Sympathomimetics Flashcards
which type of drug should you give if the pt has a “pipe” problem? Pump?
pipe-vasopressor
pump-inotrope
Before deciding ask yoursef Is there a perfusing rhythm and does the pt have adequate volume
what are the effects of inotropes?
Improve contractility
improve CO
treat pump problem
What are the effects of vasopressors?
INcrease vascular tone
Increase SVR
treat pipe problem
What role does calcium play in muscle contraction?
Actin wants to interact with myosin, but tropomysin is blocking it. Calcium binds to troponin which moves tropomysin out of the way so actin and myosin can form cross bridges.
define the following in terms of calcium: inotropy, chronotropy, and lusitropy
ionotropy–quantity of Ca in cell, maximum tension developed
Chronotropy-Rate of Ca delivery, rate of contraction
Lusitropy–removal of Ca, rate of relaxation
_______ is an important second messenger. By increasing it in the cardiac myocyte, you will increase Ca++ which will increase contractiliy
cAMP
how do B agonists increase cAMP?
Indirectly by stimulating adenyl cyclase which converts ATP into cAMP
How do phosphodiesterase inhibits increase cAMP?
prevents breakdown of cAMP
B1 receptors increase _______ and _______. B2 receptors increase _____________.
Inotropy and chronotropy
ionotroy
HOw do norepi, epi, dopamine, dobutamine and isoproteranol affect a, B1 and B2?
NOrepi, B1 with even stronger a
Epi- equal a, B@ and B2
Dopamine a is strongest , B1 and 2 are equal
Dobutamine-mostly B1 with some B2. + or - with a
Iso pure B (strong on both)
What are adverse effects of epi and norepi?
Epi-Arrythmogenic, can cause Vtach
Norepi–Intense SVR may decrease CO
What are adverse effects of dopamine, dobutamine and isoproteronol?
Dopamine–largely indirect acting
Dobutamine–tachycardia
Isopro–significant tachycardia, arrhythmias and and decreased SVR
What are the effects of cyclic nucleotides as second messengers?
activate protein kinases
open ion channels
Which family of PDEs are used for CV system?
IIIA
What are the actions of PDEIII in cardiac myocytes and vasculature?
Cardiac=increase cAMP->Ca++, increase Ca+++->contractility
Vascular tissue: INcrease cyclic nucleotide->smooth muscle relaxation. decreases PA pressures and SVR
What is loading dose and infusion rate for milrinone?
0.05mg/kg lasts 30 minutes
Infusion rate 0.5mcg/kg/min
Why is norepi the first line inotrope? What would you add if you had poor systolic function?
NOrepi provides positive inotropy (B1) and maintains perfusion pressure (a1). If systolic function is poor add dobutamine, epi or a PDE3 inhibitor
The second messenger in vasculature is cAMP? t or f
f
The end result still comes from an increase in calcium
Increasing dose of catecholamines increase _______ effects.
alpha
What is onset and duration of phenylephrine?
Onset 30 seconds
duration 2-3 minutes
what is the dose for an infusion of phenylephrine?
25-100 mcg/min
what is methoxamine?
a pure direct a1 agonist.
bolus 5-10 mg
onset 1 min
duration 5-10 min
how is ephedrine metabolized and eliminated?
Inactivated by MAO in liver (if pt is on MAOIs duration may be prolonged to 20-30 min)
40% is exreted unchanged in urine
how does ephedrine affect uterine vascular resistance?
minimally
How does vasopressin exert its effect on SVR?
Activates V1 receptor which utilizes the same second messenger system as alpha agonists. Ca++ is increased and muscular contraction happens
Name 2 other vasopressin receptors (besides V1) and give their function
V2-kidney
Dilation of renal endothelium, increases water permeability
V3-pituitary
Neurotransmitter that increases ACTH release
The principle role of vasopressin is regulating vascular tone. T/F
F
What are physiologic levels of vasopressin?
5-10 pmol/L
Onset of sepsis_____ AVP levels
increases, but in time it will decrease these levels to 1/3 of normal
Vasopressin replacement therapy may be needed after ______________
cardiopulmonary bypass
4-6 units/hour
What are side effects of vasopressin?
Intense vasoconstriction -Myocardial ischemia -decreased CO -Mesenteric ischemia -Digital necrosis However it may be beneficial for pulmonary HTN
What are potential advantages of calcium sensitizers?
Less arrhythmogenic
Do not increase O2 consumption
Since they use a different mechanism of action they may be synergist with conventional inotropes
Primobendon and levosimendon are examples of _______ _________
calcium sensitizers
how does methyline blue affect vasodilation?
blocks activation of guanlylate cyclase by NO.-> less cGMP = less vasodilation
Should only be used as a rescue drug in refractory vasodilation when MAP < 50 mmHg and Norepi>35mcg/min
What is dose, of methylene blue for vasodilation?
1.5-2mcg/kg over 10-60 min. Repeat doses have been given
What side effect may methyline blue have in doses >2mg/kg?
hyperbilirubinemia and hemolytic anemia
under 2-transient decrease in spo2 and discoloration of skin and urine
