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From the Neuromuscular Research Group (NRG), Department of Anesthesiology, Centre Hospitalier de l’Université de Montréal (CHUM) Hôtel-Dieu, Université de Montréal, Montréal, Québec, Canada.
Address correspondence to: Dr. Thomas M. Hemmerling, Department of Anesthesiology, Université de Montréal, Hôtel-Dieu, 3840 Rue St. Urbain, Montréal, Québec H2W 1T8, Canada. Phone: 514-890-8000 ext. 14570; Fax: 514-412-7222; E-mail: thomashemmerling{at}hotmail.com
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Abstract |
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Methods: In 14 patients, phonomyography was recorded via a microphone taped to the thenar region. A standard mechanomyographic device was applied to the same thumb, and attached to the force transducer. On the contralateral side, a NMT-Mechanosensor® probe was attached to the thumb and forefinger (KMG). After induction of general anaesthesia, the ulnar nerves were stimulated supramaximally using superficial electrodes at the wrists using train-of-four (TOF) stimulation every 12 sec. Onset and recovery indices measured by the three methods after mivacurium 0.2 mg·kg–1 iv were compared using ANOVA-multiple group comparisons. Agreement between methods was determined using Lin’s concordance correlation coefficient.
Results: Onset time and peak effect measured via MMG and PMG were similar. Recovery times from neuromuscular blockade (NMB) as measured via the three methods were not different. Agreement between PMG and MMG was excellent for onset and offset of NMB but unsatisfactory for peak effect. Agreement between MMG and KMG was satisfactory for TOF 0.25 and 0.50, and excellent for TOF 0.75 and 0.90 (onset and peak effect not determined for KMG). Agreement between PMG and KMG was satisfactory for TOF 0.25, 0.50 and 0.75, and excellent for TOF 0.90.
Conclusion: Mechanomyography, PMG and KMG show satisfactory agreement for determination of recovery of NMB for clinical purposes.
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Introduction |
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Kinemyography (KMG) has been available for some years in form of the NMT-Mechanosensor® integrated in the Datex anesthetic machine (NMT-Mechanosensor, Datex Instrumentations Inc., Madison, WI, USA). It consists of a moulded plastic device which can be applied into the groove of the thumb and forefinger by use of adhesive tape. In addition, as known for other methods such as acceleromyography,1 attachment of the arm to an arm board may increase the precision of measurement. The manufacturer states that the method is based upon the detection of bending and deformation of a piezo-electric sensor wafer strip by movement of the thumb, caused by contraction of the adductor pollicis muscle. Some studies have shown that its agreement with MMG for scientific purposes might be limited with unacceptably wide limits of agreement;2 in clinical circumstances it can be used reasonably well to detect time to tracheal intubation and recovery of neuromuscular block (NMB).2,3 However, the device can only be applied to measure NMB at the adductor pollicis muscle and there is only one size of the moulded probe.
Phonomyography (PMG) has been described as a new method of neuromuscular monitoring.4 The method is based upon the fact that muscle contraction evokes low frequency sounds, which can be recorded using special microphones5,6. Initially, this method was called acoustic myography and used an air-chamber interface between the skin and the microphone.7,8 It shows good agreement for several muscles with the gold standard of monitoring, MMG,9–11 and can be applied at any muscle of interest.
The purpose of this study was to compare and determine the agreement of PMG, KMG, and MMG, for detection of NMB after a dose of mivacurium 0.2 mg·kg–1 during train-of-four (TOF) stimulation.
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Methods |
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After arrival in the operating theatre, routine monitoring (non-invasive blood pressure, pulse oximetry, five-lead electrocardiography) was applied. Anesthesia was induced with remifentanil 0.25 to 0.5 µg·kg–1·min–1 iv; two minutes later, propofol 2 to 3 mg·kg–1 iv was injected. After loss of consciousness and ventilation via facemask for two minutes with 100% oxygen, a laryngeal mask airway (LMA; size: 4 for women, size 5 for men, LMA company, Wooburn Green, UK) was inserted and controlled ventilation commenced with minute ventilation set to maintain a PETCO2 of 35 to 45 mmHg. Anesthesia was maintained with sevoflurane 2–3% end-tidal in a mixture of 30% oxygen and medical air, to maintain a bispectral index of 50 (BIS; A-2000 monitoring system, Aspect Medical Company, USA). Analgesia was provided by remifentanil 0.05 to 0.25 µg·kg–1·min–1 throughout surgery. In each patient, the force of contraction of the adductor pollicis was measured using a force transducer (Grass FT-10, Grass Instruments Co., Quincy, MA, USA; preload: 300 mg). A specially molded cast was used to stabilize the arm in position. On the same hand, a piezoelectric microphone (diameter: 1.6 cm, Model 1010, Grass Instruments, Astro-Med, Inc., West Warwick, IL, USA; frequency response: 2.5 to 5 kHz, signal output: 20–40 mV into 1 M
) was attached to the thenar region to record the acoustic signals (Figure 1
). The microphone signal was amplified and band pass filtered between 0.5 and 1000 Hz using an AC/DC amplifier (Model 7P122, Grass Instruments, Astra-Med, Inc., West Warwick, IL, USA). The signals were sampled continuously at 100 Hz using the Polyview® software package (Astra-Med, Inc., West Warwick, IL, USA), digitized and stored on a portable microcomputer. The single twitch phonomyographic signal was measured peak-to-peak. On the other arm, NMB was measured by KMG by applying the KMG-probe to the hand (Datex, NMT-Mechanosensor, Datex Instrumentation) and the digits III to V taped to an armboard in routine fashion (Figure 2). Hand temperature was measured using standard temperature probes at both hands.
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The first twitch response was used to analyze onset time (time to reach maximum decrease of twitch response) and the peak effect was determined as the maximum decrease of the twitch response using MMG and PMG. Times to reach a TOF ratio of 0.25, 0.5, 0.75, and 0.9 were calculated for MMG, KMG and PMG simultaneously.
Sample size was calculated based on TOF 0.8 findings for KMG and MMG in a previous study, for a power of 0.8 and 
= 0.05.3 Data were compared between all methods using an ANOVA for multiple comparisons, P < 0.05 was considered significant (SPSS software, SPSS Inc., Chicago, IL, USA). Lin’s concordance correlation coefficient (c) was determined at all time periods for two methods each12 and presented with the lower one-sided 95% confidence limit (GenSTAT software, VSN International Ltd., Herts, UK). Agreement between two methods was assessed using the concordance correlation coefficient using the following degrees: c < 0.6, 0.6 to 0.9, and 0.91 to 1 were considered as unsatisfactory, satisfactory and excellent agreement, respectively.13 Bias as the mean of the differences and precision as standard deviation of the mean were also determined for all pharmacodynamic times.
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Results |
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Onset times and peak effect measured via MMG and PMG were similar. Offset of NMB as measured via the three methods was not statistically significant (Table I). Agreement between PMG and MMG was excellent for onset and offset of NMB, while unsatisfactory for peak effect. Agreement between MMG and KMG was satisfactory for TOF 0.25 and 0.50, excellent for TOF 0.75 and 0.90 (onset and peak effect not determined for KMG). Agreement between PMG and KMG was satisfactory for TOF 0.25, 0.50 and 0.75, excellent for TOF 0.90 (Table II).
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Discussion |
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We did not determine onset time and peak effect using KMG because the module integrated in the Datex anesthetic machine does not allow simultaneous measurement of single twitch amplitudes in real time; in our setting, it only gives the TOF-ratio (Figure 3).
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Various studies have confirmed good agreement between PMG and MMG (or MMG-alike methods) for several muscles. This is the first study to compare MMG with KMG demonstrating good agreement for determination of TOF-ratios during recovery from NMB. This means that for routine clinical use, both monitoring methods can be used, and agree well with MMG; they are both easier to apply than MMG. In contrast to the study of Motamed et al.,2 we attached the hand to the arm board even with the Mechanosensor. It is not clear whether this has an influence on the results, although Motamed et al.2 argue that it is not necessary to immobilize the hand, since the piezoelectric device only detects movement between the index finger and the thumb. There is no study confirming this theory. From a practical stand-point, stimulation of the ulnar nerve can produce movements of the hand and misplace the hand on an arm board, thus limiting the free movement of the thumb; this might alter the measurements. Therefore additional immobilization via adhesive tape was made to ensure free and repetitive movement of the thumb and index finger (Figure 2
).
The standard module used for this study does not include the possibility of simultaneously measuring the first twitch heights and TOF-ratios. Therefore, we can only present TOF ratio measurement. When the movement caused by the fourth stimulation of the TOF is not detectable, the Datex mechanosensor module no longer displays a TOF-ratio, but only the number of twitches detected (Figure 3). That is why we are not able to present onset time and peak effect for the KMG method (an optional software to analyze first twitch signal heights was not available). However, since the purpose of this study was comparison of the three methods for clinical purposes, we assume that TOF-ratios will generally be used, especially to determine complete recovery from NMB.
This study shows that PMG demonstrates a very good concordance in the recovery period with a commercial monitoring system (M-NMT). In comparison to MMG and KMG, it can be applied to all muscles of interest. The possibility of monitoring the corrugator supercilii muscle is of interest to the clinician.
Determination of agreement between the three methods, in pairs, was performed by using Lin’s correlation coefficient, a relatively new statistical method.12 Lin’s correlation coefficient evaluates the agreement between two paired measures, and the description is based on the expected value of the squared distance function. It provides an assessment of agreement between alternative methods of continuous data collection, and it appears to avoid shortcomings associated with the usual procedures (e.g., Pearson’s correlation coefficient, paired t test or least squares analysis of slope and intercept). The test is robust on as few as ten pairs of data. As with the Bland Altman test, an alternative and more widely used test of agreement between two monitoring methods,14 calculation of agreement is simple and precise. To date, however, there are no uniform classifications of the strength of the Lin agreement. Our criteria represent one of the more commonly found classifications. A difficulty of interpreting Lin’s coefficient is highlighted by the unsatisfactory strength of agreement for the peak effect when determined using PMG and MMG. However, the two monitoring methods demonstrate a minimal bias of –0.7% with a precision of 3%. Careful clinical interpretation of the Lin coefficient, together with presentation of bias and precision are the basis of meaningful comparison of two monitoring methods.
In summary, for determination of onset and TOF-recovery, MMG and PMG show satisfactory agreement for clinical purposes. These monitoring modalities can be used interchangeably to determine TOF- recovery of NMB in the clinical setting.
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Footnotes |
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Accepted for publication August 10, 2005. Revision accepted August 29, 2005.
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References |
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2 Motamed C, Kirov K, Combes X, Duvaldestin P. Comparison between the Datex-Ohmeda M-NMT module and a force-displacement transducer for monitoring neuromuscular blockade. Eur J Anaesthesiol 2003; 20: 467–9.[Medline]
3 Dahaba AA, von Klobucar F, Rehak PH, List WF. The neuromuscular transmission module versus the relaxometer mechanomyograph for neuromuscular block monitoring. Anesth Analg 2002; 94: 591–6.
4 Hemmerling TM, Donati F, Beaulieu P, Babin D. Phonomyography of the corrugator supercilii muscle: signal characteristics, best recording site and comparison with acceleromyography. Br J Anaesth 2002; 88: 389–93.
5 Barry DT, Geiringer SR, Ball RD. Acoustic myography: a noninvasive monitor of motor unit fatigue. Muscle Nerve 1985; 8: 189–94.[Medline]
6 Barry DT. Acoustic signals from frog skeletal muscle. Biophys J 1987; 51: 769–73.
7 Bellemare F, Couture J, Donati F, Plaud B. Temporal relation between acoustic and force responses at the adductor pollicis during nondepolarizing neuromuscular block. Anesthesiology 2000; 93: 646–52.[Medline]
8 Dascalu A, Geller E, Moalem Y, Manoah M, Enav S, Rudick Z. Acoustic monitoring of intraoperative neuromuscular block. Br J Anaesth 1999; 83: 405–9.
9 Hemmerling TM, Michaud G, Trager G, Deschamps S, Babin D, Donati F. Phonomyography and mechanomyography can be used interchangeably to measure neuromuscular block at the adductor pollicis muscle. Anesth Analg 2004; 98: 377–81.
10 Hemmerling TM, Babin D, Donati F. Phonomyography as a novel method to determine neuromuscular blockade at the laryngeal adductor muscles: comparison with the cuff pressure method. Anesthesiology 2003; 98: 359–63.[Medline]
11 Hemmerling TM, Michaud G, Babin D, Trager G, Donati F. Comparison of phonomyography with balloon pressure mechanomyography to measure contractile force at the corrugator supercilii muscle. Can J Anesth 2004; 51: 116–21.
12 Lin L, Torbeck LD. Coefficient of accuracy and concordance correlation coefficient: new statistics for methods comparison. PDA J Pharm Sci Technol 1998; 52: 55–9.[Medline]
13 Warke TJ, Kamath S, Fitch PS, Brown V, Shields MD, Ennis M. The repeatability of nonbronchoscopic bronchoalveolar lavage differential cell counts. Eur Respir J 2001; 18: 1009–12.
14 Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1: 307–10.[Medline]
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