1. Introduction
Neuromuscular blockade (NMB), as the name implies, refers to a battery of agents that can specifically bind to the nicotinic receptor at the neuromuscular junction and thus block impulse transmission from the upper nerve to downstream muscle fibers, leading to transient or persistent skeletal muscle relaxation and aiding in easing endotracheal intubation and providing optimal conditions for operating and mechanical ventilation
[1]. Many factors have been seen to affect the pharmacokinetics of NMB, such as age, organ function, or the apparent volume of distribution, requiring individualized NMB administration
[2][3][2,3]. Hence, it is tricky for anesthesiologists to accurately maintain a shallow, moderate, or deep neuromuscular block at a proper time. However, an airway injury during endotracheal intubation, a sudden body-movement in surgical procedure, or a postoperative residual neuromuscular block (PRNB) during the reversal phase caused by the misjudgment of neuromuscular block may end in calamity
[4][5][6][4,5,6]. Therefore, to reduce NMB-related complications, perioperative neuromuscular monitoring is highly recommended according to international guidelines to empower NMB with more controllability and to make NMB administration more individualized
[7][8][9][10][7,8,9,10].
Typical perioperative neuromuscular monitoring methods (
Figure 1) include acceleromyography (ACC), mechanomyography (MMG), electromyography (EMG), and kinemyography (KMG)
[11]. ACC-based equipment chooses a sensor that can evaluate acceleration yielded by muscle contraction
[12]. ACC can be applied in many muscles, such as the adductor pollicis muscle, the orbicularis oculi muscle, and the corrugator supercilii muscle
[13]. It is currently regarded as the gold standard for scientific research and clinical practice. MMG, which measures force generated by muscle contraction, was once considered the gold standard of neuromuscular monitoring; however, it has been phased out due to its bulky setup. EMG-based equipment records compound action potentials from the target muscle. This technique is a desirable choice for neuromuscular monitoring in clinical settings and is also able to detect neuromuscular blocks at various muscles. KMG-based facilities utilize one kind of piezoelectric mechanosensory to obtain and reflect the contraction of the adductor pollicis muscle
[13]. This method is easy to use and clinically reliable.
Figure 1. Typical neuromuscular monitoring patterns. (a) Mechanismography directly measures the force generated by the skeletal muscle. (b) Acceleromyography evaluates acceleration yielded by muscle contraction. (c) Electromyography records compound action potentials from the skeletal muscle. (d) Kinemyography employs a piezoelectric crystal to reflect muscle contraction.
However, frequently used neuromuscular monitoring patterns are always criticized for their diverse shortcomings (
Table 1). Despite its universal utilization in clinical settings, ACC is susceptible to artifacts and will probably generate an overrated block degree
[12][14][12,14]. A conventional ACC-based apparatus records the monaxial movement of the target muscle; therefore, signal quality relies heavily on the posture of the recording sites
[15]. Recently, ACC-based equipment capable of estimating the multiplanar movement of the thumb has been developed. However, its feasibility exploration is still in progress
[16]. The application of MMG demands a special posture of the hand and an elaborate setup
[17]. In addition, this method can only record signals at the adductor pollicis muscle
[18]. For EMG, the working principle limits its application intraoperatively owing to disturbances from other electronic equipment in the operating room
[19]. In addition, the recording result of the EMG is an electromechanical compound instead of absolute mechanical contraction of skeletal muscle. Similar to MMG, KMG is also subjected to hand position
[11]. Moreover, KMG is not interchangeable with MMG according to existing investigations
[20].
Table 1. Features of classical neuromuscular monitoring patterns.
Neuromuscular Monitoring Methods |
Objects Detected |
Recording Sites |
Drawbacks |
Table 2. Articles describing PMG on perioperative neuromuscular monitoring.
Author/Year |
Sample Size |
Sound
Detector |
Control |
Muscle |
Muscle
Relaxant |
Main Conclusion |
Acceleromyography |
Acceleration |
Adductor pollicis muscle |
Dascalu 1999 [21] |
| Corrugator supercilii muscle |
25
… |
Air-coupled microphoneMiscalculation of the block degree
Susceptible to outside interference
Elaborate setup |
MMG |
| EMG |
ACC |
Adductor pollicis muscle |
Tubocurarine
Atracurium
Succinylcholine |
PMG could be used for perioperative neuromuscular monitoring |
Mechanomyography |
Force |
Adductor pollicis muscle |
Bellemare 2000 [22] | Harsh conditions for the hand posture |
| Adductor pollicis muscle only |
13 |
Condenser microphone |
MMG |
Adductor pollicis muscle |
Rocuronium |
Electromyography |
Compound action potentials |
Adductor pollicis muscle
Corrugator supercilii muscle
Orbicularis oculi muscle
Laryngeal muscle
Diaphragm… |
Condenser microphoneSusceptible to electrical interference
Not purely reflection of mechanical contraction of muscles |
ACC |
Corrugator supercilii muscle |
Mivacurium |
PMG was not an alternative method for neuromuscular monitoring at the corrugator supercilii muscle when compared with ACC |
Kinemyography |
Movement |
Adductor pollicis muscle |
Hemmerling 2002 [24] |
27 | Harsh conditions for the hand posture |
Condenser microphone |
Adductor pollicis muscle only
Not interchangeable with MMG |
Phonomyography (PMG), also named acoustic myography, is a little-known neuromuscular monitoring technique. However, previous studies suggested that PMG may be a feasible alternative neuromuscular monitoring method. TheOur entrypaper provides an overview of the evolutionary trajectory of PMG on perioperative neuromuscular monitoring chronologically and summarizes the advantages and drawbacks of PMG as a means to present an avenue for further research. ResearchersWe performed a PubMed search using the keywords “phonomyography”, “acoustic myography”, and “muscle sounds” updated to December 2021. Articles describing PMG on perioperative neuromuscular monitoring are displayed in Table 2.
PMG was not an alternative method for neuromuscular monitoring at the adductor pollicis muscle when compared with MMG |
Hemmerling 2002 [23] |
20 |
ACC |
Corrugator supercilii muscle |
Mivacurium |
The best recording site at the corrugator supercilii muscle for PMG is located between the anterior midline and the lateral part of the forehead, over the eyebrow |
Hemmerling 2003 [25] |
28 |
Condenser microphone |
Cuff pressure method |
Laryngeal adductor muscles |
Mivacurium |
PMG was an alternative method for neuromuscular monitoring at the laryngeal adductor muscles when compared with the cuff pressure method |
Hemmerling 2004 [26] |
15 |
Condenser microphone |
Balloon pressure MMG |
Corrugator supercilii muscle |
Mivacurium |
PMG was an alternative method for neuromuscular monitoring at the corrugator supercilii muscle when compared with Balloon pressure MMG |
Hemmerling 2004 [27] |
12 |
Condenser microphone |
MMG |
Hand muscles |
Rocuronium |
PMG was an alternative method for neuromuscular monitoring at hand muscles muscle when compared with MMG |
Hemmerling 2004 [28] |
28 |
Condenser microphone |
MMG |
Adductor pollicis muscle |
Mivacurium |
PMG was an alternative method for neuromuscular monitoring at the adductor pollicis muscle when compared with MMG |
Hemmerling 2004 [29] |
12 |
Condenser microphone |
- |
Posterior cricoarytenoid muscle
/Lateral cricoarytenoid muscle |
Mivacurium |
The acoustic signals created by the posterior cricoarytenoid muscle and the lateral cricoarytenoid muscle after the administration of muscle relaxants are different. |
Deschamps 2005 [30] |
10 |
Piezo-electric microphone |
MMG |
Corrugator supercilii muscle/The first dorsal interosseus muscle |
- |
An apparent staircase phenomenon was found at the first dorsal interosseus muscle and the adductor pollicis muscle while no obvious staircase phenomenon occured at the corrugator supercilii muscle. |
Hemmerling 2005 [31] |
12 |
Piezo-electric microphone |
- |
Lateral cricoarytenoid muscle
/Strap muscles of the neck |
Mivacurium |
PMG signals recorded were different outside and inside of the trachea for recovery time. |
Michaud
2005 [32] |
15 |
Piezo-electric microphone |
- |
Vastus medialis muscle
Adductor pollicis |
Mivacurium |
The vastus medialis muscle is an alternative recording site for PMG |
Michaud
2005 [33] |
14 |
Piezo-electric microphone |
- |
Adductor pollicis muscle |
Mivacurium |
Whether it is the dominant hand would not influence the rustles of PMG recording at the adductor pollicis muscle |
Trager
2006 [18] |
14 |
Piezo-electric microphone |
MMG
KMG |
Adductor pollicis muscle |
Mivacurium |
PMG was an alternative method for neuromuscular monitoring at the adductor pollicis muscle when compared with MMG or KMG |
Hemmerling 2008 [34] |
28 |
Piezo-electric microphone |
- |
Adductor pollicis muscle |
Mivacurium |
The potency of mivacurium is greater after a 20 min infusion of propofol compared with a 5 min infusion of propofol |
Wehbe
2012 [35] |
1 |
Piezo-electric microphone |
- |
Adductor pollicis
/Corrugator supercilii muscle |
Not mentioned |
“Relaxofon” may be a feasible neuromuscular monitoring device |