Allison: Volume responsiveness in the ICU, the Lebowski way!

Clinical Pearls (assisted by Dr. Alison Grazioli)

• Fluid resuscitation in sepsis:
  • Surviving sepsis campaigns (SSC) since early 2000’s have advocate for more aggressive fluid resuscitation in sepsis.
  • Downside: observational studies show worse outcomes with higher volume resuscitation.
    • Critically ill patients (all cause) higher fluid balance= higher mortality.
  • In shock, patient has 50% chance of volume responsiveness with clinical goal to resuscitate those who are responsive.
• Volume Responsiveness Predictor
  • Static Measures:
    • CVP
      • SSCs (prior to 2016) have recommended static measure (ie CVP) driven resuscitation.
      • CVP and Δ CVP post-fluid challenge. Very poor predictors.
        • Even at extreme values, CVP does not reliably predict volume responsiveness.
  • Dynamic Measures:
    • Passive leg raise.
    • Heart lung interactions/end-expiratory occlusion test.
    • Respiratory variation tests (pulse pressure variation, stroke volume variability [SVV], IVC collapsibility).
    • TTE with velocity time integral (VTI) for stroke volume assessment.
  • Dynamic>Static, despite static still relied upon by large amounts of physicians!
• Volume Responsiveness Assessment: where on starling curve is a patient?

• • 2 requirements for adequate volume responsiveness assessment:
    1. Have to change preload
    2. Measure associated change in stroke volume (SV) or cardiac output (CO)
• Methods to change preload:
  • Fluid Bolus (500cc crystalloid or 250 cc colloid) + increase in 10-15% in SV or CO = Volume responsiveness
    • Not reversible.
    • Only 50% will respond.
  • Heart Lung Interactions: positive pressure ventilation decreases preload and increases afterload of RV.
    • If volume responsive, during expiration (2-3 heart beats later) there will be a greater decrease in SV
      • Validated only in mechanically ventilated at 8-10cc/kg IBW + paralysis.
        • Can’t be spontaneously breathing.
      • Not validated with patients with poor lung compliance.
      • Cannot have dysrhythmias.
  • End Expiratory Occlusion pressure: increase preload by occluding mechanical ventilation at end expiration (hold >15 sec) taking away positive intrathoracic pressure.
    • 5% or more increase in CO suggests volume responsiveness.
      • Valid at any PEEP.
      • Patient may be intolerant to long breath hold.
      • Need CO measuring device accurate enough to detect 5% change.
  • Passive Leg Raise: from semi-recumbent 45° position, lower patient’s upper body to horizontal and passively raise legs up 45° brining ~300cc increase of venous return.
    • 10% increase in SV indicates fluid responsiveness.
      • Broadest use, reversible and non-invasive.
      • Need continuous SV assessment given effect seen within 60-90 seconds.
      • Not validated with intra-abdominal hypertension.
      • Not to be used with increased ICP.
      • Okay in those spontaneously breathing, have low tidal volumes or arrhythmias.
• Methods to measure SV and CO Change:
  • Thermodilution (gold standard) with two equally accurate methods:

• • • Pulmonary artery thermodilution: Uses PA catheter. Bolus of cold saline cold saline changes temperature at thermistor tip over time. Measuring area under curve allows for calculation of CO and cardiac index.
    • Transpulmonary thermodilution: Cold saline bolus via central line and have femoral arterial line with thermistor tip measuring changes in temperature. Measuring area under curve again allows for calculation of CO.
      • Despite accuracy, shown not to change patient outcomes (with exceptions of cardiac surgical patient subsets) so not frequently used
  • Pulse pressure variation: Surrogate of SV that uses arterial line and assesses waveform variability.
    • >12% predicts volume responsiveness.

 PP variability= max-min/mean

• • • Validated in mechanically ventilated with 8-10cc/kg IBW tidal volumes.
    • Cannot be spontaneously breathing or have arrhythmia.
    • Preau, S et al. show only ~17% of ICU patients meet above criteria.
  • Stroke Volume (SV) and Stroke Volume Variation (SVV) assessments:
    • Pulse contour analysis (ie. Vigileo, EV1000):
      • Need arterial line and measures area under curve of pulse wave contour calculate SVV and SV index.
      • 3 methods:
        1. Thermodilution calibrated (LIDco system uses thermodilution to find out real CO and uses that calibrate area pulse wave under curve. most accurate).
        2. Biometric calibrated (i.e. Edwards catheter, uses patient specific details to calibrate).
        3. Uncalibrated devices (less reliable).
    • Velocity time integral (VTI): uses POC ultrasound (TTE).
      • VTI is measurement blood velocity over time from LV in systole using pulse wave Doppler at LV outflow track (LOVT) in apical 5 chamber view.
      • This calculation (LVOT VTI) and the measurement of LVOT diameter allows for quantification volume of blood leaving LV during systole (ie SV).
        • Volume cylinder (ie SV) = area x length. Therefore, SV= π (LVOT diameter/2)² x LVOT VTI.
      • Measurements of SV with each beat allow for assessment of SVV.
        • Criteria for reliability:
          • mechanically ventilated with 8-10cc/kg IBW TV.
          • No spontaneous respirations.
          • No arrhythmias.
        • Experience is critical to reliability.
        • Need high quality ultrasound.
  • IVC collapsibility: Use POC ultrasound usually in subcostal position. Inspiration (in spontaneously breathing) decreases IVC diameter given increased venous return to heart (shifts blood volume (ie preload) away from area you are viewing). The reverse is true in mechanical ventilation with decrease in diameter during expiration.
    • >15% collapse suggests volume responsiveness
      • Validated in mechanically ventilated (at 8-10cc/kg IBW) without spontaneous breaths.
      • In spontaneously breathing, not validated:
        • Airapetian et al. found, >42% collapsibility had high specificity (97%) for volume responsiveness.
  • Volume Clamp (photo-plethsymography) non-invasive:
    • Consists of pressure bladder in finger cuffs which inflate until arteries in finger do not pulse, fixing their diameter.
      • Makes arterial blood pressure tracing over time and calculates brachial artery signal. From this, calculates SVV and SV index.
    • Reliability poor thus far.
• Limitations with current methods to assess volume responsiveness:
  • Study sizes are small usually single center.
  • Potential conflicts of interest with companies behind monitoring devices.
  • Gold standard is thermodilution (not regularly used anymore), so recent literature does not have a reliable gold standard.
  • Error limits up to 30-50% on some monitoring devices.
• Conclusion about current state of clinical volume responsive assessments:
  • No one size fits all method.
  • No convincing mortality benefit from devices measuring volume responsiveness.
  • Monitoring devices have variable reliability.
  • Suggest approaches:
    1. Minimize fluids, early vasopressors, + aggressive de-resuscitation without use of unreliable volume response monitoring methods.
    2. Though volume responsive monitoring methods have limitations, if applied rationally with appreciation of limitation, in the right context it may be better than guessing.