Catecholamines

Question 1

Dobutamine actions

Answer 1

Synthetic analog of dopamine that does not have dopaminergic effects

B1 (++), B2 (+), a1 + a2 (+) stimulation
–> Increase contractility
Mild increase in HR
Decrease vasomotor tone

Forward flow is increased and blood pressure minimally changed

*in cats, doses >5-10 mcg/kg/min can cause neuro signs/seizures

Question 2

Dobutamine dose

Answer 2

5-20 mcg/kg/min

Question 3

Low-dose epinephrine

Answer 3

Stimulated beta receptors more than alpha receptors and can help with perfusion with less vasoconstriction

Question 4

Epinephrine actions

Answer 4

B1 (+++), B2 (+++), a1 + a2 (+++) stimulation

Increase CO
Increase vasomotor tone (venous and arterial)
Increase BP
Increase HR
Increase contractility
Bronchodilation

0.05-1 mcg/kg/min

Question 5

B1 receptor agonists

Answer 5

Augment HR, contractility, and ectopic pacemaker activity

Question 6

B2 receptor agonists

Answer 6

Vasodilation and bronchodilation

Question 7

Postsynaptic a1 and presynaptic a2 receptor agonists

Answer 7

Vasoconstriction
Ectopic pacemaker activity

Question 8

Venoconstriction

Answer 8

Causes increased venous return by decreasing venous capacitance but if it gets too strong it will cause decreased preload/decreased venous return

Question 9

Norepinephrine

Answer 9

Primary a-receptor agonist
Causes both arteriolar and venous constriction
Minimal B1 receptor agonist activity
Increased HR, mild increase in contractility

CO may increase, decrease or remain unchanged

B1 (+), B2 (—), a1 + a2 (+++) stimulation

Question 10

Dopamine

Answer 10

Endogenous precursor to norepinephrine

B1 (++), B2 (+), a1 + a2 (++) stimulation

Dopamine receptor agonist
D1 receptors: vasodilation
D2: inhibit norepinephrine release from sympathetic nerve endings (i.e. encourages vasodilation)

Dopaminergic vasodilatory effects predominate at low doses (1-4 mcg/kg/min)
B effects predominate at medium doses (5-10 mcg/kg/min)
Alpha effects predominate at higher doses (>10 mcg/kg/min)

Question 11

Phenylephrine

Answer 11

Alpha receptor B1 (—), B2 (—), a1 + a2 (+++) stimulation

Increased BP, vasoconstriction, DECREASE in heart rate
CO may drop or increase

Dose: 0.5-5 mcg/kg/min

Question 12

Ephedrine

Answer 12

Sympathomimetic amine (not strictly speaking a catecholamine) that acts primarily by increasing the release of norepinephrine

General CV stimulant and bronchodilator
Prolonged use can deplete norepinephrine stores and result in tachyphylaxis

Crosses the BBB and has a mild analeptic effect (central stimulation/respiratory stimulation?)

Alpha receptor B1 (+), B2 (+), a1 + a2 (+) stimulation

Dose of 0.25-1 mcg/kg can last 5-15 min
CRI 0.02-0.2 mg/kg/min

Question 13

Isoproterenol

Answer 13

Potent B-receptor agonist with no alpha activity
Positive inotrope, chrono trope, vasodilator and hypotensive agent

Increased HR and CO but decreases BP

0.02-0.5 mcg/kg/min

Alpha receptor B1 (+++), B2 (+++), a1 + a2 (—) stimulation

Question 14

Onset/Duration of action of push dose pressors

Answer 14

Phenylephrine: starts to work within one minute, lasts 10-20 min
Dose: 40-200 mcg phenylephrine

Epinephrine: starts to work within 1 minute, lasts 5-10 minutes
Dose: 5-20 mcg epinephrine