EBQ:Caval index

Complete Journal Club Article
Nagdev AD, Merchant RC, Tirado-Gonzalez A, Sisson CA, Murphy MC.. "Emergency department bedside ultrasonographic measurement of the caval index for noninvasive determination of low central venous pressure.". Ann Emerg Med. 2010. 55(3):290-295.
PubMed Full text PDF

Clinical Question

Can emergency medicine physicians performing bedside ultrasound measurement of the caval index predict a central venous pressure of less than 8 mmHg in emergency department patients?

Conclusion

  • Bedside ultrasound measurement of the caval index can reliably predict a CVP of less than 8 mmHg
  • A caval index (CI) >50% collapsibility with respiration strongly correlates with low CVP, suggesting intravascular volume depletion
  • IVC ultrasound is a rapid, noninvasive tool for volume assessment in the ED

Major Points

  • The caval index (CI) is calculated as: (IVC max diameter - IVC min diameter) / IVC max diameter x 100
  • A CI >50% had a sensitivity of 91% and specificity of 94% for predicting CVP <8 mmHg
  • IVC measurements were obtained in the subxiphoid view in the longitudinal plane, 2-3 cm from the right atrial junction
  • Emergency physicians were able to obtain adequate IVC images in 93% of patients after brief training
  • This study provided evidence supporting the use of bedside IVC ultrasound as a surrogate for invasive CVP monitoring in the ED

Study Design

  • Prospective, observational study
  • Single center: Rhode Island Hospital
  • N = 73 ED patients with central venous catheters in place
  • Study period: August 2006 - February 2008
  • Primary Outcome: correlation between caval index and CVP <8 mmHg

Population

Patient Demographics

  • Mean age: 60 years
  • Male: 52%
  • Mean CVP: 9.8 mmHg

Inclusion Criteria

  • ED patients with a central venous catheter already in place
  • Age >17 years
  • Spontaneously breathing

Exclusion Criteria

  • Mechanically ventilated patients
  • Known IVC abnormality (filter, thrombus)
  • Inability to obtain adequate subxiphoid IVC view
  • Known right heart failure or severe tricuspid regurgitation

Interventions

  • No therapeutic intervention; this was a diagnostic accuracy study
  • IVC measurements obtained by emergency medicine residents and attendings using bedside ultrasound
  • IVC diameter measured in M-mode at 2-3 cm caudal to the hepatic vein-IVC junction
  • CVP measured simultaneously via central venous catheter as reference standard

Outcomes

Primary Outcome

  • Caval index >50% for predicting CVP <8 mmHg:
    • Sensitivity: 91%
    • Specificity: 94%
    • Positive predictive value: 87%
    • Negative predictive value: 96%

Secondary Outcomes

  • Pearson correlation between CI and CVP: r = -0.74 (p<0.001)
  • Inter-rater reliability for IVC measurements was high (kappa = 0.77)
  • Image acquisition success rate: 93%

Criticisms & Further Discussion

  • Small, single-center study limits generalizability
  • Only included spontaneously breathing patients; results do not apply to mechanically ventilated patients
  • CVP itself is a poor predictor of fluid responsiveness, limiting the clinical utility of any CVP surrogate
  • The 50% cutoff was derived and validated in the same cohort; external validation is needed
  • Subsequent studies have questioned whether IVC collapsibility reliably predicts fluid responsiveness in septic patients
  • Body habitus may limit IVC visualization in obese patients

See Also

Funding

  • None reported

References

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