Sun21November0437PM 9

An 18-year-old woman sustains severe head injuries in a road traffic accident.

The following day her investigations show:

Sodium 160 mmol/L (137-144)

Potassium 3.7 mmol/L (3.5-4.9)

Chloride 120 mmol/L (95-107)

Urea 3.0 mmol/L (2.5-7.5)

Creatinine 90 µmol/L (60- 110)

Which one of the following statements is correct?

(Please select 1 option)

She has the syndrome of inappropriate antidiuretic hormone secretion (SIADH) Incorrect answer selected

Rapid rehydration with 5% dextrose is indicated

She will have a hypercholraemic acidosis

Urine osmolality will be low This is the correct answer

She should be treated with sodium restriction

Explanation

There is a marked hypernatraemia with elevated chloride but normal potassium and urea in a patient with severe head injuries.

The likely cause of this presentation is diabetes insipidus. Urine osmolality is therefore likely to be low.

You cannot say that she has a hyperchloraemic acidosis as you do not have her bicarbonate concentration but if you assume that the anion gap would be normal, that is 10-12, then this would suggest that the bicarbonate is elevated, suggesting either a metabolic alkalosis or respiratory acidosis with compensation.

Although restoration of normal volaemia and osmolality is required, giving 5% dextrose may exacerbate any cerebral oedema and so correction should be gradual.

Answer Statistics

1

8%

2

3%

3

26%

4

58%

5

7%

Times answered: 277