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Toxicology Rounds

2022; Lippincott Williams & Wilkins; Volume: 44; Issue: 4 Linguagem: Inglês

10.1097/01.eem.0000827700.58002.96

1552-3624

Leon Gussow,

Science, Research, and Medicine

Figure: medical toxicology, best practiceFigureEffective medical toxicologists develop habits that minimize the chance of overlooking small but crucial aspects of managing poison cases. Two of those stand out and can help emergency physicians in the care they deliver as well. Know the Units Units matter. Just ask the folks at NASA. The Mars Climate Orbiter was approaching the Red Planet in 1999 where plans called for it to enter into orbit and relay observational data to ground control. Suddenly, NASA lost all communication with the $125 million spacecraft. Apparently, an error had caused the Orbiter to come in at too steep an angle. Instead of entering orbit, it most likely went into the atmosphere and was destroyed. But what was that error? Scientists determined after extensive study and analysis that the proximate cause was miscommunication between two computer systems on the craft that had been developed independently. One system measured the action of rocket thrusters, reporting the results to a second computer that used the measurements to calculate course corrections and adjustments.FigureUnfortunately, the first computer measured thrust in metric units of newtons per second while the second computer was programmed to expect results in mass units (pound-force per second.) One newton equals 0.225 pounds, so this introduced a more than fourfold error into the finely-tuned math designed to keep the Orbiter on course. Given that this error existed from the time of launch nine months before, it's amazing that the spacecraft ended up anywhere near Mars at all. On a less cosmic but no less serious level, such errors in miscommunicating units happen not infrequently when managing toxicology cases. One might hear this dialogue in such a case: Physician 1: That patient who came in saying she took several handfuls of aspirin? Her salicylate level is 140. Physician 2: Start a bicarb infusion, put in a Quinton catheter, and call renal. Physician 2 (30 minutes later): What's going on with the salicylate overdose patient? Physician 1: The bicarb drip is going, the Quinton was placed, and nephrology is on their way. Physician 2: By the way, what was that initial salicylate level again? Physician 1: 140 milligrams per liter. Physician 2: Oops. What we have here is a crucial failure in communication. Salicylate levels are typically reported in units of milligrams per deciliter, with levels higher than 100 mg/dL often taken as evidence of severe toxicity and an indication to initiate hemodialysis. But as the American College of Medical Toxicology pointed out recently in a document on managing priorities in salicylate toxicity: “Attention to reported salicylate concentration units is important as they may be reported as milligrams per deciliter, milligrams per liter, or millimoles per liter.” (J Med Toxicol. 2015;11[1]:149; https://bit.ly/3BnTgDh.) Physician 1 mistakenly assumed that the level of 140 was reported in the typical units of mg/dL. Unfortunately, 140 mg/L is equivalent to 14 mg/dL, which is actually a subtherapeutic, not toxic, level. Now the team has the unpleasant duty of going back to the patient and explaining, “You know that big tube we just put in you? Our mistake; it was totally unnecessary. Sorry.” The chance for this happening is not just theoretical; I am aware of cases where exactly this took place. Similar errors can happen with toxic alcohols, where levels can be reported in mg/dL or mg/L, again a 10-fold difference. Physicians should develop a habit where they will not accept any drug level given only as a number but always insist on knowing the units involved. By the way, the website Units Lab can convert results from one unit to another. (http://unitslab.com.) Let's give the final word on this topic to the Royal Infirmary in Edinburgh: “The failure by clinicians to appreciate the importance of units of measurement is a fundamental problem in clinical toxicology and therapeutic drug monitoring. This careless omission of units together with the multiplicity of units currently used by laboratories constitute a potential source of serious misunderstanding and misinterpretation.” (Ann Clin Biochem. 1980;17[6]:328.) Get Levels Back Fast One of the recurring frustrations in medical toxicology is the general lack of bedside, point-of-care, or even in-hospital testing for ethylene glycol (EG) and methanol levels. Our poison information center is often consulted because a patient has an unexplained high anion gap and the treating team suspects possible toxic alcohol poisoning, even if no history supports that diagnosis. Standard procedure, if toxic alcohol exposure is a reasonable possibility, calls for starting fomepizole to block metabolism and then sending off specimens to an outside reference laboratory to measure EG and methanol levels. Unfortunately, sometimes it can take days to get those levels back. This presents two major problems. First, without levels to confirm or rule out the diagnosis, the team may anchor on alcohol toxicity without considering other causes of an increased anion gap. Second, the patient may be subjected to a long, expensive, and possibly unnecessary course of fomepizole treatment until levels come back. It is important to ensure minimal delay in getting these results. Send the specimens to the outside laboratory by expedited carrier. Call the outside lab to ascertain that they have received the samples and are running them STAT. Of course, your local poison control center can help with this process and should be consulted on all cases in which a diagnosis of toxic alcohol poisoning is a possibility. Dr. Gussowis a voluntary attending physician at the John H. Stroger Hospital of Cook County in Chicago, an assistant professor of emergency medicine at Rush Medical College, a consultant to the Illinois Poison Center, and a lecturer in emergency medicine at the University of Illinois Medical Center in Chicago. Follow him on Twitter@poisonreview, and read his past columns athttp://bit.ly/EMN-ToxRounds.