Can a subxiphoid (below the xiphoid process) view be used alone to confirm central venous catheter placement using the RASS (rapid assessment of sonographic sign) sign?

Subxiphoid View for RASS Sign in Central Venous Catheter Confirmation

The subxiphoid view alone is sufficient to confirm central venous catheter placement using the Rapid Atrial Swirl Sign (RASS), with excellent sensitivity and specificity when properly performed. 1, 2

Understanding the RASS Technique

The RASS technique involves:

1. Obtaining a subxiphoid (subcostal) four-chamber view of the heart using ultrasound
2. Injecting 10mL of normal saline through the central venous catheter
3. Observing for rapid opacification (swirling) in the right atrium
4. Timing the appearance of microbubbles from injection to visualization

Key Parameters:

• Positive RASS: Swirling appears within 1 second of injection (newer threshold) 2
• Delayed RASS: Swirling appears after 1-2 seconds (may indicate malposition) 2
• Negative RASS: No swirling observed (indicates malposition) 3

Evidence Supporting Subxiphoid View Alone

The subxiphoid four-chamber view has been validated as a reliable method for confirming central venous catheter placement:

• Recent studies show 100% sensitivity and 94.3% specificity when using the RASS sign via subxiphoid view 3
• The positive predictive value is 70.6% and negative predictive value is 100% 3
• The procedure takes approximately 5 minutes compared to 49.5 minutes for chest X-ray results 3

Proper Technique for Subxiphoid Assessment

1. Position the ultrasound probe in the subxiphoid region, angled toward the left shoulder
2. Obtain a four-chamber view of the heart
3. Inject 10mL of normal saline through the central venous catheter
4. Time the appearance of microbubbles/swirling in the right atrium
5. Interpret results based on timing:
   • ≤1 second: Correctly positioned catheter 2

   • 1 second: Possible malposition requiring adjustment 2

   • No swirling: Definite malposition requiring repositioning 3

Limitations and Considerations

• Adequate subxiphoid views cannot be obtained in approximately 10% of patients 4
• The American College of Critical Care Medicine recommends using both short-axis and long-axis views for complete assessment 1
• For comprehensive confirmation, combining the subxiphoid RASS with lung ultrasound to exclude pneumothorax provides a complete assessment 4

Implementation Barriers

Despite strong evidence supporting ultrasound confirmation:

• Only 1% of clinicians use ultrasound alone for central line confirmation 5
• 50.7-65.4% still rely on chest X-ray alone 5
• 33.1-49.3% use both X-ray and ultrasound together 5

Conclusion

The subxiphoid view alone using the RASS technique is sufficient for confirming central venous catheter placement when properly performed, with excellent sensitivity and specificity. The most current evidence supports using a 1-second threshold for positive confirmation 2. This approach significantly reduces time to confirmation, avoids radiation exposure, and can be effectively performed by clinicians after minimal training.