Module 3- Neuromuscular Flashcards
Absolute refractory period corresponds to the time when gated sodium channel is in what state
Inactive state
Motor nerves exit the SC via ______
Sensory nerves enter the SC via ______
Motor- Ventral (anterior) horn
Sensory- Dorsal (posterior) horn
What is responsible for fade seen with NDNMB
Presynaptic nicotinic receptor responds to Ach in the cleft by increasing synthesis of Ach and mobilization of Ach
Positive feedback mechanism
What subunits of nicotinic receptor must be occupied for the channel to open
Both alpha subunits
Acetyl cholinesterase degrades what
Ach
Ester LA
Neostigmine
Edrophonium
Remi
Esmolol
Mechanism of action for NDNMB
Competitive inhibition
The presynaptic action of succinylcholine does what to its post synaptic action
Enhances it. The presynaptic action augments the release of Ach
Metabolism is the primary route of elimination for what NM relaxants
Succinylcholine
Atracurium
Cisatracurium
Mivacurium
Biliary excretion is the primary route of elimination for what NM relaxants
Rocuronium
Vecuronium
Difference in metabolism of Atracurium and Cisatracurium
Both eliminated by Hoffman elimination
But Atracurium is also eliminated by ester hydrolysis by non-specific esterases
Which NMB associated with histamine release
Succinylcholine
Mivacurium
Atracurium
Explain MOA of succinylcholine producing bradycardia
Succinylcholine mimics action of Ach and directly stimulates muscarinic receptors of SA node
Earliest sign of MH
Elevated ETCO2
Dose of dantrolene
Max dose
2.5mg/kg every 5 minutes until episode is terminated
Max dose 20mg/kg
Active cooling of patient with MH should be stopped at what temperature
38C
Antiarrhythmic of choice for MH patient having PVCs
Procainamide or Lidocaine
Syndrome that mimics MH
Differences
Neuroleptic Malignant Syndrome
Develops over 24-72 hours
Patients taking what drugs are at risk for neuroleptic malignant syndrome
Antipsychotics (haldol) due to dopamine depletion in CNS
Disorder characterized by weakness and easy fatiguability of skeletal muscles caused by autoimmune destruction of nicotinic Ach receptors at NMJ
Myasthenia Gravis
Drugs commonly used in treatment of myasthenia gravis
Anticholinesterases
Increases risk of cholinergic crisis
Condition characterized by proximal skeletal weakness affecting the lower extremities typically
Eaton-Lambert myasthenic syndrome
Associated with small cell lung CA
Differentiate myasthenia gravis from Eaton-lambert
Muscle strength deteriorates rapidly with repeated effort with MG. Improves with Eaton-lambert
Also MG symptoms improve with anticholinesterase but unchanged with Eaton-lambert
What eye drop medication depresses plasma cholinesterase activity
Echothiophate (eye drop)
Irreversible cholinesterase inhibitor
Significance of quaternary ammonium group on muscle relaxants
Completely ionized- lipid insoluble and highly water soluble
Hoffman elimination is dependent on what 2 factors
Temperature and pH
What is the metabolite of atracurium that can cause CNS stimulation
Laudanosine
Myasthenia gravis sensitivity to NDNMB and succinylcholine
Increased sensitivity to NDNMB
Either very sensitive or resistant to succinylcholine
How does pt with Eaton-Lambert respond to NDNMB and succinylcholine
Increased sensitivity to both
What is the treatment for cholinergic syndrome
Atropine
Which antimuscarinic cross the BBB and can cause central anticholinergic syndrome
Scopolamine and atropine
Treatment for anticholinergic syndrome
Phyostigmine 15-60 mcg/kg
Explain Dibucaine test and number interpretation
Dibucaine depresses activity of pseudocholinesterase. Normal is for 75-85% activity depressed by dibucaine
Normal 80
Heterozygous atypical plasma cholinesterase- 60
Homozygous atypical plasma cholinesterase -20
What is the frequency of stimulation in TOF
2Hz (2 twitches per second or one every 0.5 seconds)
How is tetany produced with nerve stimulator
50Hz for 5 seconds
Intense stimulus for release of Ach at NMJ
What is the best stimulation pattern with nerve stimulator to determine fade during a block
Double burst stimulation
2 trains of 3 impulses 50Hz each separated by 750ms
