muscle relaxant by satish sharma

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Muscle Relaxants : 

Muscle Relaxants

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Muscle relaxant: Muscle relaxant is a term usually used to refer to skeletal muscle relaxants (drugs), which act on the central nervous system (CNS) to relax muscles. These drugs are often prescribed to reduce pain and soreness associated with sprains, strains, or other types of muscle injury. Some examples of commonly prescribed skeletal muscle relaxant medications include carisoprodol (Soma), cyclobenzaprine (Flexeril), and metaxalone (Skelaxin), which are taken in tablet form. Muscle relaxant drugs are only available by prescription in the U.S. Definition of Muscle relaxant :-

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neuromuscular blocking drugs are sometimes used during the induction of general anesthesia or during insertion of an endotracheal (ET) tube. These muscle relaxants are given intravenously (through the bloodstream) and act directly on the muscles. Examples of muscle relaxants used during surgical procedures include succinylcholine (Anectine, Sucostrin), atracurium (Tracrium), and pancuronium (Pavulon). Other types of muscle relaxant drugs :-

Muscle Relaxants : 

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

Muscle Relaxants : 

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 Relaxants : 

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 Relaxants : 

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 Relaxants : 

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 Relaxant : 

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 Relaxant : 

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 Relaxant : 

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 Relaxants : 

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

Nondepolarizing Muscle Relaxants : 

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 Relaxants : 

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 Relaxants : 

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 Relaxants : 

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 Relaxants : 

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 responses : 

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

Alteration of responses : 

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

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 Blockade : 

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 Blockade : 

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

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