Neuromuscular blockade Part 1
Myron Yaster MD and Debra Faulk MD
Regular readers of the PAAD know that I’ve been riding the cusp of the quantitative neuromuscular blocking monitoring wave for over a year and have heralded to you that new guidelines would be forthcoming from ASA. Those guidelines are now here.(1) As the sole pediatric anesthesiologist on the guideline committee I must admit that most of the recommendations in the new guidelines come from adult literature. The review process was exhaustive and I’ve got to tip my hat to the guideline reviewers and particularly to the chair, Dr. Karen Domino, who led the team with grace, determination, and true grit (it’s pretty hard herding cats).
There is really very little published information to guide pediatric anesthesia practice and most of what has been published is anecdotal and/or based on case reports or case series. The one prospective study that I do know of has had trouble getting published. I’ve asked Dr. Debra Faulk, who reviewed many of the issues discussed in the new ASA guidelines to assist me in writing today and tomorrow’s PAADs. Debra gave a PEDx talk on some of these issues at the April 2022 SPA meeting held in Tampa Fl entitled: Intraoperative monitoring: “Future quantitative neuromuscular monitoring: Can you handle the truth”?
Finally, I’ve decided to break our PAAD reviews of these guidelines into 2 PAADs. The first will review issues of monitoring, the second will discuss antagonists (reversal). Myron Yaster MD
Original article
Stephan R Thilen, Wade A Weigel, Michael M Todd, Richard P Dutton, Cynthia A Lien, Stuart A Grant, Joseph W Szokol, Lars I Eriksson, Myron Yaster, Mark D Grant, Madhulika Agarkar, Anne M Marbella , Jaime F Blanck, Karen B Domino. 2023 American Society of Anesthesiologists Practice Guidelines for Monitoring and Antagonism of Neuromuscular Blockade: A Report by the American Society of Anesthesiologists Task Force on Neuromuscular Blockade. Anesthesiology. 2023 Jan 1;138(1):13-41 PMID: 36520073
Editorial
Sorin J Brull and Aaron Kopman. Measuring Success of Patient Safety Initiatives: The 2023 American Society of Anesthesiologists Practice Guidelines for Monitoring and Antagonism of Neuromuscular Blockade. Anesthesiology. 2023 Jan 1;138(1):4-6. PMID: 36520074
The guidelines can be boiled down to this summary: “This practice guideline provides evidence-based recommendations on the management of neuromuscular monitoring and antagonism of neuromuscular blocking agents. The objective is to guide practice that will enhance patient safety by reducing residual neuromuscular blockade. It is recommended to use quantitative neuromuscular monitoring at the adductor pollicis and to confirm a recovery of train-of-four ratio greater than or equal to 0.9 before extubation. Sugammadex is recommended from deep, moderate, and shallow levels of neuromuscular blockade that is induced by rocuronium or vecuronium. Neostigmine is a reasonable alternative from minimal blockade (train-of-four ratio in the range of 0.4 to less than 0.9). Patients with adequate spontaneous recovery to train-of-four ratio greater than or equal to 0.9 can be identified with quantitative monitoring, and these patients do not require pharmacological antagonism”.(1)
Only quantitative assessment of neuromuscular function with electromyography (EMG), mechanomyography, or acceleromyography can accurately measure a train of four ratio (TOFr). As a reminder, “the train-of-four involves the delivery of four brief electrical pulses to a peripheral nerve at the rate of 2 Hz and assessing the “twitches” that result. With increasing paralysis, sequential twitches in the train decrease in amplitude with the progressive disappearance of the fourth, then the third, then the second, and finally the first twitch. The amplitude of the twitches can be measured quantitatively to permit the calculation of the train-of-four ratio: the amplitude of the fourth twitch divided by that of the first. A decreasing train-of-four ratio indicates greater degrees of paralysis”.(1)
Based on a survey of members of the Society for Pediatric Anesthesia,(2) we know that pediatric anesthesiologists primarily use clinical assessment (head lift, grip strength, tidal volume or negative inspiratory force), qualitative assessment with peripheral nerve stimulators (“four visible twitches” or “sustained tetanus”), time since last dose of relaxant (“2 hours since my last dose”), or don’t bother with any of these because they used sugammadex for reversal.(2) Unfortunately, none of these practices are reliable and can result in residual neuromuscular blockade and its negative consequences.(1,3) Indeed, in our opinion, for the most part, pediatric anesthesiologists are currently “flying blind”.
If quantitative neuromuscular monitoring reduces the risk of residual neuromuscular blockade why hasn’t it been widely adopted? Until very recently, quantitative monitoring was difficult, time consuming, and mostly relegated to research studies. This is no longer true. There are several types of quantitative monitors: electromyography (EMG), mechanomyography, and acceleromyography.(4,5)
Acceleromyography is the modality most commonly used in clinical practice and several portable, relatively user-friendly monitors are commercially available. It measures the acceleration of muscle tissues (preferably at the adductor pollicis) and therefore requires a free, unencumbered hand for use. Monitoring accuracy relies on baseline stabilization, calibration, and normalization, but even so, this modality tends to overestimate recovery and a TOFr of 0.95 or 1.0 (rather than 0.9) has been proposed to signify full recovery with its use.(6) The biggest barrier to routine adoption of acceleromyography in children is the need for a free limb. As you all know, in most pediatric cases the limbs are tucked.
Recently, several portable EMG devices have been developed that operate by measuring compound action potentials and therefore do not require unencumbered movement of the monitored muscle (adductor pollicis). Baseline stabilization is unnecessary, and the monitor calibration requires less than a minute. We think EMG devices overcome many of the barriers to neuromuscular monitoring in paediatric patients and will become the “go-to” quantitative monitors in our practice.
Finally, where you place the monitoring probes really matters. The new guidelines recommend and are quite clear to use the adductor pollicis. Using the forehead and facial muscles, which is so commonly done in pediatric practice is not recommended because these nerves and muscles overestimate the degree of neuromuscular recovery. Peripheral muscles (e.g., adductor pollicis) are more sensitive to neuromuscular blocking agents than central facial muscles (e.g., corrugator supercilii). Facial muscles are also more prone to direct muscle stimulation leading to misinterpretation of greater than actual neuromuscular recovery.(7)
In tomorrow’s PAAD will focus on reversal agents. If you have experience with quantitative monitoring or if you disagree with these new guidelines please send to Myron and we’ll post in a future Reader response.
References
1. Thilen SR, Weigel WA, Todd MM, Dutton RP, Lien CA, Grant SA, Szokol JW, Eriksson LI, Yaster M, Grant MD, Agarkar M, Marbella AM, Blanck JF, Domino KB. 2023 American Society of Anesthesiologists Practice Guidelines for Monitoring and Antagonism of Neuromuscular Blockade: A Report by the American Society of Anesthesiologists Task Force on Neuromuscular Blockade. Anesthesiology 2023;138:13-41.
2. Faulk DJ, Austin TM, Thomas JJ, Strupp K, Macrae AW, Yaster M. A Survey of the Society for Pediatric Anesthesia on the Use, Monitoring, and Antagonism of Neuromuscular Blockade. Anesth Analg 2021;132:1518-26.
3. Brull SJ, Kopman A. Measuring Success of Patient Safety Initiatives: The 2023 American Society of Anesthesiologists Practice Guidelines for Monitoring and Antagonism of Neuromuscular Blockade. Anesthesiology 2023;138:4-6.
4. Murphy GS, Brull SJ. Quantitative Neuromuscular Monitoring and Postoperative Outcomes: A Narrative Review. Anesthesiology 2022;136:345-61.
5. Murphy GS. Neuromuscular Monitoring in the Perioperative Period. Anesth Analg 2018;126:464-8.
6. Blobner M, Hunter JM, Meistelman C, Hoeft A, Hollmann MW, Kirmeier E, Lewald H, Ulm K. Use of a train-of-four ratio of 0.95 versus 0.9 for tracheal extubation: an exploratory analysis of POPULAR data. Br J Anaesth 2020;124:63-72.
7. Thilen SR, Hansen BE, Ramaiah R, Kent CD, Treggiari MM, Bhananker SM. Intraoperative neuromuscular monitoring site and residual paralysis. Anesthesiology 2012;117:964-72.