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Effect of venipuncture quality on thromboelastography | VETgirl Veterinary Continuing Education Podcast

In today’s VETgirl online veterinary continuing education podcast, we review the effect of venipuncture quality on thromboelastography. Now, if you’ve never heard of thromboelastography or TEG, you’ll need to know that it’s the best way to detect for hypercoagulability. Keep in mind that your PT/PTT test for hypocoagulability, not HYPER-coagulability. Unfortunately, TEG is really only available at academic (e.g., veterinary school) settings. So, if you have a TEG machine (or you’re an emergency critical care or internal medicine resident), pay careful attention!

So, Garcia-Pereira et al wanted to evaluate this in a prospective, observational study at Michigan State University, where the researchers collected samples from 15 healthy dogs. Two consecutive blood samples were collected into citrate-containing tubes from each external jugular vein and randomized into the following categories:

A) Clean venipuncture
B) Suboptimal venipuncture (which was defined as the need to re-position the needle at least one time with a needle insertion performed adjacent to the vein and redirected).

A total of 4 samples were taken from each dog consecutively; 2 first samples and 2 follow-up samples, all without removing the needle. The samples were then classified based on the degree of inadequate venipuncture and evaluated for hemolysis and platelet clumping. TEG was then performed on all the blood samples, and the R, K, α, and MA were recorded.

So what did this study find?

A statistically significant reduction in the Reaction time (R) was reported in the first sub-optimally collected blood sample when compared to all other samples. No statistically significant difference in R was reported between any other samples. No other TEG value was significantly altered and the degree of platelet clumping between samples was not statistically important. The authors did find a statistically significant relationship between hemolysis and the degree of difficulty during venipuncture. The more times the needle had to be repositioned, the higher the degree of hemolysis. They also reported that those significantly hemolyzed samples had a statistically significant reduction in the mean R time (2.5) when compared with samples were no hemolysis was detected (4.9).

So, what can we take away from this VETgirl podcast?

Despite suboptimal venipuncture and attempting to create mild-to-moderate venipuncture trauma, negligible effect was seen on the TEG overall, with the exception of the Reaction time being significantly affected. In other words, suboptimal venipuncture resulted in a shorter reaction time, indicating that more rapid initiation of clot formation occurred. Also, a reduction in the Reaction time can be seen with significantly hemolyzed samples. Discarding the first sample collected and using a second sample for TEG measurements decreases the degree of hemolysis and its effects on R time. But this does not appear to be clinically necessary, as the overall effects were mild. Lastly, few studies have evaluated how the degree of hemolysis affects TEG measurements in veterinary patients. The degree of difficulty encountered during venipuncture appears to be related with the degree of hemolysis in the sample. This study reiterates the importance of optimal venipuncture, especially when assessing coagulation.

Some limitations of this study were that the authors were attempting to correlate the degree of difficulty during venipuncture and hemolysis. Yet, the degree of hemolysis was not quantified in this study. Another potential limitation of this study is the small sample size. Finally, accurate assessment of platelet activation was not part of the study. That said, this is an important study for those who do have TEG in their clinic. Know that moderate trauma during venipuncture may result in a mild but significant prolongation of the Reaction time (R), but that this effect can be minimized by not using the initial sample collected, but using the second one instead to prevent any affect on TEG. Or, just have a really good atraumatic, optimal venipuncture instead.

References:
Garcia-Pereira BL, Scott MA, Koenigshof AM, Brown AJ. Effect of venipuncture quality on thromboelastography. J Vet Emerg Crit Care 2012;22(2):225–229.

Abbreviations:
TEG: thromboelastogram/thromboelastography
R: reaction time

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