Metabolic Acidosis: Easy-to-Understand Explanation of Causes, Symptoms, and Treatment
Need info on a different Acid-Base Imbalance? I’ve got you covered!
- Respiratory Acidosis
- Respiratory Alkalosis
- Metabolic Acidosis (You are here!)
- Metabolic Alkalosis (coming soon!)
What is Metabolic Acidosis? What Does Metabolic Acidosis Mean?
Metabolic Acidosis is a condition where your body (usually the kidneys) either 1) can’t get rid of enough acid from the body, or 2) can’t retain enough bicarbonate (HCO3-, which is a base), which causes the blood pH to drop below 7.35.
Additionally, if the body can’t get rid of enough acid from the body, then the available bicarbonate will start binding with the extra acid to neutralize them. However, this uses up the bicarbonate, which ALSO results in a decrease of HCO3-! That is why in both cases, you will be able to see a decrease in bicarbonate for this condition.
Your blood can become more acidic for other reasons, too (like Respiratory Acidosis!). But when your blood becomes acidic because of something related to the kidneys or digestive tract, that is what makes it Metabolic Acidosis.
How is Metabolic Acidosis diagnosed? What are the different types of Metabolic Acidosis?
Metabolic Acidosis is primarily diagnosed using an Arterial Blood Gas Test (ABG), especially if the patient is showing symptoms of the condition OR has an underlying illness that might put them at risk for this imbalance.
In order to identify which type of Metabolic Acidosis the patient has, you will need to know how to interpret ABG values.
Uncompensated Metabolic Acidosis
Uncompensated Metabolic Acidosis is the initial stage that can occur when the kidneys are no longer able to maintain the normal blood pH, but the lungs have not yet been able to compensate by adjusting pH back to the normal range.
Under normal circumstances, the lungs help the kidneys maintain correct blood pH by retaining or producing carbon dioxide (CO2). CO2 is followed by H+, which is acidic, and can be “blown off” by the lungs to reduce excess acid in the body. However, with uncompensated Metabolic Acidosis, the lungs have not yet responded to the acid/base imbalance in the blood.
The result is that there is not enough HCO3– in the blood, but there is still a normal amount of CO2 (and H+), and the blood pH dips below 7.35 to become more acidic.
Fully Compensated Metabolic Acidosis
Fully Compensated Metabolic Acidosis is usually comes on more gradually after Uncompensated Metabolic Acidosis has occurred. The slower pace of this acid/base imbalance allows time for the lungs to “blow off” enough CO2 and H+ to counterbalance decreases in HCO3-. Getting rid of acid via the lungs will allow the remaining HCO3– to be more effective at neutralizing the acids still remaining in the body.
Since the total CO2 level has time to decrease and counterbalance the pH, the results are that there is too little HCO3– AND CO2 in the blood, but the pH remains in the normal range of 7.35-7.45. The pH will lean towards the acidic side however, so you’re more likely to see a pH of 7.35-7.39.
Partially Compensated Metabolic Acidosis
Partially Compensated Metabolic Acidosis is more of an “in-between” stage for when a patient is moving from Uncompensated into Fully Compensated.
As the kidneys are less able to keep enough HCO3– circulating in the body, the blood pH gradually decreases and becomes more acidic. At the same time, however, the the lungs begin compensating by “blowing off” CO2 and H+, which are also acidic, to balance out the pH.
However, for Partially Compensated Metabolic Acidosis, the kidneys have NOT had time to completely compensate for the lungs yet (if they had, then this would be called Fully Compensated Metabolic Acidosis )
So you end up with not enough HCO3– AND not enough CO2, but the pH is still abnormal and in the acidic range (<7.35).
What is the cause of Metabolic Acidosis?
Any illness or condition that can cause the body to either 1) lose too much bicarbonate OR 2) gain so much acid that there is not enough bicarbonate to neutralize it adequately can be a cause of Metabolic Acidosis. Since there are so many different individual conditions that could have that effect, it’s best to group them into categories that have similar underlying pathophysiologies.
The kidneys are the primary organ responsible for regulating HCO3– in the body. So if they aren’t working properly, then there is a high risk that an acid-base balance will occur. Any kind of kidney failure or renal insufficiency can be a cause of Metabolic Acidosis.
Gastro-Intestinal (GI) Issues
The Gastro-Intestinal (GI) system is another major player in metabolic acid-base imbalances. In fact, it’s easy to predict when Metabolic Acidosis could occur simply by thinking through the normal anatomy! For example, the intestinal part of the GI system is more alkaline than the stomach. Therefore, if a patient has severe diarrhea, they will lose proportionally MORE base from their body than acid, leading to Metabolic Acidosis.
Too Many Ketones
Ketones are acidic, so any condition that causes ketones to increase can also be a cause. An obvious cause of increased ketones is Diabetic Ketoacidosis, but really any condition that results in some form of starvation can increase ketones. This is because ketones are created when the body runs out of glucose and has to break down fat to use for fuel. Even diabetic ketoacidosis is a form of cellular starvation!
Excessive Lactic Acid
I’m sure you already associate lactic acid with that burning and sore feeling you get in your muscles when exercising. And the name says it all…it’s an acid! So if you engage in too much strenuous exercise, you could run the risk of developing Metabolic Acidosis.
In fact, any disease that causes our muscles to continue working in an anaerobic (aka without oxygen) environment) will produce lactic acid. And if enough of that lactic acid builds up, it can overwhelm the body’s bicarbonate reserves and lead to Metabolic Acidosis. Seizures, heart failure or heart attack (aka myocardial infarction), or Lung diseases can all decrease oxygen to the muscles, making it more likely that excessive lactic acid will be produced.
What are some Metabolic Acidosis symptoms?
Nursing textbooks (and professors) are great about listing LOTS of Metabolic Acidosis symptoms. The problem is, many of these signs and symptoms are rather generic, and could be true of many illnesses that are completely unrelated.
That’s why I prefer to identify Metabolic Acidosis symptoms that are specific and unique to this condition…and then understand why they occur (a.k.a. the pathophysiology). The most specific and unique symptoms of Metabolic Acidosis include:
One identifying symptom of Metabolic Acidosis is hyperkalemia. This potentially severe complication occurs when the amount of H+ in the body overwhelms the amount of remaining HCO3-. Since the HCO3– can no longer neutralize enough H+, then the blood pH becomes more acidic and other compensation mechanisms kick in. One of those mechanisms is a “trade” between the K+ ions located inside the cells, and the H+ outside of the cells.
This “trading places” is initially helpful because it decreases H+ in the blood. But on the flip side, it increases K+ in the blood to the point of hyperkalemia. And if the root cause of Metabolic Acidosis is left uncorrected, and the hyperkalemia is not addressed quickly, then life threatening symptoms of hyperkalemia can occur.
Nausea and Vomiting (Whaaat?!?!)
Nausea and vomiting is an interesting symptom, because I almost always put it on my “generic” list. After all, soooo many different diseases present with “nausea and vomiting”. But in THIS case, it is a very useful symptom in identifying Metabolic Acidosis.
The reason why is because nausea and (especially) vomiting are one of the body’s ways of correcting the acid-base imbalance. Think about it this way…the stomach contains stomach acid. So if your body has more acid than the kidneys can handle, then getting rid of stomach acid will help lighten the overall acidic load in the body. So the vomiting in particular serves a very specific and identifying purpose as a symptom of Metabolic Acidosis.
Kussmaul respirations are an indication that the body is in a late stage of Metabolic Acidosis. It’s a breathing pattern where the patient starts breathing deeply and rapidly.
This is a major sign that the lungs are trying to compensate for Metabolic Acidosis by “blowing off” more acid. One way you can think about Kussmaul’s respirations is by comparing it to hyperventilation, which is a possible cause of Respiratory Alkalosis. Just don’t get Kussmaul’s respirations confused with Cheyne-Stokes breathing, which is a different pattern and is associated with Respiratory Alkalosis.
Abnormal ABG Results
Not surprisingly, a patient with Metabolic Alkalosis will have abnormal ABG results: HCO3– less than 22 and pH less than 7.35 (or pH between 7.35-7.39 if Compensated).
“Generic” Symptoms of Metabolic Acidosis
- decreased level of consciousness (LOC)
Do you see how impossible it is to identify these generic Metabolic Acidosis symptoms? They also occur with just about every other illness you’ll study in nursing school. Which is why exams will always highlight the specific and unique clusters of symptoms…and you should focus on them as you study, too!
What is the Metabolic Acidosis treatment?
Like any disease process you’ll face in nursing school, Metabolic Acidosis treatment is twofold:
- Manage the urgent symptoms
- Correct the root cause
Managing the Symptoms of Metabolic Acidosis
If it’s present, then hyperkalemia is definitely a priority symptom that needs to be managed. The treatment used will largely depend on what’s going on with the patient.
For example, a loop diuretic like furosemide (Lasix) might be administered for hyperkalemia…but will that be effective if the patient has Metabolic Acidosis due to kidney failure? Probably not, since loop diuretics help by causing the kidneys to excrete more K+.
Instead, you might expect an order for one of the other hyperkalemia treatments, such as IV sodium bicarbonate (which is a base!). This will bind up some of the H+, neutralizing it, which will encourage the excess H+ that already entered the cells, effectively trading places with K+, to trade back. This treatment would ALSO help correct the overall blood pH.
But another possible treatment for hyperkalemia you might see is to administer insulin, probably with a Dextrose IV Solution. The insulin helps by opening up the cells to let glucose in, which simultaneously allows the K+ to sneak back in, too.
Nausea, Vomiting, and Kussmaul’s Breathing
These symptoms are a little trickier, because they are they body’s way of responding to the Metabolic Acidosis. In that sense, they are actually helping the patient NOT to die!
So if you tried to “manage” these symptoms by suppressing or eliminating them, you would likely end up making the patient’s condition worse. Isn’t that kind of weird?
Instead, focus on managing the symptoms that carry a risk of life-threatening problems (like the hyperkalemia!), and then shift focus towards correcting the root causes of Metabolic Acidosis.
Correcting Root Causes of Metabolic Acidosis
Again, the specific treatment is going to depend on the original cause. However, the goal is always to get the body back into homeostasis as much as possible.
If the Metabolic Acidosis is caused by an episode of diabetic ketoacidosis, then insulin is going to be part of the solution! Getting the blood sugars rebalanced and under control will be key so that the body can return to getting energy from glucose rather than fats (which break down into ketones). Bonus: if the patient has hyperkalemia, then this treatment is a double whammy because it also helps reduce potassium by moving K+ back into the cells. Then some teaching on the long-term management of diabetes mellitus will be useful.
On the other hand, if the Metabolic Acidosis is caused by kidney failure, then there may not be a way to completely correct that root cause! At least, not without a kidney transplant…
In that case, then the Metabolic Acidosis can only be managed, not corrected, using dialysis. Dialysis can get the blood pH back into the normal range and correct any electrolyte imbalances…another double whammy ?
Summary: What you NEED TO KNOW about Metabolic Acidosis to be a safe, effective, beginning nurse
- Group the causes of Metabolic Acidosis into categories
- Identify the unique, identifying symptoms of Metabolic Acidosis
- Recognize abnormal ABGs (HCO3– < 22 AND pH is acidic)
- Understand the relationship between Metabolic Acidosis and Respiratory Alkalosis
- Including the difference between Kussmaul’s Respirations and Cheyne-Stokes Respirations
- Metabolic Acidosis Treatment, and how it changes depending on the root causes (pathophysiology is key!)