How is fluid responsiveness assessed in patients with hypotension using the passive leg raise (PLR) test?

Assessing Fluid Responsiveness Using the Passive Leg Raise Test

The passive leg raise (PLR) test is a highly effective method for assessing fluid responsiveness in hypotensive patients, with an increase in cardiac output after PLR strongly predicting fluid responsiveness with a positive likelihood ratio of 11 and a specificity of 92%. 1

Proper Technique for PLR Test

Starting Position and Execution

• Start with patient in 45° semi-recumbent position (preferred method)
• Lower the head of the bed to flat position while simultaneously raising the legs to 45°
• Maintain this position for 30-60 seconds while monitoring hemodynamic response
• The semi-recumbent-to-supine PLR method is superior to starting from a supine position, as it produces a larger increase in cardiac preload 2

Physiological Mechanism

• PLR rapidly mobilizes approximately 300 mL of blood from the lower extremities to the thorax
• This creates a transient increase in preload without changing the patient's total intravascular volume
• Acts as a reversible "self-volume challenge" that can be performed without administering fluids 3

Measuring Response to PLR

Primary Measurement: Cardiac Output

• A positive response is defined as ≥10% increase in stroke volume or cardiac output during PLR 1, 4
• Measurement methods (in order of preference):
  1. Real-time cardiac output monitoring (most accurate)
  2. Echocardiographic measurement of stroke volume/cardiac output
  3. Arterial pulse pressure (less reliable)

Specific Monitoring Techniques

• Echocardiography:
  • Measure left ventricular outflow tract (LVOT) velocity-time integral (VTI)
  • An increase in VTI ≥12% indicates fluid responsiveness 3
• Carotid Flow:
  • Measure carotid flow VTI using echo-Doppler
  • An increase ≥11% predicts fluid responsiveness with 77.3% sensitivity and 78.6% specificity 5
• Plethysmographic Variability Index (PVI):
  • A decrease in PVI ≤-24.1% during PLR predicts fluid responsiveness with 95% sensitivity and 80% specificity 6

Clinical Application and Interpretation

When to Use PLR Test

• Patients with hypotension (systolic BP <90 mmHg, MAP <70 mmHg)
• Patients with signs of tissue hypoperfusion (oliguria, tachycardia)
• Particularly valuable in patients with:
  • Spontaneous breathing efforts
  • Cardiac arrhythmias
  • Low tidal volume ventilation
  • Situations where other dynamic parameters are unreliable 3

Interpreting Results

• Positive PLR test (≥10% increase in cardiac output):
  • Patient is likely fluid responsive
  • Intravenous fluid administration is appropriate 1
• Negative PLR test (no significant increase in cardiac output):
  • Patient is unlikely to respond to fluid administration
  • Consider vasopressors or inotropic support instead 1

Clinical Decision-Making

• If PLR test is positive:
  • Administer 500 mL crystalloid solution over 10-15 minutes
  • Reassess after fluid bolus to confirm response
• If PLR test is negative:
  • Avoid further fluid boluses
  • Focus on vascular tone and chronotropy/inotropy 1

Limitations and Pitfalls

Situations Where PLR May Be Less Reliable

• Intra-abdominal hypertension or abdominal compartment syndrome
• Severe right ventricular dysfunction
• Patients with compression stockings or bandages on lower extremities
• Patients with significant pain during position change

Technical Considerations

• Real-time cardiac output measurement is essential for accurate interpretation
• Arterial pulse pressure alone is less reliable (60% sensitivity, 85% specificity) 3
• Ensure proper positioning technique - semi-recumbent to supine PLR produces larger hemodynamic effects than supine-to-leg-raise PLR 2

Advantages Over Other Methods

• Non-invasive and reversible
• No administration of fluids required
• Reliable in patients with arrhythmias and spontaneous breathing
• Can be performed repeatedly without cumulative effect
• Avoids unnecessary fluid administration in non-responders

The PLR test provides a reliable, non-invasive method to guide fluid management in hypotensive patients, helping clinicians make informed decisions about whether fluid administration or vasopressor support is the most appropriate intervention.