Vasopressors Flashcards
What are the general effects of alpha-1 adrenergic receptor agonists?
Sympathetic regulation (decreased insulin release, vasoconstriction, mild inotropy, negative chronotropy)
What receptors do epi and norepi target?
Epi: alpha 1, alpha 2, beta 1, and beta 2
Norepi: alpha 1, alpha 2, beta 1
How is the change in BP different when using norepi vs epi?
With epi, you have alpha-1 and beta-2 effects (constrict and dilates) so you have a more pronounced increase in SBP and minimal changes in DBP; Norepi increases both equally
How does norepi affect HR?
Increased SVR -> baroreceptor mediated bradycardia (countered by beta-1 chronotropic effect) = no real change in HR
What pressor is best for renal preservation with severe sepsis?
Norepi (raises BP and preserves CO)
What receptors does dobutamine target?
Beta-1»_space;> beta-2, alpha-1
First line pressor for hypotension? If CO is still low? If that doesn’t work? Still not working?
NE -> dobutamine -> vasopressin -> epi
What is the primary advantage of a NE gtt vs dopamine gtt?
Lower rate of arrhythmias (in particular tachyarrhythmias)
How are catecholamines metabolized in the liver vs. neurons? Final product of metabolism?
Liver: First by COMT, then MAO
Neurons: First by MAO, then COMT
Final product: Vanillymandelic acid (VMA)
What effects do you get of low-dose dopamine?
Significant DA1 agonist (renal artery vasodilation) and weak adrenergic receptor effects -> minimal increase in HR and contractility + diuresis
Are low-dose dopamine drips renal protective?
No, same number of kidneys fail with or without the drip
What effects do you get of medium-dose dopamine (5-10mcg/kg/min)? High dose (>10 mcg/kg/min)?
Medium: beta > alpha (vasodilation, increased HR, increased contractility)
High: alpha-1 + beta-1 and beta-2 (increased SVR)
What receptors do dopexamine target?
Beta-2»_space;> Beta-1 and potent DA effects (opposite of dobutamine)
What receptors do isoproterenol target?
Beta 1 and beta 2 roughly equally
What is dromotropy?
The conduction speed of electrical impulses within the heart
What is lusitropy?
Ability of the heart to relax in diastole
Mechanism of action of ephedrine?
Increased post-synaptic NE release and/or decreased NE reuptake
What happens when you activate beta receptors?
G-protein couple receptors -> adenylate cyclase -> ATP to cAMP -> activates PKA (protein kinase A) -> increased intracellular Ca++ from sarcoplasmic reticulum
What is the mechanism of action of milrinone?
Phosphodiesterase 3 inhibitor: decrease the degradation of cAMP which increases intracellular Ca++
What happens when you activate alpha receptors?
G-protein coupled receptor -> phospholipase C -> splits phosphatidyl inositol -> release of Ca++ from sarcoplasmic reticulum
What cardiac effects do you see with milrinone?
Increased intracellular cAMP -> increased contractility, increased HR, arterial and venous vasodilation
How does nitric oxide work?
Lowers PA pressures by being a direct vasodilator; stimulates guanylate cyclase -> increased cGMP -> relaxation of smooth muscles
What receptors does fenoldopam target?
Purely DA1 agonist (systemic vasodilation and increased renal blood flow)
How is sildenafil (Viagra) important in PA pressures?
Phosphodiesterase (PDA 5) inhibitor which is what breaks down cGMP (more cGMP -> more smooth muscle relaxation -> lower PA pressures)
What is a side effect of NO (nitric oxide)?
Methemoglobinemia
How does nesiritide work?
Recombinant BNP -> stimulates guanylate cyclase -> increases cGMP -> vasodilation (decreases afterload)
When would you use nesiritide?
Severe decompensated heart failure by decrease afterload and encouraging forward flow
During ACLS, what dose of vasopressin can be used instead of epi?
40 units
Forumula for SVR and PVR?
SVR: (MAP - CVP) / CO
PVR: (PAP - PWP) / CO
(both multiplied by 80)
Does vasopressin affect contractility?
No, only affects vascular tone
How does phentolamine work?
Alpha-1 and alpha-2 antagonist
How does prazosin work?
Alpha-1 antagonist
How does labetalol work?
Non-selective beta blocker with alpha-1 antagonism
Side effects of sodium nitroprusside?
Met-Hb and cyanide toxicity
What effects do you see from cyanide toxicity?
Uncoupling of the electron transport chain -> increased anaerobic metabolism -> lactic acidosis
Treatment for cyanide toxicity?
- Sodium nitrite (increase met-Hgb) to pick up cyanide and become cyanmet-Hgb, followed by methylene blue
- Sodium thiosulfate (binds cyanide producing thiocyanate)
- Vitamin B12
Why would a patient with ARDS on sodium nitroprusside therapy have a sudden profound desaturation?
Sodium nitroprusside vasodilates pulmonary vasculature -> counteracts hypoxic pulmonary vasoconstriction -> increases blood flow to poorly oxygenated alveoli -> increased V/Q mismatch
What medication can redistribute coronary blood flow to the subendocardium during ischemia?
Nitroglycerin
Mechanism of action of nitroglycerin?
Decreases preload (venodilator) and wall tension, coronary artery vasodilator
What are the beta-1 actions in the heart?
Increase inotropy, chronotropy, and dromotropy
What are the primary effects of beta-2 action?
Systemic and pulmonary arteriolar vasodilation
How does levosimendan work?
Calcium sensitizer without increasing Ca++, inotrope
Common inotrope used following cardiac transplantation to maintain an elevated HR and CO?
Isoproterenol
Which inotrope improves diastolic relaxation?
Milrinone
Low dose epinephrine vs. higher doses?
Low-dose: beta-1 effect (alpha-1 offset by beta-2)
Higher-doses: alpha-1 effect predominates
How are the catecholamines synthesized (order of compounds)?
Tyrosine -> DOPA -> Dopamine -> NE -> Epi
Inotrope of choice in early cardiogenic shock with low BP and s/s of end-organ compromise?
Dopamine (alpha-1 effects will correct organ perfusion pressure) over dobutamine (beta-2 effect would worsen perfusion)
Type of shock with elevated CO? Increased delivery of O2? Increased CVP? Decreased SVR?
Elevated CO: Distributive
Increased DO2: Distributive
Increased CVP: Cardiogenic & obstructive
Decreased SVR: Distributive
What is another name for ADH?
Vasopressin
What vasopressor is preferred in patients with aortic stenosis or HOCM?
Phenylephrine (from the reflexive bradycardia)
How does sodium nitroprusside work?
SNP consists of 5 cyanide groups and a NO group: the NO diffuses out and stimulates guanylate cyclase -> increased cGMP -> smooth muscle relaxation
What cardiovascular effects do you see with sodium nitroprusside?
Decreased SVR (arterial vasodilator), reflexive tachycardia, increased contractility, decreased preload (venodilator)
What does sodium nitroprusside do to platelets?
Decreases the number and aggregation 1-6 hours after infusion; returns to normal 24 hours after infusion
Why can you use phenylephrine in a hypotensive patient after induction with propofol who has coronary artery disease?
Phenylephrine will increase SVR, improving coronary perfusion (aortic diastolic pressure - LVEDP), and decreases HR (increases time for filling)
What state of iron does methemoglobin have?
Ferric (3+)
