Anesth Analg 2004;98:854-7
© 2004 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000100150.84698.8C
GENERAL ARTICLES
Assessing Residual Neuromuscular Blockade Using Acceleromyography Can Be Deceptive in Postoperative Awake Patients
Christophe Baillard, MD PhD*,
Sylvie Bourdiau, MD*,
Philippe Le Toumelin, MD*,
Farid Ait Kaci, MD*,
Bruno Riou, MD PhD
,
Michel Cupa, MD*, and
C. Marc Samama, MD PhD*
*Department of Anesthesiology and Intensive Care, Avicenne Hospital, Bobigny; and
Department of Emergency Medicine and Surgery, Pitié-Salpêtrière Hospital, Pierre et Marie Curie University, Paris, France
Address correspondence and reprint requests to Dr. Christophe Baillard, Département d’Anesthésie-Réanimation, Hôpital Avicenne, 125 route de Stalingrad, 93009 Bobigny Cedex, France. Address email to christophe.baillard{at}avc.ap-hop-paris.fr
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Abstract
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Postoperative awake patients may have significant residual neuromuscular block. In awake patients, the results of accelerometry are affected by extra movements to which the thumb may be subject. In this study, we evaluated the repeatability of train-of-four (TOF) ratio using acceleromyography in 253 patients recovering from anesthesia. Immediately after arrival in the postanesthesia care unit, the ulnar nerve was stimulated with TOF stimulation. The evoked response at the thumb was measured by the TOF-Watch apparatus. The current intensity was 30 mA. Two TOF stimulations were applied and recorded at 30-s intervals. A Bland-Altman test was used. The Kappa (
) test for clinical agreement between the two measurements was also calculated according to the presence or absence of a residual neuromuscular blockade, defined as a TOF ratio <0.9. According to the presence of a residual neuromuscular blockade, the paired TOF ratios were discordant in 61 patients (24%; 95% confidence interval, 21%–27%). The test indicated a moderate agreement (k = 0.47). We demonstrated that accelerometry as used in this study is not always accurate. Two isolated acceleromyograph TOF ratios are not an accurate representation of the neuromuscular status of the patient recovering from anesthesia.
IMPLICATIONS: Clinicians should be aware that acceleromyography as used in this study does not always provide precise train-of-four ratio measurements. Two isolated acceleromyograph train-of-four ratios are not an accurate representation of the neuromuscular status of the patient recovering from anesthesia.
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Introduction
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Residual neuromuscular blockade (NMB) is a risk factor for postoperative pulmonary complications (1) and is still present despite the use of intermediate duration muscle relaxants (2–3). The neuromuscular response to peripheral nerve stimulation is routinely evaluated and useful in patients recovering from anesthesia. Tactile or visual evaluation fails to detect train-of-four (TOF) fade above 0.4 and therefore, the evoked response to nerve stimulation requires a reliable quantitative measurement (4). Mechanomyography is the established standard to measure NMB (5) but acceleromyography is easier to use and better adapted in the postanesthesia care unit (PACU). As a result, acceleromyography is a frequently used and convenient clinical monitor in the PACU. It influences the physician in charge of the patient and the therapy (e.g., timing of reversal administration) according to the presence or absence of a residual NMB. However, such monitoring has not been validated in this particular setting. In awake patients, the results of accelerometry are affected to a large extend by extra movements (voluntary or not) to which the thumb may be subject. The aim of the study was to evaluate the repeatability of TOF ratio determinations using acceleromyography in patients recovering from anesthesia in the PACU.
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Methods
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Two-hundred-fifty-three consecutive adults requiring muscle relaxants during general anesthesia for scheduled surgical procedures (orthopedic, n = 21; abdominal, n = 150; thoracic, n = 67; and vascular surgery, n = 15) were evaluated prospectively during a 6-mo period. The choice of drugs used for premedication and anesthesia was at the discretion of the anesthesiologist. After arriving in the operating room (OR), patients were placed on the operating table and kept warm with a blanket. Anesthesia was induced with propofol or etomidate and sufentanil. Endotracheal intubation was facilitated by a nondepolarizing NMB drug. Anesthesia was maintained with desflurane (1–2 minimum alveolar concentration) and nitrous oxide 0.6—oxygen 0.4 and intermittent bolus of sufentanil. Doses of NMB drugs (intermittent IV bolus), use of neuromuscular monitoring (TOF-Watch® acceleromyograph (Organon-Teknika, Puteaux, France), and the reversal of residual block (neostigmine 50 µg/kg with atropine 15 µg/kg was given if at least 2 responses to the TOF were detectable) in the OR were recorded.
Immediately after patient arrival in the PACU, a pair of electrodes was applied over the ulnar nerve at the wrist. The evoked response at the thumb was measured by TOF-Watch® acceleromyograph. The probe was positioned on the distal ventral part of the thumb. The other fingertips were tightly fixed with tape (5). The ulnar nerve was stimulated with TOF stimulation (4 pulses 0.2 ms in duration, at a frequency of 2 Hz, 2 s in duration). The current intensity was 30 mA (6). Two TOF stimulations were applied and recorded at 30-s intervals. All patients were tested by the same investigator. It was a prospective, open-labeled nonrandomized, observational study, and acceleromyographic monitoring in the PACU is a routine clinical practice at our institution. This protocol was considered as a quality assurance project and part of routine clinical practice. Therefore, no informed consent was required from the patients, as confirmed by the local IRB.
Evaluation of repeatability between each paired TOF ratio determinations was performed by assessing the bias, the precision, and the limits of agreement (i.e., the coefficient of repeatability, bias ± 1.96 SD) using the Bland-Altman method (7). The bias is an index of the repeatability obtained by calculation of the average difference between paired TOF ratio determinations. The bias indicates any systematic trend toward over- or underestimation. The precision is the absolute average difference and estimates the typical size of the difference between the paired measurement. The coefficient of repeatability includes 95% of the differences, which indicates the maximum difference that is likely to occur between two measurements. The paired Student’s t-test was used to compare the differences between the paired TOF ratio measurements. The Kappa () test for clinical agreement between the two measurements was also calculated according to the presence or absence of a residual NMB defined as a TOF ratio < 0.9 (8). = 1 implies perfect agreement and = 0 suggests that the agreement is no better than that which would be obtained by chance. The results are expressed as the means ± SD or median and range. The differences were considered as statistically significant when P < 0.05. All statistics were performed using SAS version 6.12 (SAS institute, Cary, NC).
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Results
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The demographic data were as follows: age 53 ± 18 yrs; weight 69 ± 16 kg; women 40%; ASA physical status II (range, I–IV). The surgical procedure lasted 140 (range, 20–600) min. Patients received rocuronium, vecuronium, or atracurium (Table 1). NMB monitoring and the use of antagonists in the operating room were performed in 237 and 105 patients, respectively. At the arrival in the PACU the mean core temperature was 36.6°C ± 0.5°C. The mean of the paired TOF ratios measurement ranged from 0.3 to 1.3. Thirty-six patients were still intubated at the arrival in the PACU. The TOF ratios were lower in patients still intubated (0.57 ± 0.36 versus 0.98 ± 0.28, P < 0.0001) and in those who did not receive pharmacologic reversal (0.87 ± 0.32 versus 0.96 ± 0.27, P < 0.035). Reversal of residual block (neostigmine 50 µg/kg with atropine 15 µg/kg) was given in PACU in patients with residual NMB.
The bias and the precision were -0.6 ± 22.0% and 15.0 ± 17.0% respectively. The limits of agreement were +43.3/-44.5%. (Table 2, Fig. 1). According to the presence or absence of a residual NMB, the paired TOF ratios were discordant in 61 patients (24%; 95% confidence interval, 21%–27%), and the test indicated a moderated agreement, 0.47. A simple regression analysis did not find correlation between the precision and core temperature, r = 0.05; P = 0.56.
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Table 2. Train-of-Four Ratio Values in 253 Patients Recovering from Anesthesia in the Postanesthesia Care Unit: Comparison Between the Two Measurements
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Figure 1. Difference versus average measurements in 253 train-of-four (TOF) ratios from 2 stimulations. The solid line shows the bias and the dotted lines the limits of agreement (95% of the differences, which indicates the maximum difference that is likely to occur between 2 measurements).
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Discussion
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This study showed a poor repeatability of the TOF stimulation using an acceleromyograph in a large sample size of postoperative nonselected awake patients. The clinical agreement of measured TOF ratio using the test was moderate. According to the presence or not of a residual NMB, the paired TOF ratio measurements were discordant in 24% of the patients.
As explained by Bland and Altman (7), the best method to examine repeatability is to take repeated measurements on a series of subjects and to plot the difference against the mean for each patient (i.e., to analyze the bias). The mean difference should be zero because the same method is used. In this study, a nonsignificant bias was observed, but the precision was only 15%.
Factors such as electrode placement, positioning of the hand, placing of the transducer on the thumb, and core temperature may also have affected the accuracy of the measure. However, the two measurements were checked on the same arm, at the same time, and in the same condition. It is therefore unlikely that the precision had been underestimated.
Hypothermia may lead to unreliable values (9). In this study, the core temperature was monitored and maintained at normal level. It was not correlated to the TOF ratio repeatability. The patients were tested by one investigator, and only the intraobservator repeatability was evaluated. Interestingly, the poor repeatability may have a clinical implication because the diagnosis of residual NMB was discordant in 24% of the patients (Table 3).
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Table 3. Agreement Measured by Kappa Test Between Paired Train-of-Four Ratios According to the Presence or Absence of a Residual Neuromuscular Blockade Defined as a Train-of-Four Ratio < 0.9
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Assessment of NMB is a challenge in patients recovering from anesthesia. Clinical evaluation does not always exclude significant residual blockade and the degree of NMB should be monitored (10). Mechanomyography, which is difficult to set-up, is not appropriate for routine monitoring in the PACU.
Acceleromyography is theoretically more convenient than mechanomyography, but its reliability has never been demonstrated. Previous studies found unacceptably wide limits of agreement and stated that these two methods were not interchangeable (11–14). From an ethical and practical point of view, the pain associated with a high stimulation current is an insurmountable obstacle. The visual analog score associated with TOF stimulation at 50 mA is unacceptable, and the use of lower stimulating currents facilitates such monitoring (15–16). The consistency of the TOF ratio in response to currents of 30 mA as compared with 50 mA has been previously validated as long as all four responses to TOF stimulation are detectable (17). There are strong arguments to suggest that 30 mA is the best compromise of neuromuscular monitoring accuracy and patient discomfort (18). In this study, we used TOF stimulation at 30 mA according also to our practice (2).
We made no attempt to see if the evoked TOF ratio would stabilize over time. In a recent study, Debaene et al. (3) checked TOF stimulation after 3 constant TOF ratios were obtained. These authors had little problem with obtaining stable TOF ratios. According to Debaene et al. and the present study, a constant TOF ratio seems to be required to correctly apply acceleromyography.
Clinicians should be aware that the acceleromyographic method as used in this study does not always provide precise TOF ratio measurements. Two isolated acceleromyograph TOF ratios are not an accurate representation of the neuromuscular status of the patient recovering from anesthesia. How can we best assess whether postoperative awake patients have a significant degree of residual NMB? The answers could be to monitor NMB mainly in the OR in patients under anesthesia and to check the complete recovery of NMB before emergence from anesthesia.
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References
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- Berg H, Roed J, Viby-Mogensen J, et al. Residual neuromuscular block is a risk factor for postoperative pulmonary complications: a prospective, randomised, and blinded study of postoperative pulmonary complications after atracurium, vecuronium and pancuronium. Acta Anaesthesiol Scand 1997; 41: 1095–103.[ISI][Medline]
- Baillard C, Gehan G, Reboul-Marty J, et al. Residual curarization in the recovery room after vecuronium. Br J Anaesth 2000; 84: 394–5.[Abstract/Free Full Text]
- Debaene B, Plaud B, Dilly MP, Donati F. Residual paralysis in the PACU after a single intubating dose of nondepolarizing muscle relaxant with an intermediate duration of action. Anesthesiology 2003; 98: 1042–8.[ISI][Medline]
- Viby-Mogensen J, Jensen NH, Englbaek J, et al. Tactile and visual evaluation of the response to train-of-four nerve stimulation. Anesthesiology 1985; 63: 440–3.[ISI][Medline]
- Viby-Mogensen J, Englbaek J, Eriksson LI, et al. Good clinical research practice (GCRP) in pharmacodynamic studies of neuromuscular blocking agents. Acta Anaesthesiol Scand 1996; 40: 59–74.[ISI][Medline]
- Kopman AF, Lawson D. Milliamperage requirements for supramaximal stimulation of the ulnar nerve with surface electrodes. Anesthesiology 1984; 61: 81–5.
- Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 8476: 307–10.
- Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977; 33: 159–74.[ISI][Medline]
- Heier T, Caldwell JE, Sessler DI, et al. The relationship between adductor pollicis twitch tension and core, skin, and muscle temperature during nitrous oxide-isoflurane anesthesia in humans. Anesthesiology 1989; 71: 381–4.[ISI][Medline]
- Viby-Mogensen J. Postoperative residual curarization and evidence-based anaesthesia. Br J Anaesth 2000; 84: 301–3.[Free Full Text]
- Kirkegaard-Nielsen H, Helbo-Hansen HS, Lindholm P, et al. New equipment for neuromuscular transmission monitoring: a comparison of the TOF-Guard with the Myograph 2000. J Clin Monit Compu 1998; 14: 19–27.[ISI][Medline]
- Dahaba AA, Von Klobucar F, Rehak PH, List WF. Comparison of a new piezoelectric train-of-four neuromuscular monitor, the ParaGraph, and the Relaxometer mechanomyograph. Br J Anaesth 1999; 82: 780–2.[Abstract/Free Full Text]
- Kern SE, Johnson JO, Westenskow DR, Orr JA. A comparison of dynamic and isometric force sensors for train-of-four measurement using submaximal stimulation current. J Clin Moni 1995; 11: 18–22.
- Loan PB, Paxton LD, Mirakhur RK, et al. The TOF-Guard neuromuscular transmission monitor: a comparison with the Myograph 2000. Anaesthesia 1995; 50: 699–702.[ISI][Medline]
- Connelly NR, Silverman DG, O’Connor TZ, Brull SJ. Subjective responses to train-of-four and double burst stimulation in awake patients. Anesth Analg 1990; 70: 650–3.[Abstract/Free Full Text]
- Brull SJ, Ehrenwerth J, Connelly NR, Silverman DG. Assessment of residual curarization using low-current stimulation. Can J Anaesth 1991; 38: 164–8.[Abstract/Free Full Text]
- Silverman DG, Connelly NR, O’Connor TZ, et al. Accelographic train-of-four at near-threshold currents. Anesthesiology 1992; 76: 34–8.[ISI][Medline]
- Saitoh Y, Nakazawa K, Toyooka H, Amaha K. Optimal stimulating current for train-of-four stimulation in conscious subjects. Can J Anaesth 1995; 42: 992–5.[Abstract/Free Full Text]
Accepted for publication September 22, 2003.
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Abstract
Introduction
