How to remember symptoms of Acid-Base Imbalances

It’s one thing to learn what causes Respiratory (or Metabolic) Acidosis (or Alkalosis), but you also need to be able to use that knowledge to predict what symptoms those conditions can cause.  It’s easier than you might think, and doesn’t involve memorizing any lists.  But first…

How cells regulate acid-base imbalances

We have one more physiological detail to consider so that we can predict the symptoms we would expect to see in acidosis or alkalosis.  See, even though the lungs and kidneys are the two primary regulators of acid-base imbalances, there are other parts of the body that help out, too.  In fact, every cell in the body can play a role if needed!

When the body is overwhelmed with H+, like in acidosis (regardless of whether it is a metabolic or respiratory cause), then some of the extra H+ ions will start moving into the body’s cells.  That causes some of the potassium (K+), which is the most common ion inside a cell, to start leaving the cell.  Less H+ in the bloodstream (because it’s hiding in the cells) results in the pH of the body going up and becoming less acidic.

Of course, this isn’t a great long-term solution for the body!  The purpose of K+ being inside the cells is to create a difference in charge across the cell wall.  This cell wall charge differential is absolutely necessary so that an action potential can occur and the cells can do the job they are designed to do.  But when the H+ is inside the cell instead of the K+, then the action potential won’t work as intended, and will actually become easier to trigger!

Combined, these underlying cellular events lead to some of our expected symptoms for acidosis:  hyperkalemia (since K+ has left the cells and moved into the body) and hyperreflexia (since muscle cells are easier to trigger).

Now let’s consider the reverse situation.  There’s not enough H+ in the body, so the cells help to compensate by letting the little bit of H+ that usually lives inside the cell escape, helping to correct the alkalosis in the body.  In exchange, even more K+ has to enter the cell to compensate for the H+ that is leaving.  Once again, the charge differential of the cell wall is changed, but this time the change will cause the action potential to be harder to trigger.

Combined, these underlying events lead to some of our expected symptoms for alkalosis:  hypokalemia (since even more K+ is going into the cells), and weakness (since muscle cells are now harder to activate).

And then there’s the Respiratory Symptoms…

Another common symptom set to be aware of is the respiratory changes that take place in response to a metabolic imbalance.  If a patient has metabolic acidosis, then the respiratory system will attempt to compensate by “blowing off” CO2, and thus decreasing the amount of free H+ in the body.  This is type of breathing is commonly referred to as “Kussmaul’s respirations,” which describe deep, rapid breaths.

And did you notice that deep, rapid breathing can be either a cause of respiratory alkalosis, OR a symptom of metabolic acidosis?  So you always need to be looking at the patient’s context for other clues as to what is going on.  If the patient has a history of severe diarrhea, then that type of breathing is probably a symptom of metabolic acidosis.  But if the patient has a history of panic attacks, then it’s more likely that the rapid breathing may have caused respiratory alkalosis.  Always be looking for other clues to help figure out what’s going on.

There are a lot more symptoms you could potentially see with these disorders, but I think these are the most common ones that you’re most likely to see on an exam.  As you look over the other symptoms during your study time, always be trying to figure out how the underlying A&P might be causing them.

And make sure to leave a question or comment below!

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4 Comments

  1. Tajaira

    Love your page! I find it to be very helpful for the most part. Still unable to grasp ABG concept 🙁 thanks….keep it up!

  2. Nevada

    Thanks for this article! It’s very helpful. I DID get confused at the end though. Rapid breathing is a cause of respiratory alkalosis and a symptom of metabolic acidosis so you have to look at the whole picture with the patient. But if they were vomiting a lot wouldn’t that cause metabolic alkalosis instead of acidosis? I might be reading too much into it.

    • Good catch! You’re absolutely correct, I had an error 🙂 It should have said severe DIARRHEA, not vomiting. I’ve edited the article so that it is correct now. Thanks for letting me know!!

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