Anesthesia 5th year, 4th & 5th lectures (Dr. Aamir)
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Transcript of Anesthesia 5th year, 4th & 5th lectures (Dr. Aamir)
MUSCLE RELAXANTS
Muscle relaxants are drugs that interrupt transmission of neural impulses at the neuromuscular junction
History
Involved research using Banded Krait (bungarotoxins) and cobra as well as curare from South American plants
Banded Krait from Taiwan
Most potent source of curare
Clinical uses
1. Provide skeletal muscle relaxation to facilitate intubation of the trachea
2. Provide optimal surgical working conditions
3. In the intensive care setting to facilitate mechanical ventilation of the lungs
Note
MR lack anesthetic or analgesic effects and must not be used to render an inadequately anesthetized patient immobile
The choice of MR is influenced by:
1. Its speed of onset
2. Duration of action
3. Rout of elimination
4. Associated side effects
Neuromuscular junction
Consist of a prejuctional motor nerve ending separated from the highly folded postjunctional membrane by synaptic cleft
Neuromuscular transmission is initiated by arrival of an impulse at the motor nerve terminal with an associated influx of calcium and a resultant release of neurotransmitter acetylcholine
Ach binds to nicotinic cholinergic receptors on postjunctional membrane, causing a change in membrane permeability to ions, principally K & Na ions
Ach is rapidly hydrolyzed by enz. Acetylcholine esterase (true cholinesterase)
Nicotinic cholinergic receptors
1.Prejunctional
2.Postjunctional
3.extrajunctional
Neuromuscular Junction
ACh ACh (8-10,000 (8-10,000 molecules)molecules)~100mM~100mM
Acetate and Acetate and cholinecholine
50% recaptured 50% recaptured by nerve terminalby nerve terminal
Voltage-dependentVoltage-dependentCaCa2+ 2+ channelschannels
High affinity High affinity choline carriercholine carrier
Empty Empty
vesiclevesicle
CATCATAcCoAAcCoA
CoACoA
cholinecholine
AChACh
active transportactive transport
AChEAChE
cholinecholine
NaNa++
CaCa2+2+
CaCa2+2+
CaCa2+2+
AChACh
AChACh
AChACh
NaNa++
KK++nAChRnAChR
NaNa++
Muscle fibreMuscle fibre
Muscle relaxants
Depolarizing noncompetitive
Nondepolarizingcompetitive
Depolarizing (succinylcholine or Suxamethonium)
Clinical use: - - - - - -
Averse effects
1. Cardiac dysrthymia: Bradycardia, arrest
2. Myalgia
3. Myoglobinuria
4. Increased Intraocular pressure
5. Increased Intragastric pressure
6. Increased Intracranial pressure
7. Trismus
8. Allergic reactions
9. Trigger for malignant hyperthermia
10. Hyperkalemia
• Denervation injury (spinal cord transection)
• Unhealed skeletal muscle injury as produced by 3rd degree burn
• Upper motor neuron injury
• Multiple trauma
Causes of delayed recovery from succinylcholine1. Sever liver disease
2. Potent anticholine esterase (insecticides)
3. Chemotherapy (cyclophosphamide)
4. A typical pseudo cholinesterase
Nondepolarizingcompetitive
Long acting>)30 min(
PancuroniumD-tubocurarine
Gallamine
Intermediate acting)15-25 min(
VecuroniumCis (atracurium)
rocuronuim
Short acting<)15 min(
Mivacurium
Nondepolarizingcompetitive
Factors enhance effects of NDMR
1. Volatile anesthetics2. Aminoglycosides Antibiotics3. Mg4. Local analgesics5. Calcium channel blockers (verapamil)6. Cardiac antiarrythmias (quinidine) 7. Hypothermia8. Acidosis9. Hypokalemia
Drug-assisted antagonism of Nondepolarizing muscle relaxants
Anti-cholineesterase
Neostigmine edrophonium pyridostigmine
Anticholinesterase
Drug accelerates the already established pattern of spontaneous recovery at the neuromuscular junction by inhibiting the activity of acetylcholinesterase leading to accumulation of ach. At nicotinic (neuromuscular junction) and muscarinic sites
The competition between ach and a Nondepolarizing MR in favor of the neurotransmitter (Ach) and restores neuromuscular transmission
• Anticholinesterase does not cross blood brain barrier
• Peripheral muscarinic effects block by anticholinergic drugs like Atropine
Thank you