Anaemia is a common medical condition. It has several implications for both general health and perioperative practice.
Anaemia is defined as a haemoglobin (Hb) value below the normal range. The range of normal will vary slightly depending on the patient circumstances:
Female - 12-15 g/dl
Male - 13-16 g/d
Children have a slightly lower normal Hb range, varying depending on their age. In neonates, the normal Hb is higher (15-20 g/dl) due to placental transfusion. In pregnancy, there is a recognised dilution such that from the second trimester a lower threshold of 11g/dl is used.
Of note, there is ongoing reassessment of whether different values for men and women is actually a true representation of an appropriate baseline in health. As such, consideration of a normal lower value of 13g/dl in both sexes seems optimal.
A common method of classification is based on the RBC size. Macrocytic
Iron deficiency anaemia
Anaemia of chronic disease
Reduced globin chain production
Acute blood loss
Anaemia of chronic disease
Bone marrow failure
Most non haematinic causes
This can be useful as it can provide a quick idea as to what the possible cause might be just from an FBC sample.
Another way of classification, and perhaps more useful for understanding the pathophysiology is based on the cause of the anaemia: 1. Reduced Production:
Bone marrow infiltration
Chronic kidney disease
Endocrine failure e.g. thyroid
2. Increased destruction (haemolysis):
Excess reticuloendothelial activity
Warm antibody haemolysis
Cold antibody haemolysis
Intrinsic RBC defects
Congenital erythropoietic porphyria
Sickle cell anaemia
3. Dilution of Hb
4. Acute blood loss
Sampling e.g. in critical care
The reticulocyte count can be useful to help differentiate between destruction and production causes. A high reticulocyte count (e.g. >3%) suggests an increased production of RBC to try and respond to increased destruction. A low reticulocyte count suggests that the haematopoietic system isn’t responding appropriately to the anaemia, and therefore the problem may lie in the production process.
Anaemia can commonly be discovered incidentally on routine FBC. When more severe, the condition can present due to a result of an imbalance between tissue oxygen demand and delivery. Symptoms may include:
Shortness of breath
Symptoms can be affected by the pre-existing health of the patient. Young fit patients may just experience generalised symptoms of malaise. Patients with additional comorbidities may have these exacerbated e.g. angina
Anaemia is a manifestation of an underlying disease rather than a diagnosis in itself, so the assessment and investigative process should bear this in mind.
History Risk factors for specific causes of anaemia should be sought:
Dietary disturbance - elective e.g. veganism, or pathological e.g. GI surgery
Chronic inflammatory disease
Chronic blood loss e.g. menorrhagia.
Family history e.g. of Sickle cell
The history will guide further approach.
Examination In acute blood loss, this will be more an assessment of cardiovascular stability and assessment for source of bleeding. Chronically is may provide information as to the aetiology of the anaemia:
There are a number of other important parameters on a blood film that are relevant.
Red cell count
Male - 4.4-5.8 x 10^12/l
Female - 4.0-5.2 x 10^12/l
Male - 40-51%
Female - 38-48%
Mean cell volume - 76-96 fl
Mean cell haemoglobin - 27-32 pg
Mean cell haemoglobin concentration - 32-36 g/dl
Reticulocyte count - 1-2%
There are also a number of other visual finding on a blood film that provide information on the aetiology of any anaemia (though some relate to specific abnormalities of the above parameters)
Hypochromia - pale RBCs due to low Hb concentrations
Anisocytosis - the size of the RBCs is variable
Poikilocytosis - the shape of the RBCs is irregular and variable
Macrocytic - RBCs are generally larger in size
Microcytic - RBCs are generally smaller in size
Reticulocytosis - an increase in immature RBCs, seen in acute blood loss.
Other values of a full blood count can be useful in guiding the diagnosis. Abnormalities of platelets or white blood cells may be present.
Additional tests can provide further information on the cause of anaemia
Total iron binding capacity
Coombs test - identifies antibodies
Bone marrow biopsy may be required if the cause is felt to relate to failure of the bone marrow to produce new cells e.g. through infiltration.
Imaging may form a core part of investigation:
Endoscopy - to look for malignancy of the GI tract
Radiology - to look for malignancy. To assess for splenomegaly.
Perioperative anaemia is a common disturbance and can be associated with a notable increase in the risk of morbidity and mortality. As such, there has been a strong focus to minimise the impact of anaemia on the patient, particularly relating to minimising the need for blood transfusion. The Patient Blood Management (PBM) approach is a good example of this. This focuses on the 3 pillars of:
Detection and management of anaemia
Minimisation of blood loss and optimisation of coagulation
Optimising patient physiological tolerance of anaemia.
Detection and management needs to be built into pre-op pathways, with a major focus on identifying reversible causes of anaemia, especially iron deficiency. This is explored in more detail in the section on iron deficiency anaemia. Early detection is probably the key to enabling appropriate next steps to be taken, as there is often a range of options available to improve the anaemia.
Intraoperative care has a particular focus on minimising blood loss and optimising the physiology of the patient, especially coagulation. This includes:
Use of tranexamic acid
Minimising haemodilution from excess IV fluid
Surgical techniques to minimise blood loss e.g. tourniquets, minimally invasive surgery
Optimising physiology for haemostasis
This links into a focus on minimising the need for blood transfusion. A restrictive transfusion threshold (70g/L) is now well recognised as being appropriate in the vast majority of patients. A higher threshold of 80g/L is appropriate in those with acute coronary syndrome. Transfusion should be done on a single unit basis with rechecking, unless there is active bleeding.