For more information, visit www.nursing.com/cornell
Get unlimited access to lessons and study tools
In this lesson we’re going to start talking about the metabolic acid base imbalances. Specifically we’re going to start with metabolic acidosis. This is probably one of the most common acid base imbalances that you will see in any hospitalized patient.
Lab values you’ll see in metabolic acidosis are low ph and a low bicarb level. Other things you might also see our an increase lactic acid and a base deficit, which is a negative number on the base excess lab result. We will talk about these two levels in their own lessons later in this course.
Generally, metabolic acidosis could have two possible causes. One would be an increase in metabolic acids in the blood, the other would be a loss of alkaline substances or bases from the blood. These are some of the most common causes of metabolic acidosis. Diarrhea causes acidosis because there is a significant loss of bases and alkaline substances in the diarrhea itself. It also can cause dehydration. Diabetic ketoacidosis, lactic acidosis, and ingestion of poisons or toxins all cause an increase in circulating acids in the blood. A common example here is ethylene glycol (or antifreeze) poisoning. I had a patient once whose wife had put antifreeze in his gatorade. He had one of the worst cases of metabolic acidosis I had ever seen, his lactic acid was sky high and his base deficit was in the toilet – again, you’ll learn about those in their own lessons later! The other thing that can cause a metabolic acidosis is renal failure because the kidneys are responsible for regulating bicarb as well as hydrogen ion excretion. Normally they’d hang onto bicarb and excrete hydrogen ions, but when the kidneys fail, they tend to do the opposite of what they’re supposed to do – so we lose a BUNCH of bicarb in the urine and they’ll sometimes hold onto too much hydrogen as well. So those are the major causes – again any increase in acids or loss of bases.
Just like we saw with the respiratory and balances, the number one sign you’re going to see is a sign of the actual cause. So if it is diabetic ketoacidosis, for example, you will see elevated blood sugars, kussmaul respirations and fruity breath. Plus, of course, Ketones in the urine. Then, you’re going to see signs of the acidosis itself. Altered level of consciousness is one of the most noticeable symptoms, again, because the brain is very sensitive to changes in PH. They will be confused and drowsy, and they may have a headache. We will also, more often than not, see nausea and vomiting. Why is that? Well, what place in your body do you know of that stores a bunch of acid? Our stomachs are essentially a bag full of hydrochloric acid. So when our bloodstream gets too acidic, our bodies will try to compensate by forcefully ejecting as much of that acid as possible. We also know that compensation happens when the opposite system tries to fix the problem as well. Since CO2 equals acid, the lungs will start to breathe faster to try to decrease the level of acid in the system. So we’re going to see increased respirations. That is where the kussmaul respirations come from in DKA. So, signs of the cause, signs of the acidosis and compensation, and lastly we may see evidence of hyperkalemia. Remember, the extra hydrogen ions in acidosis will trade places with the potassium in the cell to try to balance out the pH. That means we end up with more potassium in the bloodstream than we had before. So you might see EKG changes, muscle weakness, and arrhythmias.
Another concept that is heavily related to metabolic acidosis is an anion gap acidosis. There is a whole lesson on anion gap in the labs course that you can check out. But what I want you to know here is that an anion gap acidosis is caused by unmeasurable acids that are not and ions are cations. It is a calculation that you could do yourself, but it is typically included on a comprehensive metabolic panel. Essentially, it is the cations, which are the positive electrolytes, Minus the anions which are the negative ones. If this acidosis is simply caused by a loss of bicarb, then you will not see an anion gap because the bicarb level is taken into consideration here. However, if the acidosis is caused by some other acid like lactic acid or ketoacids in DKA, then you will have a large gap between the cations and anions. This always refers to a metabolic acidosis, you will not see an anion gap acidosis related to respiratory acidosis. Make sure you check out the mnemonics attached to this lesson 2 get an idea of what types of conditions will cause an anion gap acidosis.
As we’ve seen with the other acid base imbalances, the number one therapeutic management for metabolic acidosis is to treat the cause. If this is a DKA issue then we will administer insulin and IV fluids. If it is sepsis or shock, then we will give IV antibiotics and work to get their blood pressure up. We also very commonly will give sodium bicarbonate as a buffer to prevent serious complications of acidosis while we work on treating the cause. Of course, if a loss of bicarb or severe diarrhea was the cause, then administering bicarb is also the treatment. We can also possibly look at ventilator settings or some quick compensation and adjustment or the pH level. We can increase the respiratory rate to try to blow off some CO2 to help increase the pH. The problem is that this is just a temporary fix, and kind of a Band-Aid. It will not fix the problem. Going back to my patient who was poisoned with ethylene glycol. He was placed on the ventilator because his breathing rate had gotten so fast that he couldn’t sustain it anymore. He was also placed on dialysis and plasmapheresis to get the ethylene glycol out of his system and a continuous bicarb drip. We pulled out all the stops for him because of how severe his metabolic acidosis was. He did survive, but unfortunately ended up with some permanent brain damage from the severe acidotic state.
So, our priority nursing concepts for a patient with metabolic acidosis are going to be acid-base balance and gas exchange, and then of course whatever priorities there are for the underlying cause.
Let’s recap. Lab values found in metabolic acidosis include a low ph and a low bicarb, as well as possibly a high lactic acid and a negative Base deficit. The two general causes of metabolic acidosis are an increase in metabolic acids like in DKA or lactic acidosis or a loss of alkaline substances like in diarrhea or renal failure. You will see symptoms of the cause, symptoms of the acidosis itself, including altered LOC, vomiting, and tachypnea. And you will see hyperkalemia and its possible complications. Management always involves treating the cause, giving sodium bicarb, and possibly making vent changes, but understanding that that is only a Band-Aid.
So those are the basics of metabolic acidosis. Make sure you check out the lactic acid and the base excess/base deficit lessons to learn more about how those lab values relate to metabolic acidosis. Don’t miss all the resources attached to this lesson, as well. Now, go out and be your best selves today. And, as always, happy nursing!!