Merck Manual

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James L. Lewis, III

, MD, Brookwood Baptist Health and Saint Vincent’s Ascension Health, Birmingham

Last full review/revision Jan 2020| Content last modified Jan 2020
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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).

  • People may have irritability, muscle twitching, muscle cramps, or even muscle spasms.

  • Blood is tested to diagnose alkalosis.

  • Metabolic alkalosis is treated by replacing water and mineral salts such as sodium and potassium (electrolytes) and correcting the cause.

  • Respiratory alkalosis is treated by correcting the cause.

Blood pH

Acidity and alkalinity of any solution, including blood, is indicated on the pH scale, which ranges from 0 (strongly acidic) to 14 (strongly basic or alkaline). A pH of 7.0, in the middle of this scale, is neutral.

Blood is normally slightly basic, with a normal pH range of 7.35 to 7.45. Usually the body maintains the pH of blood close to 7.40.


If too much bicarbonate in the blood, a loss of acid from the blood, or a low level of carbon dioxide in the blood overwhelms the body's acid-base control systems, the blood will become alkalotic. Alkalosis is categorized depending on its primary cause as

  • Metabolic

  • Respiratory

Metabolic alkalosis

Metabolic alkalosis develops when the body

  • Loses too much acid

  • 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 fluids and electrolytes (such as sodium or potassium) affects the kidneys' ability to maintain the blood's acid-base balance. For instance, loss of potassium sufficient to cause metabolic alkalosis may result from an overactive adrenal gland or the use of diuretics (for example, thiazides, furosemide, or ethacrynic acid).

Respiratory alkalosis

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, low levels of oxygen in the blood, fever, and aspirin overdose (which can also cause metabolic acidosis).


Alkalosis may cause

  • Irritability

  • Muscle twitching and cramps

  • Tingling in the fingers and toes and around the lips

Tingling (paresthesia) is a common complaint in hyperventilation due to anxiety. Sometimes alkalosis causes no symptoms at all. If the alkalosis is severe, painful muscle spasms (tetany) can develop.


  • Blood tests

  • Urine tests

A doctor evaluates a person's acid-base balance by measuring the pH, and levels of carbon dioxide (an acid) and bicarbonate (a base) in the blood. To learn more about the cause of the alkalosis, doctors also measure levels of electrolytes in samples of blood and urine.


  • Treatment of cause

  • In metabolic alkalosis, replacement of water and electrolytes

  • In respiratory alkalosis, giving oxygen if necessary or providing calming reassurance to a person who is hyperventilating due to anxiety

Almost always, treatment of alkalosis is directed at reversing the cause. Doctors rarely simply give acid, such as hydrochloric acid, to reverse the alkalosis.

Metabolic alkalosis is usually treated by replacing water and electrolytes (sodium and potassium) while treating the cause. Rarely, when metabolic alkalosis is very severe, dilute acid is given intravenously.

In respiratory alkalosis, the first step is to ensure that the person has enough oxygen. The doctor then looks for a serious cause, such as an infection. If pain is causing the person to breathe rapidly, relieving the pain usually suffices.

When respiratory alkalosis is caused by anxiety or a panic attack, a conscious effort to relax and slow breathing may make the condition disappear. Calming reassurance and emotional support can help, and 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.

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