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Caitlin Raymond: Why Red Cells Don’t Relieve Fluid Overload

Caitlin Raymond/LinkedIn

Jul 6, 2026, 12:13

Caitlin Raymond: Why Red Cells Don’t Relieve Fluid Overload

Caitlin Raymond, Assistant Professor of Pathology and Transfusion Medicine at University of Wisconsin-Madison, shared a post on LinkedIn:

”An attending I trained under used to reach for red cells whenever a patient looked fluid overloaded.

‘It’ll help pull fluid back into the vessels,’ he’d say. I finally looked up the numbers. They don’t back him up.

Packed red cells measure ~1.9 mmHg of colloid osmotic pressure. Normal plasma runs 25–28 mmHg — and almost all of it comes from albumin, not hemoglobin.
A 2020 Vox Sanguinis study found this holds regardless of storage age. RBCs just aren’t doing much osmotic work, full stop.
So albumin must be the fix, right? Not so fast — ALBIOS and SAFE both failed to show a mortality benefit, and the 2026 Surviving Sepsis guidelines now favor crystalloids alone in most septic patients.
In inflammatory states, capillary permeability increases — so infused albumin can leak right along with the fluid it was meant to hold back, worsening the very overload it’s supposed to treat.

Neither product reliably does what the physiology textbook promises.

‘It makes physiologic sense’ and ‘it’s been shown to work in patients’ are not the same claim — and medicine quietly swaps one for the other more often than we’d like to admit.

What’s the last piece of transfusion ‘common sense’ you double-checked and found didn’t hold up?”

Caitlin Raymond: Why Red Cells Don't Relieve Fluid Overload