If you wish to respond to a paper or other item already published in the BJA, please go to the abstract/full text version of that item and click on the link "E-Letters: Submit a response to the article".
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E-letters: Electronic letters published:
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Recall and the Isolated Forearm Technique
- Ian F Russell (10 May 2006)
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Utility and accuracy
- M Dylan Bould (8 May 2006)
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Re: Narcotrend monitoring vs Propofol amnesia-what does Russel’s study document?
- Ian F Russell (2 April 2006)
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Narcotrend monitoring vs Propofol amnesia-what does Russel’s study document?
- Paul M Kempen (28 March 2006)
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"Utility and accuracy"
- Ian F Russell (3 March 2006)
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Utility does not require complete accuracy
- M Dylan Bould (2 March 2006)
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Ian F Russell, Consultant Anaesthetist Hull Royal Infirmary
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Dear Editor, Dr Bould’s simple statement that the IFT “will not identify memory formation under anaesthesia” requires some clarification since his statement puts the cart before the horse. It is true to say that IFT responses have been shown not to correlate with post operative evidence of memory formation under anaesthesia: ie post operative interviews (using the Brice questionnaire) or hypnosis [1] do not show any evidence that responsive patients have recall. But this only considers one side of the “equation.” On the other side of the “equation” there is considerable evidence that patients who are unconscious (ie unresponsive to command) do not have any recall [2]. The fact that patients who respond to commands intraoperatively do not have post operative recall is not a failure of the IFT, as implied by Dr Bould, but is actually a function of the IFT: the lack of recall is a direct consequence of using the IFT to detect those patient for whom anaesthesia is inadequate and so allow anaesthesia to deepened thus preventing explicit post operative recall [2]. During surgery IFT responses identify the onset of consciousness (response to command), but it is important to understand that the conscious level at the time of the initial response to command is such that information is either not stored in memory or it is stored in such a manner that it cannot be recalled after surgery. If one were to ignore the IFT responses while anaesthesia continues to lighten, then long term accessible memory will start to be stored. Ultimately, whether long term memory is or is not retained will depend on the actual level of consciousness attained. Similar patient responsiveness without long term memory is part of every day anaesthetic practice. It can be seen in most patients recovering from general anaesthesia: they may respond to commands in theatre (or in the recovery area), but have no conscious recall of this later when back on the surgical ward. Lack of recall for intra operative events can also be observed in those patient having surgery performed under sedation – the patient may be conscious and talk quite lucidly during surgery, but has no recall of events later in the post operative period. The function of the IFT is to prevent paralysed patients from reaching a level of consciousness at which intra-operative events are capable of being stored for later recall. It would appear that Dr Bould agrees that IFT responses are not associated with recall but the correct interpretation of this is that the IFT prevents recall. This is quite the opposite of Dr Bould’s later assertion that the IFT is unlikely to affect the incidence of recall. Dr Bould cannot have it both ways! REFERENCES 1. Russell IF, Wang M. Absence of memory for intraoperative information during surgery under adequate general anaesthesia. Br J Anaesth 1997; 78: 3 - 9 2. Russell IF. Memory when the state of consciousness is known: Studies of anesthesia with the isolated forearm technique. In: Ghoneim MM, Ed. Awareness During Anaesthesia. Oxford: Butterworth Heinemann, 2001; 129– 43 Conflict of Interest:None declared |
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M Dylan Bould
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Dear Editor, In his recent e-letter, Russell discusses the deficiencies of defining awareness under anaesthesia as explicit recall (1). A useful model of anaesthesia identifies 6 linked components of the targets of anaesthesia: conciousness, memory, movement, autonomic reflexes, arousal and nocioceptive stimuli (2). The isolated forearm technique can identify failure of some of these components of anaesthesia, including conciousness as demonstrated by a purposeful response to stimuli and perception of nocioception. It will not identify memory formation under anaesthesia, which is usually found by using repeated modified Brice questionnaires. Explicit recall of intraoperative events has been shown to be a significant endpoint associated with a high incidence of posttraumatic stress disorder (3,4). I think that any trial investigating deficiencies in delivery of anaesthesia should, for completeness, include repeated structured questionnaires to look for the very important outcome measure of explicit recall. Russell also asserts that a depth of anaesthesia monitor must be 100% accurate and implies that use of the isolated forearm technique (IFT) with other methods of monitoring may achieve this level of accuracy. Although relaxant anaesthesia has been shown to increase the incidence of explicit recall, and the severity of consequent sequelae, avoidance of muscle relaxants does not abolish awareness. Patients that describe awareness during anaesthesia without neuromuscular block have been found to still have significant psychological upset 2 years after the procedure (3) and have successfully sought litigation (5). Although the IFT identifies some deficiencies in anaesthesia that can be described as awareness it has not been shown to affect the incidence of explicit recall. Moreover, as the sole strength of the IFT is maintaining neuromuscular function, which as discussed above is an imperfect solution to the problem of awareness, it seems unlikely that it will ever be found to be 100% accurate as a test for depth of anaesthesia. 1. Russell IF. "Utility and accuracy", 2006. 2. Davidson AJ, Huang GH, Czarnecki C et al. Awareness during anesthesia in children: a prospective cohort study. Anesth Analg 2005;100:653-61. 3. Lennmarken C, Bildfors K, Enlund G et al. Victims of awareness. Acta Anaesthesiol Scand 2002;46:229-31. 4. Myles PS, Williams DL, Hendrata M et al. Patient satisfaction after anaesthesia and surgery: results of a prospective survey of 10,811 patients. Br J Anaesth 2000;84:6-10. 5. Domino KB, Posner KL, Caplan RA, Cheney FW. Awareness during anesthesia: a closed claims analysis. Anesthesiology 1999;90:1053-61. Conflict of Interest:None declared |
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Ian F Russell, Consultant Anaesthetist Hull Royal Infirmary
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Dear Sir, Dr Kempen writes a provocative letter raising many points, few of which have any validity. Several of the issues suggest unfamiliarity with the Isolated Forearm Technique (IFT)1 2 and most of the others show a lack of understanding of the simple aim of this study: to titrate an anaesthetic drug (propofol) guided by the output of the Narcotrend anaesthesia brain monitor. There is an implication in Dr Kempen’s letter that “authors” were involved in the study. There was only one author, IFR. Dr Kempen is also mistaken in his belief that I chose to “NOT terminate the auditory stimulus prior to final emergence.” The sequence of events in the four patients referred to was quite different. It had been my intention to stop the auditory stimuli before the end of surgery, but these four patients awoke unexpectedly, with a Narcotrend stage indicating “anaesthesia,” shortly before I planned to switch off the minidisk player. What I “chose NOT to do” was to re-induce anaesthesia. I saw no point in giving additional drugs at this stage: the patients were comfortable and surgery was nearing an end. I am note sure why Dr Kempen uses the words “mere audible stimulation” to refer to the memory of the patients. Hearing is the first sense to recover from anaesthesia and is thus a very appropriate stimulus to use to detect the early onset of consciousness: it is not surprising that some part of the audible message was remembered. In some 25 years of research in this field it is rare indeed to find a patient who remembers any aspect of surgery but it is not too unusual for patients to remember some aspect of the taped message.1 2 Dr Kempen has misunderstood the purpose of this study and so questions the lack of information on the doses of drugs used, the rates of infusion, the units with which the drug doses were presented, and lack of information on the target controlled infusion (TCI) system used as well as the lack of blood samples to validate the accuracy of the TCI pump (Fresenius Master TCI, incorporating Diprifusor™ pharmacokinetics). None of these items of data is relevant to the question as to whether “adequate anaesthesia was actually provided”? The methodology of the study makes it quite clear that anaesthesia was titrated according to the Narcotrend stage. The philosophy of the study was simple: if the Narcotrend stage indicated light “anaesthesia” – increase the TCI target; If the Narcotrend stage indicated deeper anaesthesia – reduce the TCI target. The Narcotrend monitor does not “know” the drug concentration – it merely shows an effect and interprets this effect as a stage of anaesthesia, irrespective of actual drug concentrations. Many studies have been published where the administration of anaesthesia has been guided by a brain monitor, with claims that such guided “anaesthesia” reduces the amount of anaesthetic drugs used, speeds up recovery, and allows a faster patient turn over. I would not disagree with Dr Kempen in his assessment that my study raises questions about the adequacy of anaesthesia, specifically the adequacy of brain-monitor-guided anaesthesia. The results urge caution when using brain-monitor-guided anaesthesia in the presence of muscle relaxants without an adequate method of determining whether a patient is conscious or not. In the presence of muscle relaxants, the only method of determining whether a patient is conscious or not is to use the IFT. Another issue raised is the dose of atracurium which is described as “an inadequate dose for intubation at all.” For me, an adequate dose of atracurium is that which, taken in conjunction with the rest of the anaesthetic technique (TCI propofol, a remifentanil bolus at induction and a maintenance infusion, a low thoracic epidural), is enough to allow me to intubate the patient and to provide the muscle relaxation required by the surgeon. As regards the dose being “an inadequate dose for intubation at all,” I know of several colleagues who intubate without relaxants, using propofol and remifentanil only, thus one could argue that 10 – 15 mg of atracurium is 10 – 15 mg too much! However, in the technique as presented, 10 – 15 mg of atracurium was quite sufficient for intubation. As regards further relaxant during surgery, further increments were given as required during surgery but the isolating cuff was inflated before each increment of relaxant and deflated some 20 minutes later.1 2 I am not sure what Dr Kempen means by his comments regarding an apparent lack of muscle relaxant and the patient swallowing and opening her eyes to command. Such activity is NOT an indication for blindly administering muscle relaxant: such an action would merely hide the fact that a patient was conscious. What is required initially is a deeper anaesthetic and then possibly an increment of muscle relaxant, if this is required to facilitate the surgery. The nerve stimulator was not used to assess the patient’s general state of relaxation: the latter was assessed clinically. The function of the nerve stimulator, with electrodes over the ulnar and median nerves at the right cubital fossa, was to ensure that there was neuromuscular integrity underneath and distal to the isolating cuff at all times.1 2 There is a very small risk that the cuff, inflated for 20 minutes, could cause a pressure induced temporary block of neural transmission and, also, if too large an increment of relaxant is given, the arm could become paralysed when the isolating cuff is deflated.1 2 I am very pleased to note that, like me, Dr Kempen recognises that EMG activity influences the response of brain monitors. Indeed muscle relaxants alone have been shown to produce a BIS output indicating deep anaesthesia while the paralysed volunteers were 100% conscious.3 This is why, when muscle relaxants are being used, studies of brain-monitor-guided anaesthesia should also use the IFT to ensure that consciousness is not present. Too many studies using muscle relaxants now seem to take a brain- monitor-number as indicative of anaesthesia whereas in reality, this number represents only some probability that anaesthesia might exist. While propofol is an excellent amnesic agent, I have used the IFT for over 25 years with various anaesthetic techniques. Few patients remember responding, even though they might indicate pain at the time of the response. This is because the IFT is identifying the onset of consciousness at a stage before long term memory is being laid down: this stage occurs with all the anaesthetic agents I have studied: eg nitrous oxide, volatile agents, thiopentone, althesin, midazolam, etomidate, propofol. I trust that the above clarifies the issues with regard to why drug doses, drug blood levels etc are unimportant – the brain monitor output defines “anaesthesia” and the IFT supports or refutes this by detecting the presence of consciousness. References 1 Russell IF. Conscious awareness during general anaesthesia: relevance of autonomic signs and isolated arm movements as guides to depth of anaesthesia. In Jones JG, Ed. Depth of Anaesthesia. Baillières Clinical Anaesthesiology, December 1989. London: Baillière Tindall 1989; 511-32 2 IF Russell. Memory when the state of consciousness is known: Studies of anesthesia with the isolated forearm technique. In Ghoneim MM, Ed. Awareness During Anaesthesia. Oxford: Butterworth Heinemann, 2001; 129– 43 3 Messner M, Beese U, Romstock J, Dinkel M, Tschaikowsky K. The bispectral index declines during neuromuscular block in fully awake persons. Anesth Analg. 2003;97: 488-91 Conflict of Interest:None declared |
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Paul M Kempen, Associate Professor Univewrsity of Pittsburgh
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The recent study published by Dr. Russell reportedly studied patients consenting to "have the depth of their anaesthetic guided by the Narcotrend monitor" and the associated editorial lauded the amnestic properties of propofol. (1,2) Russel’s study appears to have systematically document conscious episodes, as all 12 studied patients responded to commands on 92 separate instances. Indeed, 4 of 9 patients had memory of mere audible stimulation specifically administered to detect recall/awareness, (although 3 "were not asked"-I would ask why not, as this was a study parameter???)! The authors rather chose to NOT terminate the auditory stimuli prior to final emergence, so "it is impossible to say with any certainty when the memories…occurred". Many aspects of the study further raise significant questions if whether adequate anaesthesia was actually provided/intended, especially in the single patient without epidural anesthesia. Essential information regarding the anaesthetic drugs is lacking: The only mention of muscle relaxant administered is a single "10-15 mg" dose of atracurium for intubation - an inadequate dose for intubation at all, unless indeed cisatracurium was actually used. NO further mention of relaxants is to be found and the only patient, where detailed information is provided, was noted to be "swallowing" and "eyes opened to name" during surgery (figure 1). Was epidural anaesthesia used to provide anesthesia and muscle relaxation? Russell reportedly placed a nerve stimulator on the ulnar nerve of each patient, but how, if at all, was it used/followed, when patients were found to move outside the isolating tourniquet while exposed to monitored muscle relaxation? Doses of propofol were reportedly administered via a "target controlled infusion" at doses of 1.5-3 mcg . ml-1, which in conjunction with opiates, should be adequate for surgical anaesthesia without concomitant perineural blockade. This would imply a computerized/programmed device, yet no information as to such programming, or actual blood samples to validate accuracy, are offered. I would be particularly interested to know what rates of propofol infusions were actually utilized in more commonly documented units like mcg . kg . min-1 or mg . Kg . hr-1. Such unit dosage was used for the remifentanil infusions! Assuming that anaesthesia exists at all, would be predicated on actual knowledge of documented doses administered, rather than projected blood levels, especially as overlying EMG activity and surgical stimulation effects neurophysiologic responses of awareness monitoring (BIS). Dose requirement is also directly proportional to surgical stimulation, especially in "light" anaesthesia! The associated editorial praises propofol as an amnestic agent, because no "horrible accounts of intraoperative awareness" to surgery itself were reported here, while Dr. Russell’s study perhaps demonstrates the opposite. (2) This result may well be thanks to effective epidural anaesthesia, but again beyond the T11-12 placement described here, no further information is offered, not even the name or concentration of the local anesthetic utilized. This study leaves me with only questions and no answers: 1) Was ethical informed consent actually obtained? 2) How/Were anaesthesia and neuromuscular blockade actually induced/maintained at what (reasonable?) level? 3)What doses of each drug were infused in these patients (mcg per Kg where appropriate)? 4)What was different in the patient without the epidural-i.e was the lack of "surgical recall" in this study due to local anesthetics eliminating surgical stimulation? Finally, why was this study approved and then published in this fashion, with the multiple shortcomings? Paul Martin Kempen, MD, PhD; Associate Professor, University of Pittsburgh, USA References: 1)Russell IF: The Narcotrend ‘Depth of anaesthesia’ Monitor cannot reliably detect consciousness during general anaesthesia: an investigation usig the isolated forearm technique. Br J Anaesth 2006; 96:346-52. 2) Veselis RA: The remarkable memory effects of propofol. Br J Anaesth 2006; 96:289-91. Conflict of Interest:None declared |
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Ian F Russell, Consultant Anaesthetist Hull Royal Infirmary
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I agree that neither MAC nor target controlled infusions of propofol can predict consciousness and as a result it is usual to err on the side of safety and give additional anaesthesia. However, if a brain monitor is used as the guide to depth of anaesthesia we do quite the opposite: we reduce the administration of anaesthetic drugs to “sail closer to the wind.” It is in this context that the monitor needs to be 100% accurate, otherwise, as shown by my results, there is a risk that by reducing anaesthetic administration to follow some number on a monitor many more patients could well be conscious. The “reliability” refers not so much to the accuracy of the monitor but to how dependable it is: end tidal monitors, ECGs, NIBP machines etc do not suddenly go blank for up to 9 or 10 minutes at a time. But even if they did, they are generally “non critical” as we are not relying on them to ensure unconsciousness. In his reference to the study by Myles and colleagues (1) Dr Bould, like the authors (1) seems to misunderstand the term “awareness.” The title of the study (1) refers to the prevention of awareness “during anaesthesia” but the authors define “awareness” as “the patient's recollection of intraoperative events.” Thus what that study (1) demonstrated, when using the BIS monitor, was a reduced incidence of “recall of intraoperative events.” This is not the same as “awareness during anaesthesia.” “Awareness” is the state of being “aware” or “conscious,” it does not imply anything about “memory” or “recall” assessed at some later time. As Ghoneim and Block (2) state, the term “awareness” is “ambiguous and confusing” “anaesthetic jargon.” Myles and colleagues (1) do not know how many of their patients were “aware” (ie conscious) during surgery (with or without the experience of pain at the time), they only know the number of patients who, in the postoperative period, had recall for intra-operative events. Also of note is the fact that in this study (1), the BIS was allowed to rise to 70 during the last 15 minutes to facilitate rapid awakening. In my limited experience of using the BIS in conjunction with the IFT in paralysed patients, it is not uncommon for patients to regain consciousness with a BIS value between 60 – 70, before reversing the muscle relaxant. Without the IFT, this fact would be unknown to investigators and, following reversal, rapid “awakening” is reported. In reality, it is likely that many of these patients were already conscious before this point – reversal of muscle relaxation merely allows the patient to communicate this fact. This is the strength of the IFT – the anaesthetist knows when a patient is conscious and responsive, irrespective of what number is output on the screen of an anaesthesia brain monitor. With my experience of the IFT and several brain monitors over the past few years, I would hesitate to titrate anaesthesia according to brain monitor output alone (with or without the usually monitored physiological parameters), but I have no such reservations when the brain monitor is backed up by the IFT, these together form a consciousness/awareness monitoring duo par excellence: with both in use you can “sail close to the wind” with confidence rather than rely on chance! 1. Myles PS, Leslie K, McNeil J, Forbes A, Chan MTV et al. Bispectral index monitoring to prevent awareness during anaesthesia: the B–Aware randomised controlled trial. Lancet 2004; 363: 1757-63. 2. Ghoneim MM. Block RI. The word “awareness”: Its ambiguous and confusing use in anesthesia literature on memory. Anesthesiology 1990; 73: 193. Conflict of Interest:None declared |
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M Dylan Bould, Anaesthetic SpR University College Hospital
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Dear Editor, In the discussion of his paper comparing the Narcotrend monitor to the isolated forearm technique Russell states that “to be clinically useful, not only must an anaesthesia brain monitor be 100% accurate but it must also be reliable” (1). This is an expectation of depth of anaesthesia monitoring that I often hear expressed by colleagues, despite the general lack of 100% accuracy in predictive tests used in clinical practice. Certainly neither measurement of end tidal concentrations of volatile anaesthetic agents, a commonly used surrogate of depth of anaesthesia, nor use of target controlled infusions of propofol predict conciousness or explicit recall with complete accuracy. Myles and colleagues (2) showed that another depth of anaesthesia monitor produces false negatives, reporting a patient who recalled sternal sawing despite BIS values of 55- 59 at that time. However, they also showed that BIS can reduce the incidence of awareness in high-risk patients by 82% within the setting of a randomised controlled trial, despite its failings. This is a benefit that has not been demonstrated for the isolated forearm technique.
1. Russell IF. The Narcotrend ‘depth of anaesthesia’ monitor cannot reliably detect conciousness during general anaesthesia: an investigation using the isolated forearm technique. British Journal of Anaesthesia; 96: 346-52. 2. Myles PS, Leslie K, McNeil J, Forbes A, Chan M T V et al. Bispectral index monitoring to prevent awareness during anaesthesia: the B -Aware randomised controlled trial. Lancet 2004; 363: 1757-63. Conflict of Interest:None declared |
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