Is My Way Always the Best Way? Drawing PTT from a Central Line

What is the best way to draw an activated partial thromboplastin time when a patient is receiving heparin therapy and has a central venous catheter?

One of the other clinical nurse specialists that I work with and I, along with several of the staff nurses, are embarking on a new research project that I think will turn out to be very interesting. The question is: how to best draw an activated partial thromboplastin time (aPTT or PTT) when a patient is receiving heparin therapy and has a central venous catheter? The PTT is ordered at intervals to monitor unfractionated (standard) heparin anticoagulant therapy. When heparin is given in therapeutic doses, it must be closely monitored. If given too much, the patient may bleed excessively; too little and the patient may continue to clot. The PTT does not directly measure the anticoagulants used but measures their effect on blood clotting. Heparin therapy is associated with medication errors and adverse events, so nurses are generally very cognizant about carefully monitoring not only the dose of heparin they are administering to the patient, but also monitoring their PTT to ensure the correct dose is indeed being given.

But the question arises as to what is the best method for obtaining the PTT especially when the patient has a central venous access device (CVAD)? If you talked to 10 nurses that you know and ask them what they do when they have to draw a PTT, I would venture to guess that you’d get at least five different techniques. Some nurses turn off the infusion for a minute, some for 5 minutes, some not at all. Others first flush, others do not. Some discard 5 ml of blood first, some discard much more. And some never use the central line at all for a PTT, only peripheal blood draws. We tested it out and sent a survey to the nurses at our facility and found just what we thought. Everyone has their own way of doing it. So what does the literature tell us is the best way or what guidelines are there for best practice? Therein lies the problem. There are no specific guidelines and no real comparisons in the literature of what method is superior. So we’re going to generate that study.

It’s been an interesting process thus far, finding out that there are so many different techniques and so many different opinions as to why one way is better than another. And it’s interesting about the lack of information that we could find on preferred methods. Even when looking at manufacturers’ information about their central lines, the entire process is unclear. For instance, I was searching for recommendations on the amount of blood that would be sufficient to discard prior to obtaining the specimen when a patient has an implanted port. There was very little out there. Many sources told you how to flush and how much, but nothing says much of anything about a discard. The things we do everyday sometimes because someone taught us how to do it that way, but not based on any real evidence are always interesting to find.

In our study, the subjects will have a central line and be on heparin therapy. They will get two specimens drawn for their PTT; one from the CVAD and one peripherally. The one drawn from the CVAD will be done following specific guidelines. Once all the subjects have been tested we will see if one method is superior to another. Again, I suspect that we will find, once we have a defined way of drawing from a CVAD, that the results will closely mimic the peripheral. What we can garner from that is the fact that we do need to have specific guidelines. With those we will see less extreme results and we can be assured that we are providing the best care to our patients.

I will keep you informed at a later date as to the results of the study.

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