Studies provide hope for dissolving clots
'Pulse spray' technique shows early promise
The biggest problems are often those that sneak up on you. According to Donna Jo Mayo RN, a graduate student at George Mason University and a hematology research nurse coordinator for the National Institutes of Health (NIH) in Bethesda, MD, recent findings as well as a study currently being conducted show that subclavian vein thrombosis could be occurring at a much higher rate in patients than many anticipate. However, the NIH is reviewing a "pulse spray" technique that could help prevent the loss of future use of a vein for intravenous therapy due to thrombosis.
"Subclavian vein thrombosis due to a venous access device isn't as rare an occurrence as most people may think," says Mayo.
The NIH conducted an initial surveillance study in which researchers took a venogram before a catheter was inserted, a second venogram six weeks after the catheter was placed, and a final venogram 12 weeks after the catheter was placed.1 The results were surprising.
"We found that six weeks after catheter insertion, 30% of patients had complete vein obstruction with no symptoms," notes Mayo, who adds that the lack of symptoms was due in large part to the development of collateral veins around the obstruction.
In fact, only 6% of patients with complete vein obstruction exhibited symptoms associated with subclavian vein thrombosis. So even though your patients may be receiving medication without complications, such obstruction puts future use of the same vein at risk because the obstructed vein obviously would not be ideally suited for future catheter placement.
"If you want to place a PICC [peripherally inserted central catheter] line, the PICC would have to follow an alternate route because of the obstruction, and that would pose more complications because the line would have to thread through a collateral vein, which is not the optimum choice of placement for that type of cathe ter," says Mayo. "Also, if the patient needed
a long-term line, inserting a Hickman or Groshong catheter would be very difficult for the radiologist."
Following the initial surveillance study, for the past two years NIH researchers have been using a pulse spray technique to treat subclavian vein thrombosis.
"We thread a catheter from the brachial vein up to the site of the obstruction, where the radiologist situates the catheter into the obstruction so it is embedded in the clot," notes Mayo.
The technique requires the use of a catheter that has numerous injection sites, rather than one. Tissue plasminogen activator (TPA) is injected into the line and comes out of the holes in the catheter directly into the clot.
The initial findings involved 12 patients with subclavian vein thrombosis.2 The results were impressive.
"We had 66% successful clot resolution, defined as greater than 50% patency of the vein," says Mayo. The majority of clots that were not successfully resolved were due primarily to two factors: thrombocytopenia, which resulted in stopping heparin; and thrombosis induced by the presence of the catheter itself.
Smaller catheters may present lower risk
Due to those initial 12-patient results, NIH has amended the pulse spray protocol. The study now includes catheter removal with the focus on preserving the vein for future catheters.
"In the patients we have treated with catheter removal, all the veins remained open, so we're seeing a better success rate," says Mayo.
As a result of the surveillance study, venograms are being done on the patient up front, allowing the radiologist placing the tunneled catheter to choose smaller catheters.
"Our radiologist speculates that the smaller the catheter, the lower the risk of thrombosis," says Mayo. "We are still seeing thrombosis with the use of smaller catheters, although not as high an incidence."
Mayo notes that a larger catheter will cause a reduction in flow in the vein, so the smaller the catheter, the better it is for the patient.
The protocol also was amended for a smaller dose of TPA and a smaller pulse spray catheter, going from 10 cm of catheter that delivered the drug to just 2 cm, with the radiologist moving the catheter back and forth along the clot to deliver TPA.
"We wanted to go with the smaller catheter and the smaller dose of TPA because we wanted to see what the minimum dose is, since we knew it was successful at the larger dose," says Mayo. She adds that the smaller length of catheter allows the radiologist to exercise more control over direction of TPA into the clot by moving the catheter itself.
Mayo points out that in some cases, removing the catheter to allow for vein preservation may not be in the patient's best interest.
"You have to weigh the risk and benefit to the patient, and the catheter and therapy may be much more important at that point," she says. "But once the catheter is removed, will the body take care of the clot? Probably not, and then you are faced with the dilemma of trying to find other access down the road should the patient need it."
Reference
1. Alexander HR, Horne M, Mayo DJ. Venographic surveillance of tunneled venous access devices in adult oncology patients. Ann Surg Oncol 995; 2:174-178.
2. Doppman J, Alexander HR, Horne M. Pulse spray treatment of subclavian and jugular venous thrombi with tissue plasminogen activator. J Vasc Interv Radiol1996; 7:845-851.
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