Anaemia

Causes of anaemia

Decreased haemoglobin production

Reduced haemoglobin synthesis
- Iron deficiency
- Thalassaemia
- Anaemia of chronic disease
Reduced DNA synthesis
- Megaloblastic anaemia
Reduced stem cell production
- Aplastic anaemia
- Myeloproliferative disorders
Bone marrow infiltration
- Carcinoma
- Lymphoma
Toxic injury
- Radiotherapy
- Chemotherapy
- Infection

Increased red cell destruction

Blood loss – acute or chronic
Haemolysis – intrinsic
- Membrane disorders – hereditary spherocytosis, elliptocytosis
- Haemoglobinopathies – sickle cell disease
- Glycogenolysis – pyruvate kinase deficiency
- Oxidation – G6PD deficiency
Haemolysis – extrinsic
- Immune – warm or cold antibodies
- Microangiopathic – DIC, TTP
- Haemolytic uraemic syndrome
- Infection – e.g. clostridial bacteraemia
- Hypersplenism

Classification of anaemia

Hypochromic microcytic

MCV less than 80 fl
MCH less than 27 pg
Causes include:
- Iron deficiency
- Thalassaemia trait
- Anaemia of chronic disease
- Lead poisoning
- Sideroblastic anaemia

Normochromic normocytic

MCV 80-95 fl
MCH greater than 27 pg
Causes include:
- Haemolytic anaemias
- Anaemia of chronic disease
- Acute blood loss
- Mixed deficiencies
- Bone marrow failure
- Renal disease

Macrocytic anaemia

MCV great than 95 fl
Causes include:
- Megaloblastic anaemia (B12 or folate deficiency)
- Non-megaloblastic causes (alcohol, liver disease)

Preoperative anaemia

Tissue oxygenation is dependent on
- Arterial oxygen content
- Capillary blood flow
- Position on the oxygen dissociation curve
Haemoglobin concentration affects all of these factors
- Anaemia reduces arterial oxygen content
- Reduced plasma viscosity increases capillary blood flow
- Increases 2,3 DPG and shifts dissociation curve to the right
Both anaemia and polycythaemia increase postoperative mortality
Perioperative haemoglobin concentration of approximately 10 g/dl is ideal
Preoperative transfusion may:
- Induce immunosuppression
- Increase risk of infection
- Increase risk of tumour recurrence
If transfusion is required it should be given at least 2 days preoperatively
Blood transfused immediately prior to operation has reduced O₂ carrying capacity

Bibliography

Armas-Loughran B, Kalra R, Carson J L. Evaluation and management of anaemia and bleeding disorders in surgical patients. Med Clin North Am 2003; 87: 229-242.

Mercuriali F, Inghilleri G. Management of preoperative anaemia. Br J Anaesth 1998; 81 (Suppl 1); S56-61.