2. Objectives
• To understand the physiology of inotropic agents
• To understand appropriate clinical application of vasopressors and inotropic agents
3. Reasons for using inotropes
To Reverse Impaired Myocardial Contractility
To support failing peripheral vasculature
To correct hypotension during anaesthesia ( General or Regional)
4. Control of blood pressure
Arterial blood pressure is tightly regulated to ensure adequate flow of blood to
tissues while avoiding the harmful effects of high pressures on the vasculature and
end-organs.
Mean arterial pressure is normally between 65-100 mmHg, with normal systolic and
diastolic blood pressures between 120-140 mmHg and 70-90mmHg respectively.
Maintaining homeostasis relies on factors affecting MAP, namely systemic vascular
resistance(SVR) and cardiac output (CO).
5. CardiacOutput
•Volume of blood flow through the ventricles
•Can be calculated by stroke volume multiplied by the heart rate.
•Any factors that causes heart rate or stroke volume or both will elevate blood
pressure.
•These factors include sympathetic stimulation, catecholamines (adrenaline and
noradrenaline), thyroid hormones and increased calcium ion levels.
6. Preload, afterload and contractility are major considerations influencing stroke
volume.
An increase in volume or speed of venous return will increase preload and through
the of the Frank-Starling law of the heart, will increase stroke volume.
Elevated afterload (Commonly measured as aortic pressure during systole) reduces
stroke volume by hindering the ventricles in ejecting blood. SV can be increased by
decreasing vascular resistance and end systolic volume.
7. Inotropic therapy is generally considered in states of shock, acute heart failure or
acute exacerbation of chronic heart failure.
Expected to benefit by pharmacological augmentation of myocardial contractility
and cardiac output.
9. Physiology basis for actions of inotropic agents
•Inotropic agents prolong the plateau phase of action potential of myofilament, by
increasing the release of ionized calcium from the sarcoplasmic reticulum.
•As a effect, myocardial contractility is increased. Stretched myofilament is also more
sensitive to Ca2+, a mechanism used by certain novel inotropic drugs.
12. Epinephrine( Adrenaline)
• Potent β-1, moderate α-1 and β-2.
• Low dose - β-1 chronotrope and inotrope
- increased CO, decreased SVR, increased MAP and coronary blood flow
• β-2 – Vasodilation, bronchondilation
• High dose - α-1 effect increases
- increased SVR and Rt ventricular afterload
• Gross cardiovascular effects – adrenaline increases myocardial oxygen demand
• Hepatic oxygen consumption and hepato-splanchnic blood flow increases.
• Other metabolic effects include increased plasma glucose and lactate concentrations
• Increase in serum lactate induced by exogenous catecholamines appears harmless.
13. Uses
• Hypotension – 1 to 70 ug/min
• Cardiac arrest – 1-3 mg every 2-3 min during resuscitation
• Anaphylaxis – 0.3-1mg IM or subcutaneous
• Children – 10ug/kg for cardiac arrest every 5 min if necessary,and subcutaneous in
severe anaphylaxis or asthma repeated at 20 min to 4 hrs.
15. Norepinephrine(Noradrenaline)
• potent arteriolar and venous vasoconstrictor, acting predominantly at α-receptors,
with a slightly greater potency there than adrenaline.
• β-receptor agonist, but β2 effects are not apparent in clinical use.
• NAD increases venous return, systolic and diastolic, systemic and pulmonary arterial
pressures and central venous pressure.
• CO increases alongside a baroreceptor-mediated reflex bradycardia.
• At higher doses, α mediated intense vasoconstriction decreased CO and
increases myocardial oxygen demand
• Decreased renal blood flow and glomerular filtration rate
• Used in the management of low SVR states such as septic shock and after cardiac
bypass.
• Dose- 0.1–1 µg/kg/min.
16. Dobutamine
• Synthetic derivative of isoprenaline
• β-1 agonist with some activity at β-2 receptors
• Primary effect is an increase in CO as a consequence of increased contractility and HR
and decreased afterload.
• Increases SA node automaticity and conduction velocity in the atria, ventricles and
AV node, with tachyarrhythmias occurring at higher doses.
• A good choice in the short-termed treatment of severe heart failure and cardiogenic
shock and usually added after a vasoconstrictor agent.
• Infusion dose range -- 0.5 to 40 ug/kg/min
17. Dopamine
• Natural precursor of adrenaline and noradrenaline
• Classified as D-1 and D-2
• D-1 receptors mediates vasodilation in kidney, intestine and heart
• D2- antiemetic action of droperidol
• Overall effects of dopamine are highly dose-dependent
19. Ephedrine
• Both direct (agonist at α- and β-receptors) and indirect activity via its potentiation of
noradrenaline release from sympathetic nerve terminals.
• Causes an increase in HR, contractility, CO and arterial pressure (systolic > diastolic)
• Brondilatory effect by β2 mediated mechanism.
• Agent of choice for hypotension induced by spinal or epidural anaesthesia.
• Tachyphylaxis can occur.
• Increases myocardial oxygen demand and requires caution in patients with ischaemic
heart disease or heart failure.
• contraindicated in patients with acute hypertension or tachycardia.
• Dose – IV bolus of 3-9mg.
20. Phenylephrine
• α1 adrenergic agonist and minimal or no β-adrenergic activity.
• Optimal choice for raising MAP by inducing vasoconstriction in both veins and
arteries and causes reflex bradycardia and decrease in cardiac output
•Used for maintaining arterial pressure during general anaesthesia or other causes of
low SVR (eg. Septic and anaphylactic shock)
• Preferred vasopressor for hypotension associated with spinal anaesthesia in obstetric
patients (Mercier et al, 2013)
• Can be topically used as nasal decongestant or mydriatic.
• Dose – IV bolus (50–100 µg) and IV infusion (50–150 µg/min ).
21. Phosphodiesterase inhibitors (Milrinone, Amrinone)
• Bipyridine group chemical
• Phosphodiesterase (PDE) III inhibitors- inotropic and vasodilatory
• Indicated for acute refractory heart failure, such as cardiogenic shock, pre or post
cardiac surgery.
• Limitations in sepsis due to vasodilatation
• An acetyl metabolite of amrinone i.e N- acetyl-amrinone is known to cause
thrombocytopenia. Thus, milrinone is more commonly used than amrinone.
• Cardiovascular effect of milrinone is comparable to that of dobutamine.
• Increased heart rate is less and decreased vascular resistance is less as compared to
that of dobutamine.
22. • Milrinone has important action on pulmonary vasculature.
• It reduces pulmonary vascular resistance and thereby, decreased pulmonary artery
pressure without much increase in myocardial oxygen demand.
• This effect may be seen by compensation by preload and afterload reductions,
leading to decreased ventricular wall stress.
• It also has important lusitropic effect which causes relaxation of left ventricle,
thereby decreasing RV afterload.
• Dose- 0.37 to 0.75 ug/kg/min.
23.
24. Levosimendan (Calcium sensitizer)
•Positive inotropic agent
•Acts by sensitizing troponin C to Ca , prolonging actin-myosin cross bridge formation
and thus increasing contractility.
•Energy-independent process and therefore does not increase myocardial oxygen
demand.
•As a consequence, appears to be free of serious arrhythmogenic effects in patients
with cardiac failure.
• Vasodilatory effect by opening ATP-sensitive K+ channels in vascular smooth muscle,
reducing pre- and afterload and improving myocardial oxygen supply.
•Have a role in management in acute heart failure and post resuscitation myocardial
dysfunction.
•Dose – 0.05 to 0.2ug/kg/min
25.
26. Omencamtiv Mecarbil (Cardiac Myosin Activator)
• A novel selective cardiac myosin activator
• Direct activation of sarcomere proteins resulting in increased cardiac contractility
and prolonged systolic ejection time.
• It accelerates the transition rate of the myosin from the weakly bound to the
strongly bound, force generating state, and thus increases cardiac contractility
• Increases systolic ejection time, stroke volume and fractional shortening to improve
haemodynamics
• Does not increase intracellular cAMP and calcium therefore, would not result in
increased myocardial oxygen consumption and heart rate, decreasing risk of
arrhythmias.
27. Vasopressors (Vasopressin)
• Nanopeptide produced by hypothalamus and released by posterior pituitary
• aka antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin
• 3 receptors
- V1 – G protein coupled – vasoconstriction
- V2 – aquaporins insertion in renal tubules, release vWF and factor VIII
- V3 – anterior pituitary release of ACTH and endorphins
28. MOA
•It increases the amount of solute-free water reabsorbed back into the circulation
from the filrate in the kidney tubules of the nephrons.
•AVP constricts arterioles, which increases peripheral vascular resistance and raises
arterial blood pressure.
•Short half-life, between 16-24 minutes
•Widely distributed throughout the body and remains in the extracellular fluid. It is
degraded by the liver and excreted through the kidneys.
•Used as second line therapy for septic shock.
•Dose infusion rate – 0.01-0.1 units/min.
