Understanding Metabolic Acidosis (Made Easy)

In nursing school, the struggle is real when studying about acid-base balance, most especially metabolic acidosis. It can take nursing students sleepless nights and several cups of coffee to fully comprehend metabolic acidosis.

In this blog, we will be discussing some useful tips and mnemonics to help you study and understand metabolic acidosis better and more efficiently. We will share:

• an easy-to-understand definition of metabolic acidosis
• the difference between metabolic acidosis and metabolic alkalosis
• metabolic acidosis: normal lab values vs. abnormal lab values
• the causes of metabolic acidosis
• mnemonics of the causes of metabolic acidosis
• metabolic acidosis: signs and symptoms
• metabolic acidosis: nursing interventions

An easy-to-understand definition of metabolic acidosis

Metabolic acidosis is easily explained in the diagram above. When the acid in the body fluids increases, the bicarbonate (HCO3) levels will elevate, this will lead to the metabolic problem called acidosis. 

What causes metabolic acidosis?

• Increased production of acids: Like in cases of Diabetic Ketoacidosis, where ketones (which are acids) increase. As a result, bicarbonate decreases.
• Decreased excretion of acids: Like in cases of renal failure, where the kidneys are unable to excrete the acids in the body. This results in increased bicarbonate levels.
• Bicarbonate loss: Too much loss of bicarbonate in such cases, like diarrhea, can lead to metabolic acidosis.

Of course, one system of the body will try to address this issue. It’s amazing how the body can fight off any abnormality that occurs. In the case of metabolic acidosis, the respiratory system tries to bring back the bicarbonate to normal levels.

The body will hyperventilate, and breathing will increase through Kussmaul’s respiration. These are rapid and deep breaths to help expel carbon dioxide (C02 is an acid). If carbon dioxide levels decrease, hopefully, the pH will increase so as the bicarbonate levels.

See summarized diagram below:

Difference between Metabolic Acidosis and Metabolic Alkalosis

Now that we understand metabolic acidosis, let’s find out what happens in the body during metabolic alkalosis.

During metabolic alkalosis, there is a decrease in hydrogen ion levels. As a result, pH levels are elevated. This will then increase bicarbonate levels. As you can see, this is the opposite of what happens to the body during metabolic acidosis.

Metabolic Acidosis: Normal lab values vs. abnormal lab values

There is no way you can finish nursing school without memorizing by heart the normal ABG (Arterial Blood Gas) values. To refresh your memory, here are the normal lab values, followed by the ABG values during metabolic acidosis and metabolic alkalosis.

Take note: The PaCO2 levels may be normal or decreased during metabolic acidosis. Remember, we mentioned earlier that the respiratory system compensates by hyperventilating? If it succeeds and expels carbon dioxide, pH levels may normalize. If it doesn’t, the PaCO2 levels remain low.

Pro-tip: It is important to memorize these values by heart. There are NCLEX questions that will make you determine the acid-base balance using only these combinations of values. Remember that every answer counts during the NCLEX.

Causes of metabolic acidosis

Normal anion gap and high anion gap factors

For simple understanding, these are the laboratory values where doctors determine the difference between cations and anions. These are composed of the electrolytes: sodium, bicarbonate, and chloride.

High anion gaps: It is then calculated if there are any gaps. If a gap is present of >14 mEq/L (Normal value: 10-14 mEq/L), a high anion gap is identified, and metabolic acidosis is present in the body. In short, an anion gap determines what type of acidosis is experienced by the body. If it is metabolic or respiratory, this is an essential pre-determining factor when figuring out the type of acid-base imbalance and the proper intervention.

High anion acids: It is the condition where the body could not produce acid or inadequate amounts of bicarbonate. This usually happens in the case of diabetic ketoacidosis, renal failure, aspirin toxicity, malnutrition, high-fat diet, and low-carb diet.

Normal anion acidosis: This condition occurs if there is a loss of bicarbonate in the body. This is in cases of diarrhea, fistula, or ostomies drainage (rich in alkaline fluids). Also, this happens with the ingestion of diuretics such as carbonic anhydrase inhibitor drugs (these are drugs that reduce bicarbonate reabsorption).

Mnemonics of Causes of Metabolic Acidosis

Here comes the mnemonic of the causes of metabolic acidosis that we promised you:

“ACIDOTIC”

Metabolic Acidosis: Signs and Symptoms

A doctor’s order to obtain ABG values comes after the assessment of the nurse. So it is essential to monitor these signs and symptoms. If a nurse cannot determine these signs and symptoms, it may worsen and can result in the patient needing intubation.

• Kussmaul’s Respiration (Hyperventilation)
• Low Blood pressure
• Cardiac activity changes
• Headache
• Hyperkalemia
• Muscle twitching
• Warm, flushed skin
• Nausea and vomiting
• Decreased muscle tone and reflexes
• Confusion
• Drowsiness

Metabolic Acidosis: Nursing Interventions

It is important to remember that the nursing interventions will depend on the cause of metabolic acidosis. There is no point in using a nursing intervention if the cause is not determined.

1. Monitor signs and symptoms
2. Monitor ABG values
3. Assess electrolyte values
4. Assess neuro status 
5. Nursing Diagnosis: Risk of falls and seizure precaution
6. Determine the need for dialysis
7. For patients with Diabetic Ketoacidosis: Administer prescribed insulin

We hope this helps you in any nursing exam or NCLEX preparation. Don’t forget to share this with your fellow nurses or nursing aspirants. If you have more tips on how to easily understand this topic or any study tips to share, let us know!