Using a hand carry ultrasound system, students and staff from the Department of Radiology/Ultrasound and Anesthesiology at Sidney Kimmel Medical College of Thomas Jefferson University recently finished a study of mechanisms related in the cause of radial artery catheter failure.

The study was presented at the 2015 WFUMB/AIUM Convention [UMB 41(4S):S125, 2015]. Radial artery catheters (RAC) are commonly used in the emergency department, operating rooms and critical care units of a hospital to accurately monitor the arterial blood pressure and acquire blood samples.

With the use of SonoScape’s S9 ultrasound system (SonoScape Medical corp.; Shenzhen, China), the researchers hoped to discover why RAC fail prematurely and the causes of complications related to RAC clinical use. The clinical trial was designed to determine the causes of RAC failure and to confirm if a low artery diameter to catheter diameter ratio leads to decreased local blood flow and thrombosis.

For this IRB-approved study, 25 patients requiring a RAC for clinical care were enrolled. To evaluate and monitor the RAC insertions as well as blood flow dynamics in the radial and ulnar arteries, the 25 patients were scanned with the S9 ultrasound system with a 12 MHz linear array probe.

They were scanned before RAC insertion, immediately after, and intermittently every two to four hours during the day and every four to six hours during the night (for 24 to 36 hours). By using the S9 ultrasound, they were able to literally see what was happening in the ulnar and radial arteries of the patients.

Using the S9’s grayscale and Doppler technology, measurements were taken of blood flow and the diameters of both the ulnar and radial arteries. Assessments of RAC insertion factors also allowed for measurements for the composite vessel trauma score for respective arteries after insertion. To analyze the data, a paired Student t-test and a Wilcoxon Rank-Sum test were used to compare results. For the purpose of the study, a RAC initial failure and final failure were classified as difficulty/inability to aspirate blood through the RAC or a dampening/loss of the blood pressure waveform.

Throughout the study, a total of 211 ultrasound scans were obtained from the 25 patients using the S9 ultrasound system. From the 25 patients, 21 experienced a RAC initial failure and four patients experienced a RAC final failure. With the S9’s high image clarity, the reasons for RAC failure were easily revealed. Each failed for a different reason: ranging from the catheter being outside of the vessel and in the subcutaneous tissue, the RA catheter tip was against the arterial wall, thrombus on the catheter tip partially/completely obstructed the RA catheter lumen, and thrombus within the RA lumen partially/completely obstructed RA blood flow.

Soon after RA catheter insertion, the RA and UA inner diameters increased from 2.21±0.4 mm to 2.54±0.45 mm and from 1.91±0.44 mm to 2.23±0.48 mm respectively (no significant differences in RA and UA diameters).

For the 24 RACs that did not have a final failure, the median number of cannulation attempts was 9 and the median CVTS was 8.5. Comparatively, the CVTS for the four RACS that developed a final failure was 8.3 and the mean number of blood draws was 5±3.3. Median time to initial dampening of the RA waveform was 5.9 hours in 22 different cases.

By using the S9’s color Doppler, the team was able to measure the velocities in the RA and UA arteries after RAC insertion. In the RA artery, the peak velocity decreased from 56.2±18.7 to 36.6 cm/s after the RAC was inserted. Peak velocity in the UA however, increased from 53.7±19.3 to 63.4±20.5 cm/s after insertion of the RAC. Ultrasound scans also did not indicate a difference in vessel diameter or blood flow velocity when comparing successful RACs to that of the four that developed a final failure; however this may be attributed to the limited number of final failures that were observed.

There was also no difference in velocity patterns or in diameter in the RACs that failed compared to those that did not fail.

The conclusions from this study are threefold. Both the RA and UA experienced significant dilation after RAC insertion. The data suggested that vasodilation and increased blood flow around the catheter may help to prevent thrombosis and protect the function of the arterial catheter. In some patients, the peak blood flow velocity significantly decreased after insertion of a 20 g catheter, especially in RA with a small inner diameter. With the S9’s high-resolution ultrasound imaging abilities, in vivo observations were possible to reveal what caused RAC failure during the patient’s clinical course. Failures consisted primarily of tortuous vascular anatomy and RAC tip obstruction, thrombus formation on the RAC tip, and partial/complete thrombosis of the RA lumen.

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