Catecholamines

Question 1

Wha are the 2 determinants of arterial BP? Which is more powerful?

Answer 1

1. CO
2. SVR –> more powerful

Question 2

Describe the stimulation of epinephrine on a- and b-adrenoceptors related to the dose of epinephrine.

Answer 2

Low dose: b > a
high dose: a>b

Question 3

What are the 2 most important functions of veins?

Answer 3

1. storage of blood volume
2. conduit for venous return

Question 4

What effect does a venoconstrictor have on the cardiovascular system?

Answer 4

1. decreases venous capacitance (unstressed volume) and increases VR
2. increased resistance to venous blood flow (which might decrease VR)

Question 5

What does the net effect of vasoconstrictors depend on?

Answer 5

1. ECV
2. pretreatment status of cardiovascular system
3. drug dosages

Question 6

In what disease states was vasopressor use independently associated with increased mortality?

Answer 6

• trauma
• hemorrhagic shock

Question 7

What are the primary effects of the following receptor stimulation:

1. b1
2. b2
3. post-synaptic a1 + pre-synaptic a2

Answer 7

b1: positive chronotropy, positive inotropy, ectopic pacemaker activity
b2: vasodilation, bronchodilation
a1 + a2: vasoconstriction, ectopic pacemaker activity

Question 8

Fill in the table.

Answer 8

Question 9

What adrenoceptors are stimulated to what extent by norepinephrine? What is its effect on contractility, HR, CO, vasomotor tone and BP?

Answer 9

a1+a2: +++
b1: +
b2: 0

contractility: +
HR: variable
CO: variable
vasomotor tone: +++
BP: +++

Question 10

What adrenoceptors are stimulated to what extent by epinephrine? What is its effect on contractility, HR, CO, vasomotor tone and BP? What is its duration of action?

Answer 10

a1+a2: +++
b1: +++
b2: +++

contractility: +++
HR: +++
CO: ++
vasomotor tone: +++
BP: +++

DUA: 5-10min

Question 11

What adrenoceptors are stimulated to what extent by dobutamine? What is its effect on contractility, HR, CO, vasomotor tone and BP?

Answer 11

a1+a1: +
b1: ++
b2: +

contractility: ++
HR: +
CO: ++
vasomotor tone: -
BP: variable

Question 12

What receptors are stimulated to what extent by dopamine? What is its effect on contractility, HR, CO, vasomotor tone and BP?

Answer 12

a1+a2: ++
b1: ++
B2: +
postsynaptic D1: vasodilation
presynaptic D2: inhibition of NE release

contractility: ++
HR: ++
CO: variable
vasomotor tone: ++
BP: ++

Question 13

What adrenoceptors are stimulated to what extent by phenylephrine? What is its effect on contractility, HR, CO, vasomotor tone and BP? What is its duration of action?

Answer 13

a1+a2: +++
b1: 0
b2: 0

contractility: 0
HR: -
CO: -
vasomotor tone: +++
BP: +++

DOA: 10-20min

Question 14

What adrenoceptors are stimulated to what extent by ephedrin? What is its effect on contractility, HR, CO, vasomotor tone and BP?

Answer 14

a1+a2: +
b1: +
b2: +

contractility: +
HR: +
CO: +
vasomotor tone: variable
BP: +

Question 15

What adrenoceptors are stimulated to what extent by isoproerenol? What is its effect on contractility, HR, CO, vasomotor tone and BP?

Answer 15

a1+a2: -
b1: +++
b2: +++

contractility: +++
HR: +++
CO: +++
vasomotor tone: —
BP: —

Question 16

What causes the variable effect of norepinephrine on CO?

Answer 16

• difference in baseline ECV
• differene in baseline contractility
• relative effect of venoconstriction on venous capacitance

Question 17

What are 4 beneficial effect of the early use of norepinephrine in patients with hypotension + shock?

Answer 17

• impreoved CO
• decreased risk of VO
• improved microcirculatory flow
• improved patient outcome

Question 18

What are 2 side effects of higher dosage epinephrine?

Answer 18

1. hyperlactataemia
2. decreased splanchnic blood flow

Question 19

Explain the different dosage regimes of dopamine and its cardiovascular effect.

Answer 19

low dose: 1-4µg/kg/min –> vasodilation + increased renal blood flow
medium dose: 5-10 µg/kg/min –> b effects dominate (vasodilation + increased inotropy, chronotropy)
high dose: > 10µg/kg/min –> a effect dominate (vasoconstriction)

Question 20

What are side effects of dobutamine in cats when higher doses are used?

Answer 20

> 5-10 µg/kg/min: CNS –> tremors, seizures

Question 21

What is ephedrine MOA? What is the consequence of this?

Answer 21

increases NE release from sympathetic nerve endings –> prolonged use leads to tachyphylaxis

–> also crosses BBB –> analeptic effect

Question 22

What is the main indication for the use of isoproterenol in shock?

Answer 22

cardiogenic shock (with close BP monitoring)

Question 23

Why is NE preferred over dopamine as vasopressor support for CI patients?

Answer 23

• stronger vasopressor response
• more consistent response
• more reliable improvement in hemodynamics (MAP)

Question 24

Name 2 indications for push-dose vasopressor therapy.

Answer 24

1. transient hypotension immediately after sedation/GA
2. improve CV stability until CRI is set up

Question 25

Name 8 side effects of catecholamines.

Answer 25

1. hyperglyycemia --> a: decreased insulin secretion + increased glycogenolysis --> b: increased glucagon + ACTH secretion 3. increased metabolic VO2 4. increased shear-induced PLT reactivity (a) 5. mitochondrial dysfunction 6. immunomodulation 7. immunosuppression (ingreased risk of infection) 8. hyperlactatemia 9. increased cellular K+ uptake (b)