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Trick of the Trade: Bubble Study for Confirmation of Central Line Placement

Timothy Montrief, MD MPH |

Ultrasound Needle

The safe placement a central venous catheter (CVC) remains an important part of caring for critically ill patients.1 Over 5 million CVCs are placed each year in the United States. It is crucial to confirm that the central line is placed in the correct position in order to rule out potential complications of the procedure (e.g. pneumothorax) and begin administration of life-saving medications. Post-procedure chest radiographs (CXR) are the standard of care for CVC placements above the diaphragm. However, the annual cost to the U.S. healthcare system for CXRs after CVC placement is estimated to be over $500 million.2 Further, in a busy ED, the limited availability of portable radiography may pose a considerable time delay. Radiography may also be limited in resource‐poor and austere settings, particularly the prehospital and military environments. We review a faster, cheaper, and more accurate alternative for evaluating CVC placement: point of care ultrasound (POCUS).

The Problem

Traditional dogma mandates that the tip of a CVC placed above the diaphragm must lie within the lower portion of the superior vena cava (SVC). This is best evaluated with a CXR. However, these can be time-consuming and expensive.

The Trick: POCUS for Confirmation of CVC Placement

Recent literature challenges the teaching that the optimal position for a CVC is within the lower portion of the SVC. Mounting evidence suggests that CVCs with its tip in the right atrium, SVC, brachiocephalic veins, or subclavian veins are well tolerated.3–5 Therefore, we only need to confirm that the CVC is placed within the venous system. This can be done with POCUS. The one exception is a catheter placed via a subclavian approach that is aberrantly directed into the internal jugular vein and points upwards towards the head.

Figure 1.6 3-step approach to using POCUS to evaluating the positioning of a CVC placed in the right internal jugular vein.

An Extension of Core EM Skills

Evaluation of CVC placement with POCUS is an extension of core proficiencies in the emergency medicine curriculum and consists of 3 steps (Fig 1):6

  1. Excluding pneumothorax by evaluating for pleural lung-sliding in the most superior aspect of the patient’s pleura.
  2. Examination of the internal jugular veins to exclude a misdirected catheter (Fig. 2).7
  3. A bubble study that consists of injecting 10 mL of saline into the CVC’s distal port while visualizing the right atrium in either a subcostal or apical four-chamber view. Observation of agitated microbubbles within the right heart provides evidence that the catheter lies within the venous system (Fig. 3).
Figure 2. Transverse (A) and sagittal (B) views of the left internal jugular vein contralateral to the site of insertion. This represents a malpositioned catheter (C, red arrow in A and B). IJ = internal jugular vein, CA = carotid artery.

Important: Appearance of microbubbles in the heart more >2 seconds after injection of saline suggests that the CVC is not positioned in the SVC.8 This is acceptable as long as CVC is not positioned cephalad in the internal jugular veins.

Figure 3. Positive bubble study confirming central line placement in the venous system using the (A) apical four-chamber and (B) subcostal views.

The Evidence

POCUS may have several advantages over traditional chest radiography:

  1. time to CVC placement confirmation
  2. specificity for placement in the venous system
  3. detection of pneumothorax

In one study, POCUS confirmed CVC placement an average of 24 minutes sooner than traditional CXR.8 Further, a meta-analysis of 15 studies and over 1,500 CVCs found that a positive bubble study has a 98% specificity for catheter placement in the venous system.9 Bubble studies are also easily adopted for those with little to no POCUS experience, including medical students.10

The sensitivity (86-98%) and specificity (97-100%) of POCUS for detecting pneumothorax has been shown to be superior to standard CXR (sensitivity of 36–56% and specificity of 99–100%).11

In cases of aberrant anatomy (such as persistent left SVC), the catheter may project over the aorta or lung while lying within the venous system. Therefore, POCUS may in fact be superior to CXRs for confirming that a CVC is within the venous system.12 Conversely, an improperly placed CVC overlying the SVC may appear to be correctly positioned on a CXR.

Take-Home Points

  • A structured use of POCUS after CVC placement combines lung ultrasound, internal jugular vein ultrasonography, and echocardiographic bubble study to rapidly confirm that a catheter is placed within the venous system.
  • Post-procedural POCUS can accurately rule out important complications such as pneumothorax.
  • The time to safe administration of vasoactive agents may be reduced by using post-procedural POCUS instead of traditional chest radiography.


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Author information

Timothy Montrief, MD MPH

Timothy Montrief, MD MPH

Emergency Medicine Resident
Jackson Memorial Hospital
University of Miami Miller School of Medicine

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