Blood acidity increases when people ingest substances that contain or produce acid or when the lungs do not expel enough carbon dioxide.
People with metabolic acidosis often have nausea, vomiting, and fatigue and may breathe faster and deeper than normal.
People with respiratory acidosis often have headache and confusion, and breathing may appear shallow, slow, or both.
Tests on blood samples typically show pH below the normal range.
Doctors treat the cause of the acidosis.
(See also Overview of Acid-Base Balance.)
If an increase in acid overwhelms the body's acid-base control systems, the blood will become acidic. As blood pH drops (becomes more acidic), the parts of the brain that regulate breathing are stimulated to produce faster and deeper breathing (respiratory compensation). Breathing faster and deeper increases the amount of carbon dioxide exhaled, which raises the blood pH back toward normal.
The kidneys also try to compensate by excreting more acid in the urine. However, both mechanisms can be overwhelmed if the body continues to produce too much acid, leading to severe acidosis and eventually heart problems and coma.
The acidity or alkalinity of any solution, including blood, is indicated on the pH scale.
Acidity and alkalinity are expressed 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.
Acidosis is categorized depending on its primary cause as
Metabolic acidosis develops when the amount of acid in the body is increased through ingestion of a substance that is, or can be broken down (metabolized) to, an acid—such as wood alcohol (methanol), antifreeze (ethylene glycol), or large doses of aspirin (acetylsalicylic acid). Many other drugs and poisons can cause acidosis.
Metabolic acidosis can also occur as a result of abnormal metabolism. The body produces excess acid in the advanced stages of shock (lactic acidosis) and in poorly controlled type 1 diabetes mellitus (diabetic ketoacidosis).
Even the production of normal amounts of acid may lead to acidosis when the kidneys are not functioning normally (kidney failure) and are therefore not able to excrete sufficient amounts of acid in the urine.
Metabolic acidosis also develops when the body loses too much base. For example, bicarbonate can be lost through the digestive tract due to diarrhea or an ileostomy.
Respiratory acidosis develops when the lungs do not expel carbon dioxide adequately (inadequate ventilation), a problem that can occur in disorders that severely affect the lungs (such as chronic obstructive pulmonary disease, severe pneumonia, heart failure, and asthma).
Respiratory acidosis can also develop when disorders of the brain or of the nerves or muscles of the chest (such as Guillain-Barré syndrome or amyotrophic lateral sclerosis) impair breathing. In addition, people can develop respiratory acidosis when their breathing is slowed due to oversedation as a result of opioids (narcotics), alcohol, or strong drugs that induce sleep (sedatives). As a result of the slowed breathing, the level of oxygen in the blood may be low.
Sleep-disordered breathing (for example, sleep apnea) can repeatedly pause breathing long enough to cause temporary respiratory acidosis.
In mild metabolic acidosis, people may have no symptoms but usually experience
Breathing becomes deeper and slightly faster (as the body tries to correct the acidosis by expelling more carbon dioxide). As the acidosis worsens, people begin to feel extremely weak and drowsy and may feel confused and increasingly nauseated. Eventually, in severe cases, heart problems may develop and blood pressure can fall, leading to shock, coma, and death.
In respiratory acidosis, the earliest symptoms are
Drowsiness may progress to stupor and coma as the oxygen in the blood becomes inadequate. Stupor and coma can develop within moments if breathing stops or is severely impaired, or over hours if breathing is less dramatically impaired.
The diagnosis of acidosis generally requires the measurement of blood pH and carbon dioxide in a sample of arterial blood, usually taken from the radial artery in the wrist. Arterial blood is used because venous blood is generally not as reliable when measuring the body’s pH status.
To learn more about the cause of the acidosis, doctors also measure the levels of bicarbonate in the blood. Additional blood tests are then done to help determine the specific cause.
Almost always, treatment of acidosis is directed at reversing the cause. Doctors rarely simply give alkaline drugs, such as bicarbonate, to reverse the acidosis.
In metabolic acidosis, treatment depends primarily on the cause. For instance, treatment may be needed to control diabetes with insulin or to remove the toxic substance from the blood in cases of poisoning.
In respiratory acidosis, treatment aims at improving the function of the lungs. Drugs that open the airways (bronchodilators, such as albuterol) may help people who have lung diseases such as asthma and chronic obstructive pulmonary disease. Sedation due to drugs and other substances can sometimes be reversed by antidotes. People who have severely impaired breathing or lung function, for whatever reason, may need mechanical ventilation to aid breathing.
Severe acidosis may also be treated directly when it does not respond to efforts to treat the cause. In such cases, bicarbonate may be given intravenously. However, bicarbonate provides only temporary relief and may cause harm—for instance, by overloading the body with sodium and water.