Neuromuscular Neuromuscular junction junction

monitoringmonitoringElectrodesElectrodes

Stimulation is achieved by passing two electrodes along a nerve and passing a current through themStimulation is achieved by passing two electrodes along a nerve and passing a current through themIt can be carried out either transcutaneously using surface electrodes or percutaneously wih needle It can be carried out either transcutaneously using surface electrodes or percutaneously wih needle

electrodeselectrodesTYPESTYPES

A- Surface Electrodes-A- Surface Electrodes-Can be those used for measuring ecgCan be those used for measuring ecg

Electrode skin resistance decreases with large conducting area, as do skin burns and painElectrode skin resistance decreases with large conducting area, as do skin burns and painLarge conducting area makes it difficult to obtain supramaximal stimulationLarge conducting area makes it difficult to obtain supramaximal stimulation

Moreover it can stimulate multiple nerves, so it may be better to use pediatric electrodesMoreover it can stimulate multiple nerves, so it may be better to use pediatric electrodesSkin should be properly cleaned end rubbed with abrasive Skin should be properly cleaned end rubbed with abrasive

Electodes for peripheral n. stimulation have different thicknessthan ecg electrodes and have chemical Electodes for peripheral n. stimulation have different thicknessthan ecg electrodes and have chemical buffers to maintainskin surface phbuffers to maintainskin surface ph

METAL ELECTRODESMETAL ELECTRODES Two metal plates or balls spaced 1 Two metal plates or balls spaced 1

inch apart,which attach directly to inch apart,which attach directly to stimulatorstimulator

--convenient to use--convenient to use --no good contact--no good contact --burns have been reported with --burns have been reported with

their usetheir use

NEEDLE ELECTRODESNEEDLE ELECTRODES Useful for providing supramaximal stimulusUseful for providing supramaximal stimulus --useful when skin is --useful when skin is

thickened,cold,edematous and in obese,thickened,cold,edematous and in obese, Also useful in hypothyroid,diabetic and renal Also useful in hypothyroid,diabetic and renal

failure ptsfailure pts Other complictions—Other complictions— Broken needles,infections burns ,nerve Broken needles,infections burns ,nerve

damagedamage There is alo a greater chance of direct muscle There is alo a greater chance of direct muscle

stimulationstimulation

POLARITY- POLARITY- Stimulators produce direct current by Stimulators produce direct current by

using one negative and one positive using one negative and one positive electrodeselectrodes

Usually positive electrode is red and Usually positive electrode is red and negative is blacknegative is black

Maximal effect is achieved when negative Maximal effect is achieved when negative electrode is placed just over nerve to be electrode is placed just over nerve to be stimulatedstimulated

Positive electrode should be placed along Positive electrode should be placed along the course of the nerve usually proximally the course of the nerve usually proximally to avoid direct muscle stimulationto avoid direct muscle stimulation

METHODS for evaluating evoked responsesMETHODS for evaluating evoked responses A--VISUAL-A--VISUAL- Observer should be at an angle of 90 deg. To the Observer should be at an angle of 90 deg. To the

motionmotion Used to count—Used to count— No of responses present in TOFstimulus, determine No of responses present in TOFstimulus, determine

PTC,detect presence of fade with TOFor DBSPTC,detect presence of fade with TOFor DBS POST TETANIC FACILITATION CAN ALSO BE POST TETANIC FACILITATION CAN ALSO BE

ASSESSEDASSESSED TOFR is difficult to determineTOFR is difficult to determine Visually assessing fade with 100hz tetanic Visually assessing fade with 100hz tetanic

stimulation is fairly accurate for analyzing residual stimulation is fairly accurate for analyzing residual paralysisparalysis

B--- TACTILEB--- TACTILE Accomplished by placing the evaluators Accomplished by placing the evaluators

fingertips lightly over ms to be stimulated fingertips lightly over ms to be stimulated and feeling the strength of contractionand feeling the strength of contraction

More sensitive for assessing NMB using More sensitive for assessing NMB using TOF.TOF.

It can be used to evaluate the presence or It can be used to evaluate the presence or absence of responses and/or fade with train absence of responses and/or fade with train of four,double burst,and tetanic stimulationof four,double burst,and tetanic stimulation

PTC can be determinedPTC can be determined TOFR CAN BE DETERMINED if there is TOFR CAN BE DETERMINED if there is

response to all fourstimuli with TOFresponse to all fourstimuli with TOF

Mechanomyography MMGMechanomyography MMG

Utilizes force displacement transducer, such as a Utilizes force displacement transducer, such as a strain gauge,attached to fingeror other part of body strain gauge,attached to fingeror other part of body that can be restrained by a preload and will move that can be restrained by a preload and will move when stimulatedwhen stimulated

The transducer converts the contrctile force into The transducer converts the contrctile force into electrical signal,which is amplified and displaced on electrical signal,which is amplified and displaced on monitor screen or recorded on chartmonitor screen or recorded on chart

Can measure single twitch height,response to tetanic Can measure single twitch height,response to tetanic stimulation and TOFR ACCURATELYstimulation and TOFR ACCURATELY

Cumbersome, difficult to setupCumbersome, difficult to setup For accurate results maintenance of muscle For accurate results maintenance of muscle

temperature within limits is requiredtemperature within limits is required Gold standard of scientific measurements of NM Gold standard of scientific measurements of NM

systemsystem

ACCELEROMYOGRAPHY(ACG,AMG)ACCELEROMYOGRAPHY(ACG,AMG) Thin piezoelectric transducer is fixed to a Thin piezoelectric transducer is fixed to a

moving part. When the part moves voltage moving part. When the part moves voltage is proportional to acceleration of the moving is proportional to acceleration of the moving partpart

Method requires unrestricted movement of Method requires unrestricted movement of the muscle being stimulatedthe muscle being stimulated

Easy and convenient to use, relative Easy and convenient to use, relative inexpensive and can be interfaced with inexpensive and can be interfaced with computercomputer

KINEMYOGRAPHY (KMG)KINEMYOGRAPHY (KMG) Utilizes bending sensor placed between Utilizes bending sensor placed between

thumb and forefingerthumb and forefinger Core of sensor is piezoelectric materialCore of sensor is piezoelectric material Movement is determined by change in Movement is determined by change in

the shape of material when it is bent by the shape of material when it is bent by adductor pollicis muscle contractionadductor pollicis muscle contraction

KMG has been compared with MMG KMG has been compared with MMG except for determining recovery from except for determining recovery from NMBNMB

PIEZOELECTRIC FILMPIEZOELECTRIC FILM Uses disposable piezoelectric film. Uses disposable piezoelectric film.

This is placed so that it spans a This is placed so that it spans a movable joint and muscle movement movable joint and muscle movement causes the bending of the film which causes the bending of the film which generates voltage which is generates voltage which is proportional to the amount of proportional to the amount of bending bending

Not as accurate as MMGNot as accurate as MMG

ELECTROMYOGRAPHY(EMG)ELECTROMYOGRAPHY(EMG) Process of recording electrical activity of muscleProcess of recording electrical activity of muscle When motor n is stimulated , a biphasic action When motor n is stimulated , a biphasic action

potential is generated in each of the muscle cells it potential is generated in each of the muscle cells it supplies unless some degree of NMB exists. The sum supplies unless some degree of NMB exists. The sum of these action potentials can be sensed by using of these action potentials can be sensed by using electrodes placed overmuscle being stimulatedelectrodes placed overmuscle being stimulated

Total 5 electrodes are used Total 5 electrodes are used 2 stimulating electrodes on the nerve to be 2 stimulating electrodes on the nerve to be

stimulatedstimulated 3electrodes –2 receiving ,and one ground are used 3electrodes –2 receiving ,and one ground are used

for recordingfor recording Best results are seen when electrodes have been in Best results are seen when electrodes have been in

contact with skin for 15 min before calliberationcontact with skin for 15 min before calliberation Carefull skin preparation helps to give good resultsCarefull skin preparation helps to give good results

EMG of larynx can also be done EMG of larynx can also be done EMG machine automatically EMG machine automatically

determines the supramaximal determines the supramaximal stimulus, establishes a control stimulus, establishes a control response stimulates at selected response stimulates at selected intervals , measures response and intervals , measures response and compares it with control .compares it with control .

With nondepolarizing NMB , the With nondepolarizing NMB , the action potential amplitude is action potential amplitude is decreased and there is fade with TOFdecreased and there is fade with TOF

Advantages of EMG over MMGAdvantages of EMG over MMG A-less immobilization is requiredA-less immobilization is required B-hand or arm need not to be B-hand or arm need not to be

extended or put on board . extended or put on board . C – can be used to monitor laryngeal C – can be used to monitor laryngeal

or diaphragmatic musclesor diaphragmatic muscles D– can be used to assess motor nerve D– can be used to assess motor nerve

blocks induced by regional blocks induced by regional anaesthesiaanaesthesia

Disadvantages—Disadvantages— Sensitive to electrical interferenceSensitive to electrical interference Response varies according to ms usedResponse varies according to ms used ExpensiveExpensive Response amplitude inc. with dec. Response amplitude inc. with dec.

temperaturetemperature Since site is not immobilized, changes Since site is not immobilized, changes

in relative position of recording in relative position of recording electrodes cause variation in EMG electrodes cause variation in EMG responseresponse

PHONOGRAPHYPHONOGRAPHY Aka acoustic myography Aka acoustic myography When ms contrcts ,sounds are emitted. When ms contrcts ,sounds are emitted.

These acoustic waves propagate through These acoustic waves propagate through skin, generating waves which can be skin, generating waves which can be recorded by small piezoelectric recorded by small piezoelectric microphonemicrophone

Easy to use and can be used on no of Easy to use and can be used on no of different muscles.different muscles.

Provides stable baseline with little Provides stable baseline with little disturbances from artifactsdisturbances from artifacts

MONITORING SITESMONITORING SITES 1– ULNAR N---1– ULNAR N--- Most commonly used and adductor pollicis is Most commonly used and adductor pollicis is

most commonly monitoredmost commonly monitored Can be stimulated at elbow , wrist or handCan be stimulated at elbow , wrist or hand Wrist– thumb adduction and finger flexionWrist– thumb adduction and finger flexion Elbow– hand adduction + aboveElbow– hand adduction + above Wrist—2 electrodes placed along medial aspect Wrist—2 electrodes placed along medial aspect

of distal forearm, 2 cm proximal toproximal wrist of distal forearm, 2 cm proximal toproximal wrist skin crease with negative electrode distalskin crease with negative electrode distal

Elbow---over sulcus of medial epicondyle of the Elbow---over sulcus of medial epicondyle of the humerushumerus

EMG monitoring of ulnar nerveEMG monitoring of ulnar nerve Recording electrodes—hypothenar , thenar , dorsal Recording electrodes—hypothenar , thenar , dorsal

interosseous ms. For dorsal inter. Ms , active interosseous ms. For dorsal inter. Ms , active receiving electrode is placed in the web between the receiving electrode is placed in the web between the index finger and the thumb and the other electrode at index finger and the thumb and the other electrode at the base of second fingerthe base of second finger

Hypothenar eminence--- Hypothenar eminence---

both electrodes are placed on palmar side both electrodes are placed on palmar side over or the active electrode is placed over over or the active electrode is placed over hypothenar eminence and the other below the second hypothenar eminence and the other below the second line on the ring finger or at the base of the dorsum of line on the ring finger or at the base of the dorsum of 55thth finger finger

MEDIAN NERVE—MEDIAN NERVE— Wrist-place the electrodes medial to where Wrist-place the electrodes medial to where

it would have been for ulnar nit would have been for ulnar n Elbow- adjacent to brachial art.Elbow- adjacent to brachial art. --stimulation causes thumb adduction--stimulation causes thumb adduction TIBIAL NERVETIBIAL NERVEPopliteal fossa—gastroecnemius ms Popliteal fossa—gastroecnemius ms

stimulated—causes significant leg stimulated—causes significant leg movementsmovements

Sensing electrodes over lateral head of Sensing electrodes over lateral head of gastroecnemius msgastroecnemius ms

POSTERIOR TIBIAL NERVE POSTERIOR TIBIAL NERVE Electrodes placed behind the medial Electrodes placed behind the medial

malleolus and anterior to achillis tendon malleolus and anterior to achillis tendon at the ankleat the ankle

Stimulation causes plantar flexion of the Stimulation causes plantar flexion of the foot and big toefoot and big toe

Especially useful in children, when it is Especially useful in children, when it is difficult to find room on the arms; or when difficult to find room on the arms; or when hand is inaccessiblehand is inaccessible

There is a lag time with slower onset of There is a lag time with slower onset of relaxation than with ulnar n.relaxation than with ulnar n.

PERONEAL NERVEPERONEAL NERVE electrodes on lateral aspect of of kneeelectrodes on lateral aspect of of knee Stimulation causes dorsiflexion of footStimulation causes dorsiflexion of foot FACIAL NERVEFACIAL NERVEMost useful in detecting the onset of relaxation in ms of jaw, Most useful in detecting the onset of relaxation in ms of jaw,

larynx ,diaphragm.larynx ,diaphragm.ACG can be used with facial nerveACG can be used with facial nerveNegative electrode—ant. To inferior part of ear lobeNegative electrode—ant. To inferior part of ear lobePositive---just posterior or inferior of the lobePositive---just posterior or inferior of the lobeThis configuration is more This configuration is more specificspecific corrugated supercilli ms should be observed . With ACG ,the corrugated supercilli ms should be observed . With ACG ,the

transducer should be placed in the middle of supercilliary archtransducer should be placed in the middle of supercilliary archThe facial n should not be used to assess recovery fromNMB becoz The facial n should not be used to assess recovery fromNMB becoz

responses may show complete recovery while significant NMB is responses may show complete recovery while significant NMB is stii present stii present

RECURRENT LARYNGEAL NRECURRENT LARYNGEAL N Innervates most of the intrinsic ms of Innervates most of the intrinsic ms of

larynxlarynx It can be stimulated percutaneously by It can be stimulated percutaneously by

using two electrodes betweenthe notch using two electrodes betweenthe notch between the thyroid and cricoid cartilagebetween the thyroid and cricoid cartilage

Response can b measured by placing Response can b measured by placing tracheal tube cuff and measuring pressure tracheal tube cuff and measuring pressure changes within cuffchanges within cuff

EMG in larynx can also be accomplished EMG in larynx can also be accomplished

USESUSES Before induction-----Before induction----- dry ,clean electrodes should be dry ,clean electrodes should be

connected to stimulator and placed over connected to stimulator and placed over selected nervesselected nerves

Skin should be thoroughly cleanedSkin should be thoroughly cleaned Electrodes should be checked to see if the Electrodes should be checked to see if the

gel is moistgel is moist Piece of tape should be placed over Piece of tape should be placed over

electrodes to prevent displacementelectrodes to prevent displacement

INDUCTIONINDUCTION Stimulator can be used to determine-Stimulator can be used to determine-

onset time of NMB, detect unusual onset time of NMB, detect unusual sensitivity to relaxants and to determine sensitivity to relaxants and to determine whether the pt is sufficiently relaxed for whether the pt is sufficiently relaxed for intubationintubation

Stimulator should be turned on after Stimulator should be turned on after induction but before giving ms relaxantsinduction but before giving ms relaxants

Output of stimulator should be inc. until Output of stimulator should be inc. until the response does not increase with the response does not increase with increasing current, then inc. 10-20%increasing current, then inc. 10-20%

INTUBATIONINTUBATION Onset of NMB will be faster in centrally located ms like Onset of NMB will be faster in centrally located ms like

diaphragm, facial , laryngeal and jaw ms than peripheral msdiaphragm, facial , laryngeal and jaw ms than peripheral ms Monitoring the response of eye ms will reflect the time of Monitoring the response of eye ms will reflect the time of

onset and level of NMB at airway musculature more closely onset and level of NMB at airway musculature more closely than monitoring peripheral ms which will underestimate the than monitoring peripheral ms which will underestimate the rate of onset of NMBin airway muscles and may overestimate rate of onset of NMBin airway muscles and may overestimate the degree of blockthe degree of block

In majority of pts dissapearence of adductor pollicis response In majority of pts dissapearence of adductor pollicis response is ass. With good intubating conditionsis ass. With good intubating conditions

In EMG monitoring hypothenar eminence may be preferableIn EMG monitoring hypothenar eminence may be preferable Single twitchat 0.1hz is used and clinician wait until the Single twitchat 0.1hz is used and clinician wait until the

response is barely perceptible before attempting intubationresponse is barely perceptible before attempting intubation double burst has been used as an indicator of optimal double burst has been used as an indicator of optimal

conditions for tracheal intubationconditions for tracheal intubation

MAINTAINENCEMAINTAINENCE During maintenance stimulator can be used to titrate relaxant During maintenance stimulator can be used to titrate relaxant

dosage to the needs of the operative procedure so both over and dosage to the needs of the operative procedure so both over and underdosages are avoidedunderdosages are avoided

It is important to correlate the reaction to nerve stimulation with It is important to correlate the reaction to nerve stimulation with pts clinical condition becoz there may discrepancy between pts clinical condition becoz there may discrepancy between degree of relaxation of the monitored site and that of ms at the degree of relaxation of the monitored site and that of ms at the site of surgerysite of surgery

TOF is considered the most important pattern for monitoring TOF is considered the most important pattern for monitoring NMB during anaesthesiaNMB during anaesthesia

Supramaximal currents are generally usedSupramaximal currents are generally used GOAL– maintain at least one response to TOF stimulation GOAL– maintain at least one response to TOF stimulation --- no response—further administration of relaxants is not indicated--- no response—further administration of relaxants is not indicated-----2 responses—abd. Relaxation adequate during balanced -----2 responses—abd. Relaxation adequate during balanced

anaesthesisanaesthesis---- 3 responses—adequate relaxation if volatile agent is used---- 3 responses—adequate relaxation if volatile agent is used one twitch is added to above recommendation if facial ms are one twitch is added to above recommendation if facial ms are

used used

RECOVERY AND REVERSALRECOVERY AND REVERSAL Nerve stimulator can detect residual NMBNerve stimulator can detect residual NMBAs recovery progresses TOF responses gradually inc. As recovery progresses TOF responses gradually inc. It is best to use a peripheral ms to monitor recovery becoz its It is best to use a peripheral ms to monitor recovery becoz its

complete recovery would indicate residual ms weakness complete recovery would indicate residual ms weakness contributing to problems with airway patency are unlikely contributing to problems with airway patency are unlikely

In past TOFR—0.7 WAS CONSIDERED ADEQUATEIn past TOFR—0.7 WAS CONSIDERED ADEQUATENow TOFR-- >90% at adductor pollicis before extubation by Now TOFR-- >90% at adductor pollicis before extubation by

MMGMMGIF EMG monitoring is used, residual anaesthetic effects IF EMG monitoring is used, residual anaesthetic effects

usually prevent the return of T1 to preanaesthetic usually prevent the return of T1 to preanaesthetic reference levels ,but TOFR should exceed 90%reference levels ,but TOFR should exceed 90%

Residual NMB cannot be reliably detected using TOF if Residual NMB cannot be reliably detected using TOF if visual/ tactile monitoring is usedvisual/ tactile monitoring is used

Detection is somewhat better with TOFDetection is somewhat better with TOF

Hazards—Hazards— Burns most commonly with needle Burns most commonly with needle

electrodeselectrodes Nerve damage—thumb paraesthesias in Nerve damage—thumb paraesthesias in

MMG due to intramural placement of MMG due to intramural placement of needle electrodesneedle electrodes

Comlications with needle electrodes---Comlications with needle electrodes--- PainPain Electrical interferenceElectrical interference