Ultrasound (US) is increasingly used as a “global” tool to assist all the steps of a central venous catheter insertion procedure: choice of vein/approach, needle guidance during venepucture, prevention of primary malposition, rule out of pleural complications. While approach choosing and needle guidance are now well standardized, US-based prevention of primary malposition and rule out of pleural complications are still a matter of debate.
rule out of catheter misdirection in the superior vena cava (SVC) tributary veins (so called “negative assessment”)
identification of the tip within the right atrium and/or in the lower part of the SVC (so called “positive assessment”). Tip position may be evaluated:
○ by direct visualization of the tip within the cardiac chambers and/or the lower part of the SVC
○ indirectly by contrast enhanced ultrasound.
Prerequisite for a reliable negative and positive assessment is a good visualization of the entire central venous axis, including the brachiocefalic veins, the lower segment of the SVC and the right atrium.
Negative assessment is usually performed by scanning the internal jugular (IJ), axillary and brachiocefalic veins.
Different scanning techniques have been described for the positive assessment, in terms of:
acoustic windows: anterior trans-thoracic or subcostal
type of probes: medium (convex) or low (conic) frequency
Both negative and positive assessment have significant limitations.
Negative assessment: a malposition in the contralateral subclavian/brachiocefalic vein may be underestimated because of a US-blind venous segment beneath the clavicule, especially on the left side
Positive assessment: a different probe from the one used during the ultrasound-guided venepuncture is required, and even using high-quality devices, the acoustic windows are often suboptimal; moreover, a high level of training is required.
Rule out of pleural complications often requires a different (usually medium-low frequency) probe from the one used during the ultrasound-guided venepuncture.