Iron deficiency is the most common cause of anaemia in the world, affecting 30% of the world’s population equivalent to 500 million people. This is because of the body’s limited ability to absorb iron and the frequent loss of iron owing to haemorrhage. Although iron is abundant, most is in the insoluble ferric (Fe3+) form, which has poor bioavailability. Ferrous (Fe2+) is more readily absorbed. Free iron is toxic, and it is bound to various proteins for transport and storage.

Practical Box 8.1 Techniques for obtaining bone marrow

The technique should be explained to the patient and consent obtained Aspiration Site – usually iliac crest Give local anaesthetic injection Use special bone marrow needle (e.g. Salah) Aspirate marrow Make smear with glass slide Stain with: Romanowsky technique Perls’ reaction (acid ferrocyanide) for iron. Trephine Indications include: ‘Dry tap’ obtained with aspiration Better assessment of cellularity, e.g. aplastic anaemia Better assessment of presence of infiltration or fibrosis. Technique Site – usually posterior iliac crest Give local anaesthetic injection Use special needle (e.g. Jamshidi – longer and wider than for aspiration) Obtain core of bone Fix in formalin; decalcify – this takes a few days Stain with: Haematoxylin and eosin Reticulin stain.

The other causes of a microcytic hypochromic anaemia are anaemia of chronic disease, sideroblastic anaemia, and thalassaemia. In thalassaemia there is a defect in globin synthesis, in contrast to the other three causes of microcytic anaemia where the defect is in the synthesis of haem.

Practical Box 10.2 Joint aspiration

This is a sterile procedure which should be carried out in a clean environment

Explain the procedure to the patient; obtain consent 1 Decide on the site to insert the needle and mark it. 2 Clean the skin and your hands scrupulously; remove rings and wristwatch. Gloves are not obligatory, but many prefer to use them. 3 Draw up local anaesthetic (and corticosteroid if it is being used) and then use a new needle. 4 Warn the patient, insert the needle, injecting local anaesthetic as it advances and, if a joint effusion is suspected, attempt to aspirate as you advance it. 5 If fluid is obtained, change syringes and aspirate fully. 6 Examine the fluid in the syringe and decide whether or not to proceed with a corticosteroid injection. 7 Cover the injection site and advise the patient to rest the affected area for a few days. Warn the patient that the pain may increase initially but to report urgently if this persists beyond a few days, if the swelling worsens, or if they become febrile, since this might indicate an infected joint.

Examination of joint (or bursa) fluid is used mainly to diagnose septic, reactive or crystal arthritis. The nature of the fluid is an indicator of the level of inflammation. Clear fluid indicates little inflammation in the joint, whereas translucent or opaque fluid indicates increasing cellularity and underlying inflammation. Purulent fluid is seen in septic arthritis, but crystal arthritis and reactive arthritis may also produce a highly cellular effusion. The procedure is often undertaken in combination with injection of a corticosteroid. Aspiration alone is therapeutic in crystal arthritis.

Peripheral blood

A low haemoglobin should always be considered in relation to:

• the white blood cell (WBC) count
• the platelet count
• the reticulocyte count (as this indicates marrow activity)
• the blood film, as abnormal red cell morphology may indicate the diagnosis.

Where two populations of red cells are seen, the blood film is said to be dimorphic. This may, for example, be seen in patients with ‘double deficiencies’ (e.g. combined iron and folate deficiency in coeliac disease, or following treatment of anaemic patients with the appropriate haematinic).

Bone marrow

Examination of the bone marrow is performed to further investigate abnormalities found in the peripheral blood (Practical box 8.1). Aspiration provides a film which can be examined by microscopy for the morphology of the developing haemopoietic cells. The trephine provides a core of bone which is processed as a histological specimen and allows an overall view of the bone marrow architecture, cellularity and presence/absence of abnormal infiltrates.

The following are assessed:

• cellularity of the marrow
• type of erythropoiesis (e.g. normoblastic or megaloblastic)
• cellularity of the various cell lines
• infiltration of the marrow
• iron stores.

Special tests may be performed: cytogenetic, immunological, cytochemical markers, biochemical analyses (e.g. deoxyuridine suppression test), microbiological culture.

Stridor or noisy breathing can be divided into inspiratory (source is glottic or above), expiratory (intrathoracic trachea or below) or mixed (subglottis or extrathoracic trachea). All patients with stridor, both paediatric and adult, are potentially at risk of asphyxiation and should be investigated fully. Severe stridor may be an indication for either intubation or a tracheostomy (Table 20.3).

Tracheostomy tubes may be:

• Cuffed or uncuffed. A high-volume, low-pressure cuff is used to prevent aspiration and to allow positive-pressure ventilation.
• Fenestrated or unfenestrated. This is a small hole on the greater curvature of the tube (both outer and inner) allowing air to escape upwards to the vocal cords and therefore the patient can speak. This tube often has a valve which allows air to enter from the stoma but closes on expiration, directing the air through the fenestration.

Most long-term tracheostomy tubes have an inner and outer tube. The inner tube fits inside the outer tube and projects beyond its lower end. A major problem with a tracheostomy tube is crusting of its distal end with dried secretions and this arrangement allows the inner tube to be removed, cleaned and replaced as frequently as required, without disrupting the outer tube.

When to decannulate a patient is often a difficult issue if laryngeal competence is unclear. Movement of the vocal cords requires an ENT examination but owing to the risk of aspiration, a speech therapist’s opinion can also be useful. The tracheostomy tube itself can also give problems due to compression of the oesophagus with a cuffed tube and by preventing the larynx from rising during normal swallowing.

Table 20-3. Indications for tracheostomy

Upper airway obstruction (real or anticipated)

Long-term ventilation

Bronchial lavage

Incompetent larynx with aspiration