The case was a young trauma victim,
he wasn't that sick, but sick enough to get admitted for
observation. As part of the trauma protocol we collect blood for labs, type and
screen and the usual stuff. Primary survey completed, we had a nice 16 g
cannula in his left AC fossa but blood had not been collected yet. The lab tech
arrived and was preparing to stick the patient in the R arm when I asked
him. Why don't you take the blood from the cannula? - I'm not allowed to do
that. He replied. I like to avoid unnecessary pain to my patients whenever
possible so I reapplied a tourniquet to the L arm, pulled 3 cc of blood to discard, then collected the blood directly into the tubes. As I was doing
that, the ED chief nurse saw me from across the room and almost had a stroke.
She went into a rant about how this was a violation of the protocols
and yara yara yara... To my amusement, she took the tubes I had
just collected from that freshly-started IV and trash them into the sharps container. Then she order
the lab tech to stick the patient again in the other arm for a
"correct" blood sample. This was a senior nurse and I just couldn't
believe she would do that. What is the difference from that blood to the blood in the other arm?!
So I did a lit search about this
topic and found some interesting data.
- The cannulas are made with soft
plastic that remains open by the positive pressure exerted by the
infusing fluid, the walls tend to collapse if too much negative pressure is
exerted, this causes turbulence and higher rate of hemolysis. This hemolysis is
more likely to occur using the larger vacutainer tubes of 10 cc because
of higher negative pressure early in the draw or when using a syringe
and pulling too hard on the plunger. So if you use a syringe, pull the plunger
just a little bit until you see blood flowing into the barrel and then
continue gently, and for the vacutainer system, use the 5 ml
tubes to minimize hemolysis.
- And what is the deal of tapping the
site to "pop" the vein into view? That doesn't work, the skin gets
red but the vein doesn't change in size and it also can cause hemolysis inside
the vein, so let's not do that either.
- Already inserted cannulas can be
used to collect a blood sample even when IV fluids of medications
have been infused through it. The only caveat is that for glucose containing fluids it is recommended to wait 3 minutes after stopping the infusion. When using the inserted IV, "washing" the cannula with 5 times its
capacity and discarding that blood will eliminate any possibility of contamination. The volume capacity of a 22g cannula is
about 0.05 ml and for a 14g 0.15 ml (yes, go ahead and measure it),
therefore drawing 1 ml is technically enough, but get 2 ml and no one will
argue.
- If you have a prolonged vein hunt for
more than 2 minutes, go ahead and get the cannula in, remove the tourniquet,
elevated the arm and then bring it down again to allow "fresh" blood
into the extremity, reapply the tourniquet and then collect the samples.
This is particularly important if you use venous lactate in sepsis
screening to avoid false positive results.
- Follow this order when filling up
the tubes: Blood cultures -> Lactate -> Coagulation -> Serum ->
Heparin -> EDTA. This will minimize the chance of contamination, false positives, hemolysis
and sample clotting.
- Don't overfill, shake too hard
or drop the tubes; and if you open the tubes transfer the blood from the syringe, do it without the needle.
And this is the summary of all of
these articles. If you have a couple of hours and there is nothing on TV, go
ahead and read...
http://bmhlibrary.info/11174369.pdf
http://www.ncbi.nlm.nih.gov/pubmed/15565033
https://www.futurelabmedicine.org/pdfs/LMBP_ReducingHemolysisSummary.pdf
http://www.who.int/injection_safety/phleb_final_screen_ready.pdf
http://www.ncbi.nlm.nih.gov/pubmed/15565033
https://www.futurelabmedicine.org/pdfs/LMBP_ReducingHemolysisSummary.pdf
http://www.who.int/injection_safety/phleb_final_screen_ready.pdf
And before I go, a final advice for my fellow physicians.
If you think that starting IV's and collecting blood is the nurses' job, then
you are missing the critical concept of team work. As leader of the team you
should know how to do this and every other procedure in the ED; from starting
lines, mixing drips, work up the pumps, etc. This will not only benefit the
patient, it will also earn some golden points with the rest of the team. So
pull up your sleeves and get busy.