Which of the following metabolic disorders is associated with hypokalemia?
Correct Answer: Metabolic alkalosis
Description: Metabolic alkalosis Metabolic alkalosis is characterised by an increase in the plasma bicarbonate concentration and the plasma pH (see Box 14.18). There is a compensatory rise in PCO2 due to hypoventilation but this is limited by the need to avoid hypoxia. Classical causes include primary hyperaldosteronism (Conn's syndrome, p. 674), Cushing's syndrome (p. 666) and glucocoicoid therapy (p. 670). Occasionally, overuse of antacid salts for treatment of dyspepsia produces a similar pattern. Pathophysiology Metabolic alkalosis is best classified according to the accompanying changes in ECF volume. Hypovolaemic metabolic alkalosis is the most common pattern. This can be caused by sustained vomiting, in which acid-rich fluid is lost directly from the body, or by treatment with loop diuretics or thiazides. In the case of sustained vomiting, loss of gastric acid is the immediate cause of the alkalosis, but several factors act to sustain or amplify this in the context of volume depletion (Fig. 14.11). Loss of sodium and fluid leads to hypovolaemia and secondary hyperaldosteronism, triggering proximal sodium bicarbonate reabsorption and additional acid secretion by the distal tubule. Hypokalaemia occurs due to potassium loss in the vomitus and by the kidney as the result of secondary hyperaldosteronism, and itself is a stimulus to acid secretion. Additionally, the compensatory rise in PCO2 fuher enhances tubular acid secretion. The net result is sustained metabolic alkalosis with an inappropriately acid urine, which cannot be corrected until the deficit in circulating volume has been replaced. Normovolaemic (or hypervolaemic) metabolic alkalosis occurs when bicarbonate retention and volume expansion occur simultaneously. Clinical features Clinically, apa from manifestations of the underlying cause, there may be few symptoms or signs related to alkalosis itself. When the rise in systemic pH is abrupt, however, plasma ionised calcium falls and signs of increased neuromuscular irritability, such as tetany, may develop (p. 663). Investigations The diagnosis can be confirmed by measurement of electrolytes and aerial blood gases Ref Davidson 23rd edition pg 366
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