vasoactive and inotropic agents
TRANSCRIPT
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•VASOPRESSORS AND INOTROPICS
SAMIR EL ANSARYICU PROFESSOR
AIN SHAMSCAIRO
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Myocardial Contraction
• Contractility increases over 1st months of life along with:
– Sympathetic nerve fibers within myocardium
– Total concentration of endogenous norepinephrine
• There is a greater dependence of CO on HR than contractility during this time
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Immature Heart
• Limited responsiveness to medications
– noncontractile content
– availability of releasable NE
– Less mature sympathetic system
– Underdeveloped intracellular calcium regulatory mechanisms
– functional reserve capacity
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Ionized Calcium
• Plays central role in maintaining myocardial contractility
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Vascular Smooth Muscle
• Calcium dependent effects
– Agents that increase intracellular cAMP increase intracellular calcium requirements for contraction,
thus encouraging smooth muscle relaxation and vasodilation
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Effects of Agents
• Pressors: increase systemic vascular resistance and increase blood pressure
• Inotropes: affect myocardial contractility and enhance stroke volume
• Chronotropic Agents: affect heart rate
• Lusotropic Agents: improve relaxation during diastole and decrease EDP in the ventricles
• Dromotropic Agents: Affects conduction speed through AV node; increases heart rate
• Bathmotropic Agents: affect degree of excitability
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Alpha-Adrenergic Agents
–Alpha1-adrenergic effects:
•Vascular smooth muscle contraction
–Alpha2-adrenergic effects:
•Vascular smooth muscle relaxation
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Beta-Adrenergic Agents
• Beta1-adrenergic effects:
– Direct cardiac effects
• Inotropy (improved cardiac contractility)
• Chronotropy (increased heart rate)
• Beta2-adrenergic effects:
• Vasodilation
• Bronchodilation
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Dopaminergic Agents
• Dopaminergic Agents
– Several types of receptors located throughout body (D1-D5)
– Certain (esp. D1-like & D2-like) dopaminergic receptors increase renal and mesenteric blood
flow
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Catecholamines
• Sympathomimetic amines that contain O-dihydrobenzene
• Dopamine, epinephrine and norepinephrine are endogenous
• Dobutamine and isoproterenol are synthetic
• Sustained use or antecedent CHF can lead to down-regulation of β-receptors and decrease efficacy
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Epinephrine
• Both an alpha- and beta-adrenergic agent 0.01 mcg/kg/min - 0.3 mcg/kg/min
– Low-dose infusion = β activation
• Increase HR, contractility, decrease SVR
– Higher doses = activation
• Increased SVR and MAP
• Increased myocardial O2 demand
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EPINEPHRINE
α1 predominantlyVasoconstriction↓ Renal BF↓ Splanchnic BF ↑ Glucose
β1 predominantly↑HR↓ Duration of Systole ↑ Myocardial contractPeriph. arteriolar dil.
↑/ ↓ Renal BF↑ Renin secretion↑/ ↓ Splanchnic BF↑ GlucoseHypokalemia
Epinephrine
Low Dose (<0.05-0.1 mcg/kg/min)
High Dose(> 0.1 μg/kg/min)
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Epinephrine
• Indications for its use as a continuous infusion are:
– low cardiac output state
• beta effects will improve cardiac function
• alpha effects may increase afterload and decrease cardiac output
– septic shock
• useful for both inotropy and vasoconstriction
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Epinephrine
• Adverse effects include:– Anxiety, tremors,palpitations
– Tachycardia and tachyarrhythmias
– Increased myocardial oxygen requirements and potential to cause ischemia
– Decreased splanchnic and hepatic circulation (elevation of AST and ALT)
– Anti-Insulin effects: lactic acidosis, hyperglycemia
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Norepinephrine
• An epinephrine precursor that acts primarily on receptors
• Used primarily for alpha agonist effect - increases SVR without significantly increasing C.O.
• Used in cases of low SVR and hypotension such as profound “warm shock” with a normal or high C.O.
state- usually in combination with dopamine or epinephrine
• Infusion rates titrated between 0.05 to 0.3 mcg/kg/min
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Norepinephrine
• Differs from epinephrine in that the vasoconstriction outweighs any increase in
cardiac output.
– i.e. norepinephrine usually increases blood pressure and SVR, often without increasing
cardiac output.
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Norepinephrine
• Adverse Effects:– Similar to those of Epinephrine
– Can compromise perfusion in extremities and may need to be combined with a vasodilator e.g.
Dobutamine or Nipride
– More profound effect on splanchnic circulation and myocardial oxygen consumption
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Vasopressin
• A peptide hormone released by the posterior pituitary in response to rising plasma tonicity
or falling blood pressure
• Antidiuretic and vasopressor properties
• Deficiency of this hormone results in diabetes insipidus
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Vasopressin
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Vasopressin
• Administration
– intravenous, intramuscular, or intranasal routes
– IV is route for vasopressor activity
– The half-life of circulating ADH is approximately 20 minutes, with renal and hepatic catabolism via
reduction of the disulfide bond and peptide cleavage
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Vasopressin• Administration
– interacts with two types of receptors
• V1 receptors are found on vascular smooth muscle cells and mediate vasoconstriction
• V2 receptors are found on renal tubule cells and mediate antidiuresis through increased water permeability and water resorption in
the collecting tubules
• Use in refractory septic shock with low SVRI in pediatrics?
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Dopamine
• Intermediate product in the enzymatic pathway leading to the production of
norepinephrine; thus, it indirectly acts by releasing norepinephrine.
• Directly has , and dopaminergic actions which are dose-dependent.
• Indications are based on the adrenergic actions desired.
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Dopamine
• renal perfusion 2-5 mcg/kg/min (dopaminergic effects) by sensitivity of vascular smooth muscle to
intracellular calcium
• C.O. in Cardiogenic or Distributive Shock 5-10mcg/kg/min ( adrenergic effects)
• Post-resuscitation stabilization in patients with hypotension (with fluid therapy) 10-20 mcg/kg/min ( adrenergic effects) peripheral vasoconstriction,
SVR, PVR, HR.
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Dose Dependent effect of Dopamine
<5 mcg 5 - 10 mcg > 10 mcg
↑Contractility
Minimal change inHR and SVR
↑ Renal BF
↑ Splanchnic BF
Modest ↑ CO
↑ Renal BF
↓Proximal Tub. Na Absorbtion
↑ Splanchnic BF
↑ HR,
Vasoconstriction
↑/ ↓ Renal BF
↓/↑ Splanchnic BF
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Dobutamine
• Synthetic catecholamine with 1 inotropic effect (increases stroke volume) and 2 peripheral
vasodilation (decreases afterload)
• Positive chronotropic effect 1 (increases HR)
• Some lusotropic effect
• Overall, improves Cardiac Output by above beta-agonist acitivity
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Dobutamine
• Major metabolite is 3-O-methyldobutamine, a potent inhibitor of alpha-adrenoceptors.– Therefore, vasodilation is possible secondary to
this metabolite.
• Usual starting infusion rate is 5 mcg/kg/min, with the dose being titrated to effect up to 20
mcg/kg/min.
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DOBUTAMINE
D- isomer
Stimulates β1 and β2
L- isomerStimulates α1
Dobutamine
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Dobutamine
• Used in low C.O. states and CHF e.g. myocarditis, cardiomyopathy, myocardial
infarction
• If BP adequate, can be combined with afterload reducer (Nipride or ACE inhibitor)
• In combination with Epi/Norepi in profound shock states to improve Cardiac Output and
provide some peripheral vasodilatation
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Isoproterenol
• Synthetic catecholamine
• Non-specific beta agonist with minimal alpha-adrenergic effects.
• Causes inotropy, chronotropy, and systemic and pulmonary vasodilatation.
• Indications: bradycardia, decreased cardiac output, bronchospasm (bronchodilator).
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Isoproterenol
• Occasionally used to maintain heart rate following heart transplantation.
• Dose starts at 0.01 mcg/kg/min and is increased to 2.0 mcg/kg/min for desired
effect.
• Avoid in patients with subaortic stenosis, and hypertrophic cardiomyopathy or TOF
lesions because increases the outflow gradient
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Milrinone/Amrinone
• Belong to class of agents “Bipyridines”
• Non-receptor mediated activity based on selective inhibition of Phosphodiesterase Type III enzyme resulting in cAMP accumulation in
myocardium
• cAMP increases force of contraction and rate and extent of relaxation of myocardium
• Inotropic, vasodilator and lusotropic effect
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Milrinone/Amrinone
• Advantage over catecholamines:
–Independent action from -receptor activation, particularly when these
receptors are downregulated
(CHF and chronic catecholamine use)
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Milrinone
• Increases CO by improving contractility, decreased SVR, PVR, lusotropic effect;
decreased preload due to vasodilatation
• Unique in beneficial effects on RV function
• Protein binding: 70%
• Half-life is 1-4 hours
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Milrinone
• Elimination: primarily renally excreted
• Load with 50 mcg/kg over 30 minsfollowed by 0.25 to 0.75 mcg/kg/min
• No increase in myocardial O2 requirement
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PDE Inhibition
Aminophylline
Milrinone
Sildenefil
PDE PDE 3 PDE 5
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Milrinone
Minimal ↑ HR
↑ CO
Minimal ↑ in O2 demand ↓ SVR
↓ PVR
Diastolic Relaxation
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Other Vasoactive Agents
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BNP{ Brain natriuretic peptide }
• Secreted by ventricles in response to ↑ wall stress and volume overload
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NESRITIDE{Recombinant Human BNP}
• Venous and arteriolar dilator, acts on Guanylate cyclase
• It reduces RA pressure, PCWP and cardiac index
• Dose: Infusion 0.01- 0.03 mcg/kg/min
• Hypotension
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Nesiritide
• Nesiritide (recombinant human BNP) is a vasodilator with other theoretical effects including:
– natriuresis, neurohormonal inhibition, and reverse remodeling
– In the setting of Heart Failure, it has been shown to reduce pulmonary capillary wedge pressure
and improve shortness of breath relative to placebo
– Linked to possible renal failure and increased mortality in some patient populations
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Vasodilators
• Classified by site of action
• Venodilators: reduce preload - Nitroglycerin
• Arteriolar dilators: reduce afterload Minoxidil and Hydralazine
• Combined: act on both arterial and venous beds and reduce both pre- and afterload Sodium Nitroprusside
(Nipride)
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Nitroprusside
• Vasodilator that acts directly on arterial and venous vascular smooth muscle.
• Indicated in hypertension and low cardiac output states with increased SVR.
• Also used in post-operative cardiac surgery to decrease afterload on an injured heart.
• Action is immediate; half-life is short; titratable action.
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Nitroprusside
• Toxicity is with cyanide, one of the metabolites of the breakdown of nipride.
• Severe, unexplained metabolic acidosis might suggest cyanide toxicity.
• Dose starts at 0.5 mcg/kg/min and titrate to 5 mcg/kg/min to desired effect. May go higher (up to
10 mcg/kg/min) for short periods of time.
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Nitroglycerine
• Direct vasodilator as well, but the major effect is as a venodilator with lesser effect
on arterioles.
• Not as effective as nitroprusside in lowering blood pressure.
• Another potential benefit is relaxation of the coronary arteries, thus improving myocardial regional blood flow and
myocardial oxygen demand.
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Nitroglycerine
• Used to improve myocardial perfusion following cardiac surgery
• Dose ranges from 0.5 to 8 mcg/kg/min. Typical dose is 2 mcg/kg/min for 24 to 48
hours post-operatively
• Methemoglobinemia is potential side effect
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Relative receptor activity of most commonly used inotropes
α1 α2 β1 β2 DA
Norepinephrine +++ +++ + - -
Epinephrine +++ ++ +++ ++ -
Dopamine ++ + ++ +++ +++
Dobutamine + - +++ + -
Isoproterenol - - ++ ++ -
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GOOD LUCK
SAMIR EL ANSARYICU PROFESSOR
AIN SHAMSCAIRO