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Neuromuscular monitoring

Neuromuscular monitoring. Dr. S. Parthasarathy MD., DA., DNB, MD ( Acu ), Dip. Diab.DCA , Dip. Software statistics PhD ( physio ). What are we monitoring ??. Definition : Neuromuscular junction :.

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Neuromuscular monitoring

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  1. Neuromuscular monitoring Dr. S. Parthasarathy MD., DA., DNB, MD (Acu), Dip. Diab.DCA, Dip. Software statistics PhD (physio)

  2. What are we monitoring ??

  3. Definition : Neuromuscular junction : • the synapse between motor neuron and muscle fiber is called the neuromuscular junction

  4. History • In 1958, Christie and Churchill-Davidson described the use of a nerve stimulator to monitor neuromuscular block. • However, it was not until the TOF pattern of stimulation was described in 1970, that such equipment came into routine clinical use.

  5. Why To monitor ??

  6. studies • 45% of patients had residual curarization (train-of four [TOF] ratio<0.9) in the postoperative recovery room after a single intubating dose of the intermediate-acting drugs atracurium • residual curarization (TOF ratio<0.7) in 42% of patients in the postoperative recovery roomaftervecuronium

  7. Clinical judgment may not be correct always

  8. Patient is fine – let there be some residual paralysis ?? • decreased chemoreceptor sensitivity to hypoxia, • functional impairment of the pharyngeal and upper esophageal muscles, • impaired ability to maintain the airway, • increased risk for the development of post operative pulmonary complications

  9. Clinical indications

  10. prolonged infusions of NM blockers • When surgery or anaesthesia is prolonged • We don’t want inadequate reversal , severe respiratory disease, morbid obesity • reversal agent may cause harm,e.g. tachy arrhythmias, cardiac failure, severe wheezing • Liver or renal dysfunction, when pharmacokinetics of muscular relaxants may be altered • Neuromuscular disorders such as myasthenia gravis or Eaton–Lambert syndrome

  11. Reliable method • Stimulate the peripheral nerve and see the response.

  12. Facial nerve and orbicularisoculi

  13. Posterior tibial nerve and flexion of great toe

  14. Other sites

  15. Which muscle • it must have a motor element; • it must be close to the skin; • contraction in the muscle or muscle group which the nerve supplies must be visible or accessible to evoked response monitoring.

  16. What’s the hope • Diaphragm • Larynx • 1.5 to 1.75 resistant

  17. Stimulation • The current needed to induce depolarization in all the fibers in a nerve bundle is the maximal current. • 25 % more – supra maximal • Mono phasic, rectangular, 50 mA, 0.2 milliseconds , constant current at 0 -5 ohms • Different patterns • Battery • ECG electrodes

  18. Stimulator - image • Subcutaneous needle electrodes • Ball electrodes described

  19. Pattern of nerve stimulation • Single twitch stimulation. • Train-of-four stimulation. • Tetanic stimulation. • Post-tetanic count stimulation. • Double burst stimulation.

  20. Single twitch stimulation • A single square wave supramaximal stimulus, at regular intervals, • The twitch response will only be depressed when a neuromuscular blocking agent occupies75% of the post-synaptic nicotinic receptors. • Twitch depression will need to be more than 90% in order to provide good conditions for abdominal surgery. • Onset of block – useful

  21. Depolarizing or NDPs ??

  22. Train-of-four stimulation • TOF supramaximal twitch stimuli, with a frequency of 2 Hz, • four stimuli each separated by 0.5 s. • 2 Hz for 2 seconds • Compare the first twitch to fourth

  23. TOF ratioNondepolarizer blockade – fade

  24. Non depolarizers and depolarizers FADE NO FADE

  25. TOF Vs single twitch • T4 disappears at about 75% depression of T1 • T3 at 80–85% depression of T1, T2 at 90% depression. TOF count and TOF ratio

  26. Studies

  27. Can we correlate Extubate reverrs

  28. Dep Vs NDPs • If larger doses of depolarizing agent are given, for example in techniques that require repeated bolus doses or infusions of succinylcholine, then a Phase 2 block may develop. • This is a block produced by a depolarizing drug which develops some of the characteristics of a non-depolarizing block. • With TOF monitoring, fade is observed.

  29. Phase 2 block • two types • normal and abnormal cholinesterase • Can we do reversal in abnormal cholinesterase ??

  30. DBS • allows manual (tactile) detection of subtle degree of NMB without the use of recording devices. • It involves application of two short bursts of 50Hz which are separated 750 ms,. • It consists of a series of 3 and 2 impulses (DBS 3, 2) or 3 and 3 impulses (DBS 3, 3). • D2 / D1 ratio – fade . • Fade is more easily detected manually with DBS than with TOF. • TOF – 0.4 or less , but DBS -- 0.6 detects

  31. Tetanic stimulation • Tetanic stimulation uses a high frequency (50–200 Hz) with a supramaximal stimulus for a set time: normally 5 s. • In healthy skeletal muscle during normal movement, the response is maintained as a tetanic contraction.

  32. Tetanic stimulation – painful • No in conscious patients • Cant be reproduced in 6-10 minutes • But • TOF can be repeated in 10 seconds

  33. Tetanic • A frequency of 50Hz is physiological as it is similar to that generated during maximal voluntary effort. • Proponents of 100 Hz and 30 Hz are there

  34. Fade -- why ? • large amounts of acetylcholine are released. • equilibrium between mobilization and synthesis of acetylcholine is present . • The muscle response caused by tetanic stimulation of the nerve at, for example, 50 Hz is maintained (given normal neuromuscular transmission) • acetylcholine released is many times greater than the amount necessary to evoke a response.

  35. Fade -- why ? • When the “margin of safety” at the postsynaptic membrane (i.e., the number of free cholinergic receptors) is reduced by nondepolarizing neuromuscular blocking drugs, a typical reduction in twitch height is seen with a fade during, for instance, repetitive stimulation. • Also some presynaptic action

  36. Fade -- also presynaptic • Pre-synaptic receptors (Bowman), implicated because: • α-Bungarotoxin, a pure post-synaptic blocker, shows no fade

  37. Nondepolarizer Depolarizer

  38. Post tetanic count • Can we gauge NM block if TOF is absent ?? • 50 Hz tetanic stimulation is applied for 5 s followed by 1 Hz supramaximal single stimuli after a gap of 3 s.

  39. TOF appears

  40. PTP and PTC • Tetanic stimulation facilitates the mobilization of Ach from the reserve pools to the immediate stores and increases the synthesis of Ach. • This enhanced synthesis and mobilization of Ach explains the phenomenon of posttetanicpotentiation.

  41. use of PTC • The main use of PTC is when profound neuromuscular block is required, for example, during retinal surgery, when movement or coughing could have devastating effects.

  42. When to use what ?? • Onset – single twitch • Intense blockade – PTC • Surgical – TOF • Recovery – TOF

  43. Assessment of responses • Visual and tactile • Mechanomyography • Electromyography • Acceleromyography • Others

  44. Assessment of responses to nerve stimulation (Recording devices)

  45. Mechanomyography

  46. Electromyography -- EMG is the recording of a compound action potential that occurs during muscular contraction, whether voluntary or evoked.

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