Circulatory Support and Vasoactive Medications

Circulatory support encompasses the interventions used to restore adequate tissue perfusion when circulation fails, as in shock. Beyond fluid resuscitation, it relies on vasoactive medications — drugs that act on the blood vessels and heart to raise blood pressure, increase cardiac output, or both — and represents the 'circulation' component of the ABC framework.

Definition

Circulatory support is the use of fluids and vasoactive medications, guided by haemodynamic assessment, to restore and maintain blood pressure and cardiac output sufficient for tissue perfusion in patients with circulatory failure.

Scope

The topic covers the goal of restoring perfusion, the broad classes of vasoactive agents (vasopressors, inotropes, and vasodilators) and how they differ in action, and the principles of haemodynamic monitoring that guide their use. The nurse's role in titration and surveillance is framed as reference knowledge, without dosing or prescribing guidance.

Core questions

• What distinguishes failure of perfusion (shock) from low blood pressure alone?
• How do vasopressors, inotropes, and vasodilators differ in what they correct?
• How is haemodynamic monitoring used to guide circulatory support?
• Why are these medications titrated and closely monitored?

Key concepts

• Shock and tissue hypoperfusion
• Vasopressors (increase vascular tone)
• Inotropes (increase contractility)
• Vasodilators (reduce afterload or preload)
• Mean arterial pressure and cardiac output
• Haemodynamic monitoring
• Titration to a perfusion target

Mechanisms

Tissue perfusion depends on cardiac output and vascular tone, which together set arterial pressure and flow. Vasopressors act mainly on vascular smooth muscle to raise systemic vascular resistance and blood pressure; inotropes increase the force of cardiac contraction and so cardiac output; and vasodilators relax vessels to reduce the resistance the heart pumps against or the venous return, which can help failing hearts or hypertensive emergencies. Because these agents are potent and short-acting, they are infused continuously and titrated against haemodynamic targets such as mean arterial pressure and indicators of perfusion, with the choice of agent matched to the type of circulatory failure.

Clinical relevance

Vasoactive infusions are a defining feature of intensive-care and emergency management of shock, and nurses titrate them and monitor the patient's haemodynamic and perfusion response. This entry describes the classes and principles as reference material and provides no dosing, drug selection, or treatment instructions for an individual patient.

Epidemiology

Shock states, including septic, cardiogenic, hypovolaemic, and obstructive shock, are common in critical care and carry high mortality, and the choice and management of vasoactive support is a major determinant of intensive-care practice.

History

The pharmacologic support of circulation developed alongside intensive care in the twentieth century, as catecholamines and related agents were characterized and invasive haemodynamic monitoring made titration possible. Comparative trials in the twenty-first century, such as the comparison of dopamine and noradrenaline in shock, refined the choice of first-line vasopressor and shifted practice toward agents with more favourable safety profiles.

Debates

Which vasopressor should be first-line in shock?

A large randomized comparison found similar overall mortality between dopamine and noradrenaline but more arrhythmias with dopamine and worse outcomes in some subgroups, supporting noradrenaline as the usual first-line agent in many forms of shock.

Seminal works

• de-backer-2010

Frequently asked questions

What is the difference between a vasopressor and an inotrope?

A vasopressor mainly tightens blood vessels to raise blood pressure by increasing vascular resistance, whereas an inotrope mainly increases the force of the heart's contraction to raise cardiac output; some agents have both effects.

Why are vasoactive drugs given as continuous infusions?

They are potent and very short-acting, so continuous infusion allows the dose to be titrated up or down against haemodynamic targets and stopped quickly if needed.