So in my ongoing quest to reframe my resuscitation step-by-step, I’ve been following up on a number of leads regarding the glycocalyx, as previously stated, and John’s reference to this article in a previous comment I feel is highly relevant. So this is it:
Synergistic Effect of Anemia and Red Blood Cells Transfusion on Inflammation and Lung Injury, Anping Dong, Manjula Sunkara, Manikandan Panchatcharam, Abdel Salous, Samy Selim, Andrew J.Morris, and Susan S. Smyth
Advances in Hematology, Volume 2012, Article ID 924042, 8 pages
S1P (sphingosine-1-phosphate) is a regulator of endothelial permeability and immune function. Uh-oh, why had I not heard of it? Hmmm…I don’t think it was in Guyton’s or in Harrison’s…and there hasn’t been an RCT about it… Ok, that about explains it.
So here are some factoids about S1P:
– serum levels correlate with HCT as RBCs serve as an S1P reservoir.
– anemic patients’ S1P levels are NOT fully replenished by transfusion, especially the older the transfused blood is.
– In fact, older RBCs may actually remove plasma S1P.
They basically took mice, and in the first group, bled them (by 20ml/kg) and looked at inflammatory markers, lung permeability and also S1P levels. That’s basically the control group, and they noted that hemorrhage significantly increased inflammatory markers (interesting in and of itself) . They then transfused these mice using wither fresh, S1P-loaded RBCs, or 14-day old RBCs, and, lo and behold, the fresh blood resulted in less inflammation, increased S1P, but most importantly, markedly decreased lung permeability. So clearly, S1P attenuates transfusion associated lung permeability.
In the next group, they injected the mice with LPS following hemorrhage, and found a synergistic effect of blood loss and LPS on inflammation and lung permeability, as could be imagined. Following the LPS, they were transfused with one of four strategies: fresh blood, old blood, fresh blood + S1P or old blood + S1P. Well, lung permeability still increased in all groups, but least in the fresh blood + S1P, and the old blood + S1P a close second.
Note, interestingly enough, that saline alone (the “control”) also increased lung permeability, highlighting yet again that NS (and probably any crystalloid) is not innocuous…
So here we’re looking at the finer effects of transfusion, and why, against “common-sense” correcting a patient’s hemoglobin level does not seem to help in all situations. We have understood the aging issue and loss of deformability, but it is time to take a finer look. We are familiar – at least in concept – with transfusion-associated lung injury or TRALI, but the mechanism remains unclear.
Summary and Take-Home message:
S1P infusions in sepsis? Maybe someday…
Yes, this is an animal study, and the results cannot be extrapolated directly to humans, but it is food for thought, as John had mentioned. Certainly at least this should tell us to keep and ear/eye out for human work with S1P, but personally, it will make me even more comfortable in not transfusing my septic patients with hb’s in the low 70’s and maybe even high 60’s (try repeating the cbc, more often than not comes back a couple points higher and you can avoid transfusion), and for those who are a little more aggressive with transfusion, maybe this should make them think twice…
I’ll add what I can dig up on human S1P studies soon.