Haemoglobin fall correlates poorly with the volume of intravasation.

Comparing volumetric and biochemical assessment of intravasation caused by hysteroscopic surgery

Oscar HaudeLucilla E. OverdijkPaul J.M. van KesterenBart F. GeertsBart M.P. Rademaker

Only a small retrospective observational study from a single centre, but the point is that the researchers were expecting to confirm that the volume of intravasation during hysteroscopic surgery correlates well with the acute change in haemoglobin concentration. It does not. This paper interests fluid physiologists because many clinical studies have measured the acute fall in haemoglobin concentration during intravasation (intravenous fluid administration) and reported the result as increase in plasma volume. Perhaps that is an assumption too far, as I suggest in Fluid Physiology: A Handbook for Anaesthesia and Critical Care (December 2019). A vast literature reporting haemoglobin concentration changes after colloid or crystalloid infusion may have misled clinicians about their effective resuscitation doses when it was the anaemia inducing doses that were being measured. I know some do not like this term, but I have labelled it The Colloid Delusion as a play on the title of Richard Dawkins’ famous book. Below is a slide from a recent lecture.

The researchers also looked at acute chloride concentration changes during intravasation. In brief, only poor correlation between volume intravasation and plasma chloride concentration change. So many unfounded presumptions about plasma chloride concentration among those who call for mixed-anion intravenous fluids, but that’s another topic.

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