compensatory changes to maintain oxygen delivery in acute anemia

Q: In an isovolemic healthy person, acute reduction in the hemoglobin (Hb) concentration induces all of the following compensatory changes to maintain oxygen delivery EXCEPT? - select one

A) Increase in heart rate from basal level

B) Increase stroke volume

C) Increase cardiac index 

D) Decrease tissue oxygen extraction

Answer: D

In a healthy isovolumic person, a reduction in the Hb concentration induces many compensatory changes to maintain the net oxygen delivery. All of the above choices are true EXCEPT choice D. With an increase in heart rate, stroke volume, and cardiac Index (remember high cardiac output failure in anemia!), there is an increase in tissue oxygen extraction.

The most important underlying factor in such compensatory mechanisms is to stay isovolemic. That's why there is a famous saying in Critical Care Medicine: "Blood does not save lives; blood volume saves lives."

Some experts even suggest that a healthy individual with such compensatory mechanisms can maintain oxygen delivery up to Hb/Hematocrit (Hct) concentration as low as 5 g/dL / Hct 15 %, given intravascular volume is maintained.

#hematology

#hemodynamics

References:

1. Weiskopf RB, Viele MK, Feiner J, et al. Human cardiovascular and metabolic response to acute, severe isovolemic anemia. JAMA 1998; 279:217.

2. Bliss S. Anemia and Oxygen Delivery. Vet Clin North Am Small Anim Pract. 2015 Sep;45(5):917-30. doi: 10.1016/j.cvsm.2015.04.006. Epub 2015 May 29. PMID: 26033442.

3. Bunn HF. Oxygen Delivery in the Treatment of Anemia. N Engl J Med. 2022 Dec 22;387(25):2362-2365. doi: 10.1056/NEJMra2212266. PMID: 36546628.