intropic and vasopressor drugs Flashcards
define inotrope
the changing force of cardiac muscle contraction (positive or negative)
describe the different types of shock
- hypovolemic (e.g. hemorrhage, dehydration)
- cardiogenic (e.g. HF)
- distributive (e.g. sepsis, anaphylaxis)
- obstructive (e.g. cardiac tamponade, PE)
goals of resuscitation
- restore BP
- normalize perfusion (inotropes, vasopressors)
- preserve organ function
- treat underlying cause
causes and characteristics of cardiogenic shock
multiple causes:
- ischaemic, valve dysfunction, acute VSD
characterised by:
- high systemic resistance (sympathetic activation)
- low CO
ensure euvolemic (to maximize CO)
describe beta 1 and give an example of an agonist
- mostly in heart
- increase contractility (positive inotrope)
- increase HR (positive chronotrope)
B1 agonist = dobutamine
describe alpha 1 and give an example of an agonist
- mostly in BVs
- increase tone/resistance
- ‘vasopressor’
a1 agonist = norepinephrine
side effects of vasopressors
- sympathetic activity already very high so vasoconstriction
- -> ischemia of heart, limbs, gut, cerebrovascular - increase cardiac work
norepinephrine pharmacokinetics
- first choice vasopressor
- potent a agonist = vasoconstriction
- given as continuous IV
- short t1/2
causes increased peripheral resistance and increased systolic/diastolic BP
describe epinephrine (=adrenaline)
- a & B agonist
- potent inotrope, chronotrope & vasopressor
- (used in cardiac arrest and anaphylaxis)
- dilates bronchi
- increased myocardial O2 demand esp in CAD
- given as continuous IV or bolus
- short t1/2
describe dopamine and the different effects
- metabolic precursor of NEP
- short t1/2
low dose = dopaminergic (increased renal BF)
medium dose = B effects
high dose = a effects
describe phosphodiesterase inhibitors and side effects
e.g. amnrinone, milrinone
- blocks breaksdown of cAMP -> vasopressor & inotropic activity
- used w/ caution due to significant side effects:
- thrombocytopenia
- hypotension
- arrhythmias
- increased mortality
side effects of inotropic drugs
- risk of tachycardia
- increased myocardial O2 demand
dobutamine
- B1 agonist (potent inotrope, variable chronotrope)
- binds to B-receptor and increases cAMP (opens Ca2+ channels)
- given as constant IV
- short t1/2 (rapidly metabolized by the liver)
- risk of tachycardia and worsening hypotension
describe digoxin
- 3rd line AF tx (B-blocker 1st, diltiazem 2nd)
- decreases HR and increases inotropy
- usually used in acute HF w/ AF
- cleared by kidneys
- long t1/2 (therefore requires loading dose)
digoxin inotropic mechanism
- inhibits myocyte Na/K/ATPase -> ↑intracellular Na -> activates NCX to extrude Na+ and bring in Ca2+
- influx of Ca2+ –> ↑ inotropy
