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.
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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

• IVC ultrasound
• Volume status assessment
• Shock

Funding

• None reported