Anesth Analg 2002;95:940-943
© 2002 International Anesthesia Research Society
ANESTHETIC PHARMACOLOGY
A Comparison Between Anterior and Posterior Monitoring of Neuromuscular Blockade at the Diaphragm: Both Sites Can Be Used Interchangeably
Thomas M. Hemmerling, MD DEAA*,
Joachim Schmidt, MD ,
Christian Schurr,
Georg Breuer, MD, and
Klaus E. Jacobi, MD
*Department of Anesthesiology, University of Montreal, Canada; and Department of Anesthesiology, University of Erlangen-Nuremberg, Erlangen, Germany
Address correspondence and reprint requests to T.M. Hemmerling, MD, DEAA, Department of Anesthesiology, University of Montreal, Hotel-Dieu, 3580 Rue Saint Urbain, Montreal (Quebec) H2W 1T8, Canada. Address e-mail to thomashemmerling{at}hotmail.com
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Abstract
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We present a novel site of monitoring neuromuscular blockade of the diaphragm at the patient’s back. After the induction of anesthesia, 12 patients were orotracheally intubated. Two Ag/AgCl-electrodes were attached at the right seventh or eighth intercostal space between the midclavicular and anterior axillary line; two Ag/AgCl-electrodes were paravertebrally attached on the right side lateral to vertebrae T12-L1 or L1-2. Two Ag/AgCl-skin-electrodes were placed over the right thenar area for an electromyography recording of the adductor pollicis (AP) muscle, and two Ag/AgCl-skin-electrodes were used to stimulate the ulnar nerve. Onset and offset of neuromuscular blockade after rocuronium 0.6 mg/kg were determined, and significant differences between diaphragm and AP muscle and agreement between the two methods were determined. Mean maximum block was more than 96% at all sites. Lag time, onset 50, and onset time were not significantly different between the diaphragm and the AP. However, time to reach 25% of control twitch was significantly longer at the AP muscle than at the diaphragm (P < 0.001). The difference of the means and limits of agreement between the anterior and the posterior site of diaphragmatic monitoring were 0 ± 11 s, 3 ± 9 s, 0 ± 19 s, and -2% ± 5% for lag, onset 50, onset time, and peak effect, respectively, and -2 ± 2 min for the time to reach 25% of control twitch of neuromuscular blockade. We conclude that anterior and posterior diaphragmatic monitoring can be used interchangeably to determine neuromuscular blockade after rocuronium.
IMPLICATIONS: We present a novel site of monitoring neuromuscular blockade of the diaphragm at the patient’s back, which shows good agreement with the conventional anterior site at the seventh or eighth intercostal space.
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Introduction
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Monitoring neuromuscular blockade (NMB) at the diaphragm using surface-skin electrodes was introduced into clinical research in 1986 by Donati et al. (1) who presented the seventh or eighth intercostal space between the midclavicular and anterior axillary line as a possible monitoring site. This site has been successfully used in the research of NMB at the diaphragm over the last decade. However, its use is limited by the fact that the electrodes have to be placed inside the surgical field during some forms of surgery, such as abdominal or cardiothoracic surgery. We (2) presented a novel site to measure NMB at the diaphragm at the patient’s back, which correlated well with IM electromyography (EMG) of the posterior part of the diaphragm (3). In this study, we evaluated how this novel site representing the response of the posterior part of the diaphragm compared with the established anterior site of monitoring the diaphragmatic response after rocuronium injection.
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Methods
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After approval of the local ethics committee and written informed consent, six women and six men (ASA physical status I–II), with a mean age of 61 ± 11 yr (range, 36–76 yr) and a mean weight of 70 ± 10 kg, undergoing general surgery were included in the study. Pregnant women, patients with neuromuscular, hepatic, or renal disease, and patients receiving medication known to interact with neuromuscular blocking drugs were excluded.
Anesthesia was induced using remifentanil 0.5 µg · kg-1 · min-1. Two minutes later, a target-controlled infusion of propofol (target concentration, 4 µg/mL) was started and was programmed to reach the target concentration within 30 s. After the induction of anesthesia, the patients were ventilated via a mask for 3 min, and the lungs were orotracheally intubated using a Woodbridge tube. Next, two Ag/AgCl-electrodes were attached at the right seventh or eighth intercostal space between the midclavicular and anterior axillary line; two Ag/AgCl-electrodes were paravertebrally attached on the right side lateral to vertebrae T12-L1 or L1-2 (Fig. 1). Two Ag/AgCl-skin-electrodes were placed over the right thenar area for EMG recording of the adductor pollicis (AP) muscle using the Datex Relaxograph® NMT 100 (Datex Instrumentarium Corporation, Helsinki, Finland), and two Ag/AgCl-skin-electrodes were used to stimulate the ulnar nerve.
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Figure 1. Position of the recording electrodes; marked is vertebra T12 and the eighth intercostal space. Two Ag/AgCl-electrodes are posteriorly placed 2–3 cm apart at T12-L1 or L1-L2 (wherever a better response can be obtained) paravertebrally; two Ag/AgCl-electrodes are simultaneously placed at the seventh or eighth intercostal space (wherever a better response can be obtained) for the anterior diaphragm.
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Anesthesia was maintained with a target-controlled infusion of propofol (target concentration, 3 µg/mL) and remifentanil 0.25 µg · kg-1 · min-1, and mechanical ventilation (30% oxygen in air) was adjusted to achieve end-tidal PETCO2 pressure of 3.5–4.5 kPa.
The phrenic nerve was transcutaneously stimulated on the right side using an external bipolar nerve stimulator (Multiliner®, Toennies Company, Wuerzburg, Germany) at the inferolateral edge of the stemocleidomastoid muscle. The stimulation site was selected where only minimal or no concomitant stimulation of the brachial plexus occurred. A stimulation current between 40 and 70 mA was used. Single-twitch stimulation (0.1 Hz; pulse width, 0.2 ms) was performed to determine the supramaximal stimulation and was recorded using Multiliner® software. The current was increased from 0 mA to the current with the maximal EMG response and then increased by 10 mA to assure supramaximal stimulation. The amplitudes of the two diaphragmatic compound action potentials (peak-to-peak) were measured and recorded. Stimulation of the ulnar nerve was performed as single-twitch (0.1 Hz), and the automatic calibration setup of the Relaxograph® NMT 100 was used to determine supramaximal stimulation.
After no change in the neuromuscular response could be detected for at least 3 min, the patients received rocuronium 0.6 mg/kg IV injected within 5 s into a fast-flowing infusion of Ringer’s lactate solution. No further dose of any muscle relaxant was applied. Body temperature was kept at more than 35.6°C using a heating blanket (Bair Hugger, Edin Prairie, MN). The time from the end of the injection of the muscle relaxant to the first twitch depression, 50% of the maximum twitch depression, and the maximum twitch depression (lag time, onset 50, and onset time) as well as the maximum block (percent reduction of the maximal neuromuscular response) of NMB at all three sites were measured. Clinical duration of NMB was measured as the time to reach 25% of control twitch height (T 25%).
Group size was chosen to reach a power of more than 0.9 with an estimated difference of mean recovery time between diaphragm and AP muscle of 30%. The results are expressed as mean ± SD. The pharmacodynamic variables were compared between diaphragm and AP muscle using paired t-test, and P < 0.05 was regarded as showing a significant difference. The pharmacodynamic variables between the two diaphragmatic sites were compared using paired t-test and Bland-Altman test for detection of difference of the means and the limits of agreement between the two sites. P < 0.05 was regarded as showing a significant difference.
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Results
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Determination of the supramaximal stimulation was successful at all sites of monitoring, with a mean maximal signal amplitude of 2.5 ± 1.4 mV at the anterior and 2.0 ± 1.2 mV at the posterior diaphragmatic site after supramaximal stimulation. No side effects caused by the simultaneous transcutaneous stimulation of the phrenic nerve with a mean of 40 ± 7 mA, like arrhythmias or skin irritation, were noted. All electrodes for the posterior diaphragmatic monitoring were left in place until after the end of surgery; no patient had any skin irritation. The pharmacodynamic data are presented in Table 1. Mean maximum block was more than 96% at all sites. Lag time, onset 50, and onset time were not significantly different between the diaphragm and the AP. However, time to reach 25% of control twitch height was significantly longer at the AP muscle than at the diaphragm (P < 0.001). The difference of the means and limits of agreement between the anterior and the posterior site of diaphragmatic monitoring were 0 ± 11 s, 3 ± 9 s, 0 ± 19 s, and -2% ± 5% for lag time, onset 50, onset time, and peak effect, respectively, and -2 ± 2 min for the time to reach 25% of control twitch of NMB. Figure 2 shows the bias and limits of agreement for all evoked twitch responses.
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Figure 2. Bias 2% and limits of agreement of +19% and -19% (anterior site/posterior site) for all single-twitch responses.
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Discussion
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The novel site for diaphragmatic monitoring agreed well with the anterior site, was easy to use, reliable, provided stable signals, and showed results with narrow limits of agreement with the anterior site. The simultaneous determination of NMB of rocuronium 0.6 mg/kg at the diaphragm and the AP revealed a similar onset and maximum effect but a shorter duration of NMB at the diaphragm.
The seventh or eighth intercostal space between the midclavicular and anterior axillary line has been used in research for more than 15 years (1). However, using the seventh or eighth intercostal space for intraoperative monitoring in cardiothoracic or abdominal surgery, e.g., laparoscopic surgery, is impossible because the monitoring electrodes would remain within the sterile field. Because the lumbar diaphragm inserts with its muscular crura into the first two to three lumbar vertebrae, it is possible to monitor its response to phrenic nerve stimulation at a paravertebral site near vertebrae T12-L3 (4). We placed two Ag/AgCl-electrodes paravertebrally 2–3 cm apart on the patient’s right back and the same type of electrodes on the seventh or eighth intercostal space. Although the signals from the patient’s back might reflect mainly the posterior portion of the diaphragm, as well as the electrodes placed on the standard site reflect the anterior portion, the minimal differences found for all pharmacodynamic variables show that both monitoring sites can be used interchangeably, and the pharmacodynamic variables measured are almost the same.
Transcutaneous stimulation of the phrenic nerve was selected in such a way that there was no or only minimal concomitant stimulation of the brachial plexus. The concomitant stimulation of the brachial plexus causes interference with the diaphragmatic monitoring, especially because of parallel contraction of the shoulder and anterior thoracic muscles. In comparison to diaphragmatic monitoring at the seventh or eighth intercostal space, the novel site seems less prone to interferences by concomitant stimulation of these muscles. One disadvantage at the present state is the difficulty to transcutaneously stimulate the phrenic nerve at the neck. A stimulation using needle electrodes produces forceful phrenic nerve stimulation, but they were not used for ethical reasons. The transcutaneous stimulation of the phrenic nerve using a hand-held stimulator is time consuming, and avoidance of neck movements is essential to obtain results unaffected by artifacts caused by concomitant stimulation of other muscles. Magnetic stimulation of the phrenic nerve is a painless, reliable, and easy to operate alternative to electric stimulation of the phrenic nerve (5,6), but high costs and technical limitations restrict its use for routine stimulation at present. There are only two studies that objectively measured the onset of NMB of rocuronium at the diaphragm using either measurement of the transdiaphragmatic pressure or surface EMG of the anterior site to determine NMB after rocuronium 0.6 mg/kg. Cantineau et al. (7) determined an onset time of 120 ± 62 seconds to reach a peak effect of 95% and recovery to 25% of control level after 23 ± 9 minutes at the diaphragm. Dhonneur et al. (8) determined a peak effect of 96% at an onset time of 130 ± 44 seconds and a time to reach 25% of control value of 17.9 ± 2.1 minutes at the diaphragm. In both studies, recovery at the diaphragm was quicker than at the AP muscle, whereas onset was the same (7) or even shorter (8) at the AP muscle than at the diaphragm. Our own data confirm these results of a similar onset of NMB at the diaphragm and the AP muscle after rocuronium and a much quicker recovery at the diaphragm than at the AP muscle. In an earlier study, we confirmed good correlation and narrow limits of agreement between surface EMG and IM EMG of the posterior diaphragm (3). In the current study, we also demonstrated narrow limits of agreement with the anterior surface monitoring site, and the pharmacodynamic data obtained from both sites can be used interchangeably. The novel site of monitoring the diaphragm at the patient’s back provides a new alternative to monitor NMB of the diaphragm.
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References
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- Donati F, Antzaka C, Bevan DR. Potency pancuronium at the diaphragm and the adductor pollicis muscle in humans. Anesthesiology 1986; 65: 1–5.[Web of Science][Medline]
- Hemmerling TM, Schmidt J, Hanusa C, et al. Simultaneous determination of neuromuscular block at the larynx, diaphragm, adductor pollicis, orbicularis oculi and corrugator supercilii muscles. Br J Anaesth 2000; 85: 856–60.[Abstract/Free Full Text]
- Hemmerling TM, Schmidt J, Wolf T, et al. Intramuscular versus surface electromyography of the diaphragm for determining neuromuscular blockade. Anesth Analg 2001; 92: 106–11.[Abstract/Free Full Text]
- Moore KL, Dalley AF. Clinically oriented anatomy. Baltimore, MD: Lippincott Williams & Wilkins, 1999: 291.
- Mills GH, Kyroussis D, Hamnegard CH, et al. Unilateral magnetic stimulation of the phrenic nerve. Thorax 1995; 50: 1162–72.[Abstract/Free Full Text]
- Mador MJ, Rodis A, Magalang UJ, Ameen K. Comparison of cervical magnetic and transcutaneous phrenic nerve stimulation before and after threshold loading. Am J Respir Crit Care Med 1996; 154: 448–53.[Abstract]
- Cantineau JP, Porte F, d’Honneur G, Duvaldestin P. Neuromuscular effects of rocuronium on the diaphragm and adductor pollicis muscles in anesthetized patients. Anesthesiology 1994; 81: 585–90.[Web of Science][Medline]
- Dhonneur G, Kirov K, Slavov V, Duvaldestin P. Effects of an intubating dose of succinylcholine and rocuronium on the larynx and diaphragm: an electromyographic study in humans. Anesthesiology 1999; 90: 951–5.[Web of Science][Medline]
Accepted for publication June 5, 2002.
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Abstract
Introduction
