The Stimpod NMS 450X

Quantitative NMT Monitoring

  • One-Touch NMT Monitoring
  • Electrode Placement Verification
  • Quick Setup & No Calibration
  • Handheld
  • Data Connectivity
  • Reusable Sensor
  • Standard ECG Electrode Compatible
  • Quantitative NMT Monitoring reduces incidence of residual paralysis, increases operating room throughput and lowers cost
  • 23 years of AMG research proves it identifies residual paralysis in 97% of patients
  • Pioneers of quantitative monitoring technology since 1998
  • Trusted by anaesthesiologists in over 40 countries

Instructional Video Series

Learn how the Stimpod NMS450X is used in the operating room.

 


 

Please note that the videos below feature the Stimpod NMS450, the predecessor of the NMS450X.

Technical Specifications

Current Range

Nerve Locating: 0.0 – 5.0mA
Nerve Mapping: 0 – 20mA
NMT Monitoring: 0 – 80mA

Load Impedance

Nerve Locating: 0 – 20kΩ (100V)
Nerve Mapping: 0 – 20kΩ (400V)
NMT Monitoring: 0 – 5kΩ (400V)

Stimulating Modes

Train-of-Four (TOF)
Double Burst (DB)
Post-Tetanic-Count (PTC)
Supra Maximal Current (SMC)
Tetanus (TET)
Twitch (1Hz, 2Hz, 5Hz)
Auto (Changes automatically depending on the depth of the block)

Dimensions

145mm x 90mm x 30mm

Operating Temperature

10 – 40° Celsius

Storage Temperature

10 – 40° Celsius

Frequently Asked Questions

Why monitor NMBAs?

  • Even moderate Post Operative Residual Curarization (PORC) decreases chemoreceptor sensitivity to hypoxia.
  • PORC is associated with impairment of muscles of the upper pharynx and upper oesophagus leading to regurgitation and aspiration.
  • Reduced upper airway volume or partial airway collapse
  • Significant risk factor for the development of pulmonary complications – increased morbidity and mortality
  • Research shows that almost half of anaesthesia-related deaths are directly or indirectly attributable to PORC.

When are TOF, DB, PTC , Twitch and Tetanus used?

Stimulation Pattern Onset of Action Deep NMB Moderate NMB Neuromuscular Recovery
TOF Suitable Not Suitable Suitable Conditionally Suitable
TOF with objective monitoring Suitable Not Suitable Suitable Suitable
DB Conditionally Suitable Suitable Not Suitable Conditionally Suitable
PTC Conditionally Suitable Suitable Not Suitable Not Suitable
Tetanus Not Suitable Not Suitable Not Suitable Not Suitable

Which mode provides a reliable indication for recovery?

Train of Four (TOF) with quantitative monitoring (objective monitoring).

What clinical indications of PORC are detectable at which objectively monitored TOF ratios?

TOF Ratio Inability to sustain headlift for > 5 sec [n=12] Inability to swallow normally [n=12] “Fade Visible” [n=12]
0.5 1 10 1
0.8 0 7 0
1.0 0 1 0


Eikermann et al. AM J Repir Crit Care Med. 2007;175:9-15 
Berg H et al. Acta Anaesthesiol Scand. 1997; 41:1095-1103 
Murphy GS et al. Anesth Analg. 2008; 107:130-137

What clinical outcomes could be expected at which TOF ratios?

What clinical outcomes could be expected at which TOF ratios?

Monitoring TOF Ratio on adductor pollicis Ratio: 0.5 Ratio: 0.8 Ratio: 1.0
Pharyngeal function (Swallowing) Significantly Impaired Impaired Mostly Normal
Integrity of upper airway Significantly Impaired Impaired Mostly Normal
Hypoxic respiratory response Frequently Impaired Mostly Normal Normal


Eikermann et al. AM J Repir Crit Care Med. 2007;175:9-15 
Berg H et al. Acta Anaesthesiol Scand. 1997; 41:1095-1103 
Murphy GS et al. Anesth Analg. 2008; 107:130-137

What is attributed to cause the fading observed during TOF or DB?

  • The reason for this is attributed to the binding of non-depolarizing neuromuscular blocking agents to presynaptic acetylcholine receptors, resulting in inhibition of the recruitment of Ach from the reserve pool.

What makes Sugammadex more effective than other reversal agents?

  • A minimum of spontaneous recovery does not need to be present before Sugammadex can be administered. Even the deepest neuromuscular blockade can be reversed rapidly within one to two minutes.
  • Fewer autonomic side effects are anticipated with Sugammadex.

The Stimpod NMS450X continually shows a reading of 100% even though the NMBA was injected – Why?

  • It could be because a depolarizing NMBA was injected.

The device showed that the patient was fully recovered, suddenly the TOF ratio dropped again – Why?

  • It could be that the core body temperature of the patient dropped again after recovery was observed.
  • In order to prevent PORC patients should only be assessed for residual NMBA once core has reached a temperature of greater than 36 °C.

Heier T, Caldwell J E, Impact of Hypothermia on the Response to Neuromuscular Blocking Drugs, Anesthesiology 2006; 104:1070-80

The device showed a TOF ratio of 0% while the patient still had good clinical signs of not being paralyzed?

  • The location of the electrode could have moved.
  • It could be that the supramaximal stimulating current was not first established.
  • It could be that the electrode dried out.
  • It could be that the polarity of the electrodes was reversed.

I am monitoring the orbicularis oculi during NMBA but I always see a TOF ratio of 100% - Why?

When facial muscles are stimulated there is a risk of direct muscle stimulation.

Why do we see TOF values greater than 100%?

  • When monitoring TOF prior and post NMBA, ratios of > 100% are often noticed (As high as 147%)
  • Effect ascribed to mobilization of presynaptic acetylcholine in NMJ after T1 promoting release in synaptic cleft during subsequent stimulations.
  • Both Stimpod NMS450 and TOF-Watch SX (uncalibrated) show values greater than 100%.

Suzuki T, Fukano N, Kitajima O, Saeki S, Ogawa S, 2006.’Normalization of acceleromyographic train-of-four ratio by baseline value for detecting residual neuromuscular block.’ British Journal of Anaesthesia; 96:44–7

I have compared the readings of two Stimpods, one on each arm of a patient with both set at 50mA and they give different TOF ratios – Why?

  • The cathodes (negative electrodes) could be placed at different distances from targeted nerves.
  • It could be that the supramaximal stimulating current was not first established for both stimulators independently.
  • It could be that one or more electrodes dried out.
  • It could be that the polarity of some electrodes was reversed.
  • It is a known fact that stimulation of the ulnar nerves on one patient’s two arms would results in different TOF ratios if all other setup factors are significantly similar.

Will a TOF ratio of >90% reliably exclude PORC (Post-operative residual curarization)?

  • It remains unclear as to what acceleromyography TOF ratio is necessary to exclude clinically significant PORC.
  • Glenn et al PORC reduced in patients monitored with acceleromyography TOF of >90%.

Claudius, C., Viby-Mogensen, J., 2008. ‘Acceleromyography for Use in Scientific and Clinical Practice – A Systematic Review of the Evidence’. Anesthesiology; 108:1117-40 
Glen S., Murphy, M. D., etc. 2011. ‘Intraoperative Acceleromyography Monitoring Reduces Symptoms of Muscle Weakness and Improves Quality of Recovery in the Early Postoperative Period

Why does the Stimpod NMS450X not require a preload device?

  • In an attempt to increase the reliability of the TOF-Watch accelerometer a preload device was introduced. According to Claudius, Viby-Mogensen (2008), there is insufficient evidence to confirm or deny that the application of a preload will increase the precision of acceleromyography.
  • The preload device attempts to restrict the movement of the thumb to one dimension. With a three dimensional accelerometer this is not necessary.

Claudius, C., Viby-Mogensen, J., 2008. ‘Acceleromyography for Use in Scientific and Clinical Practice – A Systematic Review of the Evidence’. Anesthesiology; 108:1117-40

Is acceleromyography the Gold Standard?

No. Mechanomyography is the established standard to measure neuromuscular block (NMB), however, it is impractical in a clinical setting and is only reserved for research purposes.

What is three dimensional acceleromyography and why should it provide a reliable answer?

  • Acceleromyography is based on Newton’s second law of motion, stating that: F (force) = m (mass) X a (acceleration).
  • Acceleromyography should be interchangeable with mechanomyography if the mass (in this case the mass of the thumb) is constant.
  • Surprisingly acceleromyography cannot be used interchangeably with mechanomyography in pharmacodynamic studies.
  • One difference between mechanomyography and acceleromyography is that the contractions observed during acceleromyography involve a three-dimensional movement involving three joints, frictional forces, and deformation of tissues.
  • The accelerometer of the TOF-Watch device utilizes a 1-dimensional accelerometer losing much of the information of the complex 3-dimensional movement.
  • The Stimpod NMS450, on the other hand, uses three accelerometer sensors, each positioned perpendicular on the other two, to enable the device to measure acceleration in three dimensions.
  • A specialized algorithm processes the information provided by the three accelerometers and provides a value representing the size of the vector of the three dimensional movement.
  • Xavant is of the opinion that this feature makes acceleromyography more reliable and should bring its response curves more in line with mechanomyography.

Claudius, C., Viby-Mogensen, J., 2008. ‘Acceleromyography for Use in Scientific and Clinical Practice – A Systematic Review of the Evidence’. Anesthesiology; 108:1117-40 
Baillard, C., Bourdiau ,S., Le Toumelin, P.,Ait Kaci, F., Riou, B., Cupa, M and Samama, M. 2004. ‘Assessing Residual Neuromuscular Blockade Using Acceleromyography Can Be Deceptive in Postoperative Awake Patients’, Anesthesia Analgesia; 98:854–7

Are normalization algorithms reliable?

  • TOF-Watch and TOF-Watch S will calculate and display T2/T4 and if this value exceeds 100% it would simply limit the display to 100%.
  • TOF-Watch SX has a well-implemented normalization procedure but it takes 20 minutes to perform.
  • Xavant is currently researching a practical way of implementing a normalization algorithm.

Claudius, C., Viby-Mogensen, J., 2008. ‘Acceleromyography for Use in Scientific and Clinical Practice – A Systematic Review of the Evidence’. Anesthesiology; 108:1117-40

The Stimpod switched off during surgery – Why?

The Stimpod has an automated switch off function which is activated if the device has not been in use for more than 10 minutes.

The Stimpod shows “Open Circuit Detected” with the ECG clips are connected - Why?

  • It could be because electrodes have dried out to the extent that they resemble an open circuit.
  • There could be a problem with the cable.
  • There could be a problem with the device.

The Stimpod shows “Insert Cable” but the cable is inserted - Why?

  • There could be a problem with the cable.
  • There could be a problem with the Stimpod.

The Stimpod shows “No Accel” – Why?

  • The Stimpod is in ‘TWI’ mode. In this mode, the device does not communicate with the accelerometer.
  • The Stimpod is in ‘TET’ mode. In this mode, the device does not communicate with the accelerometer.
  • There could be a momentary interference that interrupted communication between the accelerometer and Stimpod.
  • There could be a problem with the accelerometer cable.
  • There could be a problem with the Stimpod.

Is the Stimpod immune to cauterization?

  • No. In order for Stimpod to receive its certification, it has to pass certain tests to prove its immunity to electromagnetic interference (EMI) and electrostatic discharge (ESD). All versions of Stimpod have passed these criteria.
  • In beginning 2012 the Stimpod was redesigned in order to increase its immunity to EMI and ESD.
  • The new version of Stimpod has proven its immunity to cauterization in the OR under general conditions, however, extreme intensities of cauterization could still impact of the accuracy and functioning of the Stimpod.
  • All devices in the OR are generally affected by extreme intensities of cauterization.

Ordering information

The Stimpod NMS450X is available around the world through our distribution partners network. Find a distributor close to you or complete the form and we will send you a full quotation.

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