Glossary of Anesthesia Concepts II - Exam 2 - Lecture 5

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Neuromuscular Physiology

Neuromuscular Physiology
Atropine and Cocaine

Atropine and Cocaine (Do I need to know the structures by heart?)
Synthetic non-catecholamine
Primarily alpha1-adrenergic receptor stimulant
Mostly direct acting
Venoconstriction>arterial constriction
Less potent than norepi
Longer lasting
Phenylephrine Basics
Dose: 50-200 microgms IV, can be used as continuous infusion (20-50 microgms/min)
Treat hypotension in OR due to various reasons
Increases MAP, SBP, DBP, SVR
Decreases HR, CO
Not used in OB anesthesia
Double dilution/or in 100mL
Ephedrine Basics
Synthetic non-catecholamine
Indirect acting-stimulates alpha and beta adrenergic receptors
Dosage: 5-25mg IV
Treat hypotension in OR due to various reasons
Can be used in OB anesthesia
Ephedrine Continued
CV effects similar to epinephrine, longer lasting (10X)
SVR effected minimally
CV effects mostly due to an Increase in contractility Increased MAP, SBP, DBP, HR, Coronary BF
Decreased renal, splanchnic BF
Tachyphylaxis is common with this agent-due to indirect effect and occupying of receptors
Dilute once
Anticholinergic-antagonizes effect of Ach at cholinergic post ganglionic muscarinic receptors.
Muscarinics are present in: Heart, salivary glands, smooth muscles of GU and GI tract.
No/minimal effect at nicotinic receptors.
Atropine Continued
Tertiary amine-naturally occurring, is an alkaloid of belladonna plant.
Resembles cocaine in structure, and has mild analgesic activity.
Combines reversibly with muscarinic receptors and prevents Ach from binding to these sites, competitive inhibitors.
Atropine Targets Which Receptors?
Muscarinic receptor subtypes:
M1-CNS & Stomach
M2-lungs and heart
M3-CNS, airway smooth muscles, glandular tissue
M4 & M5-CNS
Atropine Basics
Drug of choice for treating intra op bradycardia.
Dose: 15-75 microgms/kg IV.
Other effects: antisialagogue, bronchodilation, mydriasis, GI motility and acid production, bronchodilation, sedation.
Similar to atropine.
Quaternary ammonium-does not easily cross BBB so no sedative effects.
Uses similar to atropine, similar effects, more potent antisialagogue, less potent at HR.
Dosage: .2-.4mg IV
Combine with anticholinestrases for reversal, .005-.007mg/kg (or 1cc of robinul for each cc of reversal drawn)
Amide local anesthetic
Prevents transmission of nerve impulses by inhibiting passage of sodium ions through ion selective sodium channels in nerve membranes.
Slows the rate of depolarization such that the threshold potential is not reached and an action potential is not propagated.
Lidocaine Continued
Used for local anesthetic activity, numbness of veins for propofol (about 30mg), and ablating response to laryngoscopy (1mg/kg).
Used as an antidysrhythmic-suppresses ventricular dysrhythmias, especially PVCs, and Vtach-2mg/kg IV followed by infusion of 1-4mg/min
In heart delays the rate of spontaneous phase 4 depolarization by preventing the gradual decrease in K+ ion permeability.
OD causes CNS toxicity/seizures.
Depolarizing muscle relaxant
SCh attaches to each of alpha subunits of the nicotinic cholinergic receptor and mimics the action of ACh, depolarizing the post-junctional membrane.
Hydrolysis of SCh is slower than ACh resulting in sustained depolarization of the receptor ion channels.
Succinylcholine Basics
Dose: 0.5-1mg/kg
Duration of action: 3-5minutes
Used for emergency a/w situations, rapid sequence induction.
Can cause: dysrhythmias (bradycardia, arrest-acts at cardiac muscarinic receptors mimics ACh), hyperkalemia, myalgias,
Increased GI pressure, ICP, and IOP.
Non selective beta blocker as well as alpha blockade.
Beta:Alpha in a ratio of 7:1.
Usual IV dose is 0.25 mg/kg.
Can repeat q 10 mins.
Bolus of 10mg-typical
Duration of action of 2-18hrs
Make sure pt has adequate HR, do not give to asthmatics.
Beta-1 selective agent at small doses.
Onset of 2 minutes.
E1/2 life of 9 minutes-metabolized by non-specific plasma esterases found in the cytosol of RBCs.
Bolus dose of 500ug/kg (IV loading dose)
In OR we typically use 10-15mg, and then dose according to response.

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