What is the purpose and interpretation of the passive leg rising (PLR) test in assessing volume responsiveness in patients?

Passive Leg Raising Test: Purpose and Interpretation

The passive leg raising (PLR) test is a bedside maneuver that predicts fluid responsiveness by mobilizing approximately 300 mL of blood from the lower extremities to the thorax, functioning as a reversible endogenous fluid challenge without actually administering fluid. 1, 2

Purpose of the PLR Test

The PLR test serves as a dynamic assessment tool to determine which critically ill patients will benefit from fluid administration, addressing a fundamental limitation of static measurements like central venous pressure that cannot reliably predict fluid responsiveness. 1, 3

Key Advantages

• No equipment required beyond basic monitoring, making it ideal for resource-limited settings where advanced hemodynamic monitoring is unavailable 2
• Reversible challenge that avoids the risks of unnecessary fluid administration, including pulmonary edema and increased mortality from fluid overload 1, 3
• Superior diagnostic accuracy compared to static measurements, with a positive likelihood ratio of 11 (95% CI 7.6-17) and pooled specificity of 92% 2, 3

How to Perform the PLR Test

Start with the patient in a semi-recumbent position (trunk elevated at 45°), then move to PLR position with lower limbs elevated at 45° and trunk in the supine position. 4, 5

• The maneuver should be maintained for at least 1-5 minutes to allow adequate hemodynamic response 1
• Assess hemodynamic parameters before and during the PLR maneuver 2

Interpretation Criteria

An increase in stroke volume of more than 12% during PLR predicts fluid responsiveness with high accuracy. 1

Specific Thresholds by Measurement Method

• Aortic blood flow (via esophageal Doppler): ≥10% increase predicts fluid responsiveness with 97% sensitivity and 94% specificity 4
• Stroke volume index: ≥8.1% increase predicts fluid response with 92% sensitivity and 70% specificity 3
• Carotid flow velocity-time integral: ≥11% increase predicts fluid responsiveness with 77.3% sensitivity and 78.6% specificity 6

Clinical Parameters to Assess

When advanced monitoring is unavailable, evaluate these clinical markers before and during PLR 2:

• Blood pressure changes (mean arterial pressure)
• Heart rate response
• Capillary refill time improvement
• Skin perfusion and temperature
• Mental status changes
• Urine output trends

Critical Limitations and When NOT to Use PLR

The PLR test is unreliable and should not be used in patients with intra-abdominal hypertension or abdominal compartment syndrome. 1, 3

Other Contraindications and Limitations

• Atrial fibrillation or other arrhythmias reduce predictive accuracy 3, 4
• Spontaneous breathing efforts or low-level pressure support invalidate results, as respiratory variation of pulse pressure shows poor specificity (46%) in these patients 3, 4
• Head injury or increased intracranial pressure where head-down positioning is contraindicated 1
• Severe right ventricular dysfunction may produce false-positive results 7

Optimal Conditions for Valid PLR Testing

• Patient must be passively mechanically ventilated with no spontaneous breathing 4
• Regular cardiac rhythm (sinus rhythm) 1
• Tidal volume of 8 mL/kg ideal body weight in volume-control mode 1
• No ventilator dyssynchrony 1

Clinical Algorithm for Implementation

When encountering a hypotensive patient with uncertain volume status, perform the following sequence: 2

1. Identify signs of tissue hypoperfusion (altered mental status, decreased urine output, elevated lactate, poor capillary refill)
2. Assess for PLR contraindications (intra-abdominal hypertension, arrhythmias, spontaneous breathing, increased ICP)
3. Perform PLR test if no contraindications exist
4. Measure hemodynamic response using available monitoring (stroke volume, cardiac output, or clinical parameters)
5. Interpret results:
   • If positive (≥10-12% increase in stroke volume): Administer fluid bolus (30 mL/kg crystalloid for sepsis) 2, 3
   • If negative: Consider vasopressors or inotropes instead of fluids 2
6. Reassess after intervention and repeat PLR if additional fluid administration is being considered 2

Common Pitfalls to Avoid

• Do not rely on pulse pressure variation during PLR as it has significantly lower sensitivity (60%) and specificity (85%) compared to direct stroke volume measurement 4
• Do not use PLR in spontaneously breathing patients without recognizing the high false-positive rate 4
• Do not delay obvious fluid resuscitation in patients with clear signs of hypovolemia to perform PLR testing—clinical judgment supersedes any single test 1
• Do not assume PLR predicts long-term fluid needs—the effects are transient, with improvements in cardiac output disappearing by 7 minutes in some studies 1

Alternative When PLR Cannot Be Performed

The Trendelenburg position (15° downward bed angulation from reverse Trendelenburg) represents a reasonable alternative to PLR, with similar predictive performance for volume responsiveness. 5

• TRENDrTREND-induced change in stroke volume index ≥13% predicts fluid responsiveness with 87% sensitivity and 76% specificity 5
• This may be preferable when leg elevation is contraindicated or impractical 5