Patients With Methanol Toxicity, Salicylate Toxicity
In this episode, Dr Harrison speaks with Paul Shiu, DO, about acid-base disorders, including a patient with methanol toxicity and a patient with salicylate toxicity.
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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.
Paul Shiu, DO, is a second-year internal medicine resident at St Joseph's Medical Center (Stockton, CA).
Dharminder Singh, MD, is an internal medicine chief resident at St Joseph’s Medical Center (Stockton, CA).
TRANSCRIPTION:
Introduction: 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 Director 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 a patient with methanol toxicity and a patient with salicylate toxicity. The views of the speakers are their own and do not reflect the views of their respective institutions or the views of Consultant 360.
Dr Paul Shiu: Good morning, everyone. Welcome to another podcast on a long standing series here on arterial blood gases. Last podcast, we recorded a single case. This podcast, you're in for a treat because it's a two-parter. And I have here the man, the myth, the legend, Dr Harrison. Dr Harrison, how are you doing this morning?
Dr Anil Harrison: Good morning, everyone. I'm doing well, Paul, thank you.
Dr Paul Shiu: Dr Harrison, I need your help on this one, as well. So I saw an intoxicated male. He was brought in with abdominal pain. His sodium was 140, a potassium of 4, a chloride of 104, a bicarb of 5, and a blood sugar of a 100, BUN of 20, a creatinine of 1.2, and a serum osmolality of 317. Blood gases reveal a pH of 7.05. The partial pressure of carbon dioxide, 20. Urine negative for ketones or calcium oxide crystals. Is this high anion gap metabolic acidosis? Normal anion gap metabolic acidosis? High anion gap metabolic acidosis, plus normal anion gap metabolic acidosis? Or is this a high anion gap metabolic acidosis, plus normal anion gap metabolic acidosis, plus respiratory alkalosis?
Folks, it would've been easier if I'd just said NAGMA and HAGMA, but essentially, we need to work out all the possible permutations. What acid-based disorder does this patient have? Dr Harrison, would you lead us with this case, please?
Dr Anil Harrison: Sure. So Paul, if you look at the pH, it confirms that the patient has acidemia. The next thing is what is the pCO2 doing?
Dr Paul Shiu: Yes.
Dr Anil Harrison: And the pCO2 is also down. And whenever the pH and pCO2 move in the same direction, it signifies a metabolic issue. So, this patient has a metabolic acidosis because if you look at the serum bicarb, the bicarb is also low. So we confirm metabolic acidosis. The next thing is to calculate the anion gap, to see if this is a high anion gap metabolic acidosis, or a HAGMA, or is this a NAGMA, which is a normal anion gap metabolic acidosis. So as you know, Paul, anion gap, which is sodium minus fluoride minus bicarbonate, in our patient is 33, which is significantly elevated. And therefore, we are going to call it a HAGMA or a high anion gap metabolic acidosis.
The next thing to do is to see if there is an osmolar gap. Measured serum osmolality is 317, whereas when the two of us calculated the calculated serum osmolality, which is two times sodium plus BUN divided by 2.8 plus blood sugar divided by 18, comes to about 290. So there is a significant osmolar gap of 27, which is abnormal.
Dr Paul Shiu: Oh, absolutely. Significantly. So if I recall correctly, anything above 10, constitutes an osmolar gap, is that right, Dr Harrison?
Dr Anil Harrison: Absolutely correct.
Dr Paul Shiu: All right guys. So, so far, our patient has an high anion gap metabolic acidosis and an osmolar gap, signifying its either methanol or ethylene glycol.
Dr Anil Harrison: You're absolutely correct, Paul. The next thing to do is to calculate the Delta gap, which is the patient's anion gap minus 12. And the patient's anion gap is 33. And if you take away 12, it equals 21. So the Delta gap is 21. As you remember, Paul, the next thing we do is to calculate what would be the expected bicarbonate. The expected bicarbonate equals 25 minus the Delta gap, 25 minus 21, in our case, equals four, which is approximately the same as the patient's bicarb of five.
Dr Paul Shiu: How about that? The math all works out, folks. So if the actual bicarb of the patient was more than the expected bicarb, this would signify a metabolic alkalosis. If the patient's bicarb was lower than the expected bicarb, this would signify a normal anion gap metabolic acidosis, in addition.
Dr Anil Harrison: You're absolutely right, Paul. Great job. So, the next thing to do is let us look at the pCO2. The expected pCO2 would be 15 plus the patient's serum bicarb. This equals 20, which is the same as the pCO2 noted on the blood gas. Hence, there is a respiratory compensation.
Dr Paul Shiu: So if the patient's pCO2 were more than the expected pCO2, this would signify a respiratory acidosis, in addition. And then if, on the other hand, the patient's PCO2 is lower than the expected pCO2, this will signify that the patient is blowing out excess CO2 and hence, has respiratory alkalosis.
Dr Anil Harrison:
Excellent, Paul.
Dr Paul Shiu:
Now that I think about it, once upon a time when I was just a wee child, I remember when people are having these anxiety attacks and they're hyperventilating. That's blowing off excess CO2.
Dr Anil Harrison:
Absolutely.
Dr Paul Shiu:
I also recall, Dr Harrison-
Dr Anil Harrison:
Somebody put a bag over your mouth?
Dr Paul Shiu:
Well, over my head actually, but there you go, folks.
Dr Anil Harrison:
Okay.
Dr Paul Shiu:
Yes. It was a brown paper bag.
Dr Anil Harrison:
Yeah. And our patients fund this exam. I look at that, Paul, shows optic disc edema and hyperemia, which is suggestive of methanol intoxication.
Dr Paul Shiu: Oh boy. This is, for all you listeners out there who are not on our YouTube channel, which you should check out because there is an entire half of the presentation that you're missing on, the video of the audio-visual presentation. What we have here is a picture of what papilledema essentially looks like. You have optic disc blurring. And we won't go into specifics because I feel like this is a subject in it of itself, but you essentially have this progressive swelling of the optic disc with blurring of the margins. And you'll see obscuring the vessels which supply the retina. It's very characteristic, and especially in methanol poisoning. And one of the sequela of optic disc edema is blindness. Is that correct?
Dr Anil Harrison: Absolutely. And you must have read of people gathering and drinking homemade alcohol, but it's actually methanol, and in droves, they go blind because of methanol intoxication.
Dr Paul Shiu: So Dr Harrison, we had so much fun with one case. Why don't we do one more?
Dr Anil Harrison: Absolutely.
Dr Paul Shiu: Okay.
Dr Anil Harrison: Game on.
Dr Paul Shiu: Alrighty. So I also saw an 85-year-old with arthritis coming in with shortness of breath. Cardiopulmonary workup was negative except for an ABG which revealed a pH of 7.27, a PCO2 of 20, lactate, which was normal, and a serum osmolality of 293, sodium 140, potassium four, chloride of 104, a bicarb of 13, and a blood sugar of 120, BUN of 15. What are your thoughts? Do you think this is a methanol toxicity? Isopropyl alcohol toxicity, ethylene glycol toxicity, diabetic ketoacidosis, or salicylic toxicity?
Dr Anil Harrison: So the pH reveals that the patient has acidemia. The next thing is you see what really is PCO2 doing? When the pCO2 is moving in the same direction as a pH, it represents a metabolic cause, as in this case. And if you look at the bicarb, which is 13, it confirms that our patient has a metabolic acidosis.
Dr Paul Shiu: So, taking it a step further here, we also see that the anion gap, which is sodium minus chloride minus sodium bicarbonate, in our patient, the anion gap is 23.
Dr Anil Harrison: Correct.
Dr Paul Shiu: Confirming that this patient has a high anion gap metabolic acidosis, otherwise known as HAGMA.
Dr Anil Harrison: Excellent.
Dr Paul Shiu: We're we're picking up some steam here, Dr Harrison. So the next step is to check for an osmolar gap. There is no osmolar gap in this case because when you calculate the osmolar gap, it's less than 10, hence methanol and ethylene glycol toxicity are unlikely.
Dr Anil Harrison: Excellent. Great job, Paul.
Dr Paul Shiu: Thank you.
Dr Anil Harrison: So our patient who has a HAGMA with no osmolar gap, the next step would be to check the Delta gap, which is the patient's anion gap of 23 minus 12. So the Delta gap is 11. Once the Delta gap has been calculated, one must calculate what should the expected bicarbonate be, which is 25 minus the Delta anion gap. 25 minus 11 is 14. In our patient, the expected bicarbonate is, therefore, 14, which is close to the actual bicarbonate of 15.
Dr Paul Shiu: Huh? So if the actual bicarb were significantly lower than the expected bicarb, there would have been an additional non-anion gap metabolic acidosis.
Dr Anil Harrison: True.
Dr Paul Shiu: NAGMA. On the other hand, if the patient's bicarb were significantly higher than the expected bicarb, this will represent a metabolic alkalosis, in addition to a HAGMA, which our patient has.
Dr Anil Harrison: Perfect. More simple. The next step is to calculate the expected PCO2, which is the patient's bicarb plus 15. The patient's bicarb is 13, and if you add 15, it equals 28.
Dr Paul Shiu: So, the actual PCO2 is significantly lower than the expected or calculated PCO2, hence the patient has a respiratory alkalosis.
Dr Anil Harrison: You are correct. So our patient has a HAGMA, and in addition, a respiratory alkalosis, and I think it possibly could be a secondary to salicylate use for arthritis.
Dr Paul Shiu: That's great detective work. Everything slots in perfectly, and this is all because we follow a systematic way to approaching acid-based. And folks, initially, it seems daunting because you have all these steps, but when you do it systematically, you don't miss anything, just like when you're reading a chest x-ray.
Dr Anil Harrison: Absolutely.
Dr Paul Shiu: Once again, I just want to say thank you so much for tuning in for yet another podcast. We have a few more cases in our acid-based series. Is that right, Dr Harrison?
Dr Anil Harrison: Absolutely. I would say another, maybe three or four.
Dr Paul Shiu: Thank you so much for your support, all you loyal listeners and even if you were disloyal listeners, I hope you come back. Thank you for coming back. Hope to see you soon. Thank you, guys.
Dr Anil Harrison: Thank you, guys. Thank you, Paul.
Dr Paul Shiu: Thank you, Dr Harrison.