Fluid Responsiveness

Fluid Responsiveness

David Ray Velez, MD

Table of Contents

Definition and Assessment
Dynamic Assessment
Assessment by Point-of-Care Ultrasound (POCUS)

Definition and Assessment

Also Known as “Volume Responsiveness” or “Preload Responsiveness”

Definition

  • The Ability of the Heart to Increase Cardiac Output or Stroke Volume in Response to Fluid Administration
    • Exact Definitions Vary
  • Goal of Fluid is to Improve Cardiac Output and Oxygen Delivery (DO2)
  • If Not Responsive, Excessive Fluid Risks Fluid Overload with Pulmonary Edema and Associated Morbidity
  • Can Be Difficult to Determine in Some Cases Such as Septic Shock with CHF
  • Only About 50% of Unstable Critically Ill Patients Will Respond Positively to a Fluid Challenge

Frank-Starling Mechanism (Law)

  • Describes How Stroke Volume and Cardiac Output Increases in Response to Increased End Diastolic Volume (Preload)
    • The Basic Theory of Fluid Responsiveness
  • The Vertical Segment is Preload Dependent and Will Respond to Fluid Administration
  • The Horizontal Segment is Preload Independent and Will Not Respond to Fluid Administration
  • Decreased Cardiac Contractility Decreases the Effect Additional Fluid Administration/Preload Will Have on Increasing the Stroke Volume and Excessive Preload Can Actually Cause a “Falling Off” with Decreased Stroke Volume

Fluid Challenge

  • The Definitive Test of Fluid Responsiveness
    • However, it Creates a Risk of Fluid Overload if Not Fluid Responsive
  • Test: Patient Given a 500 cc Bolus of Fluid as Fast as Possible (Around 10-15 Minutes)
  • Positive Results: 10% Increase in Cardiac Output or Stroke Volume
    • Surrogate Measure (If No Pulmonary Artery Catheter or FloTrac): 10% Increase in Pulse Pressure on Arterial-Line

Static Assessment of Fluid Responsiveness

  • *Static Assessments (Looking at a Static Moment in Time) are Generally Not Sensitive, Not Specific, and Have Limited Clinical Use in Determining Fluid Responsiveness
  • Vital Signs (Heart Rate/Blood Pressure)
  • Prior Urine Output
  • Chest X-Ray/Lung Ultrasound – Looking for Pulmonary Edema to Determine Fluid Overload (Indicating Lack of Responsiveness)
    • Late Marker of Fluid Overload
  • Central Venous Pressure (CVP)
  • Better Indicator of “Preload” and Not Necessarily “Preload Responsiveness”
  • Extreme Values May Be More Reliable (< 6 Indicates Fluid Responsive and > 15 Indicates Not)

Dynamic Assessment of Fluid Responsiveness

  • *Dynamic Assessments (Evaluating in Response to an Effect) are Generally More Clinically Reliable than Static Assessments Although Data to Support is Highly Variable
  • Passive Leg Raise
  • Volume/Pressure Variations:
    • Stroke Volume Variation (SVV)
    • Pulse Pressure Variation (PPV)
  • Ventilator Simulations:
    • End-Expiratory Occlusion test (EEOT)
    • Tidal Volume Challenge (TVC)
  • Point-of-Care Ultrasound (POCUS):
    • IVC Collapsibility/Distensibility
    • Internal Jugular Ultrasound

Frank-Starling Curve

Dynamic Assessment

Passive Leg Raise

  • Technique:
    • Patient Placed in a Semi-Recumbent Position with Head of Bed at 45 Degrees
    • Head Lowered Supine/Flat and Legs Passively Raised to 45 Degrees
  • Quickly Returns a Reservoir of Venous Blood into Central Circulation in 30-90 Seconds
  • Positive Results: 10% Increase in Cardiac Output or Stroke Volume
    • Surrogate Measure (If No Pulmonary Artery Catheter or FloTrac): 10% Increase in Pulse Pressure on Arterial-Line
  • *The Most Well Validated Test of Fluid Responsiveness

Stroke Volume Variation (SVV)

  • SVV (%) = (Maximum SV – Minimum SV) / Average SV
  • Measured Using a Pulmonary Artery Catheter or FloTrac/Vigileo System
  • Normal SVV: 10-13%
    • < 10%: Unlikely to Be Volume Responsive
    • > 13-15%: Likely to Be Volume Responsive
  • Accurately Measured Only if on Controlled Mechanical Ventilation and in Normal Sinus Rhythm
    • Use Contraindicated if Having Arrhythmias or Spontaneous Ventilation (Irregular Nature of Spontaneous Breaths Causes Variation)

Pulse Pressure Variation (PPV)

  • PPV (%) = (Maximum PP – Minimum PP) / Average PP
  • Pulse Pressure Can Be Used as a Surrogate for Stroke Volume if No Pulmonary Artery Catheter or FloTrac/Vigileo System are Being Used
    • Generally Proportional but Relative Change in PP After Fluid Expansion May Not Accurately Approximate Change in SV Due to the Non-Linear Relationship of Left Ventricular Pressure to Volume
    • Use is Otherwise Similar to SVV
  • Normal PPV: 10-13%
    • < 10%: Unlikely to Be Volume Responsive
    • > 13-15%: Likely to Be Volume Responsive
  • Accurately Measured Only if on Controlled Mechanical Ventilation and in Normal Sinus Rhythm
    • Use Contraindicated if Having Arrhythmias or Spontaneous Ventilation (Irregular Nature of Spontaneous Breaths Causes Variation)

End-Expiratory Occlusion Test (EEOT)

  • A 15-Second End-Expiratory Hold (Occlusion) is Performed on the Ventilator
  • Simulates a Fluid Challenge by Preventing Inspiration and the Subsequent Preload Inhibition
  • Increased Cardiac Output or Stroke Volume Predicts Volume Responsiveness
    • Can Use Pulse Pressure on Arterial-Line as a Surrogate Measure (If No Pulmonary Artery Catheter or FloTrac)
  • Must Be Able to Tolerate an End-Expiratory Hold
  • Unreliable if Spontaneously Breathing, Prone, or Intra-Abdominal Hypertension
  • Less Sensitive if Lung Compliance is Poor (ARDS, etc.)

Tidal Volume Challenge (TVC)

  • Tidal Volume is Temporarily Increased to 8 mL/kg for 1 Minute
  • Increased Intrathoracic and Transpulmonary Pressures:
    • Decreased LV Afterload and a Transient Increase in LV Preload Due to Alveolar Blood Being Squeezed Out – Transient Increase in Stroke Volume (Highest in Inspiration)
    • Decrease Venous Return/RV Preload and Increase RV Afterload – Causes a Decrease in Stroke Volume After a Few Heart Beats to Overcome Pulmonary Transit Time (lowest in Expiration)
  • Increased Cardiac Output or Stroke Volume Predicts Volume Responsiveness
    • Can Use Pulse Pressure on Arterial-Line as a Surrogate Measure (If No Pulmonary Artery Catheter or FloTrac)
    • Can Also Assess Effect by SVV or PPV
  • Risk for Lung Injury from Increased Volume and Pressure
  • Unreliable if Spontaneously Breathing or Intra-Abdominal Hypertension
  • Less Sensitive if Lung Compliance is Poor (ARDS, etc.)

Assessment by Point-of-Care Ultrasound (POCUS)

IVC Diameter

  • A Static Measurement of IVC Diameter
  • Normal Diameter: 13-17 mm and Not Completely Compressible
    • < 13 mm: Likely to Be Volume Responsive
    • > 25 mm: Unlikely to Be Volume Responsive
  • Generally Poor Accuracy, Although Extreme Values (Flat vs Full) May Be More Predictive

IVC Collapsibility Index (Caval Index)

  • Change in IVC Diameter Throughout the Respiratory Cycle in Spontaneously Breathing Patients
  • IVC CI (%) = (Max – Min) / Max Diameter
    • Maximum Diameter on Expiration
    • Minimum Diameter on Inspiration
  • Interpretation:
    • Near 50-100% Indicatives Fluid Responsiveness
    • Near 0% Indicatives Fluid Non-Responsiveness
  • Positive Pressure Ventilation is a Contraindication – Positive Pressure on Inspiration Prevents IVC Collapse

IVC Distensibility Index

  • Change in IVC Diameter Throughout the Respiratory Cycle in Mechanically Ventilated Patients
  • IVC DI (%) = (Max – Min) / Min Diameter
    • Maximum Diameter on Inspiration
    • Minimum Diameter on Expiration
  • Increase ≥ 18% Indicates Fluid Responsiveness

Other Ultrasound Evaluations

  • Heart Ultrasound/Echocardiography
    • End-Diastolic Volume (EDV) Assesses Preload
    • Left Ventricular Outflow Tract (LVOT) Velocity Time Index (VTI) Estimates Stroke Volume
  • Lung Ultrasound
    • Evaluates for Pulmonary Edema to Determine Fluid Overload (Indicating Lack of Responsiveness)
  • Carotid Artery Ultrasound
    • Carotid Velocity Time Index (VTI) Can Estimate Stroke Volume – Easier to Perform than LVOT by Echo but Less Accurate
  • Internal Jugular Vein Ultrasound
    • Can Evaluate for IJ Diameter and Collapsibility During the Respiratory Cycle (Similar to IVC Evaluation)
      • Generally Considered Less Reliable than IVC Evaluation
    • Small IJ with Collapse Throughout the Respiratory Cycle is Likely to Be Volume Responsive
    • Dilated IJ with No Collapse is Unlikely to Be Volume Responsive

IVC Collapsibility POCUS: (A) Normal 1; (B) Collapse 2

References

  1. Gaspar HA, Morhy SS. The Role of Focused Echocardiography in Pediatric Intensive Care: A Critical Appraisal. Biomed Res Int. 2015;2015:596451. (License: CC BY-3.0)
  2. Mok KL. Make it SIMPLE: enhanced shock management by focused cardiac ultrasound. J Intensive Care. 2016 Aug 15;4:51. (License: CC BY-4.0)