Rocky Versus Drago, Luke Versus Vader…Chest Radiograph Versus Ultrasound?*
The authors used ultrasound to confirm correct placement of the CVC in the distal superior vena cava (SVC) or the SVC/right atrial (RA) junction via 1) visualization of the guide wire in the distal SVC or SVC/RA junction, 2) direct visualization of the CVC tip in the distal SVC or SVC/RA junction, and 3) timing of appearance of agitated saline in the RA/right ventricle after injection into the CVC.
They performed a subxiphoid four-chamber view or an apical four-chamber view to identify the wire in the RA after its advancement through the introducer needle. The CVC was then inserted over the guide wire and the tip visualized in the SVC or SVC/RA junction. The authors concluded that the CVC was in the correct position if the guide wire and/or CVC tips were seen on ultrasound in either the distal SVC or SVC/RA junction. It is important to note that “marked” wires were used in a prior study (5), which allowed exact measurement of how many centimeters of wire were inserted into the vessel and thus the distance to the RA/SVC junction.
The authors also performed an agitated saline test as part of their protocol. This involved the injection of 10 cc of agitated saline into the newly placed catheter. If the saline immediately clouded the RA, then the CVC tip was likely located in the actual RA or inferior vena cava. If a jet of agitated saline was noted in the RA less than 2 seconds after injection, then the CVC tip was considered appropriately placed near the RA/SVC junction. If a greater than 2 seconds or greater delay existed between injection and appearance of agitated saline in the RA, then the CVC was misplaced. This technique has had mixed support in prior studies (6–8), including one that the authors cited (9), which only achieved a sensitivity of 33%. Across these studies combined, there was a 1% false positive rate in which the agitated saline test was positive, but CXR showed the CVC was misplaced in another vessel. Possible complications from a CVC tip in the proximal SVC or brachiocephalic vein include venous thrombosis and line malfunction (13–16).
Another important limitation of all ultrasound studies is an inability to obtain adequate ultrasound images (10). In this protocol, ultrasound views could not be obtained in 13 (9.5%) of the patients due to abdominal surgical incisions, patient body habitus, or poor echo windows. These patients were eliminated from the analysis of the protocol’s accuracy in detecting correct catheter placement.
In conclusion, if the CVC or marked wire tips are visualized via ultrasound in the RA/SVC junction or distal SVC, a clinician can be confident the CVC is in the correct position and the CXR can be foregone. The authors were able to confirm CVC placement by their protocol in 97.6% of line placements. Due to limitations of the agitated saline protocol, if the catheter or marked wires are not visualized, our preference would be to still order a CXR to confirm catheter placement.