthesia with the understanding that there may be a higher risk of nerve blocks. I trust that you now understand that I do not personally believe this, but we will never know. This does, however, happen to be the current prevailing wisdom in the United States. In the United States also, as you note, there is a quite vastly different medical legal climate than you are fortunate enough to experience in New Zealand at present.

Ultimately, you need to treat the patient and not your practice nor your bank account at least of all, the surgeon or the medical legal system of your country. I think your chances of doing an intraneural injection with a catheter, is negligibly low and the only change I would make to your practice, is to suggest that you get rid of the 10% failures by using stimulating catheters.

A P Boezaart

Question:
I know your thoughts on performing interscalene blocks on anesthetized patients (that is probably save when performed properly). I have performed most of my interscalene catheters in anesthetized patients and haven’t  had any persistent neuropathies. Is it your feeling that a catheter placed via a 17 or 18-gauge Tuohy needle with particular attention to minimum current levels and ejection pressure is associated with an exceeding low risk of intraneural injection?

Answer:
Thank you for this interesting question.

This debate has been ongoing for some years now. I am of the opinion that it does not matter as long as you carefully balance the risks with the benefits. It is highly unlikely, in my opinion, that you can place catheters intraneurally through any needle but certainly even more unlikely if you use a 17 or 18-gauge Tuohy needle. The injection pressure through the catheter is of no consequence and I think pressure  applies only to single injection nerve blocks when thinner and sharper needles are used. If anything was taught to us by ultrasound, it is that placing a needle into a nerve fascicle is exceedingly difficult.  It also taught us that placement outside peripheral nerve fascicles but deep to the epineurium is probably safe.  At the ROOT level, this is TOTALLY another story.  Please read my editorial in the Jan/Feb 2009 issue of Reg Anesth Pain Med.  (Boezaart AP. That which we call a rose by any other name would smell as sweet – and its thorns would hurt as much. Reg Anest Pain Med 2009; 34(1): 3 – 7).  Also Read Boezaart AP Franco CD. Thin sharp needles around the dura. Reg Anesth Pain Med 2006; 32(4): 338 – 339).

Having said all that, we default on placing all our catheters in awake un-anesthetized patients simply because it is seldom necessary to place patients under general anesthesia for blocks, and like everything else in medicine, the higher the indications, the lower the complications! (and visa versa).  The most common cause of pain during any peripheral nerve block, being that continuous or single injection nerve block, is anxiety and I personally make liberal use of midazolam to treat this anxiety. For example, in a moderately nervous patient, I start with 4 mg of Midazolam and I have absolutely no problem increasing this if necessary.

Obviously, for patients with painful conditions such as fractures or dislocations, it is necessary that the block be done under general anesthesia or heavy sedation. I am a big fan of remifentanil for this and I use 0.3 – 0.5 µg/kg for this with excellent results. I sometimes combine this with midazolam but I am aware of the respiratory depression potential. I monitor the patient carefully with a “Divided Cannula” and capnography, and I am prepared to assist the ventilation of the patient if required. Obviously, children are in a category of their own and we usually do not perform any blocks on children if not fully anesthetized. There is absolutely no benefit in placing a peripheral nerve block, or any other block for that matter, in a screaming anxious child. It teaches you absolutely nothing and the only thing that you achieve by this is frightening the child and the parents of the child.

To summarize, I have no problem placing a peripheral nerve block, being that a single injection or continuous injection, in anesthetized patients if this is indicated. I am also of strong belief that every patient should be treated as an individual and the pros and cons of placing blocks under any form of anesthesia (general, regional, local or topical), should be carefully balanced and the risks and benefits carefully considered and explained to the patient. If it is your opinion that there is higher risks of placing a block under general anesthesia, (which by the way is not my opinion), this should also be made clear to the patient and the patient’s consent should be sought for doing this.

Again: All blocks are done under some form of anesthesia, some under general anesthesia, some under regional anesthesia (for example, interscalene blocks under superficial cervical plexus block), some under local anesthesia (like most peripheral nerve blocks), and some even under topical anesthesia (for example, retrobulbar blocks). Which one of these anesthetic techniques you choose depends on the appropriateness of the situation and the preference of the operator and the patient.

I trust that this satisfactorily answers your question. Please feel free to direct any further questions to me personally or via the website to any of the consultants listed there.

Yours sincerely,

Andre Boezaart

Question:
What are your opinions on doing blocks asleep?

Answer:
We do not feel that the absence of patient discomfort (paresthesia) protects against intraneural injection of local anesthetics, since the drug that is injected is usually a local anesthetic agent, which anesthetizes the nerve immediately and renders the intraneural injection free of pain. It is certainly the case that the reports of pain on intraneural injection of contrast material from the radiology literature are true. However, when local anesthetics are injected, the sodium channels are instantaneously blocked. We see this everyday when stimulating nerves immediately stop muscle twitching and thus motor function of the nerve with local anesthetic infusion. While we understand that the electrical property at work here is the dissipation of the current density, it is also true that the motor nerve conduction is blocked. If this is the case, and it is, the sensory component of the same nerve is also blocked. Therefore, the patient will not feel pain when injecting a local anesthetic intraneurally. This does not hold true when performing retro-bulbar block (which is a root level lock),  however. In the case of retrobulbar block, patients will certainly feel pain when the dura, which surrounds the optic nerve, is contacted with a needle. Therefore, the only blocks in which it is truly helpful to have the patient awake and cooperative are the very blocks that anesthesiologists routinely sedate patients heavily for – retro-bulbar blocks.  Remember, if the needle is deep to the dura surrounding the optic nerve, (OR FOT THAT MATTER ANY NERVE ROOT AS IT EXITS THE SPINE) it is SUBDURAL.  A subdural at any level has the same desastrous effects.  (
Please read my editorial in the Jan/Feb 2009 issue of Reg Anesth Pain Med.  (Boezaart AP. That which we call a rose by any other name would smell as sweet – and its thorns would hurt as much. Reg Anest Pain Med 2009; 34(1): 3 – 7).  Also Read Boezaart AP Franco CD. Thin sharp needles around the dura. Reg Anesth Pain Med 2006; 32(4): 338 – 339).

As a result of medico-legal pressures, and because it is seldom necessary to do blocks under general anesthesia, and the fact that most patients tolerate peripheral nerve blocks with little to no sedation, we typically place blocks in awake patients, except for pediatric patients or those patients with extremely painful conditions or severe anxiety of course. We do, however, fully explain the situation to the patient before we place blocks after the induction of GA. None of the arguments on both sides are convincing and we believe that it does not really matter. Proper technique, however, matters a lot.  Solid indications for the block, the correct nerve being blocked with the correct technique and not forgetting to use the correct equipment will protect your patient from harm, and NOT doing the wrong block on the wrong patient with bad technique and wrong equipment in an awake patient.

Furthermore, the only two things, in addition to good and solid technique that will protect one from intraneural injection are proper nerve stimulator manipulation and pressure (resistance) in the syringe. We get worried if there are brisk muscle twitches at settings of 0.2mA and less and we put the most experienced person in the room on the syringe to judge the pressure of the injection. Better still to measure this pressure.  We also, as far as possible, use the same syringe and needle for every block to get used to the resistance. The pressure device proposed by Admir Hadzic hold great future in converting regional anesthesia from an art form to science.

Sincerely

André P. Boezaart


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