In an adult with unexplained hypotension and signs of hypoperfusion, how should I perform a passive leg raise to assess fluid responsiveness and what are its contraindications?

Passive Leg Raise for Assessing Fluid Responsiveness

Perform passive leg raising by moving the patient from a 45° semi-recumbent position to supine with legs elevated to 45° for at least 1–2 minutes, measuring cardiac output or stroke volume changes with echocardiography or pulse contour analysis—a ≥10–15% increase predicts fluid responsiveness with 86% sensitivity and 92% specificity. 1, 2

How to Perform the PLR Maneuver

Starting Position and Technique

• Begin with the patient in a 45° semi-recumbent position, then simultaneously lower the trunk to supine while elevating the legs to 45° 3
• This technique (PLR from semi-recumbent) mobilizes approximately 300 mL of blood from both the lower extremities AND the splanchnic venous reservoir, producing a 22% increase in cardiac output 4, 3
• Avoid starting from the supine position (simply elevating legs while already supine)—this produces only a 10% cardiac output increase and will miss 43% of true fluid responders 3

Timing and Measurement

• Measure hemodynamic response at 1–2 minutes after positioning—peak effects occur within 20 seconds but should be assessed over 1–2 minutes for accuracy 4, 1
• The hemodynamic effects completely disappear by 7 minutes, so reassessment must occur during the maneuver 4
• Continuous real-time monitoring is essential—static measurements taken before and after are inadequate 1, 2

What to Measure

Preferred Variables (Highest Accuracy)

• Measure stroke volume or cardiac output changes using:
  • Transthoracic echocardiography with LVOT velocity-time integral (VTI) in apical 5-chamber view 1, 5
  • Subcostal RVOT VTI if apical windows are poor (sensitivity 85.7%, specificity 93.1%) 5
  • Pulse contour cardiac output monitoring (e.g., PiCCO) 1, 2
  • Bioreactance non-invasive cardiac output monitoring 6

Interpretation Threshold

• A ≥10–15% increase in stroke volume or cardiac output indicates fluid responsiveness with pooled sensitivity 86% and specificity 92% 1, 2
• For RVOT VTI specifically, use a 15.36% threshold (positive likelihood ratio 12.43) 5

Inferior Measurement Technique

• Do NOT rely on pulse pressure changes alone—this shows only 58% sensitivity and 83% specificity, significantly inferior to flow-based measurements 2
• Static measurements (heart rate, blood pressure alone) have no better predictive ability than chance 1

Clinical Context and Integration

When to Use PLR

• After delivering the initial 30 mL/kg crystalloid bolus in septic shock or unexplained hypotension, perform PLR to decide whether additional fluid is warranted 1, 7
• Use PLR when pulse pressure variation cannot be applied (spontaneous breathing, low tidal volumes <8 mL/kg, arrhythmias) 8, 7
• PLR serves as a reversible endogenous fluid challenge, avoiding unnecessary fluid administration and its complications 1, 7

Interpretation and Action

• Positive PLR (≥10–15% increase): Administer additional fluid bolus of 250–1000 mL in adults 1
• Negative PLR: Favor vasopressor or inotropic support rather than further fluid 1
• Reassess after each intervention—PLR can be repeated to guide ongoing resuscitation 1

Contraindications and Limitations

Absolute Contraindications

• Intra-abdominal hypertension or abdominal compartment syndrome—PLR cannot predict fluid responsiveness in these conditions 1, 7
• Suspected pelvic or spinal injury where movement could cause harm 8

Relative Limitations

• Reduced reliability in:
  • Atrial fibrillation or other arrhythmias 7
  • Active spontaneous breathing efforts 7
  • Low lung compliance or low tidal volume ventilation (though PLR remains more accurate than pulse pressure variation in these settings) 8

Technical Pitfalls

• Measuring only blood pressure or heart rate changes—these static parameters are inadequate and will lead to incorrect decisions 1, 2
• Starting from supine position instead of semi-recumbent—this reduces sensitivity by 43% 3
• Waiting too long to measure (>7 minutes)—effects have dissipated by then 4
• Using pulse pressure as the measured variable instead of stroke volume or cardiac output 2

Special Considerations

In Mechanically Ventilated ARDS Patients

• PLR remains valuable when pulse pressure variation is unreliable due to low tidal volumes 8
• A decrease in pulse pressure variation during PLR suggests fluid responsiveness, whereas no change may indicate right ventricular afterload dependence requiring echocardiographic assessment 8

Monitoring Right Ventricular Function

• In patients with suspected acute cor pulmonale, combine PLR with echocardiographic assessment of RV end-diastolic area to LVEDA ratio (normal <0.6) 8
• High pulse pressure variation with low tidal volume plus positive PLR strongly suggests fluid responsiveness 8