FAQs – Stimpod NMS450X

Frequently Asked Questions

  • 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 anesthesia-related deaths are directly or indirectly attributable to PORC.
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

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

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

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

  • 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.
  • 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.
  • It could be because a depolarizing NMBA was injected.
  • It could be that the core body temperature of the patient dropped again after recovery was observed.
  • In order to prevent Post Operative Residual Curarization (PORC) patients should only be assessed for residual NMBA once their 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 location of the electrode could have moved or is not adhering the patient’s skin any more.
  • 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.

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

  • When monitoring Train of Four prior and post NMBA administration, ratios of more 100% are often noticed and might go as high as 147%.
  • The effect is ascribed to the mobilization of presynaptic acetylcholine in the Neuromuscular Junction (NMJ) after T1 promoting release in synaptic cleft during subsequent stimulations.
  • Both the Stimpod NMS450X 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

  • 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.
  • It remains unclear as to what acceleromyography TOF ratio is necessary to exclude clinically significant PORC.
  • Glenn et al. found that postoperative residual curarization is reduced in patients monitored with acceleromyography TOF ratio greater than 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

  • 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

  • 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 for 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 has an automated switch off function which is activated if the device has not been in use for more than 10 minutes.
  • It could be that the electrodes have dried out to the extent that they are no longer conducting and are causing an open circuit.
  • There could be a problem with the cable.
  • There could be a problem with the device.
  • There could be a problem with the cable.
  • There could be a problem with the Stimpod.
  • 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.
  • 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.
  • The latest version of Stimpod has proven its immunity to cauterization in the OR under general conditions, however, extreme intensities of cauterization could still impact the accuracy and functioning of the Stimpod.
  • All devices in the OR are generally affected by extreme intensities of cauterization.

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