Coma

Published on 01/03/2015 by admin

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Last modified 01/03/2015

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Coma

The comatose patient presents a number of problems to the physician, some in relation to initial diagnosis and some later during treatment.

The depth of coma can be defined following clinical examination using a scale such as that in Figure 63.1. This allows clinical staff to establish the severity of the coma and to monitor changes. Obtaining the correct diagnosis is paramount. To this end the most valuable information is usually obtained from the clinical history, but frequently a reliable history is not available.

Fig 63.1 The Glasgow Coma Scale.

Patency of airway, blood pressure, temperature, pupillary reflex and blood glucose concentration need to be monitored repeatedly and a search should be made for evidence of trauma or needlemarks at the time of admission. A careful history and physical examination will give the correct diagnosis in over 90% of cases. Other biochemical tests can help in diagnosis or for the continued monitoring of comatose patients.

Differential diagnosis of coma

A helpful mnemonic in the diagnosis of the unconscious patient is given in Figure 63.2. However, within each of these categories described there are many possible causes. The first priorities in treating an unconscious patient are to ensure that airways are clear and that breathing and circulation are satisfactory.

Fig 63.2 Differential diagnosis of a coma patient.

Cerebrovascular accident

Where coma of cerebrovascular origin is suspected a CSF examination may show the presence of blood and will help to differentiate a subarachnoid haemorrhage from cerebral infarction (see p. 130). When available, imaging with a CT scan or MRI is preferable.

Infectious causes

Meningitis (bacterial and viral) and encephalitis (viral) can both lead to coma. Meningococcal meningitis has a high mortality, especially in children. Diagnosis is of great importance and CSF specimens should be obtained before antibiotic therapy is commenced (Fig 63.3). The usual findings are:

Fig 63.3 Investigation of the cerebrospinal fluid.

In bacterial meningitis CSF protein is increased and glucose is low or absent. There is a leucocytosis that may be visible as cloudiness in severe cases.

In viral meningitis glucose is normal or only slightly depressed and protein may be normal.

Metabolic causes

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