Vasopressors/Sympathomimetics Flashcards
Vasopressors are NOT a replacemnt for:
- adequate volume (need fluids)
- blood (need blood)
- too much anesthesia (lessen your anesthetics)
T/F: vasopressors are used when too much anesthetics are given and cause hypotension
false
if this is the consistent cause of hypotension, lighten up on your anesthetics
What two vasopressors are commonly used in anesthesia?
- ephedrine
- phenylephrine
What is ephedrine?
a vasopressor that is a mixed-acting synthetic non-catecholamine sympathomimetic
What are the indirect effects of ephedrine?
- at alpha-1 and beta-1 receptors, it displaces norepi presynaptic vessicles
- norepi that is released and activates postsynaptic receptors cause vasoconstriction and increased myocardial contraction
What are the direct effects of ephedrine?
- directly stimulates beta-2 receptors
- increased HR, CO
- gentle SVR/BP increase
When is ephedrine given?
- low HR/bradycardia
- low BP/hypotension
- to increase BP/HR/CO/contractility
- PONV
- bronchodilator effect
Explain what alpha receptors do
- alpha 1: vasoconstriction, mydriasis (dilation), urinary retention, ejacuation
- alpha 2: inhibit presynaptic release of norepi
Explain what beta receptors do
- beta 1: increase CO in heart, increase renin in kidneys
- beta 2: smooth muscle relaxation (bronchodilator, vasodilation, decreased digestion, decreased urination), increase glucose from liver
- beta 3: lipolysis of adipose tissue, decreased urination
What happens when ephedrine binds to alpha1 and beta1 receptors?
displaces norepinephrine from presynaptic vesicles
What is a difference between ephedrine and epinephrine in their responses to BP?
- epinephrine has stronger increase in BP due to very strong alpha and beta effects
- ephedrine has gentle increase in BP due to only some SVR increase
Is ephedrine or phenylephrine safer to use in OB?
phenylephrine
- ephedrine can cause fetal tachycardia and acidosis, leading to lower umbilical artery pH at delivery
When is ephedrine contraindicated?
- MAOI inhibitors
- pheochromocytoma
Careful administration of ephedrine in what case?
coronary artery disease (CAD)
There is a risk of ______________ with excessive ephedrine administration, which causes decreased response with administration
tachyphylaxis
- there is depletion of presynaptic norepinephrine; would need to use different agent in the meantime
Ephedrine Dosing
5-10 mg at a time to increase BP/HR
Ephedrine antiemetic dosing
25mg of ephedrine/25 mg of vistaril IM, 20 min before the end of surgery
What is the concentration of ephedrine in a vial?
50 mg/1mL
How can we dilute ephedrine for safe administration?
1 ml (50mg) + 9 ml of NS = 5 mg/1ml mixture
What is the MOA of phenylephrine?
- directly stimulates alpha1 receptors
- very minimal effect on alpha2 and beta receptors
When is phenylephrine used?
- hypotension
- decreased CO in patients with LV dysfunction
- good choice if patient is hypotensive with tachycardia
What is the vasopressor of choice in OB?
phenylephrine
In what areas does phenylephrine cause vasoconstriction?
- cutaneous
- mesenteric
- splenic
- renal
Phenylephrine Dosing
50-100 mcg
What is the cardiac effect of phenylephrine?
vasoconstriction to increase BP, reflex decrease in HR, increase in coronary blood flow
When should phenylephrine not be used?
if the patient is bradycardic
Which vasopressor would be a better choice in a patient that is hypotensive and bradycardic?
ephedrine
Which vasopressor would be a better choice in a patient that is hypotensive and tachycardic?
phenylephrine
What is the concentration of phenylephrine in a vial?
10 mg/1 mL (10,000 mcg/1ml)
How can phenylephrine be diluted for safe administration?
0.1ml (1000mcg) + 9.9 ml NS = 100 mcg/cc
Why is phenylephrine the vasopressor of choice in OB?
- good for hypotension post-regional
- faster onset
- shorter duration of action
- maintains fetal pH
- ephedrine would cause fetal tachycardia and acidosis
What are the pros and cons of ephedrine in OB?
- PROS: won’t decrease uterine blood flow; antiemetic property; good for hypotension from regional
- CONS: can cause fetal tachycardia and acidosis; lowers fetal pH
What is an important thing to note when administering a patient phenylephrine, especially in an OB patient?
- make sure the patient is hydrated!!!!
- if the patient is dehydrated it may cause profound bradycardia to the 20s
Dopamine Dosing (low, moderate, and high)
Low: < 3mcg/kg/min
Moderate: 3-8 mcg/kg/min
High: 10 mcg/kg/min
What is the effect of low dose dopamine?
- low dose: < 3mcg/kg/min
- activates DA1 receptors which increase renal and splenic blood flow via arterial dilation to these organs
- reduce norepi release by DA2 receptors
Dopamine is a precursor of ______________
norepinephrine
What is the effect of moderate doses of dopamine?
- moderate dose: 3-8 mcg/kg/min
- activates a1 and b1 receptors, leading to increased BP and contractility
What is the effect of high dose dopamine?
- high doses: 10 mcg/kg/min
- act primarily on a1 receptors, increasing vasoconstriction
Dopamine is used commonly for what type of cardiac patients?
patients with acute LV dysfunction needing positive ionotrpic effect
Dobutamine Dosing
Lower doses: 2.5-5 mcg/kg/min
Higher doses: 5-20 mcg/kg/min
What is the mechanism of action of dobutamine?
- activates beta1 receptors, increasing contractility, SV, and CO
- activates beta-2 receptors, causing arterial vasodilation (slightly lower BP) to preserve preload and afterload
