Thread by @cjchiu

Day 7 of my inpatient service & number 7 of my #BreadNButterMedicine #MedThreads.

Today, Hemodilution!

I’m no expert & I don't routinely administer large volumes of IV resuscitation fluids like my EM & trauma colleagues. But, I do give maintenance fluids to many patients.

2/ (POLL) With maintenance IV fluids, which cell lines can you see decrease due to hemodilution?

3/ To unpack this, we need to first start with the definition...

What is hemodilution?

Hemodilution implies dilution of the normal blood constitutents occuring either spontaneously after injury and/or blood loss, or as a result of plasma replacement or expansion.l

4/ So, does hemodilution exist when looking at Hgb & HCT?

This 1998 study bolused 20 “healthy” non-bleeding subjects a total of 35 mL/kg over 2-4 hours. They found a drop of hematocrit of 3-6 points with the first 20ml/kg but little effect for the remaining 15mg/kg.

5/ The ideas of hemodilution were reviewed again in 1996 when Grathwohl et al sought to not only look at bolus saline infusions, but also maintenance IV fluids. Again, they focused on nonbleeding healthy volunteers… 9 of them this time.
ncbi.nlm.nih.gov/pubmed/8545692

6/ Suprisingly, they found:

1️⃣Bolus fluids had significant effect on Hgb and HCT
2️⃣Maintenance fluids demonstrated NO hemodilution

7/ They theorized that much of the maintenance IV fluids redistribute with third spacing, increased UOP (from sodium load), suppression of RAAS, & many other mechanisms that work on the cardiopulmonary volume. However, a large bolus overwhelms the system. ncbi.nlm.nih.gov/pubmed/8545692

8/ The finding of hemodilution with boluses of intravenous fluids have continued to be found in recent studies such as by the authors of the ARISE trial which evaluated it in the setting of Septic Shock. ncbi.nlm.nih.gov/pubmed/29724246

9/ Quick recap. Hemoglobin & hematocrit seem to be affected by hemodilution, at least with large boluses of IV fluids and in scenarios like septic shock. The evidence (as sparse as it is) may be less supportive of hemodilution with administration of simple maintenance IV fluids.

10/ What about the other constituents in blood? Is there an effect of IV fluids on white blood cell and platelet counts? Let’s go back to that 1996 Grathwohl et al study above. In their very small study, they found “no significant” changes to both the WBC or the Plt counts.

11/ What are some explanations for this surprising result?

They theorize:
1️⃣Effects on WBC might be attenuated by a large pool of demarginated WBCs and diurnal variation in glucocorticoids
2️⃣Platelet counts can be affected by mobilization or sequestration from the spleen

12/ Another example of poor correlation of ⬆️IV fluids and a ⬇️ in Plts is this 1982 study where they set out to develop a “dilution model”, to estimate plt dilution after infusion of RBCs, colloids & crystalloid. They found crystalloids had no statistical effect on dilution.

13/ I'm not saying that hemodilution (especially with maintenance IV fluids) doesn’t occur in WBC and Plts. However, you should be wary of jumping to the conclusions when your patient’s cell lines are all decreased because of their recent IV fluid transfusions.

FIN/ In summary:
💥Hgb/HCT can be hemodiluted. (Evidence may be stronger with bolus vs maintenance fluids)
💥 Some small studies support no dilutional effect on Plts & WBC
💥Don’t be too quick to blame the IV fluids when a patient has low WBCs or Plts.

(POLL)

PS- (POLL) This marks the halfway mark in the planned 14 days of #Tweetorials / #MedThreads. Not sure if many people are benefiting from them. Please let me know if you want me to continue. I'm hoping for at least 50 yesses.

... no edit function... Should be "the remaining 15 mL/kg"

Oh. Wow. I really underestimated that response.