Lecture 10 Treatment of Perioperative Hypotension Flashcards
Name five true catecholamines.
Dopamine, norepinephrine, epinephrine, isoproterenol, dobutamine
Name the two most popular sympathomimetics used for peri-operative hypotension.
phenylephrine (direct, hits alpha-1, reflex bradycardia is an issue) and ephedrine (indirect, hits alpha-1 and beta-1, tachyphylaxis is an issue.) Ephedrine should not be used in patients who are taking drugs that inhibit norepinephrine reuptake, such as TCAs, MAO-Is, Cocaine. People who are catecholamine depleted (think Infantry guy after a prolonged firefight or chronic cocaine user) will not respond to ephedrine, since ephedrine requires presence of endogenously produced catecholamines.
What is hypotension used as a surrogate measure for?
Cardiac output and tissue perfusion.
-Low BP suggests a potentially compromised global/regional perfusion
Is there a definitive cut off for hypotension for all ages/health statuses?
No! Different people handle different BPs differently. The same is true for higher BPs.
How do we treat hypotension (first steps)?
- Determine the cause of the hypotension.
- Determine the severity of the hypotension
- Determine what resources you have at your disposal.
What’s the DDx of hypotension? (four categories)
- Hypovolemic hypotension (bleeding out)
- Distributive hypotension (septic)
- pump failure (cardiogenic) hypotension (cardiogenic)
- obstructive hypotension
Are hypotension and shock the same thing?
NO! Though they often co-exist.
Shock occurs in the presence of decreased tissue perfusion.
What are some examples of hypovolemic hypotension?
bleeding, decreased intake, GI or other losses
What are some examples of distributive hypotension?
anaphylaxis, septic shock, neurogenic shock, drug induced (anesthesia inhalation agents)
What are some examples of cardiogenic/pump failure hypotension?
MI, myocardial depression
What are some examples of obstructive hypotension?
tension pneumothorax, cardiac tamponade, massive PE, intracardiac clot/tumor, HOCM
What steps are there to hypotension therapy?
- Address the underlying cause.
- Give fluids first
- Supplement w/ vasopressors for hypovolemic hypotension
- Add vasopressors and (maybe) fluids for vasodilation/distributive hypotension
What are the two commonly used vasopressors we use?
phenylephrine and ephedrine
How are phenylephrine/ephedrine used in ACLS?
They really aren’t. Be sure to consider ACLS during your treatment of your patients, both in the OR and out.
Which (phenyl vs ephedrine) is more potent? Does it matter?
Phenylephrine is 100X more potent, but it doesn’t really apply to these drugs since they are in different categories. (On a slide, so worth making this just in case it’s tested.)
Which (phenyl vs ephedrine) has a longer duration of action?
Ephedrine, provided it is given in its proper dosing.
What is phenylephrine’s mechanism of action?
Direct vasoconstrictor.
- Acts as an alpha agonist–>increased vascular tone (venous>arterial)
- minimal inotropic effects (no beta-1 action)
- No direct action on HR (but baroreceptors note the increased BP and will prompt reflexive bradycardia)
- Might increase myocardial work due to greater preload (and myocardial stretch w/ increased afterload)
- Can improve myocardial O2
What is ephedrine’s mechanism of action?
Some direct effects, but mostly an indirect vasodilator.
- Causes endogenous catecholamine release (mostly norepinephrine)
- Not selective for alpha or beta adrenergic receptors, so they stimulate both.
- Release beta blockers–>increased HR
- Increased systolic and diastolic BP, partially due to increased cardiac pumping–>greater cardiac work
- Myocardial O2 supply-demand relationship could improve or worsen
Does phenylephrine improve CO?
It can, but not usually.
- Total SVR increased usually leads to a decreased CO.
- Dose dependent
- If myocardial ischemia was the problem, increased perfusion from phenylephrine could improve cardiac function (and CO).
What can ephedrine cause in some patients?
tachycardia. Concommitant use of phenylephrine can decrease the chances of this happening.
What does ephedine do to SVR?
It’s unpredictable.
-Released norepinephrine could stimulate alpha receptors more (increased SVR), beta receptors more (decreased SVR), or some other unpredictable combination of different receptors in different vascular beds.
What happens when a patient is on a beta blocker and they receive ephedrine?
- HR may decrease or increase
- SVR will likely increase due to unopposed alpha agonist activity
When should you use ephedrine?
- Slow HR
- No luck w/ phenylephrine
- Young patient
- Less concern about myocardial perfusion
When should you use phenylephrine?
- HR is faster
- Ephedrine tried w/o luck
- Concerned about myocardial perfusion
- Older pt
