CV drugs Dr. Maney Flashcards
What are the CV drug classes that we are concerned with regarding anesthesia
- Anticholinergics
- Antiarrhythmics
- Vasopressors/Inotropes
Adrenergic agonists
vasopressin
What is the ultimate CV goal with anesthesia
Oxygen delivery to tissues! (DO2)
Equation to determine Cardiac Output (CO)
CO = HR x SV
How do anticholinergics affect HR
Helps to correct:
Too low → decr CO
How do antiarrhythmics fit into the CV equation
Helps correct rhythym:
Too high or irregular → decr CO
Inotropes correct
Contractility, they fix:
Too low → decr CO
Most anesthetic drugs cause vasodilation so pressors help with
Afterload/preload
make sure pt has adequate intravascular volume
2 anticholinergics
what receptors do they affect
what is their effect
Atropine, Glycopyrolate
competative antagonists at muscarinic ACh receptors (antimuscarinic), decr parasympathetic tone
incr fire rate of SA node (chronotropy) & conduction speed through AV node (dromotropy)
Where are the muscarinic receptors we are concerned about
what CS might we see when activated
M2: heart, CNS, airway smooth mm
bradycardia
Clinical indications to use anticholinergics
bradycardia 2° to incr vagal tone
incr vagal tone can be caused by:
opioids, brachycephalic conformation & doxies, ophtho, GI, vomiting, intubation
Side effects of Atropine/Glycopyrrolate
Ileus & colic (concern for horses & ruminants)
incr viscosity of saliva
mydriasis (atropine) - contraindicated in glaucoma
what can be seen with atropine/glyco administration
paradoxical bradycardia
more likely at low doses
may lead to AV block, sometimes severe/persistent
Atropine
IV, IM, SQ, IT
Onset: ≈ 1 m IV
DoA: 30-60 m
may cause marked tachycardia
crosses BBB & placenta
Glycopyrrolate
IV, IM, SQ
Onset: 1-5 m IV
DoA: 2-3 h
may cause mild tachycardia (<atropine></atropine>
does NOT cross BBB or placenta & no mydriasis
NOT for emergency use (slow onset)
Anti arrhythmics
Class 1B - Lidocaine
Na channel blocker
Use for VPDs. Vtach
Short acting: bolus → CRI
Criteria for use: hypotension/inadequate perfusion, R-on-T, multiform VPDs, HR>180
Class II - Beta blockers
use for severe sinus tachycardia or SVT
rarely used during anes except:
tachycardia associated w/ pheochromocytoma
Esmolol most common
Dopamine
Dose dependent receptor agonism:
Low dose: incr renal perfusion, Dopamine receptor agonist
Med dose: incr inotropy & chronotropy, Beta agonist
High dose: incr inotropy, chronotropy & vasoconstriction, Beat and Alpha agonist
Short 1/2 life, must be CRI
Common first line tx for hypotension in cats
Ephedrine
Mixed agonist
• Primary α
• Also ß1, ß2
• May see a reflex bradycardia due to vasoconstrictive effects
• May cause CNS stimulation (increases MAC)
• DoA: 20-30 minutes
• Less effective after repeated dosing
Norepinephrine
Mixed agonist
• Primary α ⇒ vasoconstriction
• Also ß1
• Indicated for refractory shock or non-responsive hypotension (usually a 2nd or 3rd line treatment)
• Short acting, use as a CRI
Epinephrine
Non-selective agonist: α, ß1, ß2
• Indications: CPR or anaphylactic shock
• Arrhythmogenic (vFib)
Phenylephrine
α-1 agonist ONLY → vasoconstriction, increased BP
May decrease cardiac output and perfusion
Careful patient choice and titration
Causes splenic contraction – used to treat nephrosplenic
entrapment in horses
Short half-life, must be given as a CRI
Useful topically for nasal edema in horses
(7th semester sheep lab too)
Dobutamine
ß agonist
• Primarily ß1 ⇒ increased inotropy, minimal effects on chronotropy
• Mild ß2 effects (vasodilation)
• Used commonly in equine anesthesia (~100% of horses under inhalant GA)
• Short half-life, must be given as a CRI
Isoproterenol
ß1 and ß2 agonist
• Clinical use in veterinary medicine restricted to medical tx for 3rd
degree AV block (ß1effect) and bronchodilation (ß2 effect)
• Short half-life, give as a CRI
Vasopressin (ADH)
Non-adrenergic sympathomimetic →Vasoconstriction via V1 receptors
Indicated for refractory shock or non-responsive hypotension as a CRI
May cause profound vasoconstriction and tissue ischemia – monitor patients closely!
Used in CPR interchangeably with epinephrine
Strategies for hypotension
If bradycardic give anticholinergic.
Try turning down vaporizer, if pt is light give MAC sparing drug then decr vaporizer
Opioid, benzo, lidocaine, ketamine, etc
Give crystalloid fluid bolus & evaluate response
If still hypotensive:
CV drugs, tx underlying cause (i.e. vasodilation → vasopressor, decr contratility→ inotrope)
