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Muscle Relaxants

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Muscle Relaxants Muscle Relaxants What are they used for? Facilitate intubation of the trachea Facilitate mechanical ventilation Optimized surgical working conditions ... – PowerPoint PPT presentation

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Title: Muscle Relaxants


1
Muscle Relaxants
2
Muscle Relaxants
  • What are they used for?
  • Facilitate intubation of the trachea
  • Facilitate mechanical ventilation
  • Optimized surgical working conditions

3
Muscle Relaxants
  • How skeletal muscle relaxation can be achieved?
  • High doses of volatile anesthetics
  • Regional anesthesia
  • Administration of neuromuscular blocking agents
  • Proper patient positioning on the operating table

4
Muscle Relaxants
  • Muscle relaxants must not be given without
    adequate dosage of analgesic and hypnotic drugs
  • Inappropriately given a patient is paralyzed
    but not anesthetized

5
Muscle Relaxants
  • How do they work?
  • Neuromuscular junction
  • Nerve terminal
  • Motor endplate of a muscle
  • Synaptic cleft
  • Nerve stimulation
  • Release of Acetylcholine (Ach)
  • Postsynaptic events

6
Neuromuscular Junction (NMJ)
7
Binding of Ach to receptors on muscle end-plate
8
Muscle Relaxants
  • Depolarizing muscle relaxant
  • Succinylcholine
  • Nondepolarizing muscle relaxants
  • Short acting
  • Intermediate acting
  • Long acting

9
Depolarizing Muscle Relaxant
  • Succinylcholine
  • What is the mechanism of action?
  • Physically resemble Ach
  • Act as acetylcholine receptor agonist
  • Not metabolized locally at NMJ
  • Metabolized by pseudocholinesterase in plasma
  • Depolarizing action persists gt Ach
  • Continuous end-plate depolarization causes muscle
    relaxation

10
Depolarizing Muscle Relaxant
  • Succinylcholine
  • What is the clinical use of succinylcholine?
  • Most often used to facilitate intubation
  • What is intubating dose of succinylcholine?
  • 1-1.5 mg/kg
  • Onset 30-60 seconds, duration 5-10 minutes

11
Depolarizing Muscle Relaxant
  • Succinylcholine
  • What is phase I neuromuscular blockade?
  • What is phase II neuromuscular blockade?
  • Resemble blockade produced by nondepolarizing
    muscle relaxant
  • Succinylcholine infusion or dose gt 3-5 mg/kg

12
Depolarizing Muscle Relaxant
  • Succinylcholine
  • Does it has side effects?
  • Cardiovascular
  • Fasciculation
  • Muscle pain
  • Increase intraocular pressure
  • Increase intragastric pressure
  • Increase intracranial pressure
  • Hyperkalemia
  • Malignant hyperthermia

13
Nondepolarizing Muscle Relaxants
  • What is the mechanism of action?
  • Compete with Ach at the binding sites
  • Do not depolarized the motor endplate
  • Act as competitive antagonist
  • Excessive concentration causing channel blockade
  • Act at presynaptic sites, prevent movement of Ach
    to release sites

14
Nondepolarizing Muscle Relaxants
  • Long acting
  • Pancuronium
  • Intermediate acting
  • Atracurium
  • Vecuronium
  • Rocuronium
  • Cisatracurium
  • Short acting
  • Mivacurium

15
Nondepolarizing Muscle Relaxants
  • Pancuronium
  • Aminosteroid compound
  • Onset 3-5 minutes, duration 60-90 minutes
  • Intubating dose 0.08-0.12 mg/kg
  • Elimination mainly by kidney (85), liver
    (15)
  • Side effects hypertension, tachycrdia,
    dysrhythmia,

16
Nondepolarizing Muscle Relaxants
  • Vecuronium
  • Analogue of pancuronium
  • much less vagolytic effect and shorter duration
    than pancuronium
  • Onset 3-5 minutes duration 20-35 minutes
  • Intubating dose 0.08-0.12 mg/kg
  • Elimination 40 by kidney, 60 by liver

17
Nondepolarizing Muscle Relaxants
  • Atracurium
  • Metabolized by
  • Ester hydrolysis
  • Hofmann elimination
  • Onset 3-5 minutes, duration 25-35 minutes
  • Intubating dose 0.5 mg/kg
  • Side effects
  • histamine release causing hypotension,
    tachycardia, bronchospasm
  • Laudanosine toxicity

18
Nondepolarizing Muscle Relaxants
  • Cisatracurium
  • Isomer of atracurium
  • Metabolized by Hofmann elimination
  • Onset 3-5 minutes, duration 20-35 minutes
  • Intubating dose 0.1-0.2 mg/kg
  • Minimal cardiovascular side effects
  • Much less laudanosine produced

19
Nondepolarizing Muscle Relaxants
  • Rocuronium
  • Analogue of vecuronium
  • Rapid onset 1-2 minutes, duration 20-35 minutes
  • Onset of action similar to that of
    succinylcholine
  • Intubating dose 0.6 mg/kg
  • Elimination primarily by liver, slightly by kidney

20
Alteration of responses
  • Temperature
  • Acid-base balance
  • Electrolyte abnormality
  • Age
  • Concurrent diseases
  • Drug interactions

21
Alteration of responses
  • Concurrent diseases
  • Neurologic diseases
  • Muscular diseases
  • Myasthenia gravis
  • Myasthenic syndrome (Eaton-Lambert synrome)
  • Liver diseases
  • Kidney diseases

22
Alteration of responses
  • Drug interactions
  • Inhalation agents
  • Intravenous anesthetics
  • Local anesthetics
  • Neuromuscular locking drugs
  • Antibiotics
  • Anticonvulsants
  • Magnesium

23
Monitoring Neuromuscular Function
  • What are the purposes of monitoring?
  • Administer additional relaxant as indicated
  • Demonstrate recovery

24
Monitoring Neuromuscular Function
  • How to monitor?
  • Clinical signs
  • Use of nerve stimulator

25
Monitoring Neuromuscular Function
  • Clinical signs
  • Signs of adequate recovery
  • Sustained head lift for 5 seconds
  • Lift the leg (child)
  • Ability to generate negative inspiratory pressure
    at least 25 cmH2O, able to swallow and maintain a
    patent airway
  • Other crude tests tongue protrusion, arm lift,
    hand grip strength

26
Monitoring Neuromuscular Function
  • Use of nerve stimulator
  • Single twitch single pulse 0.2 msec
  • Tetanic stimulation
  • Train-of-four series of 4 twitch, 0.2 msec
    long, 2 Hz frequency, administer every 10-15
    seconds
  • Double burst stimulation
  • Post tetanic count

27
Evoked responses during depolarizing and
nondepolarizing block
28
Hierarchy of Neuromuscular Blockade
29
Antagonism of Neuromuscular Blockade
  • Effectiveness of anticholinesterases depends on
    the degree of recovery present when they are
    administered
  • Anticholinesterases
  • Neostigmine
  • Onset 3-5 minutes, elimination halflife 77
    minutes
  • Dose 0.04-0.07 mg/kg
  • Pyridostigmine
  • Edrophonium

30
Antagonism of Neuromuscular Blockade
  • What is the mechanism of action?
  • Inhibiting activity of acetylcholineesterase
  • More Ach available at NMJ, compete for sites on
    nicotinic cholinergic receptors
  • Action at muscarinic cholinergic receptor
  • Bradycardia
  • Hypersecretion
  • Increased intestinal tone

31
Antagonism of Neuromuscular Blockade
  • Muscarinic side effects are minimized by
    anticholinergic agents
  • Atropine
  • Dose 0.01-0.02 mg/kg
  • Scopolamine
  • glycopyrrolate

32
Reversal of Neuromuscular Blockade
  • Goal re-establishment of spontaneous
    respiration and the ability to protect airway
    from aspiration

33
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