This article explains the basics of metabolic acidosis, including its symptoms, causes, and treatment.
Metabolic acidosis is an acid-base disorder. Understanding metabolic acidosis starts with an explanation of acid-base regulation.
The body’s metabolic activities process what you ingest, such as carbohydrates and fats, into energy, constantly making acids and a small number of bases.
Carbon dioxide is the main component of metabolic acids. Bicarbonate is the main base that is the byproduct of metabolism.
The balance of acid and base in the blood determines its pH. The ideal blood pH is 7.35–7.45. The blood becomes acidic when the pH drops below 7.35.
The body has three ways of maintaining acid-base balance and the correct blood pH:
- breathing out or holding onto carbon dioxide in the lungs
- chemical buffering with phosphates, acid-base pairs, and proteins in the blood
- excreting or reabsorbing bicarbonate into the kidneys
Metabolic acidosis occurs when the blood has too much acid or when too much bicarbonate is lost from the kidneys or gastrointestinal tract.
In addition to pH, the blood must also remain electrically neutral. This means the amount of positively charged particles (cations) and negatively charged particles (anions) must balance.
The anion gap is the difference between sodium and the sum of chloride and bicarbonate ions in the blood. The anion gap reflects mainly unmeasured anions in the blood. The typical range is between 4-12 mmol/L, but it can vary depending on the laboratory.
If the blood is not neutral, the difference between positively and negatively charged ions is the anion gap.
The two subsets of metabolic acidosis depend on whether the anion gap is normal or high. In either a high anion gap metabolic acidosis or normal anion gap acidosis, the bicarbonate level in the bloodstream will be below normal. However, knowing which type you have can give doctors clues as to the underlying cause of metabolic acidosis.
When the acidosis is mild, there may not be any symptoms of a problem. The main symptoms that occur are those of the underlying condition.
If the acidosis is severe, symptoms may include:
Heart arrhythmias, shock, and coma can also occur. In some cases, metabolic acidosis can be fatal.
Metabolic acidosis occurs due to one of the following:
- decreased acid excretion by the body
- increased acid production in the body
- increased loss of bicarbonate through the kidneys or gastrointestinal tract
- ingestion of acids
High anion gap metabolic acidosis
The most common conditions that cause high anion gap metabolic acidosis include:
- diabetic ketoacidosis
- kidney failure
- lactic acidosis
- toxin ingestions, such as arsenic, cyanide, methanol, propylene glycol, carbon monoxide poisoning, and excessive aspirin or acetaminophen intake
Normal anion gap metabolic acidosis
The most common conditions that result in a normal anion gap metabolic acidosis include:
Metabolic acidosis is common in people who require critical care. Other risk factors include:
Most people with healthy kidneys and lungs do not need to worry about metabolic acidosis. Preventing it depends on the cause. In some cases, it is not preventable.
Steps you can take to prevent metabolic acidosis include:
- Avoid accidental overdoses of medications such as acetaminophen, aspirin, and iron.
- Control your blood sugar if you have diabetes.
- Limit alcohol use.
- Protect against accidental poisoning from antifreeze, paint thinner, and other products containing methanol or glycols.
To diagnose metabolic acidosis, doctors will review your medical history and physical symptoms, including breathing patterns. Blood tests are critical for identifying metabolic acidosis, the type, and the cause.
Blood tests will include:
- arterial blood gas
- blood metabolic panels, which will include electrolytes, glucose, liver function markers, and kidney function markers, such as creatinine and blood urea nitrogen
- lactate level
- toxin tests
Doctors may also measure urine pH and electrolytes.
Interpreting these test results in the context of metabolic acidosis is complex. Multiple processes can occur at the same time, and results may appear deceptively standard. Various calculations help doctors sort out the meaning of these results.
Treating metabolic acidosis involves correcting the underlying cause of the imbalance. Only in severe cases do doctors use alkali therapy with sodium bicarbonate.
The potential complications of metabolic acidosis include:
- heart arrhythmias
- shock
- coma
- death
Chronic, mild metabolic acidosis can cause problems with the bones, such as osteopenia and osteoporosis. This occurs because the bones are a repository of buffers for acid. With long-term acidosis, the bones will begin releasing calcium carbonate and phosphate to neutralize blood acid levels.
Here are some questions people often ask about metabolic acidosis.
What happens to the body in metabolic acidosis?
In metabolic acidosis, the blood becomes too acidic. This can interfere with the heart, lungs, nervous system, and metabolic processes.
How serious is metabolic acidosis?
Metabolic acidosis is a serious condition that can be life threatening.
Can dehydration cause metabolic acidosis?
Fluid balance is closely related to acid-base balance and electrolyte balance. Metabolic acidosis can result from severe dehydration.
Metabolic acidosis is a disruption in the usual balance of acids and bases in the blood. It results in the blood being too acidic. It is a complex condition that requires careful interpretation to diagnose.
When kidneys and lungs function normally, people usually do not get metabolic acidosis. However, metabolic acidosis can occur with severe diarrhea and accidental or intentional overdoses or toxic ingestions. Treatment involves correcting the underlying problem. Without proper treatment, metabolic acidosis can be fatal.
