neuromuscular blocking agents

DR.CHARULATHA

Neuromuscular blocking drugs

Need for neuromuscular blocking drugs Improve intubating conditions Providing immobility Better surgical conditions

Structure of neuromuscular junction Motor neuron Axon Nerve terminals Synaptic cleft Post synaptic membrane

Action potential Electrical potential inside the cell is

negative Depolarization Sodium and calcium channels All or none response

acetylcholine Acetylcholine synthesis Receptors Vesicles Anticholinesterases Synaptic cleft Calcium and magnesium

Post synaptic events Ach receptor Ligand gated ion channel Structure of the receptor Adult ,fetal ,extrajunctional acetylcholinesterase

Presynaptic events Presynaptic receptor Preventing mobilisation of acetylcholine

vesicles

Pharmacologic characteristics Potency Onset duration

atracurium Hoffman reaction Nonspecific ester hydrolysis Dose 0.5 mg/kg Onset 3 -5 min Duration 30 – 45 min

Specific points Histamine release Intubating dose Maintenance of anaesthesia Can be used in patients with hepatic or

renal failure

cisatracurium Dose 0.1 mg/kg Duration 30 -45 min Devoid of histamine releasing properties

mivacurium Short acting Degraded by plasma esterases 0.3. mg/kg Ambulatory and laprascopic surgery

pancuronium Increase heart rate,blood pressure and

cardiac output Sympathomimetic effect Duration of action 1 hr Higher incidence of muscular weakness

after cardiac surgery than rocuronium

rocuronium 0.6 mg/kg intubating dose Duration 30 -40 min No hemodynamic effects Rapid sequence induction sugammadex

vecuronium Intubating dose 0.1 mg/kg No cardiovascular effects Excreted by the kidney Intermediate duration of action Precipitates with thiopentone

neostigmine Reversible anticholinesterase inhibitor 50 -70 mcg/kg Increased acetylcholine in the receptor Profound vagal stimulation Administered with glycopyrrolate or

atropine

sugammadex Gamma cyclodextrin Steroid nucleus –rocuronium and

vecuronium No cardiovascular adverse effects 16 mg/kg dose required

Special considerations Myasthenia gravis Myotonia Burns Muscular dystrophy UMN lesions