Cardiac power output

CPO · Derived: CPO (W) = MAP × CO / 451

Normal range & thresholds

Resting CPO ≈0.8–1.0 W in healthy adults. CPO <0.6 W marks a critically low hydraulic output; in the SHOCK trial registry CPO was the strongest independent haemodynamic correlate of in-hospital mortality (threshold ≈0.53 W) ^[114].

Pathophysiology

Power is flow × pressure — the rate at which the heart does hydraulic work. A low CO with a high MAP (vasoconstriction) and a normal CO with a low MAP (vasodilation) can have the same CO or the same MAP but different power; CPO integrates both and reflects the reserve the ventricle has left ^[114].

Raised by

• Exercise and inotropes (a rise with dobutamine = contractile reserve)
• Hyperdynamic hypertensive states

Lowered by

• Cardiogenic shock, advanced heart failure
• Profound vasodilation with a failing ventricle
• Tamponade and massive PE (obstructive)

Technique & pitfalls

• Use the best MAP available (arterial line) and an averaged CO; report both inputs with the result.
• Echo CO in the ICU is acceptably accurate when LVOT technique is strict ^[170].

Pseudo-change & artefact

• Inherits every error of CO (LVOT diameter squared) and MAP.
• Mechanical circulatory support: device flow is not measured by LVOT VTI — do not calculate native CPO without accounting for it.

Treatment thresholds

• SCAI SHOCK staging and escalation — CPO <0.6 W with hypoperfusion supports escalation of inotropic or mechanical circulatory support in cardiogenic shock ^[154].
• Echo-derived haemodynamics at CICU admission, including SVI and CPO, independently predict in-hospital death ^[190].

Next step

• Next: find the mechanism (LV, RV, valve, mechanical complication, tamponade).
• Then: reassess after each intervention; a rising CPO is a treatment response.

Drugs

Inotropes and vasopressors raise it acutely; inappropriate vasodilators or negative inotropes lower it.

Reversibility

Tracks the underlying state — improves with recovery from stunning, revascularisation, relief of tamponade or PE.