inotropic (vasopressor) drugs

Question 1

define inotrope

Answer 1

changing the force of (cardiac) muscle contraction

positive or negative

Question 2

define shock

Answer 2

characterised by inadequate organ perfusion to meet the tissues oxygenation demand leading to organ dysfunction

Question 3

categories of shock

- examples

Answer 3

hypovolemic (e.g. haemorrhage or dehydration)

cardiogenic (e.g. HF)

distributive (e.g. sepsis, anaphylaxis)

obstructive (e.g. cardiac tamponade, PE)

Question 4

features of patients in shock

Answer 4

• hypotension/hypovolemia
• LV impairment
• changes in vascular resistance
• poor renal / peripheral perfusion
• confused / sedated

Question 5

goals of shock resuscitation

Answer 5

• restore BP (ensure euvolemic)
• normalise systemic perfusion (inotropes)
• preserve organ function (renal)
• tx underlying cause (antibiotics etc)

Question 6

causes and characteristics of cardiogenic shock

Answer 6

multiple causes:

• ischemia
• valve dysfunction
• acute VSD

characterised by:

• high systemic resistance (sympathetic activity)
• low CO

ensure euvolemic (to maximise CO)

Question 7

what is the rationale behind inotropic agents

Answer 7

• increased CO improves global perfusion

Question 8

what is the risk factors of inotropic agents

Answer 8

• tachycardia and increased myocardial oxygen consumption

Question 9

beta 1 vs alpha 1

Answer 9

beta 1

• mostly in heart
• increased contractility
• increased HR
• e.g. dobutamine

alpha 1

• mostly in BVs
• increase tone/resistance
• ‘vasopressor’
• e.g. norepinephrine

Question 10

describe side effects of vasopressors

Answer 10

• sympathetic activity already very high so vasoconstriction (α agonism) → ischemia of heart, limbs, guts, cerebrovascular
• ↑ cardiac work (α & β agonism)
  - cardiac ischaemia or arrhythmias

Question 11

describe norepinephrine

Answer 11

• first choice vasopressor
• potent a agonist = vasoconstriction
• given as continuous IV
• short t1/2

causes increased peripheral resistance and increased systolic/diastolic BP

Question 12

describe epinephrine

Answer 12

• mixed a and B agonist
• potent inotrope and chronotrope
• dilates bronchi
• increases myocardial O2 demand especially in CAD

Question 13

describe the different dose effects of dopamine

Answer 13

low dose = dopaminergic

medium dose = B effects

high dose = a effects

Question 14

describe digoxins inotropic mechanism

Answer 14

1. inhibits myocyte Na/K/ATPase
2. ↑ intracellular Na
3. activates sodium calcium exchanger which extrudes Na and brings Ca in
4. influx of Ca = ↑ inotropy

Question 15

describe digoxins chronotropic mechanism

Answer 15

1. ↑ vagal activity at AV node
2. ↓ conduction
3. ↓ ventricular rate
4. ↓HR

Question 16

describe digoxin

Answer 16

• 3rd line Tx for AF (b-blocker 1st, diltiazem 2nd)
• usually used in acute HF with AF
• cautious in impaired renal function
• ↓ HR & ↑ inotropy
• long T1/2 (needs loading dose)

Question 17

describe digoxin toxicity

Answer 17

• crosses BBB -> causes dreams
• GI upset (N&V, diarrhoea, fatigue, dizziness)
• arrhythmias
• changes in ECG
• more common in hypokalaemia (take care with diuretics)

Question 18

name some drug interactions that occur with digoxin

Answer 18

• quinidine
• amiodarone
• verapamil
• diltiazem
• erythromycin