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Blood draws from central lines with TPN infusing.....

Our current policy is to stop the infusion, flush with 20ml NaCl, draw a waste and discard 3-5ml blood, then draw sample followed by a NaCl flush and restart of the infusion as ordered. That being said, we have had some questioning from the lab personnel regarding concern for altered lab results based on this practice. I do not know of any actual altered lab results if the practice is followed as stated above. In my opinion, the time it takes from shutting off the infusion, obtaining the materials to do this process and completing it from initial flush to discard of waste should more than allow for the TPN to dissipate within the SVC. I truly feel that saving the patient these multiple lab draws peripherally would be the preferred method. I have a few questions:


1. What is everyone's practice with regards to single lumen PICC lines with TPN infusion and lab draw results?

2. What is everyone's practice with regards to multi-lumen lines with TPN infusing and lab draw results?

3. Is there a certain length of time the TPN must be on hold prior to carrying out the above sequence of events?

4. The lab personnel have stated concern about the TPN having leached onto the internal lumen and therefore it may alter lab results even with the above stated practice. Does anyone have any experience with this being an issue?

5. Lastly, WHY? Is there any evidence based practice to support the argument that the above mentioned practice is not only OK but that it does not alter lab results if properly flushed, waste discarded, etc.? Where can I find that evidence?


Thank you to anyone that can take the time to reply. I have read the older posts on this issue but could really use some actual references for the practice so that we can get everyone in our facility on the same page as to how we provide patient care.

I have been doing several

I have been doing several literature searches lately and have come across several studies that touch on your question. Those studies were not applicable to what I was searching for so I can not provide the references but your own PubMed search should pull them up. Basically, no need evidence that the PN will not alter the lab results before relying on those values for treatment decisions. We do not really have all the answers on this issue but there are numerous problems with this practice.

First, excessive hub manipulation is known to increase the contamination, and therefore infection. So I would never, not ever, interupt infusion PN to draw a blood sample.

Second - The fibrin/biofilm layer inside that catheter may not release all of the sugar, lytes, etc with a flush and we certainly do not know what volume of flush is required if this layer can be cleared.

Third - you can be drawing PN from one lumen into the aspirate from another lumen - no proof either way. But it could happen with fluid moving from the tip of one lumen into the blood being pulled into the other lumen. Or there can be communication between the walls of multilumen catheters.

Fourth - no evidence to support the length of time for stopping the PN before drawing the sample

Fifth - there is evidence that drawing blood cultures from a CVAD with a used needleless connector produces wrong results. Who knows about all the other lab data? Not enough research yet.

A PN lumen should be used only and exclusively for the PN infusion. I would consider having reliable lab data to use for clinical decisions of greater importance than the discomfort from peripheral venipuncture. I am not suggesting that the patient be made a pin cushion. This would require having highly skilled phlebotomist to make these venipunctures. It is much greater risk to have the CVAD fail from this use, or to have errant lab data than to have peripheral venipunctures. That would be my risk-benefit assessment. I know there are others who disagree. You need to read the Infusion Nursing Standards of Practice - Phlebotomy - Blood Samping via a VAD, and carefully assess the ~25 studies listed there. All of these statements received a IV or V ranking of the evidence, so that means this is not very high on the evidence scale, but that is all there is.


Lynn Hadaway, M.Ed., RN, BC, CRNI

Lynn Hadaway Associates, Inc.

126 Main Street, PO Box 10

Milner, GA 30257


Office Phone 770-358-7861

Lab draws from TPN line

Our policy is to never disconnect the TPN infusion due to the risk of contamination.  If peripheral draws are too difficult and/or the pt needs other meds in addition, we use a triple connector to maintain a closed system.  One line for TPN, one for IV meds/flush, one for lab draws.  Close all line clamps, flush the lab lumen with 20 ml NS, waste minimum of 10 mls, draw lab, flush, resume infusions.  I do caution nurses to evaluate their lab results due to the possibility of contamination if flushing is inadequate. Remember the single lumen CVAD is a common pathway at the end of the connector so compatibility must be determined.  For blood cultures, the policy is to do all peripherally due to the risk of contamination, but if peripheral is not possible or if the phy wants one from the line, the injection cap must be changed prior to drawing the blood culture.

kladusau SAH Okcy

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