Haemodynamic monitoring in general terms: MAP, CVP, cardiac output, preload, afterload and perfusion signs
- Fundamental
Haemodynamic monitoring tracks pressure, blood flow and tissue perfusion, so the ICU team can see whether the circulation is meeting the body's needs.
What it is
Haemodynamic monitoring brings together three kinds of information. Pressures (arterial pressure and its mean, central venous pressure) are read from transducers. Flow (cardiac output and cardiac index) comes from specialised monitors. Perfusion is judged at the bedside from capillary refill, skin mottling, mental status, urine output and lactate. The ICU nurse keeps the measuring system accurate (levelled, zeroed, with a clean waveform), reads trends rather than single numbers, and links every value to what the patient looks like. A normal pressure does not prove that tissues are well perfused, and no number replaces looking at the patient. The physiology behind preload, afterload and oxygen delivery is explained in the linked Physiology pages.
Key points
- Preload is the stretch of the ventricle at the end of filling; it depends on venous return.
- Afterload is the load the ventricle pumps against; for the left ventricle it is mainly systemic vascular resistance.
- Contractility is the heart's own pumping strength, independent of preload and afterload.
- Blood pressure = cardiac output × systemic vascular resistance, so a normal pressure can hide a low flow.
- Cardiac index is cardiac output divided by body surface area; a range of about 2.5 to 3.5 L/min/m² is generally considered normal.
- Oxygen delivery to the tissues depends on cardiac output and on the oxygen content of arterial blood.
Components
- Pressure: invasive arterial pressure (beat by beat) and central venous pressure, through a fluid-filled line and a transducer.
- Flow: cardiac output and cardiac index from specialised monitors, and dynamic tests such as passive leg raising.
- Perfusion at the bedside: capillary refill, mottling, skin temperature, mental status and urine output.
- Perfusion in the laboratory: lactate and, when a central line is in place, central venous oxygen saturation.
What it is for
- Spotting shock and tissue hypoperfusion early, before the blood pressure falls.
- Guiding fluids, vasopressors and inotropes towards the goals set by the medical team.
- Showing the response to each treatment: what changed after a fluid challenge, a dose change or a position change.
In nursing practice
- Read every number against the patient: skin, refill time, mental status and urine output change before many monitors do.
- Record values with the time, the position of the patient and what was running, so the trend can be compared.
- Report a change in trend, not only a value outside the alarm limits: a slowly rising heart rate with falling urine output matters.
- Before a reading, check that the transducer is levelled and zeroed and that the waveform is clean (see the arterial line and CVP pages).
- Altered mental status, breathlessness, chest pain, cold extremities, slow capillary refill and low urine output are bedside signs of poor flow.
Common mistakes
- Treating one number (for example the blood pressure) while the perfusion signs get worse.
- Reading a pressure from a transducer that was not levelled or zeroed after the patient was moved.
- Comparing values taken in different positions or with different equipment as if they were the same trend.
- Ignoring a damped or noisy waveform and recording the number it shows.
- Taking a normal lactate as proof that the circulation is fine.
Test yourself
Think of the answer, then tap the question to see it.
What are the three things that determine stroke volume?
Preload (ventricular filling), afterload (the load the ventricle pumps against) and contractility (the heart's own pumping strength).
Why can a patient have a normal blood pressure and still have poor perfusion?
Blood pressure equals cardiac output times vascular resistance: intense vasoconstriction can keep the pressure up while flow to the tissues is low.
Which bedside signs suggest poor perfusion?
Capillary refill over 3 seconds, skin mottling, cold extremities, new confusion and low urine output, together with a rising lactate.
Can central venous pressure alone predict whether a patient will respond to fluid?
No. Studies show it cannot; it is read as a trend and together with the rest of the assessment and dynamic tests.
Elsewhere in DurgiPedia
Connections
Educational content for students; it does not replace your institution's protocols, supervised clinical training or a prescriber's order. Dose-calculation examples use made-up numbers: they are educational, not a clinical order.
Sources: Foundations and Advancements in Hemodynamic Monitoring: Part I - Elements of Hemodynamics (Demir ZA et al., Turk J Anaesthesiol Reanim 2025;53(3):87-97) (Turkish Journal of Anaesthesiology and Reanimation, open access in PubMed Central, 2025); Hemodynamic monitoring: basic principles in operation room and intensive care unit (Mirus M, Saugel B, Spieth PM, J Clin Monit Comput 2026;40(2):375-389) (Journal of Clinical Monitoring and Computing, open access in PubMed Central, 2026); Fluid administration for acute circulatory dysfunction using basic monitoring (Messina A, Collino F, Cecconi M, Ann Transl Med 2020;8(12):788) (Annals of Translational Medicine, open access in PubMed Central, 2020); Surviving Sepsis Campaign: international guidelines for management of sepsis and septic shock 2021 (Evans L et al., Intensive Care Med 2021;47:1181-1247) (Society of Critical Care Medicine and European Society of Intensive Care Medicine, open access in PubMed Central, 2021).
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Representative model, for educational purposes only.