ASHP Advantage e-Newsletter
Winter 2019


Neuromuscular blockade is used in conjunction with anesthetic and analgesic medications for many surgical procedures. It plays a vital role in facilitating surgery by providing muscle paralysis, which optimizes access to the surgical site and prevents patient movement during the procedure. There is wide interindividual variability in response to neuromuscular blocking agents (NMBAs).[1] Complete reversal of neuromuscular blockade and associated muscle paralysis is needed after conclusion of the procedure before the patient awakens.

Residual postoperative neuromuscular blockade and muscle weakness is a common complication that can contribute to critical respiratory events in the postanesthesia care unit (PACU).[2] Careful management of neuromuscular blockade by anesthesia providers and effective hand-off communication between the operating room (OR) and PACU staff are important strategies for avoiding these complications and optimizing patient outcomes.

This e-newsletter consists of two parts. Part 1 focuses on quantitative monitoring and the different types of available equipment. Part 2 addresses barriers to monitoring and the need for improved communication among members of the perioperative team at transitions of care. A framework to guide successful implementation of quality improvement interventions is discussed.

Quantitative Monitoring

The use of clinical tests (e.g., 5-second head lift, sustained hand grip) and clinical signs (e.g., presence of spontaneous respiration) is subjective and unreliable for assessing the depth of neuromuscular blockade after administration of a nondepolarizing NMBA and the recovery of neuromuscular function after reversal at the end of a surgical procedure.[1,2] Conventional peripheral nerve stimulator (PNS) devices have been used in the perioperative setting to provide a qualitative assessment of the depth of neuromuscular blockade and recovery of neuromuscular function. Use of these conventional qualitative PNS devices involves a subjective visual or tactile assessment of muscle contraction (usually in the adductor pollicis, a hand muscle that permits adduction of the thumb) after delivery of an electrical stimulus to a peripheral nerve, usually the ulnar nerve in the forearm.[1,3] These qualitative assessments are prone to error and are unreliable. Quantitative measurement of the evoked muscular response is not provided when conventional qualitative PNS devices are used.[1]

Train-of-four (TOF) stimulation is commonly used to assess the depth of neuromuscular blockade after administration of NMBAs, guide reversal, and monitor recovery of neuromuscular function at the end of a surgical procedure.[4] Four 2-Hz electrical stimuli are delivered to a nerve at 0.5-second intervals.[3] Use of the ulnar nerve is preferred over the facial nerve to assess the adequacy of reversal.[1] A train of four count (TOFC) can be obtained based on the number of responses to the four stimuli. The TOFC gradually decreases as the NMBA takes effect, resulting in a period of intense block followed by a period of deep block, both of which are characterized by a TOFC of 0.[4] A TOFC of 0 indicates readiness for tracheal intubation.[1]

Tetanic stimulation (i.e., the series of four 2-Hz electrical stimuli at 0.5-second intervals) induces the release of acetylcholine at the neuromuscular junction. The response to post-tetanic stimulation can be used to assess the depth of blockade during the period when TOF stimulation evokes no muscle response (i.e., when the TOFC is 0).[2,3] The post-tetanic count (PTC) is evaluated by counting the number of twitches after tetanic stimulation.[1] Monitoring the PTC is useful during certain surgical procedures when deep block is required. The PTC is inversely proportional to the depth of blockade, with a PTC of 0 during intense block and PTC ≥1 during deep block.[2] The PTC can be used to predict recovery from deep block.[3]

The TOFC can be used to determine the dose and timing of reversal agent administration and to assess recovery of neuromuscular function at the end of the surgical procedure.[3] Reversal of neuromuscular blockade is characterized by a return of all four twitches and no presence of fade (decreasing muscle contraction in response to repeated nerve stimulation).[2] The terminology used to define various levels of neuromuscular block is not standardized. The following table provides proposed definitions for levels of neuromuscular blockade in a 2018 consensus statement by anesthesia clinicians on the perioperative use of neuromuscular monitoring.[1]

Levels of Neuromuscular Blockade [Adapted from reference 1]
PTC 0*
PTC ≥1, TOFC 0*
TOFC 1-3*
TOFC 4, TOF fade present†
TOFR <0.4‡
TOFC 4, TOF fade not detected by tactile or visual observation†
TOFR 0.4-<0.9‡
Acceptable recovery
Cannot be determined†
TOFR ≥0.9‡
PTC = post-tetanic count, TOFC = train-of-four count, TOFR = train-of-four ratio
*Same for quantitative and qualitative measurement.
†Qualitative measurement.
‡Quantitative measurement.
Depth of Block Qualitative Measurement Quantitative Measurement
Complete PTC 0 PTC 0
Deep PTC ≥1, TOFC 0 PTC ≥1, TOFC 0
Moderate TOFC 1-3 TOFC 1-3
Shallow TOFC 4, TOF fade present TOFR <0.4
Minimal TOFC 4, TOF fade not detected by tactile or visual observation TOFR 0.4-<0.9
Acceptable recovery Cannot be determined TOFR ≥0.9
PTC = post-tetanic count, TOFC = train-of-four count, TOFR = train-of-four ratio

A TOF ratio (TOFR) is a quantitative measure of the return of muscle function. A TOFR can be calculated by dividing the amplitude (i.e., magnitude) of the fourth twitch (i.e., evoked muscle response to nerve stimulation) by that of the first twitch.[2] There is wide consensus that a TOFR of 0.9 or higher is needed to ensure adequate recovery of neuromuscular function and patient safety.[1] Residual neuromuscular weakness may be present in patients with a TOFR less than 0.9. A TOFR of 0.9 or higher signals readiness for tracheal extubation.

The presence or absence of fade in a patient with a TOFC of 4 using a conventional qualitative PNS device has been used to determine residual muscle weakness. This is a subjective and unreliable method because the presence of fade cannot be accurately detected by tactile or visual observation.[2] Conversely with quantitative devices, a TOFR of 0.4 up to 0.9 indicates the presence of fade.[3]

Listen to Dr. Wolfe describe methods of monitoring neuromuscular blockade.
Which of the following is recommended prior to tracheal extubation, according to a 2018 consensus statement by anesthesia clinicians on the perioperative use of neuromuscular monitoring?
A Train-of-four ratio (TOFR) ≥0.9
B Train-of-four count (TOFC) 0
C Post-tetanic count (PTC) ≥1
D Ability to sustain a head lift ≥5 sec

A TOFR ≥0.9 is recommended prior to extubation in the 2018 consensus statement because residual neuromuscular blockade may be present in patients with a TOFR less than 0.9.[1] A TOFC of 0 is associated with intense or deep block, and the PTC can be used to determine the depth of block when the TOFC is 0.[2,4] A PTC ≥1 is associated with deep block but not intense block, and the PTC can be used to predict recovery from deep block.[3] Extubation should not be performed during intense or deep block. Ability to sustain a head lift for 5 seconds or longer is a clinical test that is subjective and unreliable for assessing residual neuromuscular blockade and readiness for extubation.[1]

Quantitative PNS monitoring is preferred over the use of conventional qualitative PNS devices to provide an objective measure of the depth of neuromuscular blockade, guide intraoperative use of NMBAs, direct selection and dosing of the reversal agent, and monitor recovery of neuromuscular function after reversal. Quantitative monitoring measures, analyzes, and displays the TOFR in real time once four twitches have returned.[1] Such monitoring has been shown to reduce postoperative morbidity (e.g., the incidence of respiratory complications), length of stay in the PACU and hospital, and healthcare costs.[1] However, use of these devices is low in the United States despite their advantages.[5] The cost of quantitative monitoring equipment may be a barrier to its use for some institutions, especially if the economic costs associated with complications that result from unmonitored care are not taken into account.[1,6] The need for staff training on proper use of the device is also an important aspect of use.

Key Points

  • Train of four count (TOFC) is provided by all PNS devices (i.e., conventional qualitative PNS devices and quantitative monitoring equipment)
  • Only quantitative monitoring equipment provides the train of four ratio (TOFR) needed to assess presence or absence of fade


Various technologies and types of equipment have been developed for quantifying neuromuscular blockade. Features of the ideal quantitative monitoring device include connectivity (i.e., integration into the electronic health record), visual display, auditory or visual alarms for stimulus delivery, and memory for recording and displaying data.[2]

Mechanomyography (MMG) has been used to measure the force of contraction of the adductor pollicis muscle in response to ulnar nerve stimulation.[2] This technology was the gold standard for a long time because of its good precision and reproducibility, but it is no longer available.[4] A need for a fixed arm position, the bulkiness of the equipment, and the elaborate set up were among the shortcomings of using MMG technology.

Electromyography (EMG), acceleromyography (AMG), kinemyography (KMG), and phonomyography (PMG) may offer advantages over MMG, although these technologies are not without limitations.

EMG devices measure electrical activity in response to nerve stimulation and probably are the most precise devices for measuring neurotransmission.[2] The results obtained using EMG devices are comparable to those obtained using MMG, making it the alternative gold standard.[3] Advantages of EMG include its high precision, use of less cumbersome equipment than MMG, lack of need for equipment calibration, ease of use in small children, and usefulness for assessing several different muscle groups.[2-4] If the patient’s arms are tucked at the sides and thumb motion is restricted, EMG neuromuscular monitoring can still be used.[1] In addition, sites other than the hand (e.g., corrugator supercilii and zygomaticus major muscle groups in the face) can be used for monitoring if the arms are not available. The potential for electrical interference from electrical devices in the OR and influence of temperature changes on the measured response are potential disadvantages of using EMG.[3,4] In the 2018 consensus statement by anesthesia clinicians, EMG devices are preferred for neuromuscular monitoring.[1]

The AMG devices measure acceleration of muscle tissue in response to nerve stimulation, usually ulnar nerve stimulation, after attachment of a piezoelectric ceramic wafer transducer to the adductor pollicis muscle.[2] The simpler set up procedure compared with MMG and smaller size and portability of devices are advantages of using AMG.[2,4] The need for equipment calibration and correction (normalization) of baseline TOFR values >1 to avoid overestimation of recovery, lack of validation of most AMG devices against EMG and MMG gold standard devices, need for unrestricted thumb movement, and lack of precision and accuracy of first-generation devices are shortcomings of AMG.[1,3]

Use of KMG devices also involves attachment of a piezoelectric transducer to the adductor pollicis muscle and measures muscle movement in response to electric stimulation of a nerve. Ease of use (i.e., minimal set up procedure) is an advantage of KMG but calibration of the equipment and unrestricted thumb movement are required.[1]

The use of PMG technology involves measurement of low-frequency sounds emitted by lateral muscle fiber movement in response to nerve stimulation.[3] The PMG results correlate with MMG, EMG, and AMG results.[7] A variety of muscle groups can be tested using PMG, and muscle mobilization is not required. However, PMG devices currently are available only for use in a research setting.[4]

Which of the following types of quantitative neuromuscular monitors is preferred and probably is the most precise device currently available for measuring neurotransmission in surgical patients undergoing neuromuscular blockade and reversal?
A Acceleromyography (AMG)
B Electromyography (EMG)
C Mechanomyography (MMG)
D Phonomyography (PMG)

Quantitative monitors using EMG technology probably are the most precise devices for measuring neurotransmission.[2] They are preferred for measuring neurotransmission in surgical patients undergoing neuromuscular blockade and reversal.[1] When AMG devices are used, baseline TOFR values often exceed 1 and need to be normalized (i.e., corrected) to avoid overestimation of recovery.[4] Although MMG devices offer good precision, they are no longer available. Devices that use PMG are not yet available commercially.

Effecting Institutional Change

A 2008 survey of anesthesia practitioners in the United States revealed that quantitative monitors are not available for neuromuscular monitoring in one in four American surgical facilities, and neuromuscular monitoring is not performed at all in one in ten institutions.[5] More recently, surveys of clinicians in Australia, New Zealand, and Singapore reflect a global lack of standardized quantitative monitoring.[8,9] Effecting change in institutions where quantitative monitoring is not performed is challenging and needs to be centered around a shared strategy for eliminating postoperative residual neuromuscular muscle blockade as a cause for respiratory failure.

The process for implementing use of this monitoring involves planning, engaging staff, executing, and evaluating outcomes.[10] An interprofessional advisory group comprising anesthesiologists, certified registered nurse anesthetists (CRNAs), anesthesiologist assistants, PACU nurses, surgeons, pharmacists, and other stakeholders should be convened to oversee the process.[1] Identification and engagement of key opinion leaders and champions who support implementation may be vital to success.[10] Personal belief systems vary among individuals, and resistance to change can pose significant barriers to successful implementation.

Once senior leadership is on board, obtaining early buy-in from anesthesia clinicians will be instrumental in successful implementation of plans to use quantitative neuromuscular monitors in the institution.[11] It is equally important to engage clinician leaders who are not aligned with the change in practice, since they may have important insight into the barriers to implementation success. A nonconfrontational, nonpunitive approach is recommended to avoid undesired behaviors.

Which of the following strategies is typically NOT associated with sustainable implementation success in using quantitative monitors in an institution?
A Introduce penalties for noncompliance with intraoperative quantitative monitoring
B Engage an interprofessional team of anesthesia, nursing, surgical, and pharmacy staff to reduce the occurrence of postoperative respiratory failure
C Identify champions and active resisters early in the implementation process
D Provide comprehensive staff education about proper device use

Penalties related to noncompliance have been shown to have a variable impact on project implementation success, with significant negative effects on team member behaviors.[11] There are more effective ways to engage team members in processes that contribute to the overall success of the project. Building learning environments to enhance data visualization of critical process compliance and relevant outcomes is likely to enhance individual engagement.[10] An interprofessional group should be convened to guide the implementation process. The advisory group should also include anesthesiologists, CRNAs, anesthesiologist assistants, PACU nurses, surgeons, pharmacists, anesthesia technicians, and other local stakeholders.[1] Champions who support implementation and persons who actively resist implementation should be identified early in the implementation process because these individuals can play key roles in your success.[11] Staff education in the proper use of equipment will be needed but it can be provided later in the implementation process.


  1. Naguib M, Brull SJ, Kopman AF et al. Consensus statement on perioperative use of neuromuscular monitoring. Anesth Analg. 2018; 127:71-80.
  2. Brull SJ, Kopman AF. Current status of neuromuscular reversal and monitoring: challenges and opportunities. Anesthesiology. 2017; 126:173-90.
  3. Murphy GS. Neuromuscular monitoring in the perioperative period. Anesth Analg. 2018; 126:464-8.
  4. Fuchs-Buder T, Claudius C, Skovgaard LT et al. Good clinical research practice in pharmacodynamic studies of neuromuscular blocking agents II: the Stockholm revision. Acta Anaesthesiol Scand. 2007; 51:789-808.
  5. Naguib M, Kopman AF, Lien CA et al. A survey of current management of neuromuscular block in the United States and Europe. Anesth Analg. 2010; 111:110-9.
  6. Murphy G. Anesthesia Patient Safety Foundation. Presentation of the APSF Collaborative Panel on Neuromuscular Blockade and Patient Safety at the 2017 ASA Annual Meeting. APSF Newsletter. 2018; 32(3):68-9. (accessed 2019 Mar 5).
  7. Duţu M, Ivaşcu R, Tudorache O et al. Neuromuscular monitoring: an update. Rom J Anaesth Intensive Care. 2018; 25:55-60.
  8. Phillips S, Stewart PA, Bilgin AB. A survey of the management of neuromuscular blockade monitoring in Australia and New Zealand. Anaesth Intensive Care. 2013; 41:374-9.
  9. Teoh WH, Ledowski T, Tsent PS. Current trends in neuromuscular blockade, management, and monitoring amongst Singaporean anaesthetists. Anesthesiol Res Pract. 2016; 2016:7284146. Epub 2016 Oct 13.
  10. Damschroder LJ, Aron DC, Keith RE et al. Fostering implementation of health services research findings into practice: a consolidated framework for advancing implementation science. Implement Sci. 2009; 4:50.
  11. Saint S, Kowalski CP, Banaszak-Holl J et al. How active resisters and organizational constipators affect health care-acquired infection prevention efforts. Jt Comm J Qual Patient Saf. 2009; 35:239-46.
That concludes Part 1

View Part 2