Section 12. Disorders of Nutrition and Metabolism

Chapter 159. Acid-Base Balance

Topics: Introduction | Acidosis | Alkalosis

Alkalosis

Alkalosis is excessive blood alkalinity caused by an overabundance of bicarbonate in the blood or a loss of acid from the blood (metabolic alkalosis), or by a low level of carbon dioxide in the blood that results from rapid or deep breathing (respiratory alkalosis).

Metabolic alkalosis develops when the body loses too much acid or gains too much base. For example, stomach acid is lost during periods of prolonged vomiting or when stomach acids are suctioned with a stomach tube (as is sometimes done in hospitals). In rare cases, metabolic alkalosis develops in a person who has ingested too much base from substances such as baking soda (bicarbonate of soda). In addition, metabolic alkalosis can develop when excessive loss of sodium or potassium affects the kidneys' ability to control the blood's acid-base balance. For instance, loss of potassium sufficient to cause metabolic alkalosis may result from the use of diuretics or corticosteroids.

Respiratory alkalosis develops when rapid, deep breathing (hyperventilation) causes too much carbon dioxide to be expelled from the bloodstream. The most common cause of hyperventilation, and thus respiratory alkalosis, is anxiety. Other causes of hyperventilation and consequent respiratory alkalosis include pain, cirrhosis, low levels of oxygen in the blood, fever, and aspirin overdose (which can also cause metabolic acidosis (see Section 12, Chapter 159)).

Symptoms and Diagnosis

Alkalosis may cause irritability, muscle twitching, muscle cramps, or no symptoms at all. If the alkalosis is severe, prolonged contraction and spasms of muscles (tetany) can develop.

A sample of blood taken from an artery shows that the blood is alkaline.

Treatment

Doctors usually treat metabolic alkalosis by replacing water and electrolytes (sodium and potassium) while treating the underlying cause. Occasionally, when metabolic alkalosis is very severe, dilute acid in the form of ammonium chloride is given intravenously.

With respiratory alkalosis, usually the only treatment needed is slowing down the rate of breathing. When respiratory alkalosis is caused by anxiety, a conscious effort to slow breathing may make the condition disappear. If pain is causing the person to breathe rapidly, relieving the pain usually suffices. Breathing into a paper (not a plastic) bag may help raise the carbon dioxide level in the blood as the person breathes carbon dioxide back in after breathing it out.