What is Metabolic Acidosis?
Acid-base disorders, such as metabolic acidosis, are disruptions to the balance of acid levels in our blood. Any process that promotes the presence of more hydrogen ions in our bloodstream can be considered a type of acidosis. The term ‘acidemia’ is used to describe the overall acid-base balance of the pH level in our blood. For instance, a person can have multiple types of acidosis that together result in a net acidemia. Acidosis can either be respiratory, related to changes in carbon dioxide levels, or metabolic, which is influenced by bicarbonate (a substance that neutralizes acid in the body).
Metabolic acidosis happens when the hydrogen ion levels in our body’s circulation system are too high, resulting in bicarbonate levels of less than 24 milliequivalents per liter (mEq/L) in the blood serum. Metabolic acidosis isn’t harmless and usually indicates a more serious underlying condition. It’s important to treat it promptly to limit health risks and fatalities. Metabolic acidosis can arise from a variety of causes, primarily: increase in acid production, decrease in acid excretion, acid ingestion, and loss of bicarbonate through the kidneys or digestive system.
What Causes Metabolic Acidosis?
Understanding the type of metabolic acidosis – a condition where there’s too much acid in the body – helps doctors figure out what’s causing it. Acidemia refers to when the body’s pH level is lower than the normal range of 7.35 to 7.45. Metabolic acidosis also means that a chemical called bicarbonate is less than 24 mEq/L in your body.
Doctors classify metabolic acidosis based on the anion gap, which is just a fancy term for the concentration of certain particles (anions) in your blood that the tests don’t measure. Put simply, for your blood to have a neutral charge, anions must balance out the positive particles, or cations. The main cation in your blood is sodium (Na), and it’s balanced by the anions bicarbonate, chloride, and those unmeasured anions. These unmeasured particles can include lactate and acetoacetate, which are often major contributors to metabolic acidosis.
The anion gap can be calculated using this formula: Anion gap (AG) = [Na] –([Cl] + [HCO3]).
Anion gap metabolic acidosis often happens due to the buildup of lactic acid in your body. It’s important to know that while lactate (a form of lactic acid) is often mentioned when talking about metabolic acidosis, it’s not a separate cause but rather a result of an underlying condition.
Here’s a simple way to remember the main causes of anion gap metabolic acidosis, think of CAT MUDPILES:
- Cyanide and carbon monoxide poisoning
- Arsenic
- Toluene
- Methanol, Metformin
- Uremia
- DKA (Diabetic Ketoacidosis)
- Paraldehyde
- Iron, INH (Isoniazid, a medication used to prevent and treat tuberculosis)
- Lactate
- Ethylene glycol (a compound often found in antifreeze)
- Salicylates (certain types of medicine like aspirin)
Non-gap metabolic acidosis mainly happens due to loss of bicarbonate in the body. Common causes of this are diarrhea and a kidney condition called renal tubular acidosis. Additional, and less common causes include Addison’s disease (where your body doesn’t produce enough hormones.), ureterosigmoid or pancreatic fistulas (abnormal connections between different parts of the body), use of the medication acetazolamide, and over-nutrition through TPN (total parenteral nutrition, feeding a person intravenously).
To tell the difference between the loss of bicarbonate from the digestive system or the kidneys, doctors can use a urine anion gap test. The formula for this is: Urine AG = Urine Na + Urine K – Urine Cl. A positive result suggests the loss is due to kidney conditions, like renal tubular acidosis, while negative values suggest non-kidney losses, like diarrhea.
Risk Factors and Frequency for Metabolic Acidosis
Metabolic acidosis, a condition that could suggest a deeper health problem, is somewhat common, especially amongst patients suffering from acute illnesses. However, it’s hard to pinpoint the exact prevalence of this condition in the general population.
Signs and Symptoms of Metabolic Acidosis
If you’re having issues with your body’s acid-base balance – that is, the acidity or alkalinity of your body’s fluids – a few things could be causing it. These might include vomiting, diarrhea, certain medications, potential overdoses and chronic conditions that can cause acidosis, like diabetes. When your doctor examines you, they could find signs specific to each potential cause. For example, if you have diabetic ketoacidosis, your mucous membranes might be dry. You could also be breathing rapidly in an attempt to get rid of excess carbon dioxide and correct the acidity of your blood. Unfortunately, your body can’t completely fix an acid-base balance problem just by adjusting your breathing.
Testing for Metabolic Acidosis
Understanding acid-base balance in the body is essential to pinpoint and correct any imbalances that can significantly affect a patient’s health. Doctors often follow a step-by-step process, using laboratory values and mathematical equations, to determine if a patient has a medical condition called metabolic acidosis, along with any other acid-base imbalances.
The first thing doctors examine is the pH value of the patient’s blood. The normal blood pH range is between 7.35 to 7.45. When the pH is less than 7.35 then the patient has excess acid in their body, which is called acidemia. If the pH is more significant than 7.45, the patient’s body contains excessive alkaline or basic substances, referred to as alkalemia.
Next, doctors use the pCO2 value (a measure of carbon dioxide in the blood) to decide whether the acidosis issue is respiratory or metabolic. Respiratory acidosis is when pCO2 is higher than 40 to 45 because of reduced breathing. Metabolic acidosis is identified by a decreased bicarbonate level with the pCO2 value less than 40. Bicarbonate is a substance that neutralizes acid in the body; its normal concentration range is between 21 to 28 mEq/L.
The third step involves determining if metabolic acidosis involves anion gap or non-anion gap. The anion gap is calculated as AG= Na – (Cl + HCO3), where Na is sodium, Cl is chloride, and HCO3 is bicarbonate. A normal anion gap is 12. If the result is higher than 12, then there’s an anion gap metabolic acidosis.
Then they assess how well the body is compensating for the acidosis condition naturally through respiratory compensation. Respiratory compensation never fully corrects an acidemia, but it’s crucial to determine if it’s sufficient or if there is an additional respiratory disorder at play. To do this, doctors use Winter’s formula, which is Expected CO2 = (Bicarbonate x 1.5) + 8 +/- 2. With this formula, if the pCO2 is within the calculated range, then there’s no additional respiratory problem. If the pCO2 value is more than expected, then an additional respiratory acidosis is signified. If the pCO2 is less than expected, it indicates an additional respiratory alkalosis.
Lastly, doctors would ascertain the presence of any additional metabolic disturbances if they find an anion gap. They use the Delta gap calculation, which is Delta gap = Delta AG – Delta HCO3 = (AG-12) – (24-bicarbonate). A value less than -6 hints at a non-anion gap metabolic acidosis. If the value exceeds 6, there’s likely a metabolic alkalosis issue underneath. If the delta gap ranges between -6 and 6, they consider only an anion gap acidosis as present.
Treatment Options for Metabolic Acidosis
When treating metabolic acidosis, it’s important to address the root cause of the disorder. Metabolic acidosis is a condition that occurs when the body produces too much acid or when the kidneys are not removing enough acid from the body. For instance, if someone has sepsis or diabetic ketoacidosis, they might need adequate fluid replenishment and correction of any electrolyte problems. Electrolytes are minerals in your body that have an electric charge, such as potassium, calcium, and sodium; they help balance the amount of water in your body and ensure that your nerves, muscles, heart, and brain work the way they should.
Depending on the exact situation, other treatments might be needed. These can include antidotes for poisons, dialysis (a procedure to remove waste products and excess water from the blood when the kidneys stop working properly), antibiotics (drugs that fight infections caused by bacteria), and sometimes the administration of bicarbonate (a substance that can neutralize acid in certain cases).
Every situation is different hence the treatment plan can vary greatly. Always refer to advice from healthcare professionals for understanding the best treatment plan for your specific condition.
What else can Metabolic Acidosis be?
Figuring out what’s causing metabolic acidosis—a condition that occurs when your body has too much acid in your blood—involves considering different potential causes. What’s causing the issue will decide the unique factors that will help the doctor identify the real cause.
What to expect with Metabolic Acidosis
The outcome of metabolic acidosis, a condition where there’s too much acid in the body, heavily depends on its cause and the disruption in the body’s acid-base balance. The outlook can be concerning if the disruptions are significant and the patient’s vital signs, like heart rate and blood pressure, are not stable.
