Metabolic acidosis is a condition resulting from an accumulation of acid within the body’s fluids, disrupting the pH balance necessary for normal function. The body strives to maintain a blood pH within the narrow range of 7.35 to 7.45. When this balance shifts and the blood becomes too acidic, various physiological processes can be affected, impairing the function of organs and cells. This disturbance requires medical evaluation to identify and address its underlying cause.
Underlying Causes of Metabolic Acidosis
The origins of metabolic acidosis are diverse and can be grouped into how the body’s acid-base balance is disrupted. One major category is increased acid production. A primary example is diabetic ketoacidosis (DKA), which occurs in individuals with poorly controlled diabetes when the body breaks down fat for energy, producing acidic compounds called ketones. Similarly, alcoholic ketoacidosis can develop in cases of chronic alcohol use, and lactic acidosis arises from excess lactic acid, a situation triggered by conditions like heart failure or severe infection.
Another pathway to metabolic acidosis is through the kidneys’ diminished capacity to excrete acid. The kidneys are responsible for filtering waste products, including acids, from the blood and eliminating them through urine. When kidney function is compromised, as seen in both chronic kidney disease (CKD) and acute kidney injury (AKI), they are unable to remove enough acid, leading to its accumulation in the bloodstream.
The body can also enter an acidic state through the loss of bicarbonate, a substance that acts as a buffer to neutralize acid in the blood. Severe diarrhea is a frequent cause, as intestinal fluids are rich in bicarbonate. Certain kidney diseases, distinct from general kidney failure, can also cause the body to excrete too much bicarbonate in the urine, a condition known as renal tubular acidosis.
Finally, the ingestion of specific toxins can lead to metabolic acidosis. Overdosing on aspirin is one such cause. Other potent sources include methanol, found in some adhesives and varnishes, and ethylene glycol, the primary component of automotive antifreeze. These substances are metabolized in the body into strong acids, rapidly overwhelming its buffering systems.
Recognizing the Symptoms
The signs of metabolic acidosis can be subtle, especially in mild cases or when the condition develops slowly. When symptoms do appear, they often reflect the body’s systemic struggle with the acid imbalance. Indicators include a general feeling of weakness, fatigue, headache, and a loss of appetite. Nausea and vomiting may also occur.
As the condition progresses, more distinct symptoms can emerge. Confusion, dizziness, or a decreased level of consciousness can manifest because the acid buildup affects brain function. An accelerated heartbeat, or tachycardia, is another common sign as the heart works harder. In cases related to diabetic ketoacidosis, a person’s breath may have a characteristic sweet or fruity odor due to the presence of ketones.
One of the most prominent signs is a change in breathing patterns known as Kussmaul breathing. This rapid and deep breathing is the body’s compensatory mechanism to restore pH balance. By breathing more deeply and rapidly, the lungs expel more carbon dioxide, a component that forms an acid in the blood, to reduce the overall acid load.
The Diagnostic Process
Confirming a diagnosis of metabolic acidosis involves specific tests to measure the body’s acid-base balance and identify the underlying cause. The process relies on laboratory analysis of blood and urine to get a clear picture of the body’s internal chemical environment.
A primary diagnostic tool is a set of blood tests. An Arterial Blood Gas (ABG) test directly measures the pH and level of carbon dioxide in arterial blood for an accurate assessment of acid-base status. A basic metabolic panel (BMP) or comprehensive metabolic panel (CMP) measures blood electrolytes, including bicarbonate, with a level below 22 mEq/L indicating metabolic acidosis. The results from the BMP are also used to calculate the anion gap, which helps doctors narrow down potential causes.
In addition to blood work, urine tests offer valuable clues. A urinalysis can measure the pH of the urine, which helps determine if the kidneys are properly excreting acids. The presence of ketones in the urine, for instance, would strongly suggest diabetic ketoacidosis. Depending on the suspected cause, a physician may order further tests, such as blood lactate levels or screens for specific toxins.
Medical Treatments
Treatment for metabolic acidosis is directed at resolving the specific underlying cause. Correcting the root problem allows the body’s natural buffering systems to restore a normal pH balance and is the most effective way to manage the condition.
For instance, if the cause is diabetic ketoacidosis, treatment involves insulin to allow the body to use glucose for energy again, along with intravenous (IV) fluids to correct dehydration. In cases where kidney failure is the culprit, dialysis may be necessary to remove excess acids from the body. If the acidosis is caused by ingesting a toxin like methanol or ethylene glycol, specific antidotes may be administered. Resolving lactic acidosis requires treating its trigger, such as managing an infection or improving oxygen delivery to tissues.
Supportive care is also a component of treatment. Intravenous fluids are given to improve circulation and kidney function, aiding the natural clearance of acid. The use of buffering agents like sodium bicarbonate is reserved for severe cases, as it does not fix the underlying issue and can have complications. For chronic conditions like kidney disease, oral medications such as sodium citrate may be prescribed to manage long-term acid-base balance.