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Clinical validation of electromyography and acceleromyography as sensors for muscle relaxation

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Abstract

The aim of this study was to determine which of two clinically applied methods, electromyography or acceleromyography, was less affected by external disturbances, had a higher sensitivity and which would provide the better input signal for closed loop control of muscle relaxation. In 14 adult patients, anaesthesia was induced with intravenous opioids and propofol. The response of the thumb to ulnar nerve stimulation was recorded on the same arm. Mivacurium was used for neuromuscular blockade. Under stable conditions of relaxation, the infusion-rate was decreased and the effects of turning the hand were investigated. Electromyography and acceleromyography both reflected the change of the infusion rate (P = 0.015 and P < 0.001, respectively). Electromyography was significantly less affected by the hand-turn (P = 0.008) than acceleromyography. While zero counts were detected with acceleromyography, electromyography could still detect at least one count in 51.1%. Electromyography is more reliable for use in daily practice as it is less influenced by external disturbances than acceleromyography.
European Journal of Anaesthesiology 2007; 1–7
r 2007 Copyright European Society of Anaesthesiology
doi: 10.1017/S0265021506002353
Original Article
Clinical validation of electromyography and acceleromyography
as sensors for muscle relaxation
P. H a
¨
nzi
*
, D. Leibundgut
*
, R. Wessendorf
y
, R. Lauber
*
, A. M. Zbinden
*
University Hospital of Bern,
*
Department of Anaesthesiology, Murtenstrasse, Bern, Switzerland;
y
Department of
Anaesthesiology, Kreiskrankenhaus Erding, Bajuwarenstrasse, Erding, Germany
Summary
Background and objective: The aim of this study was to determine which of two clinically applied methods,
electromyography or acceleromyography, was less affected by external disturbances, had a higher sensitivity
and which would provide the better input signal for closed loop control of muscle relaxation. Methods: In 14
adult patients, anaesthesia was induced with intravenous opioids and propofol. The response of the thumb to
ulnar nerve stimulation was recorded on the same arm. Mivacurium was used for neuromuscular blockade.
Under stable conditions of relaxation, the infusion-rate was decreased and the effects of turning the hand were
investigated. Results: Electromyography and acceleromyography both reflected the change of the infusion rate
(P 5 0.015 and P , 0.001, respectively). Electromyography was significantly less affected by the hand-turn
(P 5 0.008) than acceleromyography. While zero counts were detected with acceleromyography, electro-
myography could still detect at least one count in 51.1%. Conclusions: Electromyography is more reliable for
use in daily practice as it is less influenced by external disturbances than acceleromyography.
Keywords: NEUROMUSCULAR BLOCKING AGENTS, mivacurium; NEUROMUSCULAR BLOKADE,
acceleromyography, electromyography; EQUIPMENT AND SUPPLIES.
Introduction
Mechanomyography (MMG) is general ly used as
gold standard to measure neuromuscular function
[1]. However, its clinical use in daily practice is
limited
[2]. Electromyography (EMG) gives com-
parable results to MMG and can be used as well
[1].
Subjective estimation of the extent of the train-
of-four (TOF, T4/T1) fade is poor, especially when
the TOF ratio exceeds 0.40–0.50
[3,4]. Manually
measured counts cannot be used as a continuous
input for a feedback-controlled system. However, an
advantage of the TOF is the fact that no calibration
is needed before the measurement
[5]. This reduces
induction time and avoids the problem of baseline
shift. The disadvantage is the fact that it cannot be
determined once there are only three counts left. For
this reason, we used T1% (percentage of first twitch
to initial twitch before relaxation) as reference value,
which had to be calibrated before starting the
measurements. A waiting period of 10 min was
introduced to minimize the effect of the baseline
drift.
Despite potential adverse effects of using neuro-
muscular blocking agents, there is no quantitat ive
routine monitoring of neuromuscular function
during anaesthesia
[6] using MMG or EMG as these
measurement techniques tend to be more time
consuming. Clinical estimation of neuromuscular
blockade may be biased
[13]. Acceleromyography
(AMG) was introduced in 1988 by Viby-Mogensen
as a new method for monitoring neuromuscular
function, fulfilling the basic requirements for a
Correspondence to: Daniel Leibundgut, Department of Anaesthesiology,
Section of Research, University Hospital of Bern, 3010 Bern, Switzerland.
E-mail: daniel.leibundgut@dkf.unibe.ch; Tel: 141 31 632 27 58; Fax: 141 31
632 88 48
Accepted for publication 18 November 2006 EJA 3498
simple and reliable clinical monitoring tool [7].It
became popular because of its straightforward
and easy application
[8]. As a resear ch instrument,
it may be used after careful calibration
[8,9].
However, AMG cannot be directly compared to
MMG
[10,11] or EMG with respect to the esti-
mation of neuromuscular blockade and stimulating
patterns
[12]. Furthermore, as AMG works dyna-
mically and MMG works isometrically, it is not
possible to use the two methods simultaneously on
the same arm. AMG has been investigated and
comparisons have been made with EMG and MMG
[1,11,13–18]; however, sensitivity and robustness
to artefacts have not been investigated in AMG and
EMG so far.
For delivering short-acting newer neuromuscular
blocking agents, a continuous, accurate and reliable
signal would be useful, specially if these agents
should be given using automatic feedback control
systems
[19]. Input signals for control loops should
be discrete and of a higher resolution, compared to a
categorical signal such as a TOF value. They must
give a rapid and true measurement of what should
be controlled and should not be subjected to arte-
facts or to drifts as these are difficult to detect by an
automatic control system.
The objective of this study was to answer the
question if the AMG response to the ulnar nerve
stimulation using a common clinically established
device gives reliable, discrete input signal, which
could be routinely used. We tested EMG against
AMG using two manipulations: (a) the change
of infusion rate (lowering the dose) and (b) the
position change of the sensor hand, answering
the fact that the two measurement methods quan-
tify different effects but answer the same clinical
question.
Materials and methods
The study was approved by the Ethics Committee of
the District of Bern. Written informed consent was
obtained from each patient. Fourteen patients (nine
females and five males, mean age 41.7 yr (26–55),
mean body mass index (BMI) 24.85 kg m
22
(17.3–32.5)), ASA Class I or II, who were scheduled
for elective surgery, were included in the study. The
patients were free of any known neuromuscular
diseases, or renal and hepatic diseases, and did not
take any drugs known to interfere with neuromus-
cular transmission.
Anaesthesia and the measurement of neuro-
muscular blockade was performed in accordance
with the Good Clinical Research Practice (GCRP)
in pharmacodynamic studies of neuromuscular
blocking agents
[1] to keep bias as low as possible.
All patients were premedicated orally with 7.5
or 15 mg of midazolam or 1 mg of lorazepam
30–60 min before induction of anaesthesia. On
arrival in the oper ating theatre, an intravenous
(i.v.) catheter was inserted to administer fluids
and drugs. Pulse oximetry, electrocardiogram and
non-invasive blood pressure were monitored on the
same arm. The other arm was used for neuromus-
cular monitoring. Bispectral index was routinely
monitored. After preoxygenation, anaesthesia was
introduced with bolus doses of propofol 2%
2–2.5 mg kg
21
, fentanyl (0.1–0.2 mg) and remi-
fentanil (1–2 mgkg
21
). The trachea of the patients
was intubated without the use of neuromuscular
blocking agents. In case of problems or danger for
the patient, succinylcholine 1 mg kg
21
was used for
relaxation. Anaesthesia was maintained with an
infusion of remifentanil (100–800 mgh
21
), a target
controlled infusion of propofol 2% 1.5–8 mgmL
21
and bolus doses of fentanyl (0.05–0.1 mg). Core
temperature was monitored and maintained using
forced air warming blankets (Bair Hugger
TM
;
Augustine Medical Inc., Eden Prairie, MN, USA).
The ulnar nerve was stimulated on the forearm
with the TOF (four supramaximal square wave
pulses of 0.2 ms duration and a frequency of 2 Hz).
The recording electrodes for EMG were set up fol-
lowing the manufacturer guid elines at the adductor
pollicis muscle. We compared EMG (Datex-
Ohmeda AS/3; Helsinki, Finland) with AMG
(TOF-Watch SX, Organon Teknika; Boxtel, The
Netherlands), both devices being installed on the
same stimulus-electrodes of the arm of the patient
using an electrical switch. The electrodes (Ag/AgCl-
ECG electrodes for children, recording diameter of
10 mm; REF 1008, Nessler Medizinaltechnik,
Innsbruck, Austria) were stuck to the skin, which
had been cleaned beforehand. Temperature of the
stimulated hand was measured with a surface elec-
trode (TOF-Watch SX) and ke pt constantly above
328C
[1]. The acceleration transducer was attached
to the flexor-side of the thumb over the distal
interphalangeal joint. The thumb was able to move
freely while hand and arm were fixed with the splint
from Organon-Teknika on a rigid board
[10,20].
The counts (T1–T4), T1% (T1/Tref * 100) and the
TOF were continuously measured by computer,
separately for each device (TOF-Watch SX-Monitor,
software version 1.2 by Organon-Teknika), for
TOF-Watch SX and Labview (National Instruments
Corporation, Austin, TX, USA) and for the EMG-
Monitor (Datex-Ohmenda, Helsinki, Finland).
After induction, the AMG was calibrated according
to the instructions of the manufacturer using its
automatic start-up procedure. A period of at least
10 min was allowed for baseline drift of the nerval
2 P. H a ¨nzi et al
r 2007 Copyright European Society of Anaesthesiology, European Journal of Anaesthesiology, 1–7
responses by using the 0.1 Hz mode (supramaximal
stimuli with square wave pulses of 0.2 ms duration
every 10 s). A second calibration of the AMG was
performed in a similar fashion. EMG was set up and
also calibrated according to the instructions of the
manufacturer. Supramaximal current was deter-
mined separately for each device. The T1% of EMG
was used as reference value for all measurements.
After the stabilization phase and second calibration,
both devices were started with a time difference of
30 s and then the TOF was measured every minute
for each device.
Patients were normoventilated and end-tidal CO
2
was kept constant. A syringe pump (Asena GH;
Alaris Medical Systems, Basingstoke, Hampshire,
UK) was used to apply a continuous infusion of
mivacurium chloride (mivacron
s
; Glaxo Wellcome
Gmbh & Co, Zeneca Gmbh) with an initial rate
of 0.2–0.3 mg kg
21
h
21
. Once T1% of the EMG
was stable (criteria for stabilization of T1%: ampli-
tude within 15%, during 15 min), the infusion rate
of mivacurium was lowered to 0.05 or 0.1 mg
kg
21
h
21
. After this change, we waited again for
signal stabilization using the above-mentioned cri-
teria, then turned the sensor-hand by 908 from
a vertical position with the thumb up to a palmar-
side-down position (hand turn) (Fig. 1; first trace).
Mean T1% over 5 min before lowering the miva-
curium dose (5HD), mean T1% over 5 min before
hand turn (5LDb) and mean T1% over 5 min
after hand turn (5LDa) were used for comparing
these events.
Statistical analysis
To measure the reaction to lowering the mivacurium
dose, HD was compared with the LDb of each
device. The effect of turning the hand was shown by
comparing LDb with LDa. To compare AMG with
EMG for both effects, lowering the dose or changing
the hand position, the differences of the mean T1%
before the event to the mean T1% after the event
were compared using t-test (normality test passed) or
U-test (normality test failed). To compare EMG and
AMG for their potential to be used in situations
with high neuromuscular blockade, no-twitch
response measurements of one method were com-
pared to twitch responses of the other, and vice versa.
To compare the overall deviation of EMG-counts to
AMG-counts, the L1-Norm value was used:
L
1
5
Dt
T
X
n
i51
jEMGðiÞAMGðiÞj
Dt 5 sampling time.
T 5 total time of observation of one period.
n 5 total number of measurements during obser-
vation period.
The differences were considered as statistically sig-
nificant when P , 0.05 (F
0.95
).
Results
Seventeen patients were selected to participate, of
which 14 are presented in the results. Three patients
dropped out because of surgical complications
during operation, the duration of the operation or
because of inadequate depth of relaxation with
respect to the surgical demands. The average
temperature of the sensor-hands was 33.78C
(31.5–35.68C). The mean BMI was 24.85 kg m
22
(range: 17.3–32.5 kg m
22
); three of the patients
were obese (BMIs of 30.7, 31.2 and 32.5 kg m
22
).
Succinylcholine was used due to expected difficult
intubation in three patients.
The stimulation power of both devices after
searching for the supramaximal current for each
sensor was significantly different (P , 0.001, using
a U-test): the median current of AMG was 60 mA
(range 55–60 mA) while the median current of
EMG was 37.5 mA (range 23–64 mA), despite the
fact that the same stimulating electrodes wer e used.
The mivacurium dose was not lowered according
to a scheme but based on the experience of the
anaesthetist and depending on the phase of surgery.
Figure 1 shows a sample recording of one experi-
ment, with inaccurate high T1% values at the
beginning of mivacurium infusion.
On lowering the dose (mean of
0.086 mg kg
21
h
21
), both devices reacted compar-
ably in the expected direction. Both EMG and
AMG show a significant change of mean T1%
between the phase before lowering the dose to the
phase afterwards (P 5 0.015 and P 5 0.004,
respectively, Table 1).
The hand turn disturbed the EMG signal (P 5
0.863) much less than the AMG signal (P 5 0.007)
(Table 1). For control, we compared two phases
under stable conditions that showed no significant
differences (AMG: P 5 0.953 and EMG: P 5 0.972)
(Fig. 2). The comparison of EMG and AMG showed
no significant difference with respect to lowering
the dose (P 5 0.306) compared to turning the hand
(P 5 0.008) (Table 2). The difference of mean T1%
before and after hand turn was significantly
(P 5 0.008) smaller for EMG (20.26%) than for
AMG (210.01%) (Fig. 3).
In situations with hig h neuromuscular blockade,
a comparison of the twitch response records between
EMG and AMG is as follows: in measurements
where EMG recorded no answers, AMG detected
EMG and AMG validation 3
r 2007 Copyright European Society of Anaesthesiology, European Journal of Anaesthesiology, 1–7
one or more count in 30% of the non-twitch
response periods; whereas where AMG recorded no
answers, EMG detected one or more counts in 51%
of the non-twitch response periods (Fig. 4). The
overall deviation of EMG counts to AMG counts
calculated as mean L1 was 0.56 (0.47).
20 40 60 80 100 120 140 160 180 200
T1%
0
20
40
60
80
100
120
EMG
AMG
20 40 60 80 100 120 140 160 180 200
EMG counts
0
1
2
3
4
TOF ratio (%)TOF ratio (%)
0
20
40
60
80
100
120
20 40 60 80 100 120 140 160 180 200
Infusion rate [mg
kg
–1
h
–1
]
0.0
0.1
0.2
0.3
0.4
Time
(
min
)
20 40 60 80 100 120 140 160 180 200
AMG counts
0
1
2
3
4
0
20
40
60
80
100
120
140
Counts
TOF ratio
Lower the
Infusion rate
Hand turn
Counts
TOF ratio
Figure 1.
Sample trial data traces. The vertical lines mark the events for lowering the mivacurium dose and the hand turn. The first trace shows the
mivacurium infusion rate. The second, the T1% values for both EMG and AMG. The last two traces show the TOF ratio and the count
values for EMG and the bottom one for AMG.
4 P. H a ¨nzi et al
r 2007 Copyright European Society of Anaesthesiology, European Journal of Anaesthesiology, 1–7
Discussion
This study compared the AMG and EMG sensors
with respect to accuracy and artefact tolerance, with
the objective of evaluating which sensor is more
suitable to integrate in a feedback-controlled system
for the application of muscle relaxants. AMG, in
contrast to EMG, was more affected by external
disturbances such as movement and was less sensi-
tive at high degrees of neuromuscular blockade. The
difference between the measurements of AMG and
EMG may be caused by the fact that these devices
do not measure the same physiological phenomenon
Table 1. Influence of lowering the mivacurium-infusion-rate (HD vs. LDb) and of hand turn (LDb vs. LDa) on EMG and AMG.
T1% HD (SD) LDb (SD) Lda (SD) P value
AMG Lowering mivacurium-rate 10.053 (7.269) 32.933 (27.058) 0.004
**
Hand turn 32.933 (27.058) 42.947 (26.814) 0.007
*
EMG Lowering mivacurium-rate 21.934 (16.950) 39.049 (19.861) 0.015
**
Hand turn 39.049 (19.861) 39.305 (18.625) 0.863
T1% values are given as mean (standard deviation).
**
Indicates a significant value for lowering the infusion rate.
*
Indicates a significant value
for AMG for the hand turn. EMG: electromyography; AMG: acceleromyography.
90
80
80
70
60
50
40
30
20
10
70
60
50
T1%
T1%
40
30
20
10
0
AMG phase 1 AMG phase 2 EMG phase 1 EMG phase 2
Figure 2.
Comparison of two phases (each 5 min) under stable
conditions for AMG (left) and EMG (right). The
box plots show median (notched), 25% and 75%
quartiles, range of data and outliers (for values
beyond 1.5 times the inter quartile range of upper or
lower quartile).
Table 2. Differences of T1% values of EMG and AMG at
lowering mivacurium-infusion rate and at hand turn.
DEMG (SD) DAMG (SD) P values
Lowering dose 217.12 (23.98) 222.88 (26.20) 0.306
Hand turn 20.26 (5.65) 210.01 (12.30) 0.008
*
Values are given as mean (standard deviation).
*
Indicates a
significant difference between EMG and AMG for the hand turn.
EMG: electromyography; AMG: acceleromyography.
Counts
1 2 3 4 Invalid
Percent EMG/AMG twitches of
no-twitch responses of AMG/EMG (%)
0
5
10
15
20
25
30
35
40
45
EMG twitches (no-twitch response of AMG)
AMG twitches (no-twitch response of EMG)
Figure 4.
No twitch response of EMG compared to the twitch response of
AMG (shaded) and reverse (black). Number of twitch responses
outside the valid range of 0 to 4 counts are summarized under
‘Invalid’.
10
0
10
T1%
20
30
40
EMG AMG
Figure 3.
Comparison of the two devices for hand turn. Mean T1% before
the hand turn minus mean T1% after the turn. The box plots
show median (notched), 25% and 75% quartiles, range of data
and outliers (for values beyond 1.5 tim es the inter quartile range
of upper or lower quartile).
EMG and AMG validation 5
r 2007 Copyright European Society of Anaesthesiology, European Journal of Anaesthesiology, 1–7
[21]. AMG and EMG are preferred in the clinical
routine to MMG because they are easier to use.
We followed the guidelines for GCRP in phar-
macodynamic studies of neuromuscular blocking
agents
[1]. We allowed a period of 10 min for
stabilization of the baseline, as according to earlier
studies the most significant drift occurs during this
time
[22].TOFratiosmaygoupto1.3withoutany
neuromuscular blocking agent on board as also
reported in other studies
[23], even though the
thumb was able to move freely with the hand totally
fixed to a board. Non-relaxed thumbs might not
return to the starting point and might not move in
one direction only. Previous studies using AMG and
EMG showed that the measurement of neuromus-
cular blockade cannot be compared between both
arms of one individual
[10]. For that reason, the
patient’s response to neuromuscular stimulation was
determined on the same arm, stimulating with the
same electrodes for both devices. To take into con-
sideration that EMG and AMG measure different
physical effects, supramaximal stimulation current is
different as well. So far, no further data on supra-
maximal stimulation current while comparing dif-
ferent methods have been published. AMG and EMG
recorded on the same limb are published by Kopman
and colleagues
[24] andshowedanoverestimationof
AMG TOF values compared to EMG TOF.
In operations where full relaxation is required,
such as brain or ophthalmic surgery, any sudden
movement by the patients may result in complica-
tions. It is therefore essential to use a system that
provides reliable and highly sensitive measure-
ments. The L1-norm showed a difference between
the two devices during the observed periods of half
a count: EMG sensors showed higher sensitivity and
seemed to be more reliable.
In conclusion, these findings suggest that in
situations where reliable monitoring is essential such
as in cases where short acting drugs are applied,
feedback control is used, or in especially critical
operations, EMG should be given preference over
AMG despite the fact that its installation is more
time-consuming. EMG, as a more accurate method,
is preferable for research, while AMG, as a simpler
and stable method, is preferable for routine practice.
Acknowledgments
Stiftung zur Foerderung der wissenschaftlichen
Forschung an der Universitaet Bern.
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EMG and AMG validation 7
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... The different matters are required for installation of the different measuring techniques. The AMG was affected by stabilization of transducers [9], whereas the EMG was more affected by skin resistance than the AMG. In the present study, the calibration time of the AMG is significantly longer than the EMG. ...
... One possible explanation is the difference of sensitivity between the two devices. That is, the EMG can detect muscle activities more sensitively than the AMG [6,9,10]. Additionally, the EMG can yield more consistent responses because it is not affected by restriction of a movement of a muscle [9,11]. ...
... That is, the EMG can detect muscle activities more sensitively than the AMG [6,9,10]. Additionally, the EMG can yield more consistent responses because it is not affected by restriction of a movement of a muscle [9,11]. The AMG may need a higher stimulation current to properly detect muscle contractions than the EMG. ...
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Background: Electromyography and acceleromyography are common neuromuscular monitoring devices. However, questions still remain regarding the use of acceleromyography in children. This study compared the calibration success rates and intubation conditions in children after obtaining the maximal blockade depending on each of the devices. Methods: Children, 3 to 6 years old, were randomly allocated to the TOF-Watch SX acceleromyography group or the NMT electromyography group. The induction was performed with propofol, fentanyl, and rocuronium. The bispectral index and 1 Hz single twitch were monitored during observation. The calibration of the each device was begun when the BIS dropped to 60. After successful calibration, rocuronium 0.6 mg/kg was injected. A tracheal intubation was performed when the twitch height suppressed to 0. The rocuronium onset time (time from administration to the maximal depression of twitch height) and intubating conditions were rated in a blinded manner. Results: There was no difference in the calibration success rates between the two groups; and the calibration time in the electromyography group (16.7 ± 11.0 seconds) was shorter than the acceleromyography group (28.1 ± 13.4 seconds, P = 0.012). The rocuronium onset time of the electromyography group (73.6 ± 18.9 seconds) was longer than the acceleromyography group (63.9 ± 18.8 seconds, P = 0.042) and the intubation condition of the electromyography group (2.27 ± 0.65) was better than the acceleromyography group (1.86 ± 0.50, P = 0.007). Conclusions: Electromyography offers a better compromise than acceleromyography with respect to the duration of calibration process and surrogate for the optimal time of tracheal intubation in children.
... It is based on the assumption that the peak acceleration of an extremity in response to nerve stimulation is directly proportional to the force applied to the extremity by muscle contraction (Jensen et al. 1988;Viby-Mogensen et al. 1996). Electromyography (EMG) is another alternative to MMG that has been used to assess neuromuscular transmission in dogs and people under anesthesia (Hanzi et al. 2007;Clark et al. 2012). This technique measures the compound motor action potential produced in muscles after electrical stimulation of a peripheral nerve. ...
... Unimpeded paw movement is difficult to arrange in dogs in sternal recumbency, virtually precluding the use of AMG. Others have suggested that EMG may be less affected by external disturbances than AMG, such as position of the limb or movement (Hanzi et al. 2007). EMG is not as widely used as AMG in clinical practice, however, its use may gain traction in the future for the reasons mentioned above. ...
Article
Objective Quantitative neuromuscular monitoring is essential for studies of potency and duration of neuromuscular blocking agents, and for detecting residual paralysis in anesthetized patients. This investigation evaluates whether there are systematic differences between acceleromyography (AMG) and electromyography (EMG); two quantitative methods for monitoring neuromuscular block.Study designProspective.AnimalsTen healthy Beagle dogs.Methods Dogs were anesthetized with isoflurane and dexmedetomidine. Both ulnar nerves were stimulated with a train-of-four (TOF) pattern every 15 seconds. The magnitude of the first twitch (T1) and the TOF ratio (magnitude of T4/T1; TOFR) were quantified simultaneously with AMG and EMG, applied randomly to each extremity. The extent of maximal block (T1 depression) and onset time were measured by AMG and EMG during TOF monitoring after the administration of cisatracurium (0.05 mg kg−1). In addition, recovery of T1 to 25% and 75%, the recovery index (time between T1 of 25% and 75%), and recovery of the TOFR to 0.9 were used to characterize recovery from cisatracurium and were compared between monitors. Regression and Bland-Altman plots for T1 and TOFR were also created.ResultsMaximal block and onset time were not different between monitors. Time to recovery of T1 to 25% and 75%, and time to TOF ratio 0.9 was significantly shorter with AMG. The recovery index was not different between monitors. When the TOFR returned to 0.9 with AMG, EMG still measured considerable residual block (TOFR 0.47).Conclusions and clinical relevanceElectromyography consistently detected residual NMB when recovery from NMB was complete as assessed by AMG.
... EMG has several advantages, including the fact that it can be applied to detect evoked compound action potentials at most muscles and is less affected by external disturbances [19]. However, there are also disadvantages associated with the use of EMG, such as the fact that it is difficult to assess neuromuscular block at smaller muscles because of the small action potentials created. ...
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Recent advances in neuromuscular monitors have facilitated the development of a new electromyographic module, AF-201P™. The purpose of this study was to investigate the relationship between post-tetanic counts (PTCs) assessed using the AF-201P™ and the acceleromyographic TOF Watch SX™ during rocuronium-induced deep neuromuscular block. Forty adult patients consented to participate in this study. The integrated AF-201P™ stimulating and sensing electrode was placed over the ulnar nerve on the distal volar forearm and the belly of the abductor digiti minimi muscle of one arm. The TOF Watch SX™ was applied with the provided hand adaptor on the opposite arm, to observe twitch responses of the adductor pollicis muscle. After stabilization of train-of-four (TOF) responses, rocuronium 0.9 mg kg−1 was administered intravenously. Then, PTCs were observed every 3 min using both monitors. Whenever the TOF count was detected with the TOF Watch SX™, rocuronium 0.2 mg kg−1 was administered, and successive PTC measurements were continued. A total of 1732 paired PTC data points were obtained and analyzed. Regression analysis showed no significant difference in PTCs between the two monitors (PTCs measured by the TOF Watch SX™ = 0.78·PTCs measured by AF-201P™ + 0.21, R = 0.56). Bland–Altman analysis also showed acceptable ranges of bias [95% CI] and limits of agreement (0.3 [0.2 to 0.5] and − 4.6 to 5.3) for the PTCs. The new EMG module, AF-201P™, showed reliable PTCs during deep neuromuscular block, as well as the TOF Watch SX™.
... Temperature changes affect EMG measurements to a lesser extent than they do MMG measurements, with every 1°C decrease in skin temperature increasing the CMAP amplitudes by 2-3% [68]. In a comparative investigation, Hänzi et al. found EMG more reliable for use in daily practice as it was less influenced by external disturbances than acceleromyography [69]. However, EMG is susceptible to direct muscle stimulation or interference from surgical cautery. ...
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Purpose of Review The purpose of this review is to summarize various quantitative neuromuscular monitoring modalities and describe strategies to implement them into routine practice. We will contrast these objective modalities with unreliable clinical tests and subjective techniques that expose patients to unnecessary risk associated with postoperative residual weakness. Recent Findings As major specialty societies publish guidelines and consensus statements urging anesthesiologists to utilize quantitative monitors, clinicians must familiarize themselves with this equipment. Furthermore, new monitors are emerging as the industry tries to address the need for user-friendly, reliable monitors. Summary Clinical assessment is an unacceptable technique to guide neuromuscular blockade management in patients receiving neuromuscular blocking agents. The use of a peripheral nerve stimulator can provide some information regarding the level of neuromuscular blockade in patients; however, it cannot reliably confirm adequate recovery. The use of objective, quantitative monitoring is an essential practice that helps guide the administration of neuromuscular blocking agents and excludes deleterious postoperative residual weakness.
... Train of four (TOF) is the standard technique for monitoring the described clinical effect. 2 Following administration of a non-depolarising agent, levels of NMB are classed as intense, deep, moderate and recovery level, depending on the dose and the time elapsed from administration 3 (Appendix A, Table A, additional online material). ...
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Introduction: Neuromuscular blockade enables airway management, ventilation and surgical procedures. However there is no national consensus on its routine clinical use. The objective was to establish the degree of agreement among anaesthesiologists and general surgeons on the clinical use of neuromuscular blockade in order to make recommendations to improve its use during surgical procedures. Methods: Multidisciplinary consensus study in Spain. Anaesthesiologists experts in neuromuscular blockade management (n=65) and general surgeons (n=36) were included. Delphi methodology was selected. A survey with 17 final questions developed by a dedicated scientific committee was designed. The experts answered the successive questions in two waves. The survey included questions on: type of surgery, type of patient, benefits/harm during and after surgery, impact of objective neuromuscular monitoring and use of reversal drugs, viability of a multidisciplinary and efficient approach to the whole surgical procedure, focussing on the level of neuromuscular blockade. Results: Five recommendations were agreed: 1) deep neuromuscular blockade is very appropriate for abdominal surgery (degree of agreement 94.1%), 2) and in obese patients (76.2%); 3) deep neuromuscular blockade maintenance until end of surgery might be beneficial in terms of clinical aspects, such as as immobility or better surgical access (86.1 to 72.3%); 4) quantitative monitoring and reversal drugs availability is recommended (89.1%); finally 5) anaesthesiologists/surgeons joint protocols are recommended. Conclusions: Collaboration among anaesthesiologists and surgeons has enabled some general recommendations to be established on deep neuromuscular blockade use during abdominal surgery.
Chapter
This chapter covers the spectrum of equipment used to provide anesthesia to children safely. Specifically, advantages and disadvantages of devices for warming the child, maintaining temperature, intravenous catheter types and issues, fluid and blood warming devices, airway adjuncts (laryngeal mask airways, oral airways, and nasal trumpets), equipment for intubation, anesthesia workstations, waste gas scavenging, humidification systems, capnography (both sidestream and mainstream), pulse oximetry (and oximetry engineering approaches to improve accuracy and additional information such as hemoglobin estimate or the presence of abnormal hemoglobins [e.g., carboxyhemoglobin]), reflectance oximetry and near-infrared spectroscopy, neuromuscular blockade monitors, processed EEG monitors (bispectral index, entropy, and others, particularly in infants and young children), as well as a detailed assessment of a multitude of continuous and intermittent cardiac output measurement devices are discussed. The noninvasive continuous cardiac output devices are likely to be standard of care in the near future. When purchasing new equipment, it is vital that the equipment is tested in the environment where it will be used and by the practitioners intended to use it.
Chapter
The pharmacokinetics (PK) and pharmacodynamics (PD) of most medications in children especially neonates, differ from those in adults. Children exhibit different PK and PD from adults because of their immature renal and hepatic function, different body composition, altered protein binding, distinct disease spectrum, diverse behavior, and dissimilar receptor patterns. PK differences necessitate modification of the dose and the interval between doses to achieve the desired concentration associated with a clinical response and to avoid toxicity. In addition, some medications may displace bilirubin from its protein binding sites and possibly predispose to kernicterus in premature neonates. Drug effect may be influenced by altered capacity of the end organ, such as the heart or bronchial smooth muscle, to respond to medications in children compared with adults. In this chapter we discuss basic pharmacologic principles as they relate to drugs commonly used by anesthesiologists.
Article
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Neuromuscular blockade enables airway management, ventilation and surgical procedures. However there is no national consensus on its routine clinical use. The objective was to establish the degree of agreement among anaesthesiologists and general surgeons on the clinical use of neuromuscular blockade in order to make recommendations to improve its use during surgical procedures.
Article
Disturbances in the thumb's movement interfere with the functioning of acceleromyography in many clinical settings. The short and light (SL) train-of-four (TOF)-Tube is a new version of a rigid tubular device that was designed to protect the thumb from external disturbances during surgery, even when the hand is not accessible by the anaesthesiologist. To compare the precision and performance of acceleromyography performed with the aid of the SL TOF-Tube (AMGTT) with standard isometric mechanomyography (MMG). Simultaneous arm-to-arm comparison of both methods in the same anaesthetised patient. A monocentric study, performed from September 2007 to June 2008. Nineteen ASA I to II patients scheduled to undergo lower limb orthopaedic surgery under general anaesthesia. Neuromuscular transmission monitoring during baseline, onset and spontaneous recovery of rocuronium-induced neuromuscular block. Initial baseline and repeatability coefficients were assessed during 10 consecutive measurements of the first twitch height (T1) and TOF T4/T1 ratio and compared using a z test. The spontaneous recoveries of defined blockade levels (onset, T1 25% of initial calibration and TOF ratio 0.9) were compared in terms of duration and intensity. Agreement between both techniques was assessed by the Bland-Altman method. The mean ± SD control TOF ratios were 98 ± 1% (MMG) and 103 ± 2% (AMGTT). The repeatability coefficients were higher (P < 0.001) and the onset was longer (mean 0.44 min) (P < 0.001) when they were measured by AMGTT. The recoveries of T1 25% and TOF ratio 0.9 were not significantly different between the two methods, and the limits of agreement were in the usual range of contralateral comparisons (-19 and +24% for TOF ratio 0.9). Compared with mechanomyography, acceleromyography performed with the aid of an SL TOF-Tube offered acceptable precision and equivalent performance during neuromuscular block recovery.
Article
The main goals of general anaesthesia should include (not exclusively) adequate hypnosis, analgesia and maintenance of vital functions. In addition, neuromuscular blockade (NMB) may be needed for a number of surgical procedures. Patient safety and cost reductions via the minimization of drug consumption and the shortening of post-operative recovery represent some of the main issues and motivations of automation of anaesthesia.Since the early eighties engineers and physicians joined efforts towards the development of sophisticated closed-loop control systems for drug delivery in the operating theatre and post-operatively.First, this paper should be seen as a review about the automatic drug delivery in anaesthesia. A summary is given about the methods of measurement, modelling and general progress of closed-loop control systems in anaesthesia. In particular, the development of the ‘Rostock assistant system for anaesthesia control (RAN)’ is also described. This system has been developed during the last 15 years at the University of Rostock and various systems and control-based ideas have been integrated since. With this system the multiple-input–multiple-output (MIMO) control of the depth of hypnosis and NMB has been shown to be possible as well as the closed-loop control of a deep arterial hypotension. Promising results have already been obtained from a first study, which has so far included as many as 22 patients using MIMO control. Copyright © 2008 John Wiley & Sons, Ltd.
Article
A new method for monitoring neuromuscular function based on measurement of acceleration is presented. The rationale behind the method is Newton's second law, stating that the acceleration is directly proportional to the force. For measurement of acceleration, a piezo-electric ceramic wafer was used. When this piezo electrode was fixed to the thumb, an electrical signal proportional to the acceleration was produced whenever the thumb moved in response to nerve stimulation. The electrical signal was registered and analysed in a Myograph 2000 neuromuscular transmission monitor. In 35 patients anaesthetized with halothane, train-of-four ratios measured with the accelerometer (ACT-TOF) were compared with simultaneous mechanical train-of-four ratios (FDT-TOF). Control ACT-TOF ratios were significantly higher than control FDT-TOF ratios: 116 +/- 12 and 98 +/- 4 (mean +/- s.d.), respectively. In five patients not given any relaxant during the anaesthetic procedure (20-60 min), both responses were remarkably constant. In 30 patients given vecuronium, a close linear relationship was found during recovery between ACT-TOF and FDT-TOF ratios. It is concluded that the method fulfils the basic requirements for a simple and reliable clinical monitoring tool.
Article
This paper presents preliminary observations on an acceleration-responsive transducer designed to monitor neuromuscular transmission. Simultaneously evoked acceleration and tension responses of the adductor pollicis muscles were studied. Registrations were obtained during recovery from atracurium-induced block in 29 individuals in neurolept II anaesthesia (Group I) and in 4 ICU patients (Group II) sedated with pentobarbital or midazolam. Regression analysis of 1567 train-of-four (TOF) registrations, in regard to TOF-ratio (T4/T1) and first twitch ratio (T1/T0), demonstrated regression coefficients (b) and correlation coefficients (r) in the range 0.91-1.06 and 0.89-0.98, respectively. During 1 Hz single twitch stimulation and post-tetanic count stimulation, b and r were in the range 0.85-1.03 and 0.77-0.90, respectively. Following administration of edrophonium (n = 6, Group I) a deviation of T1/T0 regression values was observed in four individuals, i.e. 0.48 (b) and 0.56 (r). This investigation proved a good level of accuracy of the acceleration transducer compared to the force displacement transducer during spontaneous and neostigmine-induced recovery from atracurium block. The acceleration transducer-based system does not require a rigid suspension and seems to have a good monitoring potential in clinical assessment of neuromuscular transmission.
Article
A new and simple acceleration transducer (ACT)-based system of neuromuscular monitoring has recently been introduced. The precision of this transducer has been evaluated as compared to a conventional force displacement transducer (FDT) in the present study. Ten progressions of spontaneous recovery from atracurium-induced block with simultaneous measurements using the ACT on one hand and the FDT on the other were studied. Five individuals undergoing elective surgery in modified neurolept anaesthesia and one ICU-patient requiring prolonged neuromuscular blockade, sedated with pentobarbital, were included. Measurements were carried out on the latter patient on 5 consecutive days. Train-of-four (TOF) stimulation was used, readings were given in twitch heights (TH) (T1/control value), and when four responses were obtained in TOF-ratios (T4/T1). Linearity was achieved after logit-transformation and the values regressed on time for each progression of recovery. Analysis of variance was applied to the regressions for the TH and TOF-ratio readings of each transducer. No significant differences were found, either between variation due to differences between slopes or variation due to technical error between the two transducers. The study indicates that the ACT is equal to the FDT with regard to precision in clinical recordings on atracurium-relaxed individuals.
Article
Manual evaluation of the response to TOF nerve stimulation is of value in the adjustment of individual dose regimens for neuromuscular blocking agents during anesthesia in order to avoid overdose and secure reversibility. However, postoperative absence of visual and manual fade in the TOF response does not exclude residual neuromuscular blockade.
Article
The TOF-Guard neuromuscular monitor uses an accelerometer to measure the response to nerve stimulation. In this study, we have compared it to a standard mechanomyographic monitor, the Myograph 2000, for neuromuscular monitoring in 28 subjects. A train-of-four mode of stimulation was used in both cases. The times taken for onset of block, and for the recovery of T1 (the first response in the train of four) to 25% of control, the time from recovery of T1 from 25-75% and for the recovery of the train of four ratio to 0.7 were compared with the two monitors. There was a good correlation between the two devices for both onset and recovery times. However, differences were highlighted when the data were analysed by the method of Bland and Altman. The 95% limits of agreement for the T1 recovery to 25%, as measured by the TOF-Guard, ranged from 5 min less to 8 min more than when measured by the Myograph 2000. For recovery of the train of four ratio to 0.7, the limits of agreement were approximately 6 min in either direction. The 95% limits for the TOF-Guard measured train of four ratio were from 0.47 to 0.99, at the Myograph reading of 0.7. We recommend that information from the TOF-Guard and the Myograph 2000 should not be used interchangeably. However, the TOF-Guard is likely to improve considerably on tactile evaluation of the responses to stimulation.
Article
Considerable advances have been achieved in developing new techniques and equipment for the assessment of neuromuscular transmission during anaesthesia. This paper is a review of the methods currently used in research as well as in daily clinical practice. The principles of nerve stimulation and the evoked muscular response, the function of the nerve stimulator, features of the stimulation electrodes, possible stimulation sites, and the various stimulation patterns with their responses are described. The methods for measurement of neuromuscular function with mechanomyography, electromyography and acceleromyography are reviewed, and commercially available equipment for each purpose is described. The clinical evaluation of the responses to nerve stimulation, and which stimulation patterns to prefer during onset, maintenance and recovery of neuromuscular block are dealt with, as well as possible errors to be encountered. Arguments are given for routine use of neuromuscular monitoring in the clinical setting, and situations where monitoring of neuromuscular function are of particular importance are noted.
Article
Mivacurium's rapid rate of recovery has led to the suggestion that routine reversal of its residual effects may be unnecessary once signs of spontaneous recovery are evident. When antagonism is attempted at 90% twitch depression, the time saved to return to train-of-four (TOF) ratios > 0.70 compared to control has been reported to average < or = 8 min. This study was an attempt to determine whether similar savings in time could be achieved once spontaneous recovery was well underway. Also investigated was the ability of a TOF count of 4 to serve as a marker that might predict the dose of edrophonium necessary for satisfactory antagonism of mivacurium. Fifty-eight adult patients were studied under nitrous oxide/propofol/opioid anesthesia. Neuromuscular block was monitored electromyographically and maintained by infusion of mivacurium at a level sufficient to abolish any palpable response of the thumb. TOF stimuli were delivered to the ulnar nerve at the wrist every 20 s throughout the period of observation. When the infusion was terminated, an observer was asked to note the time when the 1st through the 4th twitches first became detectable. In group 1, recovery to a TOF ratio > 0.90 was allowed to proceed spontaneously. In groups 2, 3, and 4, 0.3, 0.5, and 0.75 mg/kg edrophonium, respectively, was administered when the 4th response to TOF stimulation first became palpable. Times to TOF ratios of 0.70 and 0.90 were recorded in all groups. TOF counts of 1, 2, 3, and 4 first became palpable at 8 +/- 4% (SD), 20 +/- 6%, 33 +/- 9%, and 44 +/- 10% of control twitch height. Fade on TOF stimulation could no longer be detected once the TOF ratio exceeded a value of 0.41 +/- 0.07 (range 0.25-0.51). Once the 1st evoked response was palpable, the 2nd, 3rd, and 4th responses could be detected 2.5 +/- 1.1 (SD), 4.6 +/- 1.6, and 6.1 +/- 1.6 min later. Spontaneous recovery to TOF fade ratios of 0.7 and 0.9 occurred on average 10.7 +/- 2.3 and 16.9 +/- 4.7 min, respectively, after a threshold count of 4. Administration of 0.3 mg/kg edrophonium shortened the recovery process by about 7.5 min. Increasing the dose of edrophonium beyond 0.3 mg/kg did not further accelerate recovery. After recovery from profound mivacurium-induced neuromuscular block, TOF counts of 1, 2, 3, and 4 approximate 10%, 20%, 30%, and 40% return to control twitch height, respectively. Finally, > or = 0.3 mg/kg edrophonium will accelerate recovery from mivacurium by approximately 7-8 min.
Article
The precision of the compact Mini-Accelograph (M-A) was compared with the Myograph 2000 (MYO). Neuromuscular block resulting from atracurium was measured simultaneously by the MYO and the M-A applied to contralateral thumbs. During onset, the M-A frequently underestimated the extent of block (maximal at approximately 50% twitch depression). The M-A control train-of-four (TOF) ratio was characteristically > 1.0 and remained greater than the MYO ratio during the onset of atracurium. During recovery, the difference between the MYO and the M-A was maximal at approximately 50% twitch depression, but the M-A frequently overestimated the extent of block. The mean differences between the MYO and the M-A were small in respect of the recovery index (RI) and the TOF. However, the limits of agreement were unacceptably wide for both TOF and RI. When the MYO TOF was 0.7, the corresponding M-A TOF varied between 0.4 and 1.0. The M-A was more susceptible to drift than the MYO. (Br. J. Anaesth. 1994; 72: 411–414)