Drawing labs from CVC locked with heparin

paolo962000 · Jul 28, 2015

Hi Sir.

Some say that instilling heparin 5000 IU/mL at each of the ports will not affect the result of the INR/PT. What I do personally is I take out 5mL of the blood with the previously instilled lock then discard. Then I will assess the patency of the lumens, remove another 10 mL of blood (set aside) then finally draw the blood needed for the PT/INR. After the drawing of the bloods, I will return the 10 mL I previously took to the patient before I drew labs.

I hope that helped you.

JollyGreenGiant · Jul 30, 2015

I had this situation come up last week. We had a pt/inr drawn on one of our patients with a CVC locked with heparin 1000units/ml. I didn't observe my technician's technique when the lab was drawn but out result was around 17. On the redraw it came back as

malestunurse · Jul 30, 2015

I keep hearing conflicting information on this. Some people saying that not discarding 5mls doesn't make a difference and some do. I need to do some research.

IVRUS, BSN, RN · Aug 4, 2015

The last research that I found on this subject was that in order to truly get accurate labs, one must withdraw and waste 25 mls. Also remember thta you should be flushing with a good 20 cc s/p lab draw and then heparinize as necessary.

JollyGreenGiant · Aug 4, 2015

Wow 25mls Is a lot of blood to waste. That could add up doing it a few times per week on a patient with kidney disease.

Rocknurse, MSN, APRN, NP · Aug 6, 2015

I guarantee that if you only draw 5ccs from a heparin locked CVC that your PT/INR will be hugely off. I've worked both acute dialysis and ICU and I can vouch for the fact that this is an issue frequently. I would either draw from a completely different line or withdraw more from the CVC, flush, and then withdraw again. You may re instill some blood if you do it immediately after drawing the lab so as to not drop the Hb/Hct. The first blood you draw will have 1000u of Heparin in it though so you'd have to discard that.

JollyGreenGiant · Aug 6, 2015

I feel a little nervous about instructing my techs to pull off all that blood. What about holding heparin infusion/bolus and drawing the lab 15min into treatment?

MunoRN, RN · Aug 7, 2015

Older reagents used in INR testing are sensitive to heparin and can throw off the result, although I was under the impression that none of those were used anymore.

There is a fair amount of evidence out there on the amount of waste required and it's consistently 2-3 times the lumen volume, or about 5 mls at the most. I'd be curious to here what source suggests 25mls. Based on the current evidence, I'd argue anyone who wastes and tosses 25 mls for a lab draw should be charged with felony assault.

IVRUS, BSN, RN · Aug 7, 2015

Muno,

It was a NIH study from around 2005 which stated that accurate results were NOT seen unless that much was wasted. I am not advocating for this to be done, but rather am encouraging all coag studies to be done peripherally, unless you have a catheter which has NOT been exposed to heparin. Assault for wasting this amount????... Get real boy!!!.. But, I would worry about anemia for this patient.

MunoRN, RN · Aug 7, 2015

Muno,
It was a NIH study from around 2005 which stated that accurate results were NOT seen unless that much was wasted. I am not advocating for this to be done, but rather am encouraging all coag studies to be done peripherally, unless you have a catheter which has NOT been exposed to heparin. Assault for wasting this amount????... Get real boy!!!.. But, I would worry about anemia for this patient.

Are you maybe confusing the amount of flush required with the amount of waste? Blood should not be used to flush the catheter, it should be sufficiently flushed with saline or other appropriate solution, then the solution is removed from the line with the waste.

We know that blood draws and wastes represent a significant iatrogenic harm to patients which is one thing if it's justified in the care of the patient. Causing unjustifiable harm is what "assault" means and yes, I'm aware we don't take that as seriously as we should.

IVRUS, BSN, RN · Aug 10, 2015

Are you maybe confusing the amount of flush required with the amount of waste? Blood should not be used to flush the catheter, it should be sufficiently flushed with saline or other appropriate solution, then the solution is removed from the line with the waste.
We know that blood draws and wastes represent a significant iatrogenic harm to patients which is one thing if it's justified in the care of the patient. Causing unjustifiable harm is what "assault" means and yes, I'm aware we don't take that as seriously as we should.

If I meant FLUSH, that is what I would have said. I would not say Blood discard amounts if the research article stipulated that your flush should be 25 mls s/p withdraw of specimen. Why do you assume that I didn't mean what I said? I like you, am well read.

Here is the author:

Mayo DJ, Dimond EP, Kramer W, McDonald KH. Discard volumes necessary for clinically useful coagulation studies from heparinized Hickman catheters. Oncology Nursing Forum.