A survey of peripheral nerve stimulator (PNS) use
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EDITOR: Non-depolarizing muscle relaxants retain a vital place in anaesthetic practice. The number of available muscle relaxants has increased in recent years. All of these drugs vary in speed of onset, duration of action and in speed of offset. The manufacturers produce guidance for the use of these drugs in the form of data sheets. These may give recommendations for initial dose, speed of onset and duration of action. Clinical practice is however, likely to vary considerably with the manufacturer's guidance for the following reasons: 1. Variable individual response to muscle relaxants. Marked variation has been shown between healthy individuals for the same dose of muscle relaxant [1] 2. Renal function. Impaired renal function may prolong the duration of action. 3. Liver disease or reduced hepatic blood flow. These may prolong the duration of action. 4. Electrolyte disturbances. These may prolong the duration of action. 5. Other drugs. Aminoglycosides prolong the duration of action, other drugs may also affect the duration of action. 6. Obesity. Dose requirements are affected with variation between the different muscle relaxants. Knowledge about the state of neuromuscular blockade is important from induction through to recovery. Inadequate neuromuscular blockade during the procedure may make surgery difficult, and has the potential to be extremely dangerous to the patient. At the end of the procedure there is the potential for an awake patient with residual paralysis or for recurarization during the recovery period. Residual neuromuscular blockade may increase the risk of postoperative pulmonary complications [2]. The peripheral nerve stimulator is not the perfect monitor; it measures neuromuscular function in the periphery, which is more sensitive to non-depolarizing muscle relaxants than is diaphragmatic muscle [3]. It may give an inaccurate test due to poor electrical contact or incorrect placement. At present, it is the most common monitor of neuromuscular function. This is due to its simplicity, ease of use, portability and cost. We have undertaken a survey to establish current practice in respect of PNS usage at five hospitals. We aimed to assess use and availability of the PNS. We also wanted to identify the factors which influence PNS usage, such as duration of anaesthesia and the muscle relaxant used. A questionnaire was sent to all grades of anaesthetist at five hospitals. Three teaching hospitals and two district general hospitals. The questionnaire asked a number of questions about PNS usage. One hundred questionnaires were returned with a response rate of 57%, of these, replies were from consultants (48%), from training grades (48%) and from other grades (4%). Question 1: Is there a place for using a peripheral nerve stimulator while using a non-depolarizing muscle relaxant in your practice? Yes 89% No 11% Question 2: If a PNS is available in the theatre, how often do you use it? Never 8% Sometimes 74% Always 17% Question 3: Will you use a peripheral nerve stimulator if the duration of operation is less than 20 min, 20-40 min, 40-60 min and over 60 min? (Table 1)Table 1: Use of PNS with duration of operation Question 4: How often is a peripheral nerve stimulator available? (Table 2)Table 2: Availability of PNS in theatre (%) Question 5: How often do you use a peripheral nerve stimulator with different muscle relaxants? (Table 3)Table 3: Use of PNS with particular relaxants as percentage The response rate of 57% was disappointing but did show some marked differences. The large majority of anaesthetists (89%) in our survey have a need for a peripheral nerve stimulator in their practice. Most use it for selected cases, with a small group using it for all cases in whom a non-depolarizing muscle relaxant is used (17%). This survey found that a factor affecting usage was the duration of anaesthesia with the number of anaesthetists always using a PNS rising from 11% for operations of 20-40 min duration to 21% always using a PNS for operations of 40-60 min. This may reflect the fact that an induction dose of muscle relaxant will often last between 20 and 40 min, but repeat doses are likely if the duration exceeds 40 min. There appeared to be a relation between the choice of muscle relaxant and the duration of drug action, with the least use for the short-acting mivacurium and most use for the long-acting pancuronium. It was interesting to find no increase in PNS use for the newer agents. This may reflect their predictability, although there are reports of recurarization with rocuronium [4]. It is of concern that in some hospitals there are insufficient nerve stimulators. The Association of Anaesthetists of Great Britain and Ireland recommends that a means of assessing neuromuscular block should be available whenever neuromuscular blocking drugs are used [5]. In the case of one teaching hospital, 40% of respondents reported that peripheral nerve stimulators were 'rarely available' or 'never available'. While their use is not mandatory they should be readily available in every theatre complex. The results of this survey were presented to this hospital and have resulted in the provision of four extra peripheral nerve stimulators for the theatre complex. The use of the PNS helps with anaesthetic training and with the introduction of new or modified muscle relaxants but above all it may improve anaesthetic standards by preventing over- or under-curarization. We are grateful to Dr Hugh James and audit secretary Dawn Burt for their help in carrying out this survey. J. SHAH O. OWEN-SMITH S. COLEY Department of Anaesthesia, Leicester General Hospital NHS Trust, Gwendolen Road, Leicester LE5 4PW, UK J. RANGASAMI Nuffield Department of Anaesthesia, Oxford, UKKeywords:
Onset of action
Neuromuscular monitoring
Background and Aim: After introduction of train of four (TOF) monitoring residual neuromuscular blockade was reduced but without quantitative recording of evoked response it is difficult to estimate the TOF ratio. Thus, when TOF ratio is recovered to more than 0.4 -0.5 fade in response cannot be identified visually or manually. To overcome this double burst stimulation (DBS) was introduced. The aim of this study is to assess whether DBS is more sensitive than TOF in assessing neuromuscular blockade.Methods: 55 patients, aged 18 to 60 years undergoing elective surgery under general anaesthesia using endotracheal intubation where randomised selected. Neuromuscular transmission was not monitored until following reversal of neuromuscular blockade. Following neostigmine administration, TOF stimulation was given with 50mA every 30 seconds. DBS was given only when there was absence of fade of TOF. if fade is present in DBS stimulation was given every 30 seconds till there was no fade.Results: In our study the duration from TOF equal to DBS equal varied from 2.6 minutes to 6.7 minutes with mean of 4.6minutes. More number of patients where extubated on DBS equal group.Conclusion: DBS is more helpful than TOF in detecting residual neuromuscular blockade.
Neuromuscular monitoring
Neuromuscular transmission
Fade
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This article provides an update on residual neuromuscular blockade for nurse anesthetists. The neuromuscular junction, pharmacology for producing and reversing neuromuscular blockade, monitoring sites and methods, and patient implications relating to incomplete reversal of neuromuscular blockade are reviewed. Overall recommendations include using multiple settings when employing a peripheral nerve stimulator for monitoring return of neuromuscular function and administering pharmacologic reversal when the train-of-four ratio is below 0.9.
Neuromuscular monitoring
Nerve stimulator
Neuromuscular Blocking Agents
Neuromuscular transmission
Nerve stimulation
Reversing
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Editor, I read with great interest the article by Dubois et al.1 evaluating the impact of deep neuromuscular blockade on surgical conditions during laparoscopy. It represents a welcome contribution to the field of the management of neuromuscular blockade during laparoscopic surgery. However, two important issues about the study deserve consideration.1 Firstly, after an intubating dose of rocuronium 0.6 mg kg−1, patients in the deep neuromuscular blockade group received a bolus dose of rocuronium 5 mg to deepen their neuromuscular blockade whenever a second twitch (T2) or more appeared on train-of-four stimulation.1 In doing so, the authors essentially included patients with moderate neuromuscular blockade in the deep neuromuscular blockade group,1 as moderate neuromuscular blockade is characterised by the appearance of T1-T2 on train-of-four stimulation.2 Secondly, the authors defined deep neuromuscular blockade as the absence of T1 on train-of-four stimulation;1 however, it is more appropriate to define deep neuromuscular blockade as the presence of no twitches on train-of-four stimulation and only one to five twitches observed as the posttetanic count during posttetanic stimulation.2,3 In a previous study evaluating recovery from deep to moderate neuromuscular blockade after rocuronium 0.6 mg kg−1, the posttetanic count was 8 when T1 first appeared on train-of-four stimulation.4 Thus, with a posttetanic count of 5 to 20 on electromyography, the probability of inadequate deep neuromuscular blockade is high, and a repeat dose of rocuronium is necessary to avoid moderate neuromuscular blockade.4,5 Indeed, it has been reported that when the posttetanic count is 1, T1 appears in approximately 10 min, whereas when the posttetanic count is more than 5, the appearance of T1 is imminent.4 The posttetanic count may not only predict the return of the reactivity of the adductor pollicis muscle during recovery from deep neuromuscular blockade,5 but, most importantly, it may also be a reliable indirect method of estimating diaphragm recovery.6 A posttetanic count of 5 or less signifies deep neuromuscular blockade of the diaphragm, whereas a posttetanic count more than 5 does not.5,7 Deep neuromuscular blockade of the diaphragm is crucial for providing superior surgical conditions during laparoscopic surgery.3,6 Furthermore, maintaining the posttetanic count less than 5 may prevent hiccups, bucking and coughing, all of which can occur during surgery despite total abolition of train-of-four responses at the adductor pollicis muscle.5,6 Both of the aforementioned issues likely led to at least some patients in the deep neuromuscular blockade group exhibiting only a moderate degree of neuromuscular blockade at least part of the time. The presence of moderate neuromuscular blockade may explain the surgical conditions being rated as ‘good but not optimal’ in 22% of patients in the deep neuromuscular blockade group and ‘poor but acceptable’ in another 10% of patients in the deep neuromuscular blockade group.1 Indeed, the authors noted that unfavourable surgical conditions only occurred when the train-of-four response was T1 or more.1 Moreover, it is quite possible that deep neuromuscular blockade at the diaphragm recovered in some instances despite the absence of a train-of-four response at the adductor pollicis, which may have also reduced the percentage of patients in the deep neuromuscular blockade group with ‘excellent’ surgical conditions.1 Martini et al.3 reported that good and optimal conditions were observed in almost all patients undergoing laparoscopic surgery when deep neuromuscular blockade was maintained with a posttetanic count in the range of 1 to 5. Despite these methodological issues that may have reduced the observed effectiveness of deep neuromuscular blockade, the results of Dubois et al.1 support the view that adequate rocuronium-induced deep neuromuscular blockade allows to optimise surgical conditions during laparoscopy. Acknowledgements relating to this article Assistance with the letter: none. Financial support and sponsorship: none. Conflicts of interest: the author has received payments for lectures from Merck Sharp & Dohme (MSD), Italy.
Neuromuscular monitoring
Sugammadex
Rocuronium Bromide
Neuromuscular transmission
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The authors conducted a randomized controlled clinical trial to evaluate the usefulness of perioperative manual evaluation of the response to train-of-four (TOF) nerve stimulation. A total of 80 patients were divided into four groups of 20 each. For two groups (one given vecuronium and one pancuronium), the anesthetists assessed the degree of neuromuscular blockade during operation and during recovery from neuromuscular blockade by manual evaluation of the response to TOF nerve stimulation. In the other two groups, one of which received vecuronium and the other pancuronium, the anesthetists evaluated the degree of neuromuscular blockade solely by clinical criteria. The use of a nerve stimulator was found to have no effect on the dose of relaxant given during anesthesia, on the need for supplementary doses of anticholinesterase in the recovery room, on the time from end of surgery to end of anesthesia, or on the incidence of postoperative residual neuromuscular blockade evaluated clinically. The median (and range of) TOF ratios recorded in the recovery room were 0.75 (0.33-0.96) and 0.79 (0.10-0.97) in the vecuronium groups monitored with and without a nerve stimulator, respectively. These ratios were significantly higher than those found in the pancuronium groups, which wre 0.66 (0.06-0.90) and 0.63 (0.29-0.95), respectively. However, no difference was found between the vecuronium and pancuronium groups in the number of patients showing clinical signs of residual neuromuscular blockade, as evaluated by the 5-s head-lift test.(ABSTRACT TRUNCATED AT 250 WORDS)
Neuromuscular monitoring
Vecuronium bromide
Nerve stimulator
Neuromuscular transmission
Muscle relaxant
Nerve stimulation
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Neuromuscular monitoring
Neuromuscular transmission
Vecuronium bromide
Atracurium besilate
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The authors determined the onset time and the duration of action of neuromuscular blockade by a 100-150 micrograms.kg-1 vecuronium random administration in 30 ASA I and ASA II patients during urological surgery. Neuromuscular blockade was evaluated by the electromyographic response to stimulation of the ulnar nerve train of four. The time from vecuronium administration to complete abolition of twitch response (T1 = 0%) did not change significantly, in spite of 50% increased dose of neuromuscular relaxant. The duration of action of neuromuscular blockade, that is the time from T1 = 0% to T1 = 25%, increased from 38.2 +/- 7.5 min to 52.5 +/- 19.8 min by the increasing of neuromuscular relaxant dose (p < or = 0.018). Vecuronium increased doses did not shorten significantly the onset time.
Vecuronium bromide
Muscle relaxant
Neuromuscular monitoring
Onset of action
Neuromuscular transmission
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Neuromuscular monitoring
Repeatability
Neuromuscular transmission
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Neuromuscular monitoring
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Double burst stimulation (DBS) is a new nerve stimulation pattern introduced to facilitate tactile evaluation of recovery from neuromuscular blockade. DBS consists of two bursts of high frequency stimulations separated by a short time interval. The relationships between DBS, post-tetanic count (PTC) and train-of-four (TOF) on the evoked twitch response was investigated in 16 surgical patients and 7 intensive care patients given atracurium for muscle relaxation. A significant correlation between the twitch height of the first response to DBS and the number of post-tetanic responses was demonstrated when PTC was more than five (r = 0.47, p < 0.0003). When the first twitch of TOF was still not measurable, the first twitch of DBS ranged from 0 to 20% of the TOF-control twitch height. Furthermore the DBS ratio was significantly correlated to the TOF ratio (r = 0.92-0.96, p < 0.0002). It is concluded that DBS not only can be used for monitoring of recovery from neuromuscular blockade, but also for monitoring of intense degrees of neuromuscular blockade.
Neuromuscular monitoring
Tetanic stimulation
Muscle relaxation
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During recovery from non-depolarizing neuromuscular blockade the evoked response to train-of-four (TOF), 100-HZ tetanus (T100) and 50-HZ tetanus (T50) was measured in 10 patients. When the TOF fade ratio exceeded 0.70, tetanic tension to T50 was well sustained. However, even at TOF ratios as high as 0.88 a 2-second tetanic response to T100 showed marked fade. T100 stimulation appears to be too sensitive a test to residual curarization for routine clinical use. Fade on T100 may be quite apparent at a time when the use of additional neuromuscular antagonists are not indicated and may be counterproductive.
Neuromuscular monitoring
Fade
Neuromuscular Blocking Agents
Tetanic stimulation
Neuromuscular transmission
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