I&M I: Lecture 5 - NMBs Monitoring

Question 1

What is the purpose of neuromuscular blockade monitoring?

Answer 1

To prevent overdosing and underdosing of paralytic medications

Question 2

What are the main components of nerve stimulators?

Answer 2

• Compact
• Lightweight
• User-friendly
• Relies on current for nerve stimulation
  Maximal current: I required for all muscle fibers supplied by nerve to contract
  Threshold current: lowest I that elicits evoked response
  Supramaximal current: ~2.5-3X higher than threshold current
• Waveform
  Square wave, monophasic

Question 3

Stimulation Patterns, Single Twitch

Answer 3

T1: 0.1-1 Hz frequency

Once control response established: subsequent twitches expressed as % of control (T1%, T1%, T1:Tc)

Useful to establish supramaximal stimulus and monitoring deep NMB

Drawbacks
Unable to distinguish DMR vs. NDMR
Needs a control
Return to control level does not mean full NMB recovery

Question 4

Define ‘maximal current’ in the context of nerve stimulation.

Answer 4

The current required for all muscle fibers supplied by the nerve to contract

Question 5

What is the ‘threshold current’?

Answer 5

The lowest current that elicits an evoked response

Question 6

What does ‘supramaximal current’ refer to?

Answer 6

Approximately 2.5-3 times higher than the threshold current

Question 7

What is the stimulation pattern for single twitch?

Answer 7

T1: 0.1-1 Hz frequency

Question 8

What does T1% represent?

Answer 8

Subsequent twitches expressed as a percentage of control

Question 9

What is the drawback of using single twitch monitoring?

Answer 9

Unable to distinguish DMR vs. NDMR and needs a control

Question 10

Stimulation Patterns, Train-of-four (Part 1)

Answer 10

TOF, T4, T4/T1

Four equal pulses transmitted at 2 Hz

Control: all 4 twitches are equal

TOF ratio: T4:T1
Ratio of amplitude of 4th response to 1st response
% or fraction, only useful for low-grade blockade (needs 4 twitches)

Depolarizing vs. Nondepolarizing
Depolarizing: 4=twitches or 0 (magnitude may change, but TOF all or nothing
Nondepolarizing: 4=twitches fade 3210 and vice versa

Question 11

Stimulation Patterns, Train-of-four (Part 2)

Answer 11

Advantages
More sensitive than single twitch
No need for a control
Can detect DMR vs. NDMR
Useful to follow phase II block after sux administration (high or repeat dose)
Phase II block usually >4mg/Kg doses, but some reported as low as 0.3mg/kg

Disadvantages
Not useful at extremes of NMB range

(KNOW THE TOF RATIOS… LOOK A LITTLE MORE TIME WITH THIS)

Question 12

TOF Ratio

Answer 12

Question 13

What is the Train-of-Four (TOF) stimulation pattern?

Answer 13

Four equal pulses transmitted at 2 Hz

Question 14

What does a TOF ratio indicate?

Answer 14

The ratio of amplitude of the 4th response to the 1st response

Question 15

How does a depolarizing block manifest in TOF monitoring?

Answer 15

4 twitches or 0, all or nothing response

Question 16

What is a characteristic of nondepolarizing block in TOF monitoring?

Answer 16

4 twitches fade to 3, 2, 1, 0 and vice versa

Question 17

What is the advantage of the TOF pattern over single twitch?

Answer 17

More sensitive and can detect DMR vs. NDMR

Question 18

Stimulation Patterns, Tetanus

Answer 18

Sustained contraction of stimulated muscles
Rapidly repeated stimulation at 50, 100, 200 Hz

Depolarizing block: decreased amplitude, but sustained tetany

Nondepolarizing block: amplitude decreases; tetany not sustained
fade

Post-tetanic facilitation (PTF)
Hold 50 Hz tetany for 5 seconds
Wait 3 seconds
Apply 1 Hz single twitch stimulus and count responses
Time to first TOF twitch is inversely proportional to # of post-tetanic twitches
Only use on unconscious patients

Tetanic stimulation should not be repeated but every 2 minutes.

PTF- temporary increase in response to stimulation. Seen in NDMR but not DMR

To measure deep NMB, you can use tetanic stimulation of 100Hz followed by a TOF.

Question 19

Posttetanic Count

Answer 19

Not getting count cant just Neo and Glyco??? Look up

Question 20

What is tetanus in the context of neuromuscular monitoring?

Answer 20

Sustained contraction of stimulated muscles with rapid stimulation

Question 21

What does post-tetanic facilitation (PTF) involve?

Answer 21

Holding 50 Hz tetany for 5 seconds and applying a 1 Hz single twitch stimulus

Question 22

Double Burst Stimulation Pattern

Answer 22

DBS, minitetanus: 2 short tetanic stimuli separated by 750 msec
3,3: three 0.2 msec pulses at 50 Hz, repeated 750 msec later
3,2: three 0.2 msec pulses at 50 Hz followed by two 0.2 msec pulses at 50 Hz

Detects residual NMB
Easier to detect fade with DBS than TOF

Can be useful in deep blockade
First twitch detected with DBS at deeper blockade levels than TOF

Question 23

What is Double Burst Stimulation (DBS)?

Answer 23

Two short tetanic stimuli separated by 750 msec

Question 24

What is a key benefit of using DBS?

Answer 24

Easier to detect fade than TOF and useful in deep blockade

Question 25

What is the recommended DBS interval?

Answer 25

12 seconds

Question 26

Patience is a Virtue

Answer 26

DBS interval: 12 seconds (Not getting TOF, patient is deeper, better option) Up to 90 seconds between DBS and TOF Tetanus: at least 2 minutes Single twitch: at least 10 seconds TOF: at least 10-12 seconds

Question 27

Stimulator Electrodes

Answer 27

2 electrodes: +(red)/-(black): maximal effect when – electrode is directly over the most superficial part of the nerve In general, think red closest to the heart Transcutaneous Surface electrodes: gel patch with adhesive foam contains a metal disc that can attach to electrical lead (EKG electrodes) Smaller pads and clean skin facilitate better readings Metal electrodes: small metal bulbs/plates ~1” apart Percutaneous Needle electrodes: small needles often work when surface electrodes fail ESRD, DM, edema, burns, obesity, thick/cold skin May cause direct muscle stimulation vs. nerve stimulation ⇧ risks: burn, needle breakage, infection, nerve damage ## Footnote Red closest to heart

Question 28

What types of electrodes are used in neuromuscular monitoring?

Answer 28

* Transcutaneous * Percutaneous

Question 29

What are common sites for stimulating the ulnar nerve?

Answer 29

* Wrist * Elbow

Question 30

Which muscle is monitored for the ulnar nerve?

Answer 30

Adductor pollicis muscle

Question 31

What is the significance of the facial nerve in neuromuscular monitoring?

Answer 31

Useful for onset of relaxation but not for recovery estimation

Question 32

What clinical criteria indicate adequate muscle strength in an awake patient?

Answer 32

* Open eyes for 5 seconds * Sustain tongue protrusion * Sustained head lift >5s * Sustained leg lift (peds) * Coughing effectively * Swallowing

Question 33

True or False: A single twitch indicates 90% blockade.

Answer 33

True

Question 34

What are potential hazards of neuromuscular monitors?

Answer 34

* Burns * Nerve damage * Pain from needle electrodes

Question 35

What is the relationship between the number of twitches and blockade level?

Answer 35

10 twitches: 100% blockade; 1 twitch: 90% blockade; 2 twitches: 80-90% blockade; 3 twitches: 70-80% blockade; 4 twitches: 65-75% blockade

Question 36

Evaluating Evoked Responses

Answer 36

Visual: TOF response, PTC, and TOF/DBS fade Difficult to determine TOFR or single-twitch height difference to control Tactile: more sensitive than visual for TOF monitoring Determine PTC, TOFR estimation Fade difficult to assess unless ratio < 0.4-0.5 DBS fade easier to detect, but unreliable for residual paralysis determination

Question 37

Evaluating Evoked Responses Kinds

Answer 37

Mechanomyography (MMG): Gold Standard, but rarely used clinically Force-displacement transducer on finger (or any body part that can be restrained by a preload & moves when stimulated) Contractile force converts to electrical signal and displays on monitor Single twitch, tetany, and T4 ratio accurately measured with MMG Acceleromyography (ACG, AMG) Piezoelectric transducer/Al rod on moving part Voltage generated ∝ acceleration of movement Kinemyography (KMG) Sensor b/n thumb & index finger Change in sensor shape redistributes electrical charge and electrons flow: measured as a potential change ∝ amount of distortion Tof, DBS, and single twitch Piezoelectric Film Disposable film covers movable joint Evoked stimulation bends film and voltage ∝ bending is generated accuracy than tactile/visual (maybe) Electromyography (EMG) Records electrical activity of muscle using 5 electrodes 2 stimulating over nerve, 1 ground (b/n stimulating & receiving), 2 receiving Active receiving over muscle belly, reference/indifferent receiving over tendon insertion site EMG TOFR less temp dependent than MMG, less bulky than MMG, less mobilization needed (no board necessary) EMG sensitive to electrical interference, expensive, 15 min cure time before calibration Phonomyography (acoustic myography) Piezoelectric mic detects low frequency sounds emitted from contracting muscles Wave amplitude ∝ degree of muscle contraction ECU, vessel pulses may cause interference

Question 38

Monitoring Sites

Answer 38

Monitor away from surgical field Be sure anesthesia provider has access to monitor site NIBP on opposite limb Avoid limbs affected by upper-motor-neuron lesions

Question 39

Ulnar Nerve

Answer 39

Stimulate at wrist: thumb adduction/ index finger flexion Electrodes at medial, distal forearm 2cm proximal to wrist crease, ~1” apart Positive electrode on dorsal wrist, negative on ventral wrist Stimulate at elbow: hand adduction Electrodes over sulcus of medial epicondyle of humerus Take care to avoid ulnar nerve compression ## Footnote Adductor pollicis muscle note: onset and duration of NMB at larynx and diaphragm are shorter than peripheral muscles

Question 40

Median Nerve

Answer 40

Stimulate at the wrist with electrodes medial to ulnar nerve placement Stimulate at the elbow with electrodes next to brachial artery Thumb adduction is the resultant movement

Question 41

Tibial Nerve

Answer 41

Place electrodes along lateral side of popliteal fossa Stimulates gastrocnemius: significant leg movement may bother surgeon

Question 42

Posterior Tibial Nerve

Answer 42

Place electrodes behind medial malleolus and anterior to achilles tendon at the ankle Foot and big toe plantar flexion Slower onset of paralysis than ulnar nerve Similar recovery time to ulnar nerve

Question 43

Peroneal Nerve

Answer 43

Place electrodes on lateral knee, lateral to neck of fibula Slower onset of paralysis and greater resistance to NMB than ulnar nerve Dorsiflexion of the foot

Question 44

Facial Nerve

Answer 44

Useful for onset of relaxation of jaw/larynx/diaphragm muscles, not useful for recovery estimation Facial muscles fairly resistant to NMB drugs Negative electrode anterior to inferior part of earlobe, positive electrode posterior or inferior to the lobe One electrode lateral and below lateral canthus of the eye, 2nd electrode anterior to earlobe Corrugator supercilii muscle 2nd most used one because of how close to the anesthesia provider it is ## Footnote Low Temple = eyebrow; Ear Split = Jaw

Question 45

Use of TOF Monitors

Answer 45

Select nerve to be monitored Attach stimulator electrodes to selected nerve Induction: can detect onset of NMB or resistance to NMB Intubation: Determine NMB level for optimal intubation conditions Maintenance: titrate NMB throughout case with frequent checks **BELOW IS ALL REALLY IMPORTANT!!!** Centrally located muscles have faster onset of NMB than peripheral muscles Diaphragm, eye muscles, and laryngeal muscles more resistant to nondepolarizing agents than peripheral muscles Diaphragm resistant to succinylcholine Masseter muscle sensitive to nondepolarizing and depolarizing agents MMR more common with sux, especially in peds Eye muscle monitoring closely reflects airway musculature onset of NMB Recovery and Reversal Use peripheral muscle to determine recovery Clinical criteria in asleep patient for muscle strength determination Adequate TV Inspiratory force of >25 cmH2O negative pressure Clinical criteria in an awake patient for muscle strength determination Open eyes for 5 seconds Sustain tongue protrusion Sustained head lift >5s Sustained leg lift (peds) Coughing effectively Swallowing

Question 46

Neuromuscular Monitor Hazards

Answer 46

Burns Needle electrodes and metal ball electrodes Nerve damage Electrode pressure or intraneural needle placement Pain from needle electrodes

Question 47

99 Problems, But a Twitch Ain’t 1

Answer 47

0 twitches: 100% blockade 1 twitch: 90% blockade 2 twitches: 80-90% blockade 3 twitches: 70-80% blockade 4 twitches: 65-75% blockade (why its important to measure for Sustained Tetany at Emergence)