Patients With Mixed Acid-Base Disorders
In this episode, Anil Harrison, MD, speaks with Paul Shiu, DO, about 3 patient case presentations with mixed acid-base disorders, including concomitant metabolic acidosis and metabolic alkalosis.
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Anil Harrison, MD, is the Associate Program Director of the Internal Medicine Residency Program and the Ambulatory Care Director at Touro University and St Joseph’s Medical Center-Dignity Health (Stockton, CA). Dr Harrison is board certified in India and the United States.
Dharminder Singh, MD, is an internal medicine chief resident at St Joseph’s Medical Center (Stockton, CA).
Moderator: Hello, everyone and welcome to Multidisciplinary Dialogue: Clinical Rounds and Case Reviews, with your host, Dr Anil Harrison, who is the associate program director for the Internal Medicine Residency Program and the Ambulatory Care Program at Touro University and St. Joseph's Medical Center Dignity Health in Stockton, California.
Today, we have a case review that Dr Harrison and Dr Paul Shiu will analyze and provide treatment insights. Dr Shiu is a second-year internal medicine resident at St. Joseph's Medical Center in Stockton, California. In this episode, we'll discuss three patient case presentations with mixed acid-base disorders. The views of the speakers are their own and do not reflect the views of their respective institutions or the views of Consultant360.
Dr Paul Shiu: Lights, camera, and action. We cover and we have basically laid down the foundation on how to analyze systematically arterial blood gases. If you're just tuning in now, you have some homework to do. We have seven podcasts already in the making. And so, we invite you and implore you to check us out. We always like to open up with a joke. Dr Harrison's rolling his eyes. I can see it. But I can't help it. Dr Harrison, did you hear about the person who lost the left side of his body?
Dr Anil Harrison: No. Is he all right now?
Dr Paul Shiu: You obviously looked at the script. That is cheating. Folks, we do have a script, but we also want to sprinkle in some non sequiturs and impromptus. Speaking of impromptu, I did not expect this patient to show up. But I have a 65-year-old with sleep apnea presented with abdominal pain, associated with fever and diarrhea. His labs and vitals confirm SIRS, which stands for systemic inflammatory response syndrome. His white cell count is 24,000. His sodium is 144. His chloride is 114. Potassium is 3.2. Bicarb is 8. BUN is 36. Creatinine is 1.5. Blood sugar is 120. The arterial blood gas reveals a pH of 7.10. A partial pressure of carbon dioxide of 28. Serum osmolality of 310.
Now the question I have for you, Dr. Harrison and our audience, is this a high anion gap metabolic acidosis, a high anion gap metabolic acidosis plus respiratory acidosis, a high anion gap metabolic acidosis plus non-anion gap metabolic acidosis plus respiratory alkalosis, or is it a high anion gap metabolic acidosis plus respiratory alkalosis, or a high anion gap metabolic acidosis plus non-anion gap metabolic acidosis plus respiratory acidosis? Long story short, what do you think is afflicting this patient? Dr. Harrison, would you lead us through this case?
Dr Anil Harrison: Sure. So once again, Paul, the first thing to see is what is the pH doing? The pH is low. Hence, the patient has acidemia. The next thing is to see what the PCO2 is doing. And it seems to be moving in the same direction as the pH. And you'd agree that this signifies a metabolic issue primarily. And if you look at the bicarb. The bicarb is low. And hence, we confirm this to be primarily a metabolic acidosis. After this, once you confirm a metabolic acidosis, the next thing is you want to calculate the anion gap, which is sodium minus chloride minus bicarbonate. In our patient, the anion gap is 22. So this confirms a HAGMA or a high anion gap metabolic acidosis. Now because there is no significant osmolal gap, methanol and ethylene glycol being positive agents for a HAGMA are unlikely.
The next thing, Paul, is to calculate the delta gap, which is the patient's anion gap minus 12. And over here, we have the anion gap is 22, 22 minus 12 equals 10. So once we have the delta gap, then the next step is what is our expected bicarbonate, which equals a normal serum bicarb of 25 minus the delta gap. In our patient, it is 25 minus 10, which equals 15. The interesting thing is Paul if you take a look at the patient's bicarb is actually 8, which is much lower than what we calculated the bicarb to be. Hence, the patient is losing bicarbonate, which are unaccounted for. And therefore, this represents a NAGMA as well, a non-anion gap metabolic acidosis.
Therefore, our patient has a HAGMA along with a NAGMA. The next step is to calculate what would the expected PCO2 be, which would equal the patient's bicarb plus 15, so 8 plus 15 equals 23. However, the actual PCO2, if you take a look of the patient, is 28, which is higher than the expected PCO2 of 23. Would you agree this represents that the patient has a respiratory acidosis as well? So to summarize, our patient has a HAGMA plus a NAGMA along with respiratory acidosis.
Dr Paul Shiu: Sounds like a fun time, Dr. Harrison.
Dr Anil Harrison: Absolutely.
Dr Paul Shiu: Maybe not for the patient, but definitely for our audience, right?
Dr Anil Harrison: So let me ask you a question, Paul.
Dr Paul Shiu: Sure.
Dr Anil Harrison: What do you think the etiology is?
Dr Paul Shiu: I'm very glad you asked Dr. Harrison. It's as if I did not prepare for this question. So the high anion gap metabolic acidosis is probably secondary to his sepsis and lactic acidosis. The normal anion gap metabolic acidosis is probably because of the diarrhea, while the respiratory acidosis is possibly because of sleep apnea.
Dr Anil Harrison: Awesome. That is great, Paul.
Dr Paul Shiu: Team effort, Dr. Harrison. We are going to move on to our next case. Here's another joke for you guys. What did the Buffalo say to its son?
Dr Anil Harrison: Bison.
Dr Paul Shiu: Oh, that sounds familiar. That brings back some tragic memories. Let's not go there guys. All right. Moving on. Onwards and forwards. I have another patient here. A 25-year-old gravida female with insulin dependent diabetes presents to the ER with vomiting and orthostatic hypotension.
Dr Anil Harrison: Goodness.
Dr Paul Shiu: I know, right? Sodium of 145, a chloride of 100, bicarb of 15, BUN of 30, and a creatinine of 2. Blood sugar of 300, lactate of 5, and urine ketones of 4+. Blood gases show a pH of 7.24. A partial pressure of carbon dioxide of 20. Serum osmolality of 320. Dr. Harrison, would you help us with this case?
Dr Anil Harrison: Sure. So once again, Paul, the pH is low and therefore the patient has acidemia. Take a look at the PCO2, the PCO2 is moving in the same direction as the pH. And therefore, it has to be a metabolic issue primarily. And with a serum bicarb of 15, this confirms this to be a metabolic acidosis. Once you confirm a metabolic acidosis, you calculate the anion gap, which is sodium minus chloride minus bicarbonate. In our patient, the anion gap is 30. And so, our patient has a HAGMA or high anion gap metabolic acidosis. Then you take a look at the measured serum osmolality, which is 320, and the calculated osmolality is 315. The difference of 5 is not significant. The next step is to calculate the delta gap, which is the patient's anion gap minus 12. In our patient, this equals 30 minus 12, which is 18.
Dr Anil Harrison: After the delta gap, the next step is to calculate the expected serum bicarbonate. Expected bicarbonate is 25 minus the delta gap. In our patient, the expected bicarb you'd agree would be 25 minus 18, which equals 7. However, the patient's bicarb is 15, which is actually more than the expected bicarb implying that there is more than expected bicarb. We confirm that the patient has a high anion gap metabolic acidosis and a metabolic alkalosis. So when your actual bicarb is greater than your estimate, your retaining bicarb. So that is why I feel that this patient also has a metabolic alkalosis on top of the HAGMA. Does it make sense?
Dr Paul Shiu: Oh, absolutely. I still remember from medical school, how confusing it seemingly was in the beginning, how you can have concomitant acidosis and alkalosis, but if you really think about it's about the relative amounts of bicarb and protons, right?
Dr Anil Harrison: Absolutely.
Dr Paul Shiu: The only thing is you can't have concomitant respiratory acidosis and alkalosis.
Dr Anil Harrison: Very true.
Dr Paul Shiu: You only have one pair of lungs.
Dr Anil Harrison: Absolutely. So the next thing we do, Paul, is to calculate the expected PCO2, which equals 15 plus the patient's bicarb of 15. In our patient, the expected PCO2, therefore is 30. But our patient's PCO2 is only 20, which is lower than the expected PCO2 implying that our patient is blowing off more PCO2 than expected and therefore has a respiratory alkalosis also. Therefore, we confirm that our patient has a HAGMA plus a metabolic alkalosis plus a respiratory alkalosis.
Dr Paul Shiu: Folks, just a recap on this patient. Our patient probably has a high anion gap metabolic acidosis because of DKA and renal insufficiency. The reason for the metabolic alkalosis perhaps due to the vomiting, while pregnancy could be the reason for the respiratory alkalosis.
Dr Anil Harrison: Great job. So what happens when the actual PCO2 is different from the calculated or expected PCO2? If the PCO2 and the blood gas is more than the calculated PCO2, this implies that the lungs are not getting rid of carbon dioxide signifying a respiratory acidosis. However, if the blood gases reveal PCO2 lower than the expected PCO2, this implies that the lungs are blowing off more carbon dioxide than expected signifying a respiratory alkalosis.
Dr Paul Shiu: Guys, all this information is driving me crazy. I just want to...
Dr Anil Harrison: Do you feel energized now, Paul?
Dr Paul Shiu: Yeah. After some coffee, for sure.
Dr Anil Harrison: Okay.
Dr Paul Shiu: Why did the Energizer bunny go to jail, Dr. Harrison?
Dr Anil Harrison: I'm not sure.
Dr Paul Shiu: He was charged with battery. Onwards and forwards.
Next case, we have an intellectually, disabled 40-year-old male brought into the emergency department in an obtunded state. His clothing is soiled with urine and stool. He's orthostatic and has Kussmaul's respirations. Sodium of 135, chloride of 118, bicarb of 5, BUN of 52, a creatinine of 3.4, blood sugar of 100, serum osmolality of 295. Urine pH is 5. Urine anion gap is negative. Blood gases reveal a pH of 7.25 and a PCO2 of 20. What do you think is going on folks? Now, remember, we have some options, of course. Is this a HAGMA, a NAGMA, a HAGMA plus respiratory acidosis, or is it a HAGMA plus respiratory alkalosis, and finally is this just a pure metabolic alkalosis? Dr. Harrison, would you do us the honor?
Dr Anil Harrison: Absolutely, Paul. So this can't be just a metabolic alkalosis, because if you take a look at the pH of 7.2, it signifies that there is acidosis going on. And if you take a look at the PCO2, which is also trending in the same direction as the pH, so it has to be a metabolic issue. And with a bicarb of 5, this confirms a metabolic acidosis. So the next thing is, as we discussed before, you calculate the anion gap and in our patient, the anion gap is 12. So this is a NAGMA, a normal anion gap metabolic acidosis. When you get a NAGMA, the next step is to calculate the serum osmolality and see if there is an osmolal gap. There is no osmolal gap because both the calculated as well as the measured serum osmolality are the same at 295.
Now, what is the expected PCO2? The expected PCO2 is 15 plus a bicarb of 5, which equals 20, which is the same as a PCO2 in the blood gases. The next step is very important to calculate the urine anion gap, which is sodium plus potassium minus chloride. Since you mentioned Paul, that the urine anion gap is negative. I would say this is pointing towards a GI issue, or it could be a secondary to proximal renal tubular acidosis. But you mentioned that the patient has a history of diarrhea. Hence, I would say that the NAGMA that the patient has is secondary to diarrhea.
Dr Paul Shiu: Wow. What a closing to a fantastic series of three cases.
Dr Anil Harrison: Awesome.
Dr Paul Shiu: Awesome. Folks, we had a segment that focused strictly on the value of urine anion gap. And once again, a shameless self-promotion to check out that particular episode. I thank Dr. Harrison so much for walking us through three extraordinary cases.
Dr Anil Harrison: It's my pleasure, Paul. Thank you, everybody.
Dr Paul Shiu: Thank you, everybody. Until next time.
Dr Anil Harrison: Bye.
Dr Paul Shiu: Bye.