POCUS: Moretti


Inferior vena cava distensibility as a predictor of fluid responsiveness in patients with subarachnoid hemorrhage

Moretti. Neurocrit Care. 2010 Aug;13(1):3-9. doi: 10.1007/s12028-010-9356-z

Clinical Question

  • In mechanically ventilated patients with subarachnoid hemorrhage (SAH) and a low cardiac index, does the distensibility of IVC on ultrasound, predict fluid responsiveness?


  • Prospective observational study
  • Consecutive patients
  • Statistics:
    • No sample size calculation
    • Comparisons of:
      • Quantitative variables between groups: independent, two-tailed t test
      • Categorical data: Fisher’s test
      • Repeated measurements: paired t test
      • Inter-rater reliability: Pearson’s correlation coefficient
  • Blinding: ultrasonographers blinded to haemodynamic parameters and not involved in patient care
  • Intra and inter-observer variability of test of interest determined with repeated measurements in 10 patients


  • Single 10 bedded intensive care unit, Italy
  • August 2008 and July 2009


  • Inclusion criteria:
    • Adult patients with SAH (Fisher Grade 3/4)
    • Requiring advanced haemodynamic monitoring, sedation, and mechanical ventilation
    • Haemodynamic instability: Cardiac index (CI) <2.5 l/min/m2 or a cerebral perfusion pressure (CPP) <60 mmHg
  • Exclusion criteria:
    • Pre-existing heart failure, cardiac arrhythmias, ARDS, extravascular lung water (ELWI) >14 ml/kg, inability to perform femoral artery cannulation or ultrasonography
  • 31 patients recruited. 2 patients excluded, due to suboptimal visualisation of the IVC (n=1), ELWI >14 ml/kg (n=1)

All patients

  • Sedated with propofol and remifentanil to achieve bispectral index <60
  • Paralysed with cisatracurium. Confirmed with peripheral nerve stimulator
  • Given fluid challenge of 7 ml/kg infusion of 6% hydroxyethyl starch over 30 minutes
  • Test of interest and gold standard investigation performed at baseline and immediately post fluid challenge

Test of Interest

  • IVC sonography
    • Performed by 2 intensivists with at least 3 years (60 scans+) ultrasound experience
    • Use of 3.5-MHz ultrasound probe
    • Performed supine
    • During ultrasonography patients ventilated with standardised settings: volume-controlled ventilation, inspiratory:expiratory ratio of 1:2, respiratory rate of 12/min, tidal volume of 8 ml/kg and a positive end-expiratory pressure (PEEP) of 0 cm H2O
    • IVC diameter measured in M-mode, 2cm upstream of the origin of the suprahepatic vein. M-mode tracing perpendicular to the IVC
    • Maximum IVCD on inspiration (IVCDi) and minimum IVCD on expiration (IVCDe) measured
    • IVC distensibility index (dIVC) = (IVCDi-IVCDe)/IVCDe

Gold Standard Investigation

  • Thermodilution derived cardiac index
    • Measured with femoral PICCO line and internal jugular or subclavian central line
    • PEEP set at 5 cm H20 for measurements of stroke volume variation (SVV)
    • Patients classified as fluid responsive if cardiac index increased ≥15% with fluid challenge


  • Primary outcome: the reliability of dIVC as a predictor of fluid responsiveness
    • Area under the ROC curve
      • dIVC: 0.902 (95% C.I. 0.73-0.98)


  • Secondary outcomes:
    • 17 patients classified as fluid responders (FR) and 12 patients classified as non-responders (NR)
    • At baseline
      • dIVC (%) significantly higher in FR than NR (16 vs. 10, p < 0.0001)
      • SVV (%) significantly higher in FR than NR: (11.8 vs. 4.4, p=0.03)
    • Post fluid bolus
      • In fluid responders significant decrease in
        • dIVC (%) 16 ± 3.3 vs. 11.9 ± 2.3, p < 0.001
        • SVV (%) 11.8 ± 4.4 vs. 7 ± 2.4, p < 0.001
      • In non responders no significant change in
        • dIVC (%) 10 ± 3.4 vs. 8.7 ± 2.2, p = 0.42
        • SVV (%) 7.5 ± 2.9 vs. 8 ± 4.1, p=0.68
      • ROC curves to determine the best predictor of fluid responsiveness: Area under the curve (AUC)
        • SVV: 0.779 (95% C.I. 0.587-0.911)
        • dIVC: 0.902 (95% C.I. 0.733-0.979)
        • CVP: 0.667 (95% C.I. 0.468-0.829)
    • Intra- and inter-observer variabilities in the measurement of IVCDe were 4 ± 4% and 6 ± 4%, respectively.

Authors’ Conclusions

  • IVC distensibility was a reliable measure for predicting fluid responsiveness in critically ill patients with SAH


  • Blinding of ultrasonographers
  • Appropriate gold standard investigation
  • Clear description of how test of interest was performed
  • Tested for inter and intra-observer variablitiy


  • No sample size calculation, with small numbers of patients included
  • External validity may be limited as:
    • Restrictive inclusion/exclusion criteria
    • PEEP changed to zero for measurement of dIVC. This will not be possible for all patients
    • Single centre

The Bottom Line

  • In patients with a grade 3/4 SAH and a low cardiac index, who are mechanically ventilated with tidal volumes of 8ml/kg, and are sedated and paralysed, dIVC was a useful predictor of fluid responsiveness. Further trials will need to determine if these results can apply to other populations.

External Links


Summary author: David Slessor
Summary date: 25th October 2016
Peer-review editor: Duncan Chambler

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