Vasopressor and Inotrope Mechanisms and Clinical Principles

Vasopressor Mechanisms

The α1-mediated peripheral vasoconstriction caused by norepinephrine is the dominant effect, redistributing blood flow from extremities to vital organs, in patients with shock states 1
Dopamine has dose-dependent effects, with low doses (<3 μg/kg/min) acting on δ-receptors, moderate doses (3-5 μg/kg/min) having β-adrenergic inotropic effects, and high doses (>5 μg/kg/min) having α-adrenergic vasopressor effects, in patients with cardiogenic shock 1
Dopamine is associated with increased mortality and more arrhythmic events compared to norepinephrine in cardiogenic shock patients, according to the European Society of Cardiology 2

Dobutamine stimulates β1-receptors to increase cardiac contractility while also relaxing vascular smooth muscle to reduce afterload, but causes severe hypotension due to its vasodilatory effects, limiting its use in hypotensive patients, as recommended by the American Heart Association 2, 3
Milrinone increases intracellular calcium levels, enhancing myocardial contractility and cardiomyocyte relaxation through phosphodiesterase-3 inhibition, but causes both arterial and venous vasodilation, which reduces preload and afterload but can lead to hypotension, according to the American College of Cardiology 2, 3
Levosimendan acts as an inodilator with a unique mechanism distinct from traditional inotropes, and the SURVIVE study showed reduced mortality in cardiogenic shock patients receiving levosimendan compared to dobutamine, as reported by the European Society of Intensive Care Medicine 2, 3

The latest recommendations suggest a mean arterial pressure objective of 65 mmHg, though this may need individualization based on baseline blood pressure and comorbidities, according to the Society of Critical Care Medicine 2
Inotropes cause sinus tachycardia, may induce myocardial ischemia and arrhythmias, and carry long-standing concerns about increased mortality, as warned by the American Heart Association 1
In critically ill pulmonary hypertension patients, replacement-dose vasopressin can offset the SVR drop from dobutamine, as suggested by the European Respiratory Society 4

The American College of Cardiology and other guideline societies recommend the use of vasopressors to increase mean arterial pressure by augmenting vascular tone, which is critical when hypotension threatens organ perfusion 5
The European Society of Cardiology states that inotropes enhance cardiac output through improved contractility, with dobutamine providing direct beta-1 adrenergic receptor stimulation 5, 6

The American Heart Association recommends the use of phenylephrine, an alpha-1 agonist, to increase systemic vascular resistance without cardiac stimulation 7
The European Heart Journal suggests that epinephrine, with strong alpha and beta effects, can be used as both a vasopressor and an inotrope 6

The Surviving Sepsis Campaign recommends the use of norepinephrine as the preferred first-line vasopressor for septic shock and most hypotensive emergencies, with a lower risk of adverse events than other catecholamines 5
The American College of Cardiology recommends that vasopressors should never be used before correcting hypovolemia, as uncorrected hypovolemia is an absolute contraindication 8

The European Society of Intensive Care Medicine recommends ensuring adequate fluid resuscitation before starting vasopressors, and using norepinephrine as the first-line vasopressor to achieve a mean arterial pressure of at least 65 mmHg 5, 8
The American Heart Association suggests that dobutamine can be added if tissue perfusion remains inadequate despite adequate mean arterial pressure and cardiac output is insufficient 5

The European Heart Journal warns that high-dose dopamine can cause tachyarrhythmias, and that uncorrected hypovolemia is an absolute contraindication for all vasopressors and inotropes 6, 8
The American College of Cardiology recommends continuous monitoring of patients receiving vasoactive agents, including ECG monitoring, arterial blood pressure monitoring, and tissue perfusion assessment 8, 9