Passive Leg Raise Cardiac Output Change: Clinical Guide

Overview

Calculates percentage change in cardiac output or stroke volume during a passive leg raise. The calculator is intended to make the underlying equation transparent while preserving the requirement for clinical assessment and source-data verification.

Clinical Significance

A reproducible increase in measured flow during a correctly performed passive leg raise suggests preload responsiveness. Thresholds depend on monitoring method and test quality.

When to Use

• Assess reversible preload responsiveness without administering fluid.
• Use a rapid-response flow measure such as cardiac output, stroke volume or validated surrogate.
• Perform the manoeuvre from a semi-recumbent position using standard technique.

How It Is Calculated

• Percentage change = (PLR value − baseline value) ÷ baseline value × 100.
• MedicalC validates required values, applies the stated equation and rounds only the displayed result.
• Review intermediate measurements and assumptions whenever the result appears discordant with the clinical picture.

Interpretation

• A reproducible increase in measured flow during a correctly performed passive leg raise suggests preload responsiveness. Thresholds depend on monitoring method and test quality.
• Interpret trends only when the same technique, units and clinical conditions are reasonably comparable.

Worked Example

Enter the required measurements in the displayed units. MedicalC applies: Percentage change = (PLR value − baseline value) ÷ baseline value × 100. Confirm the result against the original observations before using it in a clinical decision.

Patient Considerations

• Consider age, body size, pregnancy, organ support, medication, rhythm, ventilation, measurement conditions and acute physiological change where relevant.
• Use the earliest reliable values for prognostic trauma scores unless the score definition specifies otherwise.
• Repeat calculations only when a changed result could influence care and the source data remain valid.

Limitations

• Blood pressure alone is an insensitive response measure.
• Intra-abdominal hypertension, compression stockings, pain and poor positioning can impair the test.
• Preload responsiveness does not establish that fluids are clinically indicated.

Clinical Pearls

• Treat the calculator as a transparent equation, not an autonomous recommendation.
• Record the exact time and method of important measurements.
• Resolve a clinically implausible result by checking inputs before assuming unusual physiology.

Common Mistakes

• Entering values in the wrong unit.
• Combining measurements obtained at different clinical time points.
• Applying a published threshold outside its validated population or setting.
• Allowing a score to delay urgent treatment.

Evidence Base

The calculator implements the stated published or established relationship. Principal source: Monnet X, Teboul JL. Passive leg raising: five rules, not a drop of fluid. Crit Care. 2015.

References

1. Monnet X, Teboul JL. Passive leg raising: five rules, not a drop of fluid. Crit Care. 2015. — Primary publication, authoritative guideline or recognised specialty source.