MOFFITT AM REPORT PEARLS 6/14/16: Volume Status

Thanks to Katie for presenting a case of a woman with a history of possible heart failure after an MI who presented with sepsis from a urinary source. We had an awesome discussion about volume status assessment!

 

Physical exam

JVP alone:

  • Sensitivity 57%, Specificity 93%, PPV 95%, NPV 47% (Butman et al, J Am Coll Cardiol 1993)
  • Low JVP predicts low CVP with LR 3.4 (Cook et al, JAMA rational clinical exam series)
  • High JVP predicts high CVP with LR 4.1 (Cook et al, JAMA rational clinical exam series)

HJR:

  • Sensitivity 24%, Specificity 96%, +LR 6.4, -LR 0.8

JVP + HJR:

  • Sensitivity 81%, Specificity: 80%, PPV: 91%, NPV: 63% (Butman et al)

Straight leg raise

  • Studied in mechanically ventilated patients
  • When stroke volume assessed by TTE, sensitivity 81%, specificity 93%, PPV 91%, NPV 85%
  • However, when pulse pressure increase of 12% was used, sensitivity 60%, specificity 85%

 

Ultrasound/TTE

JVP ultrasound

  • Sensitivity 64-89%, Specificity 77-81%

IVC ultrasound

  • Sensitivity 84%, specificity 96% in one study (Nakao et al), but did not correlate well in all studies
  • Correlation coefficient variable (**see table below for correlation):
    • 0.57-0.76 for IVC collapsibility index
    • 0.72-0.86 for IVC diameter

pic

TTE

  • Sensitivity 62-100%, Specificity 78-100%

 

Invasive monitoring:

Arterial line waveform

  • Pulse pressure variation (10-15% respiratory variation): Sensitivity 88%, Specificity 89% (mechanically ventilated patients)

CVP

Controversial! 2008 Chest systemic review and 2013 Critical Care Medicine metaanalysis found very poor relationship with volume status (r = 0.11-0.28), but other studies and opinion pieces support use. Overall, most recommend using it as just one piece of data among the whole picture.

Central venous oxygen saturation (CVO2 or ScvO2):

  • Normal SVC saturation is 75% (“central venous sat”)
  • IVC saturation 5-7% higher than SVC due to highly saturated renal venous blood and high brain O2 extraction
  • Mixed venous sat = combination of SVC sat, IVC sat, and coronary sinus sat
  • Coronary sinus sat very low since heart extracts a lot of O2, thus central venous sat generally overestimates mixed venous sat (but literature suggests the two do not correlate well)
  • In one study, ScvO2 at threshold of <70% had low sensitivity (40%) but higher specificity (77%) for predicting a mixed venous O2 sat <60%.
  • Use Fick equation to calculate cardiac output to assist with management

Cardiac output calculation relies on hemoglobin, arterial sat, and mixed venous sat (practically often estimated by central venous sat). VO2 is oxygen consumption, usually estimated.

Fick Equation:

CO = VO2/(1.36 * Hgb * [SaO2 – SvO2])

PA line is gold standard:

  • True mixed venous sat
  • Accurate cardiac output calculation
  • Directly measured pressures

 

SVR calculation:

SVR = 80 x (MAP-CVP)/CO

Normal SVR = 900-1200

e.g. If on pressors and SVR remains 900, very likely distributive shock.

 

Evernote link: https://www.evernote.com/shard/s272/sh/f5e6af56-601d-4d69-ba1d-816a9b37bc5b/b94b6bc03d5e39c01172dc5a6d3df0f5

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