Isopropyl alcohol toxicity
The case
A 30-year-old man is brought in by ambulance after a suicide attempt. His roommate came home and found him poorly responsive on his bed next to a suicide note and a bottle of rubbing alcohol (70% isopropyl alcohol) which was approximately 1/2 full. There was no evidence of other ingestions/bottles, drug paraphernalia, or trauma. He last saw the patient acting normally about 1 hour prior to arrival. He tells you the patient has been depressed due to a recent separation from his wife, but had no known medical problems and took no medications.
Vital signs are within normal limits. The patient is very somnolent and withdraws only to painful stimuli. Pupils are equally round and reactive to light bilaterally. Skin is warm and dry. There are no external signs of trauma. During the evaluation, he starts to vomit (non-bloody). He is subsequently intubated for airway protection and an orogastric tube is placed to suction the stomach.
CT of the head is negative. Chest X-ray is negative for focal opacities or free air. Pertinent labs are shown here:
The brush up
Ingestion of isopropyl alcohol is the most common route, though inhalation of highly concentrated air levels can also result in significant toxicity. As an interesting aside, inhalation of an alcohol prep pad has actually been studied (and may be effective) as a treatment for nausea!
Aggressive supportive care alone will manage the majority of isopropyl alcohol toxicity. Fomepizole (a competitive inhibitor of alcohol dehydrogenase) is not indicated because of the lack of organic acid metabolites. Note that with its small volume of distribution, hemodialysis is a potential treatment modality, but it's really only indicated for refractory hypotension.
There are really only 3 things you need to know about toxic alcohol poisoning, which we will discuss in the context of isopropyl alcohol:
- Distinct clinical features
- Metabolites
- Gaps
Distinct clinical features
Patients poisoned by isopropyl alcohol look incredibly drunk (perhaps out of proportion to the reported ingestion). The CNS depressant effect is much greater than other alcohols, and patients commonly present with coma and even respiratory arrest (probably due to brainstem depression). You may note a fruity odor on the breath (due to acetone, see below).
Metabolites
This is how I like to think about toxic alcohol metabolism. Recall that there are 2 enzymes responsible for processing alcohols: alcohol dehydrogenase and aldehyde dehydrogenase. Note that isopropyl alcohol only undergoes metabolism by alcohol dehydrogenase to form acetone.
Why does this matter? It's the only metabolite that's NOT an organic acid, so it's the only one that will NOT lead to an anion gap acidosis (as evidenced by our patient's normal anion gap of 15 and normal pH). But you will see ketonemia and ketonuria. Think ketosis without acidosis. So despite the fact that patients often appear very intoxicated, this unique feature actually makes isopropyl alcohol much less toxic than the other alcohols.
Gaps
Let's calculate the serum osmolality (roughly) and osmol gap based on our patient's lab data:
Calculated serum osm: (2 x Na) + (BUN / 2.8) + (glucose / 18) = 270 + 7 + 6 = 283
Osmol gap: measured serum osm - calculated serum osm = 330 - 283 = 47 (elevated)
Why the elevated osmol gap? It's because the parent compound contributes to the measured serum osmolality (but is not accounted for in the calculated osmolality). The concept to grasp here is that an elevated osmol gap typically indicates early toxicity (when much of the parent compound (in this case, isopropanol, is present in the serum). As metabolism ensues, the osmol gap decreases. Now, with buildup of organic acid metabolites (as seen with methanol, ethylene glycol, and propylene glycol), you'll see a progressive increase in the anion gap as the osmol gap decreases. Remember, this is NOT the case for isopropyl alcohol; the anion gap will remain stable (since acetone is not contributing to it).
The conclusion
The patient remained hemodynamically stable and was admitted to the medical ICU for continued care. He suffered no other immediate complications. His mental status returned to baseline and he was extubated within 24 hours. He was placed on an involuntary psychiatric hold following medical clearance.
References
1. Olson KR & California Poison Control System. (2012). Poisoning & drug overdose. New York: Lange Medical Books/McGraw-Hill.
2. Sivilotti MLA. Isopropyl alcohol poisoning. In: UpToDate, Grayzel J (Ed), UpToDate, Waltham, MA, 2015.
3. Beadle KL, Helbling AR, Love SL, April MD, Hunter CJ. Isopropyl alcohol nasal inhalation for nausea in the emergency department: a randomized controlled trial. Ann Emerg Med 2016 Jul;68(1):1-9.
4. Slaughter RJ, Mason RW, Beasley DM, Vale JA, Schep LJ. Isopropanol poisoining. Clin Toxicol (Phila) 2014 Jun;52(5):470-8.