Author: Annie Arens, MD
Internal Reviewer: Justin Corcoran, MD
External Reviewer: Daniel Sessions, MD
We’re going to start this post with a case:
Case
A 26 year old female presents to your emergency department with a chief complaint of “intoxicated” after having been found intoxicated in her vehicle. The patient has a breathalyzer ignition interlock system (BAIID) in her car, preventing her car from starting if her breath alcohol concentration is greater than (0.02). It looks like she may have tried to start her vehicle, to no avail. Police and EMS arrive on scene – police check a breathalyzer, that comes back at 0.200. They decide to bring the patient to the ED.
Here are her initial vital signs:
HR 105; BP 115/80; RR 20; T 34.0; O2 Sat on room air: 98%
Clinically, the patient appears intoxicated. There is no evidence of trauma.
As part of her triage process, serum ethanol level and a BMP are obtained.
Here’s the important ones:
Chemistry: CO2 12, AG 20
Serum ethanol NEGATIVE
WTF?!*
*As a side note – never do I ever (almost) complete a serum ethanol in these cases – this case furthers the old adage “it’s better to be lucky than to be good”.
You send the serum ethanol again, TWICE, and still…negative (also, you have now met the definition of insanity).
So fine, you expand your work-up:
“Toxic” Alcohols:
Ethylene glycol: 0.00
Isopropyl alcohol: 0.00
Methanol…225 mg/dL (!!!)
I repeat…WTF?! You find out later that she had an open bottle of windshield wiper fluid in the car next to her. You didn’t have that information up front, but lucky you picked up the discrepancy in the serum concentration and breathalyzer. So let’s talk about breathalyzers, baby…
How do breathalyzers actually work?
In our community, there are two different major types of breathalyzers, which use two different mechanisms to measure breath ethanol:
- Infrared spectroscopy. This includes the Intoxilyzer© brand of breathalyzers, those used in the vehicle, and by police for this patient. There’s a great case report of a similar case from Caravati and Anderson (2010). These take advantage of a principle that we’re already familiar with: specific wavelengths of infrared energy are absorbed by differently molecules. SO, you blow your ethanol breath into a chamber, an infrared source is shown through the chamber, and on the other end, you have a detector to measure the change in infrared wavelength. From there, the processor can calculate a breath ethanol concentration. Are you a visual person? Have I got a treat for you:
intox.com/intrared-spectroscop
How does this get funked up with methanol? Because methanol and ethanol have similar infrared absorption spectra, you may have a false positive ethanol concentration on your breathalyzer.(Caravati and Anderson 2010)
- Fuel cell technology (sounds fancy, right?). These include the Alco-Sensor© series. This takes advantage of the same fuel cell technology that we use for other applications (cars etc…). Essentially, you blow your ethanol-laden breath into a chamber which then blows past electrodes. The electrodes oxidize the ethanol, and now you’ve basically got protons and electrons. Those electrons create a current, the higher the ethanol concentration, the stronger the current. A mathematical algorithm is then applied to calculate the concentration of ethanol.
Image: intox.com/fuel-cell-white-paper
Are these tricked by methanol? Well, the company so happens to have a white paper: (“Fuel Cell White Paper – Intoximeters” n.d.)
Why would there be a potential interference? Methanol will still be oxidized by the electrodes because of science. However, the same algorithm used to calculate an ethanol concentration will be applied to your current generated by methanol. So, you still have a current, the processor thinks it’s ethanol and hence you get an “ethanol” concentration result. Pretty groovy.
This is obviously a gross oversimplification of these technologies, but you get the idea. Your result is only as good as your test.
How did your patient do? Because you are such a rockstar clinician, you treat your patient with fomepizole and folate and decide to dialyze her (this post isn’t about how to treat methanol, that’s for another day) and she does just fine. Good job you.
References:
- Caravati, E. Martin, and Kathleen T. Anderson. 2010. “Breath Alcohol Analyzer Mistakes Methanol Poisoning for Alcohol Intoxication.” Annals of Emergency Medicine 55 (2): 198–200.
- “Fuel Cell White Paper – Intoximeters.” n.d. Intoximeters. Accessed February 19, 2020. https://www.intox.com/fuel-cell-white-paper/.
Everything is Osm 