How is the passive leg raise (PLR) test performed and interpreted to assess fluid responsiveness in critically ill, mechanically ventilated or septic patients with uncertain volume status?

Passive Leg Raise Test for Fluid Responsiveness

Direct Answer

The passive leg raise (PLR) test is a reversible, endogenous fluid challenge that mobilizes approximately 300 mL of blood from the lower extremities to the thorax, and should be used as a superior alternative to static measurements like CVP for predicting fluid responsiveness in critically ill patients. 1, 2

Physiological Mechanism

The PLR functions by:

• Mobilizing approximately 300 mL of blood volume from the lower extremities and splanchnic circulation to the central compartment 2, 3
• Creating a reversible preload challenge without actually administering fluid, making it ideal when you want to test responsiveness before committing to volume expansion 2, 4
• Producing hemodynamic effects within seconds, allowing real-time assessment of cardiac preload dependence 5

How to Perform the PLR Test

Patient Positioning Sequence

1. Start with the patient semi-recumbent (head of bed elevated 30-45 degrees) and obtain baseline measurements 2, 5
2. Lower the head of the bed to flat while simultaneously raising the legs to 45 degrees 2
3. Maintain this position for 60-90 seconds while continuously monitoring hemodynamic parameters 5, 6
4. Return the patient to the semi-recumbent position after measurements are complete 7

Critical Technical Points

• The maneuver must be passive—do not have the patient actively lift their legs 2
• Measurements should be taken continuously during the PLR, not just at the end, as peak effects occur within 30-60 seconds 5
• The test is reversible, so hemodynamic changes should normalize when returning to baseline position 7

How to Interpret the PLR Test

Gold Standard Measurement Methods

Cardiac output or stroke volume monitoring is required for accurate interpretation—clinical parameters alone are insufficient. 2, 4

The most validated approaches include:

• Echocardiographic measurement of left ventricular outflow tract velocity-time integral (LVOT VTI): An increase ≥10-15% predicts fluid responsiveness with high accuracy 2, 5, 6
• Stroke volume index (SVI) increase ≥8.1% predicts fluid response with 92% sensitivity and 70% specificity 3
• Right ventricular outflow tract VTI (RVOT VTI) from subcostal view: An increase ≥15.36% predicts fluid responsiveness with 85.7% sensitivity and 93.1% specificity, useful when apical windows are difficult 5

Alternative Monitoring Methods

• Pulse contour cardiac output monitoring can be used if available 7
• Carotid flow VTI: An increase >11% has 77.3% sensitivity and 78.6% specificity, though correlation with cardiac output changes is weaker than direct cardiac measurements 6
• Thoracic electrical bioimpedance (TEB): Shows moderate correlation (r=0.47) with fluid responsiveness but has limited accuracy (sensitivity 41%, specificity 80%) 4

What Constitutes a Positive Test

A positive PLR test (indicating the patient will respond to fluid administration) is defined as:

• ≥10-15% increase in stroke volume or cardiac output 2, 3, 5
• ≥15% increase in LVOT VTI or RVOT VTI 5, 6

Diagnostic Performance

The PLR test demonstrates superior accuracy compared to static measurements: 1, 2

• Positive likelihood ratio of 11 (95% CI 7.6-17) 2, 3
• Pooled specificity of 92% 2, 3
• Significantly better than CVP, which has <50% positive predictive value 1, 8

For comparison, pulse pressure variation in mechanically ventilated septic patients has sensitivity of 0.72 and specificity of 0.91, making PLR a reasonable alternative when pulse pressure variation cannot be used. 1

Clinical Integration Algorithm

When to Use PLR

Use PLR after the initial 30 mL/kg crystalloid bolus in sepsis/septic shock to determine if additional fluid is needed: 1, 2, 3

1. Administer initial 30 mL/kg crystalloid within first 3 hours for sepsis-induced hypoperfusion 1, 2, 3
2. Reassess clinical perfusion parameters: capillary refill, skin temperature and mottling, mental status, urine output, lactate 1, 8
3. If perfusion remains inadequate and volume status is uncertain, perform PLR test with cardiac output monitoring 2
4. If PLR positive (≥10-15% increase in stroke volume): Administer fluid bolus of 250-1000 mL in adults 2
5. If PLR negative: Consider vasopressors or inotropes rather than additional fluid 2
6. Reassess after each intervention and repeat PLR if needed 2

Critical Limitations and Pitfalls

When PLR is Unreliable

Do not rely on PLR in these situations: 3

• Intra-abdominal hypertension or abdominal compartment syndrome—the test cannot predict fluid responsiveness in these conditions 1, 3
• Atrial fibrillation or other arrhythmias—beat-to-beat variability confounds measurements 3
• Spontaneous breathing or low-level pressure support—respiratory effort affects venous return unpredictably 3

Common Measurement Errors

• Using clinical parameters alone (heart rate, blood pressure) to interpret PLR is inadequate—these showed no better predictive ability than chance in research studies 4
• Measuring only at a single time point rather than continuously—peak hemodynamic effects occur within 30-60 seconds and may be missed 5
• Using carotid flow parameters as a surrogate—while showing moderate baseline correlation with cardiac output (r=0.60), changes during PLR correlate poorly (r=0.05) with actual fluid responsiveness 9

Avoiding Fluid Overload

• A negative PLR test helps avoid unnecessary fluid administration that can lead to pulmonary edema and other complications 3
• Static measurements like CVP should never be used alone to guide fluid decisions, as they may lead to inappropriate fluid administration or under-resuscitation 1, 8
• In mechanically ventilated patients, using CVP to direct fluid may cause under-resuscitation with resultant organ dysfunction and increased mortality 8

Practical Considerations in Resource-Limited Settings

PLR is particularly valuable when advanced monitoring is unavailable: 2

• Requires no equipment beyond basic monitoring if using clinical assessment 2
• Can be performed at bedside without specialized training once technique is mastered 2
• However, objective measurement of cardiac output or stroke volume is still necessary for accurate interpretation—clinical parameters alone are insufficient 4, 9

If echocardiography is unavailable, focus on clinical perfusion parameters (capillary refill, skin temperature, mental status, urine output, lactate) to guide ongoing resuscitation rather than attempting PLR interpretation without objective measurements. 8