Muscle Relaxants Flashcards
What enzyme breaks down acetylcholine (Ach) at the neuromuscular junction (NMJ)?
Acetylcholinesterase breaks down acetylcholine (Ach) at the NMJ.
What is the neurotransmitter at the neuromuscular junction?
The neurotransmitter at the neuromuscular junction is acetylcholine (Ach).
How is acetylcholine (Ach) formed?
Ach formation: Choline + acetyl co A (via choline acetyl transferase) → Ach.
How is acetylcholine destroyed?
Ach destruction: By acetylcholinesterase present in the synaptic cleft.
Describe the process of neuromuscular transmission.
Neuromuscular transmission: Depolarization of motor nerve → Ach release → Ach binds to receptors → muscle contraction.
What factors influence neuromuscular transmission (NMT)?
Factors: Prevent Ach synthesis (hemicholinium), prevent Ach release (↓ calcium, ↑ magnesium, botulism, aminoglycosides), deplete Ach stores, block Ach receptors, and block acetylcholinesterase action.
What are muscle relaxants?
Muscle relaxants are drugs used to impair neuromuscular transmission and provide skeletal muscle relaxation during anesthesia or critical care.
What are the indications for using muscle relaxants?
Indications: Facilitate tracheal intubation, ventilation, and surgical access.
What is the classification of depolarizing muscle relaxants?
Depolarizing MR: Resemble Ach, bind to receptors, cause initial depolarization (fasciculations), not metabolized by acetylcholinesterase.
Describe the depolarizing block mechanism of muscle relaxants.
Depolarizing block: Suxamethonium stimulates receptors causing fasciculations, then prevents Ach from reacting with receptors.
What is the classification of non-depolarizing muscle relaxants?
Non-depolarizing MR: Bind to Ach receptors without initial depolarization; exhibit fade and post-tetanic potentiation.
How is neuromuscular junction monitoring performed?
Monitoring NMJ: Using a peripheral nerve stimulator to assess responses to electrical stimuli.
What is the Train of Four (TOF) twitch test?
TOF twitches: 4 twitches at 2 Hz used to monitor neuromuscular block.
What are the TOF twitch results indicating different levels of muscle block?
TOF results: 3 twitches → 75% block, 2 twitches → 80%, 1 twitch → 90%, no twitch → 100% block.
What happens before muscle relaxants are administered?
Before MR administration: Ach crosses NMJ and stimulates receptors, producing full twitches.
What happens after a complete block with muscle relaxants?
After complete block: Non-depolarizing MR blocks Ach receptors, preventing further NMT, and no twitches are produced.
Describe the concept of “fade” in muscle relaxant usage.
Fade: Gradual decrease in twitch amplitude with non-depolarizing MR.
What is post-tetanic facilitation?
Post-tetanic facilitation: Ach molecules increase in the synaptic cleft, enhancing subsequent twitch amplitude.
What are the key properties of suxamethonium?
Suxamethonium: Fast onset, short duration, used in rapid sequence induction.
What are the cardiovascular and muscular side effects of suxamethonium?
Side effects of suxamethonium: Bradycardia, fasciculations, increased intragastric pressure, hyperkalemia, malignant hyperthermia.
How is suxamethonium metabolized?
Suxamethonium metabolism: By pseudocholinesterase; decreased in pregnancy, liver disease, and other conditions.
What is the genetic enzyme defect associated with atypical pseudocholinesterase?
Atypical pseudocholinesterase: Genetic defect leading to prolonged apnea.
What are the classifications of non-depolarizing muscle relaxants?
Non-depolarizing MR classifications: Benzylisoquinolines and aminosteroids.
What are the key properties of atracurium?
Atracurium properties: CV stability, bronchospasm potential, metabolism by Hoffman’s degradation and ester hydrolysis.
