CV118 ANS inotropes and vasopressors Flashcards
What type of sympathetic receptors are found in the SA and AV node of the heart?
Beta - 1
What type of parasympathetic receptors are found in the SA and AV node?
muscarinic
What do beta-1 receptors do?
1) increase chronotropy (rate)
2) increase inotropy (strength)
What do beta-2 receptors do?
1) dilates veins and arteries
2) increases renin release
what do alpha-1 receptors do?
constrict veins and arteries
what do D1 receptors do?
Dopamine D1 receptors dilate renal, splanchnic, coronary and cerebrovascular beds
what do activating alpha 1 receptors do to the preload?
increase it.
what do activating beta 2 receptors do the preload?
decrease it
what do activating alpha 1 receptors do the after load?
increase it
what do activating beta 2 receptors do to the after load?
decrease it
what do activating D1 receptors do to the after load?
decrease it
what is afterload?
outflow resistance. Pressure in the wall of the [left ventricle] during ejection
hypovolemia
decreased blood volume of blood circulating in the body
What are the 3 major compensatory mechanisms that occur in response to a decrease in BP?
1) increase in Na retention (slow)
2) increase in renin release and subsequent increase in angiotensin II
3) increased SNA (sympathetic nervous activation)
Where are the baroreceptors located?
aortic arch and carotid artery
what is the mechanism behind how the baroreceptors respond to changing blood pressures?
during a decrease in blood pressure, the baroreceptors in the aortic arch and carotid artery respond by activating the sympathetic nervous system and inactivating the parasympathetic nervous system to increase BP. Also responds by increasing fluid retention.
What is the formula for BP?
BP = CO x TPR
Blood pressure = cardiac output x total peripheral resistance
When would one use vasopressors?
used in hypotension or shock to increase blood pressure
when treating shock, what is the first step?
correcting for intravascular volume (replacing fluids) f
What receptors does phenylephrine act on?
alpha- 1 adrenergic receptors
What are the effects of phenylephrine?
it is an alpha-1-receptor agonist
1) mydriatic - increases pupil size by constricting iris muscles
2) decrease blood flow in nasal turbinates (for nasal congestion
3) reflex slowing of the heart
4) used for hypotension to increase total peripheral resistance
Where does NE work?
alpha 1, alpha 2 and beta 1
what is the route of administration for NE?
IV
What is the action of NE when given IV?
works at alpha 1 receptors (agonist) to constrict vessels.
When is NE used?
used in emergency situations where it is given by IV when the blood pressure becomes dangerously low such as in heart failure and shock.
What is the proper order to treat shock?
1) first give fluids
2) then give vasopressors
3) identify infection
4) then treatment
*only give vasopressin if fluids alone fail
why is dopamine falling out of favour?
because it is likely to produce dysrhythmia
What is another term used to describe total peripheral resistance?
systemic vascular resistance
what is cardiac index?
cardiac output/ body surface area
what is the best type of receptor agonist that should be used to treat warm sepsis?
alpha 1 agonist such as NE or phenylephrine
What are the characteristics of warm sepsis?
1) hyperdynamic shock so decrease in systemic vascular resistance
2) decrease in BP, decrease in SVR, and increase in Cardiac index
What is cold sepsis?
1) hypodynamic shock - SVR and CI are low
2) decrease BP, decrease SVR, decreased CI
what is the best type of receptor agonist that should be used to treat cold sepsis?
an alpha 1 and beta 1 agonist which would increase vasoconstriction as well as isotropy. Use NE but add epinephrine or dobutamine as inotrope if beta 1 agonist activity is required.
in what ways are epinephrine administered?
topically, subcutaneously, and intravenously
on which receptors does epinephrine work?
beta 1, then alpha 1 and beta 2
Explain how epinephrine’s effects are dose dependent
at low doses, it is predominantly a b1-agonist and at high doses, it is predominantly an alpha1 agonist
What drug is used as a topical hemostatic agent?
epinephrine. Works by means of alpha receptors which cause local constriction of blood vessels and causes decreased bleeding.
What is the first drug choice for anaphylaxis?
epinephrine
During shock, what is the best agent to use if norepinephrine fails?
epinephrine
How does dopamine work at low doses?
works at D1 receptors to dilate vessels.
How does dopamine work at a medium dose?
works at D1 and beta-1 adrenergic receptors. Cardiac effects
how does dopamine work at high doses?
mostly affects alpha 1. used for hypotension due to sepsis or cardiac failure
what is another name for vasopressin?
antidiuretic hormone
hypoantremia
low sodium concentration in the blood
How do inotropes work?
they increase intracellular calcium which then increases contractility
What type of drug is digoxin?
cardiac glycoside
What are the 2 major actions of digoxin?
- increases contractility
2. stimulates the vagus nerve - decreases conduction.
How does digoxin work?
it blocks Na/K ATPase causing increased intracellular sodium. This decreases the driving force of the Na/Ca exchanger so there is a decreased extrusion of Ca into the extracellular space
Does digoxin improve mortality ?
no, but it improves quality of life
When is digoxin used?
used late in heart failure when appropriate treament fails to improve
what receptors does dobutamine act on?
mainly beta 1 but also alpha 1 and beta 2
what is dobutamine used for?
mainly for beta 1 inotropic effect
How can dobutamine’s Beta 2 effects be both useful and detrimental?
useful in heart failure because beta 2 causes vasodilation which decreases afterload (which is increased in heart failure); detrimental in sepsis or cardiogenic shock because lowers SVR
how is dobutamine administered?
by infusion
what is the half-life of dobutamine?
2 min
What kind of drug is milrinone?
It is a phosphodiesterase (PDE) - 3 inhibitor
How do PDE-3 inhibitors work?
they decrease cAMP breakdown
What is milrinone used for?
short-term use in advanced congestive heart failure
how is milirinone administered?
intravenously
