Have you ever administered albuterol (aka salbutamol) to a ventilated patient and witnessed the anesthetic gas analyzer detect halothane even though there hasn’t been a bottle of halothane in your hospital in decades? How can a machine so advanced make such an error?

The gas analyzer on your anesthetic machine is an underappreciated technological marvel found in every operating room in every industrialized country in the world. It consists of a paramagnetic analyzer to detect oxygen and a gas phase infrared spectrometer for all other gases. Because oxygen does not absorb infrared light, it can not be analyzed by infrared spectroscopy and requires its own analyzer. All companies that produce anesthetic gas analyzers use Paramagnetic and IR technology.

In a chemistry lab, when we try to identify a molecule with IR spectroscopy we may be trying to identify an unknown molecule from a possible list of millions of molecules. In the operating room, we are only concerned with around 5 molecules. Instead of scanning the whole spectrum and identifying all possible peaks; an anesthetic gas analyzer only scans 2 limited areas of the spectrum and instead of searching for hundreds of possible peaks in these areas, the analyzer will only search for a few specific peaks in those ranges. By limiting the scanning spectrum and recognizing only a handful of absorption peaks This allows for a rapid response time on the order of milliseconds.

Albuterol and halothane have very little structural similarities. Most importantly Albuterol’s structure contains double bonds and hydroxyl groups that will produce unique infrared absorption peaks not found in halothane.

And if we look at the IR spectrums we continue to see little similarity

So if the machine isn’t detecting albuterol, what is it detecting? One clue lies in the fact that albuterol administration via metered dose inhaler will result in halothane detection by the gas analyzer but albuterol administration via nebulized solution will not. Perhaps the inhaler contains an extra ingredient that is similar to halothane. That ingredient is HFA. HFA, the propellant in most albuterol inhalers, stands for hydro fluoro alkane.

 Interestingly, halothane contains the components of a hydro flouro alkane. If we reference the albuterol HFA package insert, we see that the specific HFA used, is HFA 134a. Now this molecule looks quite similar to halothane. Interestingly, HFA 134a is an anesthetic of moderate potency, and was investigated for use as an inhaled anesthetic in humans in the 1960s.

Loooking at the IR spectra, we can clearly see that it is HFA-134a and not Albuterol that is responsible for your anesthetic gas analyzer reading Halothane.

Prepare yourself for the greatest technological leap of all time: The Toilet Paper Ventilator.

A large pet peeve of mine is seeing the general public use surgical gloves incorrectly as a means of infection control and protection. I most commonly see gloves being worn by grocery checkout attendants and by law enforcement. Gloves offer little direct protection from day to day interactions and provide a false sense of security that prevents the wearer from performing hand hygiene as frequently as they should.

In order to protect oneself and prevent the spread of infection, an individual needs to clean their hands between each interaction with a new individual. The typical use of gloves by non-medical individuals involves continuing to wear the same gloves for hours or even days at a time. Every time the wearer touches a new surface, object, or person, their gloves pick up whatever was there; when they touch the next surface, object, or person with those gloves, they transfer it and facilitate the spread of disease.

In addition to spreading the disease to others, most people subconsciously touch their clothing and face constantly throughout the day and since they have interacted with hundreds of people with their gloves, its like hundreds of people have touched them.

When I care for a patient in the operating room I use hand sanitizer, don gloves, interact with my patient or dirty equipment, remove my gloves, then use hand sanitizer again before I can interact with a clean environment again. Although we seem pretentious when we do it, we should constantly be reminding the people that wear gloves in public, to change their practice. Grocery workers and law enforcement such as the TSA are facilitating the spread of disease to countless people every day though ignorance of basic hand hygiene techniques.

Here’s a video I made addressing similar concerns over every day, seeing dozens of people wearing surgical gloves in public during the COVID-19 crisis:

The oridion and nellcor portable capnometers are valuable tools offered by Medtronic for continuous etCO2 monitoring outside the OR. I frequently bring the handheld device with me to floor intubations and codes allowing for rapid troubleshooting of ETT placement and monitoring of effective chest compressions.

At the time of this writing there appears to be an abundance of AS-IS devices available on eBay for minimal cost; the majority of the devices do not come with the power cable. I was betting that these items were sold AS-IS because the device uses an unusual RJ-45 (Ethernet) based charging cable and the sellers did not want to invest $200+ on a new cable from Medtronic to test the devices.

I purchased a lot of 3 Oridion Microcaps sold “AS-IS for parts only” from eBay for $75.00.

Since we have a couple of the Nellcor devices at our institution I was able to use the OEM power brick as a reference. The brick has all the necessary info to produce a similar device:

I purchased the following power supply from amazon and wired up a rough adapter following the wiring diagram on the OEM power supply:



The result? All three Microcaps are fully functional. The last component was to produce a more finished product:




Items used for this project:
– Universal DC adapter.
– Female 2.1mm x 5.5mm connector Amazon item listed as an example, however, I purchased mine off eBay for $1 (if you don’t mind waiting 1-2 months).
– Ethernet Cable You likely have one of these sitting around, unused.
– Electrical Tape or wire heat shrink for a nicer appearing repair.
– Wire stripper.