Neil Canavan

April 11, 2013

NEW YORK, New York — Bedside ultrasound imaging could be poised to replace the gold standard of chest x-ray for the confirmation of central venous catheter placement, according to preliminary data from a pair of ongoing studies.

The ability to detect catheter placement complications with ultrasound imaging has not been established, but results from both studies, presented here at the American Institute of Ultrasound in Medicine 2013 Annual Convention, are promising.

The first study, presented by Kathleen Calabrese, MD, an emergency medicine physician at the George Washington University Medical Center in Washington, DC, focused on the question of central line placement.

The work, elegantly straightforward, hypothesized that if the line is properly placed, a saline flush will be seen on ultrasound.

"There's not much to it. You switch [the unit] over to a cardiac monitor, visualize the right side of the heart, then you flush and look at the images," Dr. Calabrese explained. Proper placement will be characterized by an immediate opacification of the right atrium and right ventricle as the saline flows through.

To compare bedside transthoracic echocardiography with chest x-ray, the researchers, led by Yiju Teresa Liu, MD, also at George Washington University, looked at 28 patients who underwent catheter placement in the critical care setting. A bedside sonographer obtained the images; 20 patients were imaged concurrent with catheter placement and 8 were imaged within 24 hours of placement. "We had no involvement with the actual placement of the central line unless one of our faculty was taking care of the patient," Dr. Calabrese said.

Using a standard 10 cc saline flush, ultrasound results were in 100% agreement with chest x-ray for catheter placement. Even in the presence of a Swan-Ganz catheter (1 patient) or a pacemaker (1 patient), the turbulence of saline flow was clearly seen, Dr. Calabrese reported.

Recruitment to this study is ongoing, but the results will have to be validated in a larger multicenter study.

A second study, the Sonographic Evaluation of Central Line Placement (SECLiP), used the same methodology to examine an expanded list of questions: Can you confirm catheter placement? What about complications? What about timing?

SECLiP Study

"Ultrasound has already been shown to improve accuracy when placing lines," said SECLiP lead investigator Eric Mervis, MD, from the University of California, Irvine. "There are fewer needle sticks and fewer complications, but we're still relying on chest x-ray for permanent placement," he said.

There are disadvantages to this gold standard, he explained. Chest x-ray results take more than 10 minutes to obtain, complications cannot be detected during the procedure, and chest x-ray can detect a pneumothorax with only 50% sensitivity in a supine patient.

In contrast, ultrasound offers immediate assessment of complications, can detect a pneumothorax with up to 95% sensitivity in a supine patient, and does not expose the patient to radiation.

Dr. Mervis reported results for the first 55 of 140 patients enrolled in the SECLiP observational study.

Correct catheter placement was defined as the tip being within 2 cm of the cavoatrial junction. Ultrasound images were obtained by emergency department residents, pulmonary fellows, and attendings. All sonographers were blinded to the results of the chest x-ray.

With ultrasound, correct placement results in an immediate saline "splash" upon injection. "If it takes longer than a second to see, you're probably too proximal. If you can see the tip inside the have your answer."

To further the aims of the first study, SECLiP investigators looked for evidence of misplacement or contralateral migration in images of central veins, and visualized lungs to find evidence of "lung sliding."

Results of this point-of-care ultrasound imaging were good, but not perfect. It detected 2 misplaced lines, whereas chest x-ray detected 5 (91% agreement). No pneumothorax was detected with either method.

Perhaps more significant were the timing observations, Dr. Mervis pointed out. "There was a 17-minute time difference between ultrasound and x-ray, which could mean more expeditious use of central lines for intravenous fluids, antibiotics, and vasopressors in potentially unstable patients."

Dr. Calabrese and Dr. Mervis have disclosed no relevant financial relationships.

American Institute of Ultrasound in Medicine (AIUM) 2013 Annual Convention: Abstracts 1540969 and 1540557. Presented April 9, 2013.