How do you perform a passive leg raise (PLR) test and assess fluid responsiveness?

Passive Leg Raise Test: Technique and Assessment of Fluid Responsiveness

The passive leg raise (PLR) test should be performed by elevating the legs to 45° from a semi-recumbent position while monitoring hemodynamic parameters, with a positive response defined as a ≥10% increase in cardiac output or stroke volume, indicating fluid responsiveness.

Proper Technique for Performing PLR

Starting Position

1. Place the patient in a semi-recumbent position (head elevated at 45°)
2. Obtain baseline hemodynamic measurements
3. Ensure proper monitoring equipment is in place

PLR Maneuver

1. Lower the head of the bed to flat position
2. Raise both legs to approximately 45° angle
3. Hold this position for 1-2 minutes
4. Monitor hemodynamic parameters during and after the maneuver

Key Points About Positioning

• Starting from semi-recumbent position rather than supine is crucial, as it provides greater hemodynamic effect 1
• The semi-recumbent to leg-raised position recruits the splanchnic venous reservoir, creating a more effective "self-volume challenge" 1, 2
• Maintain the position for at least 1 minute but not longer than 5 minutes to observe maximal effect

Monitoring Parameters to Assess Response

Primary Parameters (Most Reliable)

• Stroke volume (SV) or cardiac output (CO): ≥10% increase indicates fluid responsiveness 2, 3
• This can be measured using:
  • Transthoracic echocardiography (subaortic flow increase ≥12%) 3
  • Esophageal Doppler (aortic blood flow increase ≥10%) 2
  • Non-invasive cardiac output monitors using thoracic electrical bioimpedance 4

Secondary Parameters (Less Reliable)

• Pulse pressure: ≥9-12% increase (less sensitive and specific than direct flow measurements) 2, 5
• Femoral artery peak flow velocity: ≥8% increase 5
• Mean arterial pressure (MAP): less reliable but may be used if other measurements unavailable

Interpreting Results

Positive Response (Fluid Responsive)

• ≥10% increase in stroke volume or cardiac output during PLR 2, 3
• Indicates patient will likely benefit from fluid administration
• Sensitivity of 86-97% and specificity of 90-94% for predicting fluid responsiveness 2, 5

Negative Response (Not Fluid Responsive)

• <10% increase in stroke volume or cardiac output during PLR
• Suggests patient may not benefit from additional fluid and alternative interventions should be considered

Clinical Applications and Advantages

• Particularly valuable in patients with spontaneous breathing or cardiac arrhythmias where other dynamic parameters are unreliable 2, 3
• Reversible "self-volume challenge" without actual fluid administration
• Can be repeated as needed without cumulative fluid overload
• Applicable in various shock states including septic shock and hypovolemia 5

Limitations and Pitfalls

• Requires real-time cardiac output monitoring for optimal assessment 3
• Less accurate when using only blood pressure changes as surrogate markers 2
• May be contraindicated in patients with:
  • Traumatic injuries (especially spinal injuries) 6
  • Increased intracranial pressure
  • Pain upon movement 6
• Limited accuracy when using thoracic bioimpedance alone (sensitivity 41%, specificity 80%) 4

Position Recommendations for Shock

If PLR testing indicates fluid responsiveness in a patient with shock:

• Place the patient in a supine position 6
• If no evidence of trauma or injury, raising the feet about 6-12 inches (30-45°) from supine position may be reasonable while awaiting EMS arrival 6
• Return to supine position if the patient experiences pain or discomfort 6
• If the patient is at risk for airway obstruction or cannot be continuously monitored, consider the recovery position 6

Remember that the hemodynamic effects of PLR are temporary, typically lasting less than 7 minutes, so fluid administration decisions should be made promptly if indicated 6.