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

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Muscle Relaxants

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Muscle relaxants

Muscle Relaxants


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


Neuromuscular junction nmj

Neuromuscular Junction (NMJ)


Binding of ach to receptors on muscle end plate

Binding of Ach to receptors on muscle end-plate


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


Evoked responses during depolarizing and nondepolarizing block

Evoked responses during depolarizing and nondepolarizing block


Hierarchy of neuromuscular blockade

Hierarchy of Neuromuscular Blockade


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


Muscle relaxants

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