Lecture 10 Treatment of Perioperative Hypotension

Question 1

Name five true catecholamines.

Answer 1

Dopamine, norepinephrine, epinephrine, isoproterenol, dobutamine

Question 2

Name the two most popular sympathomimetics used for peri-operative hypotension.

Answer 2

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.

Question 3

What is hypotension used as a surrogate measure for?

Answer 3

Cardiac output and tissue perfusion.
-Low BP suggests a potentially compromised global/regional perfusion

Question 4

Is there a definitive cut off for hypotension for all ages/health statuses?

Answer 4

No! Different people handle different BPs differently. The same is true for higher BPs.

Question 5

How do we treat hypotension (first steps)?

Answer 5

• Determine the cause of the hypotension.
• Determine the severity of the hypotension
• Determine what resources you have at your disposal.

Question 6

What’s the DDx of hypotension? (four categories)

Answer 6

• Hypovolemic hypotension (bleeding out)
• Distributive hypotension (septic)
• pump failure (cardiogenic) hypotension (cardiogenic)
• obstructive hypotension

Question 7

Are hypotension and shock the same thing?

Answer 7

NO! Though they often co-exist.
Shock occurs in the presence of decreased tissue perfusion.

Question 8

What are some examples of hypovolemic hypotension?

Answer 8

bleeding, decreased intake, GI or other losses

Question 9

What are some examples of distributive hypotension?

Answer 9

anaphylaxis, septic shock, neurogenic shock, drug induced (anesthesia inhalation agents)

Question 10

What are some examples of cardiogenic/pump failure hypotension?

Answer 10

MI, myocardial depression

Question 11

What are some examples of obstructive hypotension?

Answer 11

tension pneumothorax, cardiac tamponade, massive PE, intracardiac clot/tumor, HOCM

Question 12

What steps are there to hypotension therapy?

Answer 12

• Address the underlying cause.
• Give fluids first
• Supplement w/ vasopressors for hypovolemic hypotension
• Add vasopressors and (maybe) fluids for vasodilation/distributive hypotension

Question 13

What are the two commonly used vasopressors we use?

Answer 13

phenylephrine and ephedrine

Question 14

How are phenylephrine/ephedrine used in ACLS?

Answer 14

They really aren’t. Be sure to consider ACLS during your treatment of your patients, both in the OR and out.

Question 15

Which (phenyl vs ephedrine) is more potent? Does it matter?

Answer 15

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.)

Question 16

Which (phenyl vs ephedrine) has a longer duration of action?

Answer 16

Ephedrine, provided it is given in its proper dosing.

Question 17

What is phenylephrine’s mechanism of action?

Answer 17

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

Question 18

What is ephedrine’s mechanism of action?

Answer 18

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

Question 19

Does phenylephrine improve CO?

Answer 19

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).

Question 20

What can ephedrine cause in some patients?

Answer 20

tachycardia. Concommitant use of phenylephrine can decrease the chances of this happening.

Question 21

What does ephedine do to SVR?

Answer 21

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.

Question 22

What happens when a patient is on a beta blocker and they receive ephedrine?

Answer 22

• HR may decrease or increase
• SVR will likely increase due to unopposed alpha agonist activity

Question 23

When should you use ephedrine?

Answer 23

• Slow HR
• No luck w/ phenylephrine
• Young patient
• Less concern about myocardial perfusion

Question 24

When should you use phenylephrine?

Answer 24

• HR is faster
• Ephedrine tried w/o luck
• Concerned about myocardial perfusion
• Older pt