Words By Glenn Ryan
Vasopressor and Inotrope agents are often used in the management of cardiogenic shock (CS). Vasopressors are recommended as a first line management for CS patients who are unresponsive to fluids. Vasopressors MOA is to encourage vasoconstriction resulting in an increase in mean arterial pressure (MAP), allowing for improved organ and tissue perfusion. Vasopressors are also considered as having a lower risk profile then inotropic agent which is why they are regarded as first line management agents.
The MOA of inotropes is to increase cardiac output through the increase inmyocardial contractility, however can also result in a decrease in myocardial contractility due to its oxygen consumption requirements producing adverse events such as ventricular arrhythmias, increase in infarct size leading to myocardial necrosis.
A naturally occurring catecholamine and acts mainly onα-adrenergic receptor but has small effect on beta receptor. Norepinephrine isprimarily used to increase BP by constricting small vessels. This increase in BP aims to stimulate the parasympathetic system tone, with little change in heart rate or cardiac output. Norepinephrine has adverse effects of reducing renal and splanchnic blood flow which can be problematic in patients needing volume expansion. Norepinephrine is associated with fewer arrhythmias in comparison to other vasopressors which is why it’s considered the vasopressor of choice in patients with CS.
like norepinephrine, Epinephrine is a naturally occurring catecholamine, however epinephrine acts on both α- and β-receptor. In small doses Epinephrine has predominantly β-adrenergic effects which increases myocardial contraction and heart rate. However, in higher dosage, it acts on α-adrenergic receptor and increases small vessels peripheral constricts which can increase BP. Epinephrine is associated with increased rick of arrhythmia and decreases splanchnic blood flow. There have been no beneficial effects of epinephrine over norepinephrine in septic shock studies. Which could explain epinephrine being regarded as a second-line agent for severe cardiogenic shock.
Dobutamine is considered as the first-line inotrope for managing cardiogenic shock (Levy et al., 2019). This positive inotrope increases cardiac output, increases heart rate and stroke volume.Dobutamine acts on the myocardium, stimulating β1-adrenergic receptors, increasing heart rate and increasing myocardial contractility force. This agent also acts on smooth muscle via β2 receptors to induce system vasodilation and lower blood pressure. When given in combination with norepinephrine can improve cardiac contractility improving capillary perfusion in patients with septic shock. However, in CS patients dobutamine is less likely to see tachycardia than agents such as isoproterenol. Its limited effects on MAP, although in patients with myocardial dysfunction or underlying hypovolemia pressure may increase slightly.
Dopamine is a natural precursor of norepinephrine andepinephrine. Its effects on patients are often dose-dependent. At low doses(1–2 μg/kg/min), it binds to dopaminergic receptors and has a vasodilatory effect. At higher doses (5–10 μg/kg/min), it acts as a β1 receptor agonist and thus has inotropic effects. At levels above (>10 μg/kg/min), dopamine stimulates α-adrenergic receptors, leading to vasoconstriction and an increase in BP.
Amado, J., Gago, P., Santos, W., Mimoso, J., & de Jesus, I.(2016). Cardiogenic shock: Inotropes and vasopressors. RevistaPortuguesa de Cardiologia (English Edition), 35(12),681–695. https://doi.org/10.1016/j.repce.2016.08.004
Manaker,S. (2020). Use of vasopressors and inotropes. UpToDate. https://www-uptodate-com.ezproxy.csu.edu.au/contents/use-of-vasopressors-and-inotropes?search=inotropic%20vs%20vasopressors&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1