Anaemia: Adaptive Mechanisms and Consequences

Abstract

Abstract Human life depends on the availability of oxygen and its conversion into energy used by living cells. Reduced oxygen to tissues is referred to as hypoxia, and may result from decreased oxygen delivery or mitochondrial dysfunction. In the setting of tissue hypoxia due to anaemia or other causes, several adaptive and coordinated physiologic processes are initiated to maintain oxygen delivery and limit oxygen consumption. Mechanisms to increase oxygen delivery in the face of anaemia or global hypoxia include the stimulation of erythropoiesis, and increasing cardiac output. Oxygenation availability is further maximised by decreases in the haemoglobin‐oxygen binding affinity, increases in tissue oxygen extraction, and via changes in regional blood flow. Mild to moderate anaemia, especially if chronic, is generally well tolerated given these adaptive processes. In states of inflammation or chronic disease, down regulation of haemoglobin occurs and may represent an important adaptive mechanism. Key Concepts: Aerobic metabolism and human life depend on the availability of oxygen. Anaemia results when the haemoglobin levels are below normal and, if severe, may result in tissue hypoxia. Adaptive mechanisms exist to compensate for anaemia or other causes of tissue hypoxia so that oxygen delivery is maintained and balanced with oxygen consumption. A major adaptive mechanism in response to anaemia is to increase production of the growth hormone erythropoietin, leading to the formation of red blood cells. The anaemia associated with inflammation has features of an adaptive response, is generally well tolerated and rarely requires treatment.