The 2023 American Society of Anesthesiologists Practice Guidelines for Monitoring and Antagonism of Neuromuscular Blockade were published last month.The paper is backed by strong science, and references an exhaustive list of no less than 277 previous publications on the topic, including this review. The paper concludes that quantitative neuromuscular (NM) monitoring is the most accurate and clinically useful technology for detecting residual neuromuscular block.

The problem? Very few anesthesia professionals have access to a quantitative NM monitoring device at present.

Currently a large number of anesthesia practitioners don’t monitor neuromuscular blockade level at all. A 2010 survey documented that 9.4% of American anesthesiologists didn’t use a peripheral nerve stimulator, and most survey respondents felt that neither conventional nerve stimulators nor quantitative neuromuscular monitors should be part of minimum monitoring standards. An editorial accompanying the 2023 ASA Guidelines states, “it is impossible to accurately predict the depth of neuromuscular block or the adequacy of reversal by using clinical tests such as tidal volume, negative inspiratory force, ability to sustain head lift, or grip strength. Similarly, qualitative assessment of responses to peripheral nerve stimulators cannot be relied upon in deciding the appropriate time for tracheal extubation.”

The most important recommendations from these ASA Practice Guidelines, each backed by Strong Strength of Recommendation (bold text by me) are:

  1. When neuromuscular blocking drugs are administered, we recommend against clinical assessment alone to avoid residual neuromuscular blockade, due to the insensitivity of the assessment.

  2. We recommend quantitative monitoring over qualitative assessment to avoid residual neuromuscular blockade. When using quantitative monitoring, we recommend confirming a train-of-four ratio greater than or equal to 0.9 before extubation.

  3. We recommend using the adductor pollicis muscle for neuromuscular monitoring.

  4. We recommend against using eye muscles for neuromuscular monitoring.

  5. We recommend sugammadex over neostigmine at deep, moderate, and shallow depths of neuromuscular blockade induced by rocuronium or vecuronium, to avoid residual neuro- muscular blockade.

Recommendation #2 will be the most challenging to follow, because, as an October 2021 study published in Anesthesiology states, “The paucity of easy-to-use, reliable objective neuromuscular monitors is an obstacle to universal adoption of routine neuromuscular monitoring.” In 2016 there were more than 224,000 operating rooms in the United States, so tens of thousands of devices could be needed.

What type of quantitative NM monitoring device should we aim to acquire? There are three types of quantitative monitors of neuromuscular blockade discussed in a 2021 Anesthesiology editorial. I quote from this reference:

1. Acceleromyography. Depolarization of the ulnar nerve results in contraction of the adductor pollicis, which flexes the thumb, producing an acceleration detected by the sensor. . . . the thumb must be entirely free to move, which precludes monitoring the hand that has been tucked at the patient’s side during surgery. The second problem is that the baseline, unparalyzed train-of-four ratio (the ratio of the fourth to the first twitch of a train-of-four), which should theoretically be equal to 1, is often greater than 1.

Acceleromyography monitoring

2. A mechanomyograph is an instrument that directly measures the isometric force of contraction of the thumb, using a force transducer. . . . A mechanomyograph is a somewhat cumbersome instrument that has been used primarily for research, and very seldom for routine clinical practice. Currently, mechanomyography is not commercially available.

3. Electromyography directly measures the compound action potential of the adductor pollicis muscle. . . No movement is required for this measurement to be made. The hand can be tucked at the patient’s side without any significant effect on the electromyogram. . . . A baseline, unparalyzed train-of-four ratio is not required. 

electromyography (EMG)

Electromyography (EMG) is the most promising of the three devices. The Nemes et al study, performed in Hungary, established that EMG compares favorably to acceleromyography, stating, “The EMG-based device is a better indicator of adequate recovery from neuromuscular block and readiness for safe tracheal extubation than the acceleromyography monitor.” The Nemes study utilized an EMG called a TetraGraph.

Where can you buy a TetraGraph? A Google search for this device leads us to a website for a company called Senzime.

TetraGraph and TetraSens EMG unit

The TetraGraph received FDA 510 clearance in 2019. Dr. Sorin J. Brull, the author of the Anesthesiology editorial on the 2023 NM Practice Guidelines, is a principal, shareholder, and the Chief Medical Officer in Senzime, as well as a Professor Emeritus of Anesthesiology and Perioperative Medicine at the Mayo Clinic.

I contacted a representative of Senzime, who demonstrated the device to me. I learned the following:

  • Senzime’s TetraGraph is manufactured in Sweden. The device has been improved and modified over the past 3 years.
  • The TetraGraph NM monitoring device clamps to an IV pole, and is slightly larger than an iPhone.  A disposable TetraSens sticker of sensing electrodes attaches to the patient’s wrist over the ulnar nerve, and extends distally to adhere to the skin over either the pinky or the thumb. The hand can be tucked out of sight and the EMG technology will still reveal accurate data.
  • The Tetragraph attaches to the TetraSens via a cable.
  • The Tetragraph screen displays a button labelled “AUTO,” which will activate serial trains-of-four at a preselected interval, for example, every 20 seconds.
  • The screen on the device is usually set to display four bars in a bar graph, representing  the measured EMG amplitude of the train of four. At control the quantitative NM score will be 100%, as all four twitches are equivalent. Once a muscle relaxant is administered to the patient, the bar graph will change, showing decreased heights of the bars dependent on the dose and time of the muscle relaxant.

TetraGraph bar graph screen depicting Train-of-Four


  • The anesthesiologist should wait until the quantitative NM score is 90% or greater, prior to extubation.
  • The hardware retails for $2000 – $2500 per unit. The disposable stickers that adhere to the patient’s hand are $20 each. The unit can be annexed to certain patient monitoring systems, and data can be input into an Electronic Medical Record system. Senzime’s website  outlines the company’s intention to combine TetraGraph with Masimo’s patient monitoring system, stating “Our ambition is to submit the module developed to connect TetraGraph® with Masimo’s patient monitoring system Root® for approval at the end of 2023, and to launch at the beginning of 2024.”
  • To date Senzime has sold 300+ units in the United States. Several large hospital systems, including the University of Arizona, Duke, University of North Carolina, and the Medical College of Wisconsin have purchased the devices for their operating rooms. Multiple other large hospital systems are on the verge of completing purchases of 100-200 units as of January 2023. Senzime has an inventory to accommodate such purchases, and a clinical team positioned to help medical centers or surgery centers try out and/or adopt the technology.


Will Senzime have a monopoly or near-monopoly on this new technology? Time will tell. A Google search for “quantitative neuromuscular monitoring device” yields only a few companies competing with Senzime, including: TwitchView by Blink, Xavant, and GE Healthcare.


Are the 2023 ASA Practice Guidelines for Monitoring and Antagonism of Neuromuscular Blockade now a standard of care for practicing anesthesiology?

No. Guidelines are not Standards.

In these 2023 Practice Guidelines, the ASA states, “Practice guidelines are systematically developed recommendations that assist the practitioner and patient in making decisions about health care. . . . practice guidelines developed by the American Society of Anesthesiologists are not intended as standards or absolute requirements, and their use cannot guarantee any specific outcome.”

Expect quantitative NM monitors to become available where you work. Expect most hospitals to purchase these devices. What will you do until quantitative NM monitors become available where you work?

1. Since clinical assessment alone to avoid residual neuromuscular blockade is inaccurate, I believe a qualitative NM monitor is better than no NM monitor.

Qualitative Twitch Monitor

2. Monitoring twitch at the adductor pollicis at the wrist is more accurate than monitoring the periocular muscles, so apply your qualitative twitch monitor to the wrist.

3. Have sugammadex available when using non-depolarizing muscle relaxants such as rocuronium or vecuronium. If a patient shows signs of residual NM blockade at the end of an anesthetic, 2 mg/kg of IV sugammadex will usually resolve the NM blockade within a minute or two. Sugammadex, for the reversal of rocuronium-induced NM blockade, is one of the biggest advances in the field of anesthesiology in the past 10 years.

4. Following a general anesthetic, don’t leave your patient’s side in the PACU until you are certain that their airway is open and they are breathing adequately without any sign of residual respiratory difficulty.

Until your hospital and your surgery centers supply you with quantitative neuromuscular EMG monitors, be aware of the recommendations of the 2023 ASA Practice Guidelines for Monitoring and Antagonism of Neuromuscular Blockade, and comply with them as best as you can. When quantitative NM units arrive, I encourage you to use them. The device I tested was quick to apply, easy to use, and provided valuable information to assure patient wellbeing.




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