Anemia: Physiologic Consequences

• Reduced hemoglobin concentration with anemia decreases the ability of blood to deliver oxygen. The body uses several compensatory mechanisms to mitigate the impact of this.

• At the level of microcirculation, the effective hematocrit can stay almost unchanged because of the dynamics of the RBCs in plasma as they travel through blood vessels of smaller sizes.

• Various oxygen sensors within the body initiate compensatory mechanisms via the hypoxia-inducible factor signaling pathway

• The renal cortex increases its release of erythropoietin.

• Respiratory rate and ventilation are increased. V/Q matching improves via nitric oxide-related mechanisms.

• Cardiac output is increased

• Aortic/carotid body chemoreceptors detect hypoxia and activate the SNS, promote positive inotropy and chronotropy.

• Venous return and preload are increased. Afterload is decreased secondary to vasodilation (mediated by NO and hypoxia).

• O₂ curve shifts to the right secondary to increased 2,3-DPG and reduced pH and thus facilitates oxygen release to tissues.