Inferior Vena Cava Ultrasound for Volume Status

Aka: Inferior Vena Cava Ultrasound for Volume Status, Caval Index, Caval Aorta Index, IVC Ultrasound for Volume Status, Respirophasic IVC Variation, Distensibility Index

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II. Indications: Volume status assessment

  1. Diagnosis
    1. Volume depleted (e.g. Hemorrhagic Shock, Dehydration, Sepsis)
    2. Volume overload (e.g. Congestive Heart Failure)
  2. Serial monitoring of volume status (e.g. Sepsis)
    1. Repeat Ultrasound measurement after each fluid bolus
  3. Predict fluid responsiveness (response to IV fluid bolus)
    1. IVC collapsibility >50% (see Respirophasic IVC Variation below)
    2. IVC Diameter <2 cm
      1. Predicts CVP <10 mmHg with Test Sensitivity 85%, Test Specificity 81%
      2. Prekker ME (2013) Crit Care Med 41(3):833-41 +PMID: 23318493 [PubMed]
    3. Distensibility Index >18% (see below)
    4. IVC Change with Passive Leg Raise Maneuver (PLR, see below)

III. Physiology

  1. Inferior Vena Cava (IVC) diameter is a marker of Preload
  2. Spontaneous Breathing
    1. Expiration
      1. Increased intrathoracic pressure
      2. Decreased cardiac venous return (slowing flow into the right atrium)
      3. IVC dilates
    2. Inspiration (of sniffing)
      1. Decreased intrathoracic pressure
      2. Increased cardiac venous return (speeding flow into the right atrium)
      3. IVC collapses
  3. Mechanical Ventilation
    1. Mechanical Ventilation has an opposite effect on IVC diameter as with spontaneous respiration
    2. Expiration on Mechanical Ventilation is associated with decreased intrathoracic pressure and IVC collapse
    3. Inspiration on Mechanical Ventilation is associated with increased intrathoracic pressure and IVC dilation

IV. Views: Subcostal Longitudinal (volume status view)

  1. Pearls to improve view window
    1. View improves with the patient taking a deep inspiration
  2. Transducer orientation
    1. Transducer placed right lateral to sub-xiphoid
    2. Transducer indicator pointed towards 12:00 with energy toward left atrium
  3. Landmarks
    1. Inferior vena cava
    2. Right atrium
  4. Images
    1. ultrasoundProbePositionAbdIvcLong.jpg
    2. ultrasoundBMP_abdIVC_lax.jpg

V. Interpretation: Volume status based on IVC alone (Respirophasic IVC Variation)

  1. Inferior vena cava (IVC) is normally 1.5 to 2.5 cm in diameter (measured 3 cm from right atrium)
    1. IVC <1 cm in Trauma is associated with a high likelihood of Hemorrhage requiring Blood Transfusion
    2. IVC <1.5 cm suggests volume depletion
    3. IVC >2.5 cm suggests volume overload
  2. Inferior vena cava (IVC) normally collapses more than 50% with inspiration or sniffing
    1. Consider measuring in M-Mode
      1. Allows for graphical display over time of IVC diameter in both inspiration and expiration
    2. Caval Index = (IVC-exp diameter - IVC insp diameter) / (IVC-exp diameter) * 100
      1. Collapse <50% suggests volume overload
      2. Caval Index >50% suggests fluid responsiveness
  3. Correlation between RA pressure (CVP) and IVC appearance
    1. CVP 0-5 cm: IVC totally collapses on inspiration and is <1.5 cm in diameter
    2. CVP 5-10 cm: IVC collapses >50% on inspiration and is 1.5 to 2.5 cm in diameter
    3. CVP 11-15 cm: IVC collapses <50% on inspiration and is 1.5 to 2.5 cm in diameter
    4. CVP 16-20 cm: IVC collapses <50% on inspiration and is >2.5 cm in diameter
    5. CVP >20 cm: No change in IVC on inspiration and is >2.5 cm in diameter

VI. Interpretation: Volume status by Caval Aorta Index

  1. Step 1: Measure maximal internal IVC anteroposterior diameter (in M Mode)
    1. Subxiphoid level in longitudinal axis
    2. Measure just caudal to confluence of hepatic veins (~3 cm from right atrium)
  2. Step 2: Measure maximal internal aorta anteroposterior diameter (in M Mode)
    1. Subxiphoid region in longitudinal axis
    2. Measure just to the left of the IVC
  3. Step 3: Calculate the Caval Aorta Index as IVC/Ao
    1. CVP <7 cm H2O: Caval Aorta Index of 0.72 (+/- 0.09)
    2. CVP 8-12 cm H2O: Caval Aorta Index of 1.23 (+/- 0.12)
    3. CVP >13 cm H2O: Caval Aorta Index of 1.59 (+/- 0.05)
  4. Reference
    1. Sridhar (2012) ISRN Emergency
      1. http://www.isrn.com/journals/em/2012/828626/cta/

VII. Interpretation: Distensibility Index (DI)

  1. Indication
    1. Assess fluid responsiveness (expected status change following fluid bolus) in a mechanically ventilated patient
  2. Contraindications (cases in which DI is unreliable)
    1. Spontaneous respirations during Mechanical Ventilation
    2. Tidal Volume <7 ml/kg Ideal Body Weight (based on gender and height)
    3. Non-sinus rhythm
    4. Right ventricular dysfunction
  3. Mechanism
    1. Mechanical Ventilator generates positive pressure with each breath that distends the IVC
    2. Positive Pressure Ventilation increases intrathoracic pressure and decreases venous return to the right atrium
    3. Inferior vena cava distends with PPV delivered breath due to resistance to right atrial filling
      1. Inferior vena cava returns to baseline diameter between ventilations
      2. Contrast with IVC collapse with spontaneous breaths (generates negative chest pressure)
  4. Step 1: Set-up M-Mode view of Inferior vena cava (IVC) for anteroposterior diameter measurements
    1. Subxiphoid level in longitudinal axis
    2. Visualize inferior vena cava as it enters right atrium
    3. Set M-Mode caliper marker at a point 3 cm from the right atrium along the anterior surface of the inferior vena cava
    4. Measure just caudal to confluence of hepatic veins (~3 cm from right atrium)
  5. Step 2: Obtain anteroposterior diameter measurements of IVC at maximal and minimal diameters
    1. Measure maximal internal IVC anteroposterior diameter (inspiratory, Positive Pressure Ventilation phase)
    2. Measure minimal internal IVC anteroposterior diameter (expiratory phase)
  6. Step 3: Calculate Distensibility Index (DI) as a percentage
    1. DI = (maxIVC - minIVC) / minIVC
  7. Step 4: Interpretation
    1. Distensibility Index <18% indicates patient is not volume responsive (unlikely to benefit from fluid bolus)
    2. Efficacy in predicting fluid responsiveness (7 ml/kg bolus) if DI >18%
      1. Test Sensitivity 90% and Test Specificity 90% for an increase in Cardiac Index of 15% with fluid bolus
      2. Barbier (2004) Intensive Care Med 30(9):1740-6 +PMID: 15034650 [PubMed]

VIII. Protocol: IVC change with Passive Leg Raise (PLR) in Prediction of Volume Responsiveness

  1. Technique
    1. Obtain initial maxium and minimum IVC measurements
    2. Perform Passive Leg Raise Maneuver (PLR Maneuver)
    3. Repeat maxium and minimum IVC measurements
  2. Interpretation
    1. Improved hemodynamic parameters by IVC measurement suggests volume responsiveness (benefit with fluid bolus)

IX. Resources

  1. Inferior Vena Cava Ultrasound Video (SonoSite)
    1. http://www.youtube.com/watch?v=ci9W4MvyMHI
  2. Echocardiographer
    1. http://echocardiographer.org/

X. References

  1. Hallemat (2013) Crit Dec Emerg Med 27(10): 14-21

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