ANS: Pharmacology & Pathophysiology Flashcards
Which agent is NOT removed from the synaptic cleft by reuptake?
a. phenylephrine
b. dopamine
c. norepinephrine
d. epinephrine
a. phenylephrine
The ANS contrlols our
involuntary regulatory functions, “fight or flight responses”
_______ is a commonly used sympathomimetic in routine anesthetic care.
Phenylephrine
Phenylephrine has _____________________ activity
selective and direct alpha 1 agonist
What is the MOA of clonidine and dexmedetomidine?
centrally acting alpha 2 receptor agonists
Clonidine and dexmedetomidine produce
sedation
anxiolysis
decreased BP & HR
cause analgesia
What are examples of categories of ANS modifiers?
adrenergic agonists
synthetic catecholamines
ARBs,
direct vasodilators/nitrodilators
antimuscarinics
Examples of adrenergic agonists include
epinephrine, norepinephrine, dopamine
Examples of synthetic catecholamines include
isoproterenol, dobutamine
Examples of synthetic noncatecholamines include
ephedrine
phenylephrine
Examples of selective beta-adrenergic agonists
albuterol, salmeterol
Examples of anesthetic agents include
volatile agent, propofol, local anesthetics
The ANS relies on two neurotransmitters:
ACh and norepinephrine
All ganglionic neurotransmission is
cholinergic (ACh)
Postganglionic parasympathetic neurotransmission is
cholinergic (ACh)
Postganglionic sympathetic neurotransmission is
adrenergic (NE)
How is phenylephrine metabolized?
MAO
How is the effect of phenylephrine on renal blood flow?
decreased
Does phenylephrine affect the venous AND arterial vasoconstriction?
yes, pure agonist at alpha 1 adrenoreceptors in venous and arterial
Significant reflex bradycardia may occur with the administration of phenylephrine because of
baroreceptor activity
Just as with norepinephrine, with phenylephrine there is a risk of
end-organ damage especially with high dose and/or prolonged duration of infusion
_______________ increases with phenylephrine due to direct vasoconstrictive action of the drug in the lung vasculature.
pulmonary artery pressure
If there is a phenylephrine overdose, what is the best course of action?
an alpha 2 adrenergic receptor antagonist such as phentolamine
depending on degree of hypertension and patient’s baseline condition time may be all that is needed
DO not treat with a beta receptor antagonist
Beta receptor antagonists are contraindicated in a phenylephrine overdose because
they may induce pulmonary edema and catastrophic, irreversible cardiovascular collapse
What are the three ways in which the location of alpha 2 receptors are classified?
- presynaptic: NE-releasing neurons in the CNS and PNS (negative feedback mechanism reduces NE release)
- postsynaptic: smooth muscle and several organs
- Nonsynaptic: platelets
Alpha 2 receptors in the GI tract have the physiologic effect of
decreased gut motility
Alpha 2 receptors in the salivary glands have the physiologic effect of
dry mouth (thick, viscous saliva)
Alpha 2 receptors in the platelets have the physiologic effect of
increased platelet aggregation
Alpha 2 receptors in the pancreas have the physiologic effect of
decreased insulin release
Alpha 2 receptors in the renal tubules have the physiologic effect of
inhibiting ADH (diuresis)
Alpha 2 receptors in the vasculature have the physiologic effect of
vasoconstriction
Alpha 2 receptors in the nervous system can be in the
medulla
vagus nerve
locus coeruleus
spinal cord (dorsal horn)
Alpha 2 receptors in the nervous system have the physiologic effect of
decreased SNS tone
increased PNS tone
sedation, hypnosis
analgesia
anti-shivering effect
What is the alpha 2 vs. alpha 1 binding of clonidine?
200:1
What is the alpha 2 vs. alpha 1 binding of dexmedetomidine?
1600:1
Clonidine MOA
acts as an alpha 2 agonist at central presynaptic receptors inhibiting norepinephrine release causing vasodilation
Abrupt discontinuation of clonidine may cause
rebound hypertension, tachycardia, and arrhythmia
tapered discontinuation is best
Clonidine has been used for
diagnosis of pheochromocytoma
controlling opiate and nicotine withdrawal manifestations
treating hypertension
Rapid administration of dexmedetomidine can stimulate the postsynaptic alpha-2 receptors in the
arterial and venous circulations leading to vasoconstriction and hypertension
Which adrenergic agonist is NOT arrhythmogenic?
phenylephrine
Which selective alpha-2 agonist is more highly protein-bond?
dexmedetomidine at 94%
