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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. Muscle Relaxants. How skeletal muscle relaxation can be achieved? High doses of volatile anesthetics

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muscle relaxants1
Muscle Relaxants
  • What are they used for?
    • Facilitate intubation of the trachea
    • Facilitate mechanical ventilation
    • Optimized surgical working conditions
muscle relaxants2
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
muscle relaxants3
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
muscle relaxants4
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
muscle relaxants5
Muscle Relaxants
  • Depolarizing muscle relaxant
    • Succinylcholine
  • Nondepolarizing muscle relaxants
    • Short acting
    • Intermediate acting
    • Long acting
depolarizing muscle relaxant
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 > Ach
    • Continuous end-plate depolarization causes muscle relaxation
depolarizing muscle relaxant1
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
depolarizing muscle relaxant2
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 > 3-5 mg/kg
depolarizing muscle relaxant3
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
nondepolarizing muscle relaxants
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
nondepolarizing muscle relaxants1
Nondepolarizing Muscle Relaxants
  • Long acting
    • Pancuronium
  • Intermediate acting
    • Atracurium
    • Vecuronium
    • Rocuronium
    • Cisatracurium
  • Short acting
    • Mivacurium
nondepolarizing muscle relaxants2
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,
nondepolarizing muscle relaxants3
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
nondepolarizing muscle relaxants4
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
nondepolarizing muscle relaxants5
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
nondepolarizing muscle relaxants6
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
alteration of responses
Alteration of responses
  • Temperature
  • Acid-base balance
  • Electrolyte abnormality
  • Age
  • Concurrent diseases
  • Drug interactions
alteration of responses1
Alteration of responses
  • Concurrent diseases
    • Neurologic diseases
    • Muscular diseases
      • Myasthenia gravis
      • Myasthenic syndrome (Eaton-Lambert synrome)
    • Liver diseases
    • Kidney diseases
alteration of responses2
Alteration of responses
  • Drug interactions
    • Inhalation agents
    • Intravenous anesthetics
    • Local anesthetics
    • Neuromuscular locking drugs
    • Antibiotics
    • Anticonvulsants
    • Magnesium
monitoring neuromuscular function
Monitoring Neuromuscular Function
  • What are the purposes of monitoring?
    • Administeradditional relaxant as indicated
    • Demonstrate recovery
monitoring neuromuscular function1
Monitoring Neuromuscular Function

How to monitor?

  • Clinical signs
  • Use of nerve stimulator
monitoring neuromuscular function2
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
monitoring neuromuscular function3
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
antagonism of neuromuscular blockade
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
antagonism of neuromuscular blockade1
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
antagonism of neuromuscular blockade2
Antagonism of Neuromuscular Blockade
  • Muscarinic side effects are minimized by anticholinergic agents
    • Atropine
      • Dose 0.01-0.02 mg/kg
    • Scopolamine
    • glycopyrrolate
reversal of neuromuscular blockade
Reversal of Neuromuscular Blockade
  • Goal : re-establishment of spontaneous respiration and the ability to protect airway from aspiration