Anaemia is a condition in which the number of red blood cells, or the amount of haemoglobin within them, is below normal, resulting in reduced oxygen-carrying capacity of the blood. Haemoglobin is the protein inside red blood cells that binds oxygen in the lungs and releases it to tissues throughout the body. When haemoglobin levels fall, the body’s tissues receive less oxygen than they need, producing the characteristic symptoms of fatigue, breathlessness, pallor, and reduced exercise tolerance.
Anaemia has many possible causes. Iron deficiency (the most common cause worldwide) results from inadequate dietary intake, poor absorption, or chronic blood loss. Other common causes include vitamin B12 or folate deficiency, which impairs red blood cell production; chronic kidney disease; chronic inflammatory conditions; and haemolytic disorders where red cells are destroyed prematurely. In a cardiac context, anaemia is frequently encountered as a comorbidity in patients with heart failure and after cardiac surgery.
Anaemia has significant effects on the cardiovascular system. The heart compensates for reduced oxygen delivery by beating faster and with greater output (increased cardiac output). In patients with pre-existing heart disease or reduced cardiac reserve, this additional demand can worsen heart failure symptoms, cause or exacerbate angina, and potentially trigger arrhythmias. A haemoglobin level below 8 g/dL is generally considered severe; blood transfusion may be required at this level, or at higher levels in symptomatic patients with significant cardiac conditions.
After cardiac arrest, anaemia may develop or worsen due to haemodilution from resuscitation fluids, blood sampling in the intensive care unit, or underlying illness. Treatment depends on the cause and severity: iron, B12, or folate supplementation for deficiency states; erythropoiesis-stimulating agents in renal disease; and blood transfusion for acute or severe symptomatic cases.
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