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Overview of the introduction of neuromuscular monitoring to clinical anaesthesia.

SUMMARY

Muscle relaxants were introduced into clinical practice in the early 1940s. From 1949, assessments were being made of the efficacy of various agents in awake volunteers, usually the researchers themselves. From the early to mid 1950s, while interest in using muscle relaxants was keen, concern emerged in the surgical literature that there was a higher mortality rate seen in patients receiving muscle relaxants. In fairness, the major article highlighted lack of randomisation, bias and confounding variables but this was largely regarded as showing a toxicity associated with muscle relaxants. By 1961 the matter had been settled that muscle relaxants were not toxic but required careful management and administration. Perhaps fortuitously, measurement of the degree of muscle relaxation was introduced to clinical practice with the use of nerve stimulation. These were measured responses to single twitch stimulus or tetanic stimulation. In 1970, train-of-four ratio was introduced, then in 1981 post-tetanic count, and in 1989 double burst stimulation. This article reviews the introduction of these techniques.

Key Words: monitoring, neuromuscular, anaesthesia

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This paper aims to address the development of neuromuscular monitoring as employed in clinical anaesthesia. It provides an overview of the progression of the different techniques and reviews them chronologically. The earliest description of curare was written by Peter Martyr d'Anghera in 1516 (1). Curare's subsequent journey to introduction into clinical practice in 1940 is well documented (2,3).

DEVELOPMENT OF NEUROMUSCULAR MONITORING

A. E. Bennett introduced curare into clinical practice in 1940 in convulsive therapy practice in order to prevent injuries from unmodified seizures that had been induced with metrazol (pentamethylenetetrazol) (4). Harold Griffiths and Enid Johnson introduced curare in the operating theatre in 1942 for abdominal relaxation during surgery (5). However it was not until 1949 that reports emerged outlining assessment of the degree of neuromuscular blockade.

We have divided this period into five sections:

1. Early assessment of neuromuscular block, including voluntary muscle action, twitch height, tetanic contraction (1949 to 1952)

2. Commencement of electrical nerve stimulation under anaesthesia (1952-)

3. Train-of-four (TOF) assessment (1970-)

4. Post-tetanic count (1981-)

5. Double burst stimulation (DBS) (1989-)

1. Early assessment of neuromuscular block (1949 to 1952)

Geoffrey Organe et al reported investigating various agents thought to be muscle relaxants in 1949 (6). Of note, there were three authors and all three were the volunteers upon whom the agents were tested. The assessment of clinical efficacy of the drug was based on clinical measurements that were recorded as "leg lifting, 50% hand strength, abdominal tone, ocular muscles and ability to stand". However, they did assess strength of handgrip and graphed that as a percentage of normal. These agents were administered to the point of "respiratory depression".

Also in 1949, Prof W. Mushin reported clinical studies with the drug gallamine (7). These were performed in volunteers and again mechanically assessed depression from 'normal/baseline' was recorded. The observations made were: 1) power to flex the fingers--a dynamometer was constructed in which a pointer moved over a graduated scale and showed 'flexing power'; 2) power to contract the rectus abdominis muscles--the volunteer lay supine with knees firmly strapped down, a spring-loaded pad bore on the centre of the recti abdominis, and on the command 'raise your legs', the recti became taut and the pad was pushed upwards against a spring which moved a pointer over a scale; 3) respiration was recorded with a spirometer and the ventilation over one-minute periods was calculated from the record obtained; 4) the movements of the diaphragm were recorded on a fluorescent screen in two cases by a technique devised by members of the Medical Research Council's Pneumoconiosis Research Unit at Llandough, Cardiff; 5) blood pressure was recorded; 6) the plantar reflex was tested at short intervals to demonstrate reflex activity unrelated to conscious effort. These all required an awake and co-operative patient.

In 1950, A. A. Guild reported in the Lancet (8) the use of muscle relaxants in hypertonus. His assessment of neuromuscular blockade was made by hand strength and the ability of the subject to squeeze and hand grip.

2. Commencement of use of nerve stimulation under anaesthesia (1952-)

From the early 1950s the use of muscle relaxants in clinical anaesthesia was rapidly taken up. In 1954, Beecher and Todd (9) in a seminal paper in Annals of Surgery looked at death rates amongst 600,000 patients receiving anaesthetics. They highlighted an increased mortality rate in patients receiving muscle relaxants. They considered this to be a warning requiring further investigation. However, this paper was widely interpreted as suggesting a toxicity associated with muscle relaxants. In 1961, Dripps et al demonstrated that the increased mortality of patients receiving muscle relaxant was associated with pre-morbid condition and not an inherent toxicity of muscle relaxants; "When deaths were related to the use of muscle relaxants, errors of omission or commission were always apparent" (10). Hence the requirement for improving the safety of use of muscle relaxants was becoming established.

In 1952, Thesleff studied the effect of increasing doses of succinylcholine on muscle tension in humans (11). This was performed under anaesthesia with intravenous thiopentone that would have appeared to be used as an infusion:

The patient's right hand was fixed on the Brown-Schuster myography stand. On the right elbow a small electrode was placed over the ulnar nerve and a larger indifferent electrode on the upper arm. The electrodes were connected to a stimulator which delivered condenser discharges at the rate of one every 10 seconds. Stimulation of the ulnar nerve produced a flexion twitch in the ulnar fingers. This twitch in the middle phalanges of digits IV and V was recorded by the myography on a kymograph.

It appears that this is the first record of the use of nerve stimulation in an anaesthetised human study group to determine the degree of muscular tension depression with muscle relaxants. It seems that they may have run the risk of direct stimulation of the flexor policis longus muscles rather than purely neuromuscular transmission.

In 1954 Hanquet (12) used needle electrodes in the upper arm of anaesthetised patients and recorded twitches produced in the third finger.

In 1955, Mapleson and Mushin from Cardiff described the direct stimulation of motor nerves and recorded muscle activity distally (13). This was done using the median nerve at the wrist and assessing muscle movement in the thumb. Muscle movement was recorded on a rotating drum. The stimulus was tetanic at 50 Hz:

This frequency was chosen because it was available as a reliable standard in the supply mains and because it was thought to be within the physiological range ... The tetanic stimulus used consisted of square wave current pulses of about 9 msec. width at a frequency of 50/sec., locked to the mains frequency. The duration of each tetanus was made 1.2 sec. to give plenty of time for a steady contraction to become established. The repetition rate of 10/min, was high enough to give a detailed picture of rapid changes in relaxation but low enough to avoid fatigue. The current amplitude, usually 3 to 5 mA, was set to give a normal developed tension of about 800 g. Such a current, of course, represented a submaximal stimulus, and was adopted despite the obvious advantages of a supramaximal one. A supramaximal stimulus was sufficiently painful to be likely to impose a marked restriction on the supply of volunteers!

After stabilisation, gallamine was administered and the depression of thumb muscle tension and the subsequent recovery were recorded.

In 1958, Christie and Churchill-Davidson reported in the Lancet the development of a robust, easy to use neuromuscular monitor designed specifically for anaesthetists to be used in operating theatres (14). The incentive for this was to distinguish the apnoea following succinylcholine from residual narcotisation. This was sold as the St Thomas' Hospital Nerve Stimulator and described as:

The present apparatus (fig. 1) has been designed for use in the operating-theatre and is now produced commercially. It is capable of stimulating at either slow rates (twitch--3 per sec.) or fast rates (tetanus--50 per sec.). In man, ordinary volition uses a rate varying from 30 to 50 per sec. according to the force of the muscle contraction. The intensity of the stimulus can be altered at will, but in the unconscious subject it is advisable to use the maximum possible to ensure that all the muscle-fibres served by that nerve will contract.

In the event of an abnormal response to a muscle relaxant this machine can be used to stimulate the ulnar nerve at the wrist or the elbow (fig. 2). Then, if neuromuscular block is present, the 4th and 5th fingers will not move; on the other hand, if normal neuromuscular transmission is present, the typical picture of main-en-griffe will result.

We believe this nerve-stimulator will prove very useful to anaesthetists. It can be used to study the action of muscle relaxants during routine anaesthesia or (by changing the electrodes) to detect the whereabouts of the facial nerve at operation.

In 1965, published in Anesthesiology under the section labelled "Gadgets", Churchill-Davidson announced the development of the new nerve stimulator (15). The main advantage of this unit was the ability to administer twitch and tetanus stimulation.

The width of the stimulus pulse is 0.3 millisecond and the trigger control enables the stimulus to be delivered singly (at any desired rate) or with a train of tetanic stimuli (approximately 50-60per second).

Interestingly, while Churchill-Davidson does not specifically describe TOF monitoring, he does report: ... the first characteristic of a nondepolarizing block is a fade of successive responses occurring principally in the first four responses both on a slow rate of stimulation (i.e., twitch) and during a train of fast (tetanic) stimuli.

3. Train-of-four assessment (1970-)

The TOF ratio is a technique that compares the twitch height of the fourth twitch with that of the first when supramaximal stimulus is applied at routinely 2 Hz. This demonstrates a reduction in acetylcholine release seen in curarised states and represents states where neuromuscular function is impaired. It was initially described to diagnose and to follow treatment of myasthenia gravis.

In 1968, Roberts and Wilson reported the phenomenon of fade in twitch height when four twitches were applied in patients with myasthenia gravis (16). The frequency of applied current was 4 Hz. Furthermore, they reported that following the ratio of fourth to first twitch height can be used to follow the treatment of myasthenia gravis. "This decline in e.m.g, is a characteristic feature of myasthenia gravis and may be used diagnostically".

Thereafter in 1970 and 1971 there were a series of articles published in the British Journal of Anaesthesia by Ali, Utting and Gray that described the use of TOF monitoring in the assessment of the degree of curarisation in humans (17). In these articles they acknowledge the article by Roberts and Wilson. Their initial reports described the use of stimuli of increasing frequency and demonstrated that in cases of curarisation the twitch height dropped as frequency increased. The frequencies ranged from 0.1 to 10 Hz. They wrote:

It was found that the use of the train of four stimuli had advantages over the use of the simple change of frequency for the quantitative estimation of non-depolarizing block; for though the two indices ran pari passu the train of four stimuli appeared to be a more sensitive index.

They also demonstrated in this paper the absence of fade seen with depolarising block after the administration of suxamethonium. They conclude their paper with an extremely appropriate prediction of where this technique may have a role and how it may be best employed.

... the same degree of block might possibly be significant if it were present for long periods in a patient in the postoperative period. It is important, therefore, to establish the degree of reversal of neuromuscular block, which is compatible with safe return to the ward, and it seems probable that this can be achieved using the train of four stimuli ... This test may also prove to be useful in assessing sensitivity to relaxants, and the likely dose requirements for particular operations. It could also be used as a tool for investigating the effects on neuromuscular transmission of other drugs and inhalation agents used during anaesthesia.

The above work was performed on volunteers.

In their 1971 publication 18, these authors performed similar research in 26 patients undergoing muscle relaxant surgery and introduced the concept of a TOF ratio where the height of the fourth twitch was presented as a percentage of the height of the first as an indication of the degree of neuromuscular block. Until this time the reduction in twitch height was referred to as merely a 'reduction of twitch height'. They went on to set the stimulus rate and number of twitches recorded thus:

The limitation of the stimuli to four at 2 Hz is to ensure maximum depletion of acetylcholine release from the immediately available store at the motor nerve ending, without the complicating factors on the muscle response attributed to the effect of tetanic stimulation at high rates of stimulation.

In their next publication in 1971 (19), these authors examined the evidence for clinical applicability of the TOF ratio and, by comparison with head lift, determined that not only did head lift reflect a higher TOF ratio but that a TOF ratio below 0.6 was associated with an inability to head lift. Clinical recovery from the relaxant was assessed by the ability to lift the head.

The ratio of the height of the fourth response of the train to that of the first (ratio (c)) gave a good indication of the degree of residual neuromuscular block as indicated by this simple clinical test. As ratio (c) increased muscle power improved. Obvious muscle weakness was associated with values of ratio (c) of less than 0.6 ... no patient with a value of ratio (c) less than 0.4 was able to lift his head off the pillow, and all patients with a value of ratio (c) greater than 0.6 were able to lift the head for a period of 3 sec or more ... at this' stage the patient could lift his head off the pillow for 5 seconds and clinical recovery appeared to be good, there was no drooping of the eyelids and tracheal tug had disappeared.

This is the first report we could find that mentions the five-second sustained head lift as being an assessment of adequate reversal of block. Clearly as the years have gone by, the TOF ratio that is now accepted as 'fully reversed' is still debatable but much closer to 0.95, rather than the 0.6 of this era. However the five-second head lift has retained a place in clinical assessment. In this article they also raised the concept of differential blockade and differential levels of reversal between the fine muscles of the hand and other muscle groups:

It must be remembered that the behaviour of the small muscles of the hand towards antidepolarizing neuromuscular blocking agents may not be quantitatively identical with the behaviour of the other muscles.

In 1972, Waud showed that a 100 per second tetanus lasting longer than five minutes was more effective than a TOF ratio in assessing reversal/ recovery from neuromuscular block (20). His opinion was that failure to demonstrate fade under these conditions was more worthwhile. However this work was done in dogs and cats and he acknowledged that it was far more painful. Of note, this is the first article we have found that employed the term fade as 'tetanic fade ratio'.

In 1975, Savarese and colleagues published on the role of TOF ratio in prolonged neuromuscular block with succinylcholine (21). Describing the role of the TOF ratio, they wrote:

In contrast to tetanus, train-of-four nerve stimulation has the advantage of patient comfort, since the train-of-four stimulus is much less painful to a non-anaesthetized individual than a tetanic stimulus. Furthermore there is no need for normal baseline comparison since the train-of-four serves as its own control.

In this paper they describe four patients with pseudocholinesterase deficiency, all of whom demonstrated TOF ratio fade during the block, which they claimed demonstrated that the block had features of a non-depolarising block. Of note, this is the first paper that uses the term 'fade' to describe the failure to sustain twitch height during blockade and the TOE They use the term in inverted commas, so this may be the first use of the term as applied to TOF ratio.

In 1980 Viby-Mogensen and colleagues designed a new type of clinically applicable nerve stimulator that permitted TOF ratio and post-tetanic count (PTC) to be assessed readily in the operating theatre (22).

TOF (train-of-four) (Ali, Utting and Gray, 1970, 1971a, b) comprising four stimuli given at O. 5-s intervals. The train is repeated each 10s.

1 s (single twitch), frequency 1.0 Hz.

10 s (single twitch), frequency O. 1 Hz.

TETANY. When this button is pressed, tetanic stimulation (50 Hz, duration 5 s) begins at the time when the next impulse (dependent on the chosen form of stimulation) is due.

This provided a modern nerve stimulator that permitted assessment of the various modalities which had been introduced since the introduction of earlier stimulators.

4. Post-tetanic count (1981-)

In 1969, David Heisterkamp described post-tetanic potentiation and diminution in twitch height with repeated stimulation under neuromuscular block 23. He commented:

The use of electrical stimulation can give reliable and useful clinical information to the anesthetist. Of the three parameters we have discussed, twitch tension appears to be the most useful single index of the action of d-tubocurarine. (The effect of even one-mg doses could be detected in our study.) The ability to sustain tetanus and visual examination of posttetanic twitch tension are considered less important ...

Also in 1969, Gissen and Katz demonstrated the fade seen during tetanic stimulation at higher frequencies and that this was a sensitive index of neuromuscular blockade 24. This required stimulators with various tetanic frequencies and that the response be measured with a linear displacement transducer. They also demonstrated post-tetanic potentiation but concluded:

In summary, we have examined in detail neutrally-evoked muscle responses as exemplified by twitch, tetanus and posttetanic potentiation. The response to repetitive stimulation is a more accurate index of the level of block than twitch or PTP.

This work was quoted by Viby-Mogensen and colleagues in 1981, when he first described the use of PTC to detect deep levels of neuromuscular block and as a method of predicting return of the first twitch in monitoring (25). The adduction force of the resultant thumb twitch was measured by a displacement transducer and recorded on a polygraph. After administration of pancuronium, tetanic stimuli were applied at 50 Hz for five seconds, then after three seconds 1 Hz single twitch stimuli were applied. TOF was also tested for and time to return of the first twitch of a TOF was recorded as was the post-tetanic twitches present. The findings were that:

... 1) An intense nondepolarizing neuromuscular blockade can be evaluated by the response to posttetanic single twitch stimulation; 2) Magnitude of posttetanic facilitation was negatively correlated with time to first response to TOF nerve stimulation; and 3) Time to return of response to TOF nerve stimulation may be derived from the number of posttetanic twitch responses present (PTC).

This study showed that the average number of PTC to have return of the first twitch in TOF is ten.

This was then followed in 1984 by Howardy-Hansen and colleagues describing the use of a peripheral nerve stimulator to clinically count posttetanic twitches and correlate this with return of single twitch response (26). This study confirmed that a mean PTC of 10.9 correlates with return of one in a TOF count. Importantly, this put the testing of PTC into tactile assessment of PTC and introduced PTC into routine clinical practice for assessment of intense neuromuscular blockade.

5. Double burst stimulation (1989-)

DBS is a technique that compares the twitch height of two consecutive twitches. DBS consists of two sets of three rapid stimuli of 200 microseconds' and 20 milliseconds' duration, each at 50 Hz and separated by 750 milliseconds. This technique helps demonstrate residual neuromuscular blockade, particularly when the TOF ratio is between 0.4 and 0.5, where fade in the response is difficult to identify manually.

The first article that referenced this technique to assess degree of neuromuscular blockade was in 1966 when F. Berry (27) wrote:

Neuromuscular transmission which was suppressed by tubocurarine in the in vitro preparation could be briefly restored by application to the nerve of two or more very closely spaced stimuli; this occurred because of summation of endplate potentials. In this preliminary communication a technique for the detection of neuromuscular block is suggested which utilizes this facilitation phenomenon. The summation of endplate response was demonstrated to occur in an in vivo preparation when a double stimulus is applied.

Thereafter the technique appears to have lain dormant until 1989, when Engbaek et al reported the use of DBS to assess residual neuromuscular blockade where manual detection of residual curarisation with TOF was difficult (28):

We present a new pattern of nerve stimulation--double burst stimulation (DBS)--to detect residual neuromuscular block manually. The DBS consists of two short lasting, 50-Hz tetanic stimuli or bursts separated by a 750-ms interval.

The response to this pattern of stimulation is two separated muscle contractions of which the second is less than the first during non-depolarising neuromuscular blockade. The ability to identify fade manually at different TOF ratios was compared in four DBS patterns in which different numbers of impulses in the individual bursts were combined. The DBS with three impulses in each burst was considered to be the most sensitive and the least painful and thus most suitable for clinical use. It is concluded that the DBS is more sensitive than the TOF in manual detection of residual block (28).

Later in 1989, Drenck et al compared TOF and DBS (29). They acknowledged the role that TOF played in detecting neuromuscular blockade over the preceding 20 years and made note of the work from the previous study discussed above. They undertook their study to directly compare whether DBS was more sensitive than TOF in manual detection of residual neuromuscular blockade during clinical anaesthesia. They enrolled 52 patients of American Society of Anesthesiologists physical status I or II undergoing elective lower abdominal or mastectomy procedures; no patient with neuromuscular disease or taking medications that might interfere with neuromuscular transmission was included in the study. They found that a significantly higher rate of fade to DBS was detected than with TOF ratio, also that when TOF fade was felt invariably fade was present with DBS. DBS allows for detection of a TOF ratio below 0.6; however it is noted that it was generally agreed that a TOF ratio [greater than or equal to] 0.7 was required to ensure adequate clinical recovery from neuromuscular blockade. Their results also showed that when there was no manual detection of fade with either DBS or TOF response that there was still a "47% risk that the true TOF ratio was <0.7". Of note, this was not improved with increased experience in manual detection of fade.

REFERENCES

(1.) Ball C, Westhorpe RN. Muscle relaxants--d-tubocurarine. Anaesth Intensive Care 2005; 33: 431.

(2.) Ball C, Westhorpe RN. Muscle relaxants--the early history. Anaesth Intensive Care 2005; 33: 155.

(3.) Ball C, Westhorpe RN. Muscle relaxants--intocostrin. Anaesth Intensive Care 2005; 33: 289.

(4.) Bennet AE. Preventing traumatic complications in convulsive shock therapy by curare. JAMA 1940; 114: 322-324.

(5.) Griffith HR, Johnson GE. Use of curare in general anesthesia. Anesthesiology 1942; 3: 418-420.

(6.) Organe G, Paton WDM, Zaimis EJ. Preliminary trials of bistrimethylammonium decane and pentane diiodide (C10 and C5) in man. Lancet 1949; 1: 21-23.

(7.) Mushin WW, Wien R, Mason D, Langton G. Curare-like actions of tri-(diethylaminoethoxy)-benzene triethyliodide. Lancet 1949; 1: 726-728.

(8.) Guild AA. Decamethonium iodide in muscular hypertonus. Lancet 1950; 2: 251-252.

(9.) Beecher HK, Todd DP. A study of the deaths associated with anesthesia and surgery: based on a study of 599, 548 anesthesias in ten institutions 1948-1952, inclusive. Ann Surg 1954; 140: 2-35.

(10.) Dripps RD, Lamont A, Eckenhoff JE. The role of anesthesia in surgical mortality. JAMA 1961; 178: 261-266.

(11.) Thesleff S. An investigation of the muscle-relaxing action of succinyl-choline-iodide in man. Acta Physiol Scand 1952; 25: 348-367.

(12.) Hanquet M. Study of neuromuscular transmission blockage in man. Acta Anaesthesiol 1954; 5: 103-110.

(13.) Mapleson WW, Mushin WW. Relaxant action in man; an experimental study. 1. Method. Anaesthesia 1955; 10: 265-278.

(14.) Christie TH, Churchill-Davidson HC. The St. Thomas's Hospital nerve stimulator in the diagnosis of prolonged apnoea. Lancet 1958; 1: 776.

(15.) Churchill-Davidson HC. A portable peripheral nerve-stimulator. Anesthesiology 1965; 26: 224-226.

(16.) Roberts DV, Wilson A. Electromyography in the diagnosis and treatment of myasthenia gravis. Br J Pharmacol 1968; 34: 229P-230P.

(17.) Ali HH, Utting JE, Gray C. Stimulus frequency in the detection of neuromuscular block in humans. Br J Anaesth 1970; 42: 967-978.

(18.) Ali HH, Utting JE, Gray TC. Quantitative assessment of residual antidepolarizing block. I. Br J Anaesth 1971; 43: 473-477.

(19.) Ali HH, Utting JE, Gray TC. Quantitative assessment of residual antidepolarizing block. II. Br J Anaesth 1971; 43: 478-485.

(20.) Waud BE, Waud DR. The relation between the response to "train-of-four" stimulation and receptor occlusion during competitive neuromuscular block. Anesthesiology 1972; 37: 413-416.

(21.) Savarese JJ, Ali HH, Murphy JD, Padget C, Lee CM, Ponitz J. Train-of-four nerve stimulation in the management of prolonged neuromuscular blockade following succinylcholine. Anesthesiology 1975; 42: 106-111.

(22.) Viby-Mogensen J, Hansen PH, Jorgensen BC, Ording H, Kann T, Fries B. A new nerve stimulator (Myotest). Br J Anaesth 1980; 52: 547-550.

(23.) Heisterkamp DV, Skovsted P, Cohen PJ. The effects of small incremental doses of d-tubocurarine on neuromuscular transmission in anesthetized man. Anesthesiology 1969; 30: 500-505.

(24.) Gissen A J, Katz RL. Twitch, tetanus and posttetanic potentiation as indices of nerve-muscle block in man. Anesthesiology 1969; 30: 481-487.

(25.) Viby-Mogensen J, Howardy-Hansen E Chraemmer-Jorgensen B, Ording H, Engbaek J, Nielsen A. Posttetanic count (PTC): a new method of evaluating an intense nondepolarizing neuromuscular blockade. Anesthesiology 1981; 55: 458-461.

(26.) Howardy-Hansen R Viby-Mogensen J, Gottschau A, Skovgaard LT, Chraemmer-Jorgensen B, Engbaek J. Tactile evaluation of the posttetanic count (PTC). Anesthesiology 1984; 60: 372-374.

(27.) Berry FR. Detection of neuromuscular block in man. Preliminary communication. Br J Anaesth 1966; 38: 929-935.

(28.) Engbaek J, Ostergaard D, Viby-Mogensen J. Double burst stimulation (DBS): a new pattern of nerve stimulation to identify residual neuromuscular block. Br J Anaesth 1989; 62: 274-278.

(29.) Drenck NE, Ueda N, Olsen NV, Engbaek J, Jensen E, Skovgaard LT et al. Manual evaluation of residual curarization using double burst stimulation: a comparison with train-of-four. Anesthesiology 1989; 70: 578-581.

T. E. LOUGHNAN *, A. J. LOUGHNAN ([dagger])

Department of Anaesthesia, Frankston Hospital, Peninsula Health, Frankston, Victoria, Australia

* FANZCA, Director of Anaesthetic Research.

([dagger]) MB, BS, Anaesthetic Registrar, Monash Anaesthetic Training Scheme, Monash Medical Centre, Clayton.

Address for correspondence: Dr T. E. Loughnan. Email: terence. loughnan@monash.edu

Accepted for publication on June 5, 2013.
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Title Annotation:Original Papers
Author:Loughnan, T.E.; Loughnan, A.J.
Publication:Anaesthesia and Intensive Care
Article Type:Report
Geographic Code:8AUST
Date:Jul 1, 2013
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