From: "Steven Belknap, M.D." <sbelknap@uic.edu> Newsgroups: sci.med Subject: Re: Awareness under anesthesia Date: Thu, 11 Feb 1999 23:27:14 -0600 [[ This message was both posted and mailed: see the "To," "Cc," and "Newsgroups" headers for details. ]] Hey, Cecil- The British medical journal letter writer raises a very interesting point. First, the dogma. Neuromuscular blocking agents are given to reduce muscle tone during surgical anesthesia. This allegedly provides several advantages: 1. Prior to the beginning of the surgical procedure, a neuromuscular blocker is given to relax the muscles of the head and neck, which simplifies placement of the endotracheal tube and avoids overstimulation of vagal and other reflexes which can cause hypotension and arrhythmias. This tube is connected to the ventilator, which delivers inhalant anesthetics and oxygen and removes carbon dioxide from the lungs. For some very short surgical procedures, the tube is not used; a tightly fitting mask being used instead. 2. In cases of orthopedic trauma, a neuromuscular blocker may be given so as to allow manipulation of fractured or dislocated limbs. For example, a femur fracture is often complicated by contracture of the quadriceps (the strongest muscle in the body), which makes realignment of the bone extremely difficult. By paralyzing the muscle, it is possible to set the fracture. 3. For abdominal surgery, neuromuscular blockade relaxes the muscles of the abdomen, which facilitates access to the peritoneal space and abdominal viscera. This allows the surgeon to use a smaller incision than would be otherwise necessary, and shortens the duration of surgery. Also, since muscular relaxation no longer depends upon maintaining deep general anesthesia, lighter levels of anesthesia suffice, which minimizes the risk of adverse drug events such as cardiac or respiratory depression and shortens post-surgical recovery time. 4. Neuromuscular blockade suppresses involuntary movement by the patient during surgery, which can happen despite adequate analgesia and amnesia. (Hmmm.) That is the dogma. But now you've got me wondering Cece. Neuromuscular blockers have some serious toxicities. I know of a patient who inadvertently got no general anesthetic, and who thus underwent surgery while conscious, but paralyzed. He developed severe post-traumatic stress disorder. Interactions with glucocorticosteroids can lead to diaphragmatic weakness and skeletal muscle damage. Occasionally, life-threatening potassium release occurs after neuromuscular blockade, typically in patients with burn injury or denervation due to spinal injury or other neurologic pathology. So these drugs are not entirely benign. Some combinations of general anesthetics such as propofol + fentanyl + nitrous oxide possess relatively few adverse effects, even in large doses. Recovery is rapid. Adequate relaxation of muscle could perhaps be achieved without neuromuscular blockers by achieving very deep anesthesia. Given this, it would be nice if someone had done some randomized, controlled, clinical trials comparing shallow general anesthesia + neuromuscular blockers to deep general anesthesia with some of the better tolerated anesthetic drugs. There are techniques, such as EEG spectral edge monitoring which would allow monitoring of the depth of anesthesia. I don't think such studies have been done. At least, I've never seen such a study, and I couldn't find any controlled clinical trials addressing this question via KnowledgeFinder or OVID. It is entirely possible that standard anesthesiology practice includes neuromuscular blockade unncessarily. If you could send me the reference to the letter you cited, I could perhaps comment further. -Steven In article <19990208175520.21048.00000145@ng94.aol.com>, Ed Zotti <edzotti@aol.com> wrote: > I'm researching a newspaper column about awareness under anesthesia - > that is, patients who are given insufficient general anesthesia prior to > surgery but are unable to alert the OR staff due to the muscle relaxant > and suffer unimaginable agonies on the operating table. A letter writer > in a British medical journal claims that this problem is a holdover from > the days "when general anesthetic drugs were highly unsatisfactory." > (Unsatisfactory how? Wore off too quick? Too many side effects?) Anyway, > the writer believes that muscle relaxants are not as important as they > used to be and that greater emphasis should be placed on general > anesthesia, there by eliminating many cases of accidental awareness.. > > Is there any truth to this? How has the practice of anesthesia evolved > over time? Is too much emphasis placed on muscle relaxants? And what > exactly goes into the chemical cocktail used in general anesthesia, > anyway? > > Thanks for any info. CCs by E-mail greatly appreciated. -Ed From: sbharris@ix.netcom.com(Steven B. Harris) Newsgroups: sci.med Subject: Re: Awareness under anesthesia Date: 12 Feb 1999 08:44:01 GMT In <sbelknap-110219992327145312@mac0.uicomp.uic.edu> "Steven Belknap, M.D." <sbelknap@uic.edu> writes: >[[ This message was both posted and mailed: see > the "To," "Cc," and "Newsgroups" headers for details. ]] > >Hey, Cecil- > >The British medical journal letter writer raises a very interesting >point. First, the dogma. Neuromuscular blocking agents are given to >reduce muscle tone during surgical anesthesia. This allegedly provides >several advantages: > >1. Prior to the beginning of the surgical procedure, a neuromuscular >blocker is given to relax the muscles of the head and neck, which >simplifies placement of the endotracheal tube and avoids >overstimulation of vagal and other reflexes which can cause hypotension >and arrhythmias. This tube is connected to the ventilator, which >delivers inhalant anesthetics and oxygen and removes carbon dioxide >from the lungs. For some very short surgical procedures, the tube is >not used; a tightly fitting mask being used instead. > >2. In cases of orthopedic trauma, a neuromuscular blocker may be given >so as to allow manipulation of fractured or dislocated limbs. For >example, a femur fracture is often complicated by contracture of the >quadriceps (the strongest muscle in the body), which makes realignment >of the bone extremely difficult. By paralyzing the muscle, it is >possible to set the fracture. > >3. For abdominal surgery, neuromuscular blockade relaxes the muscles of >the abdomen, which facilitates access to the peritoneal space and >abdominal viscera. This allows the surgeon to use a smaller incision >than would be otherwise necessary, and shortens the duration of >surgery. Also, since muscular relaxation no longer depends upon >maintaining deep general anesthesia, lighter levels of anesthesia >suffice, which minimizes the risk of adverse drug events such as >cardiac or respiratory depression and shortens post-surgical recovery >time. > >4. Neuromuscular blockade suppresses involuntary movement by the >patient during surgery, which can happen despite adequate analgesia and >amnesia. (Hmmm.) > >That is the dogma. > >But now you've got me wondering Cece. Neuromuscular blockers have some >serious toxicities. I know of a patient who inadvertently got no >general anesthetic, and who thus underwent surgery while conscious, but >paralyzed. He developed severe post-traumatic stress disorder. >Interactions with glucocorticosteroids can lead to diaphragmatic >weakness and skeletal muscle damage. Occasionally, life-threatening >potassium release occurs after neuromuscular blockade, typically in >patients with burn injury or denervation due to spinal injury or other >neurologic pathology. So these drugs are not entirely benign. > >Some combinations of general anesthetics such as propofol + fentanyl + >nitrous oxide possess relatively few adverse effects, even in large >doses. Recovery is rapid. Adequate relaxation of muscle could perhaps >be achieved without neuromuscular blockers by achieving very deep >anesthesia. > >Given this, it would be nice if someone had done some randomized, >controlled, clinical trials comparing shallow general anesthesia + >neuromuscular blockers to deep general anesthesia with some of the >better tolerated anesthetic drugs. There are techniques, such as EEG >spectral edge monitoring which would allow monitoring of the depth of >anesthesia. > >I don't think such studies have been done. At least, I've never seen >such a study, and I couldn't find any controlled clinical trials >addressing this question via KnowledgeFinder or OVID. It is entirely >possible that standard anesthesiology practice includes neuromuscular >blockade unncessarily. If you could send me the reference to the letter >you cited, I could perhaps comment further. > >-Steven Comment: An excellent reply. Should the paralytic agents still be found to be necessary, spectral edge monitoring is getting easier. The new machines are not the old clunkers where you got more information than anyone knew what to do with, and required a lot of scalp needles. The spectral edge, for those who are unfamiliar with it, is the frequency below which 95% of the spectral power of the EEG lies. Since it's a sort of measure of integrated high frequency EEG power (of the sort associated with consciousness), it can be used to monitor wakefulness and alertness. These days, the machines that do this are about the size of a palmtop computer, which they basically are, and they have one electrode that sticks on your forehead, a lot like something out of a Steve Martin movie. Now the machine does not show you the Fourier transformed EEG power spectrum, and the statistics. No, that was beyond the intellect of the average schlub who passes gas, I suppose. Instead, now what we have on the market is a little a machine which computes the EEG spectral power, figures out the point under which 95% of the spectral power lies, and then converts THIS into one easy-to-use number from 10 to 100, for use by those who need Anaesthesiology For Dummies. Which is a surprising number of people who put other people to sleep, it turns out. Your dentist, just for beginners. Ceders Sinai in L.A. just bought one of these Dummed Down gismos for every O.R. in their hospital. They figured out what fraction of people would bring suits, and what fraction of suits would be won once the average jury figured out just what CAN happen to you, and there was no objective evidence whatsoever that it hadn't to the guy bringing the suit, and .... they geeked. It's all too bad, because a lot of very expensive research went into this technology by several companies that failed utterly, because they could not sell the big machines that gave the interesting data. They did the work, and they didn't reap the benfits. We have a LifeScan, made in Germany, which we use in research on animals. It puts out a 3-D EEG power spectrum, bihemispheric, in real time, in a moving rectangular virtual box which appears on a TV screen. Output to computer data aquisition. Awesome. A lot of them, which each cost God knows how many 10s of thousands of dollars new, were thrown in the garbage, and we rescued a few. When they break we'll have to canibalize them or toss them, because the company that made them does not support them. I believe it no longer exists. Steve Harris, M.D. From: sbharris@ix.netcom.com(Steven B. Harris) Newsgroups: sci.med Subject: Re: Awareness under anesthesia Date: 15 Feb 1999 04:05:22 GMT In <sbelknap-130219992256482580@slip6b-08.dialin.uic.edu> "Steven Belknap, M.D." <sbelknap@uic.edu> writes: >The "Hmmm." refers to my concern that maybe its not such a good idea to >hide evidence of awareness, which involuntary movement may represent. Or may not (since even brain dead people have been seen to do a fair amount of random limb moving when removed from ventilators). It's simply impossible to tell one way or the other. I agree, of course, that it's not a good idea to interpose one more block to awareness of inadequate anaethesia without very good reasons. And probably EEG spectral monitoring of anaesthesia plane will be standard of care in 5 years. |
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