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? In this video I will briefly review IR spectroscopy, anesthetic gas analyzer functionality and how your gas analyzer can mistake albuterol and halothane.
Hello, i’m dr. rodriguez, thanks for joining me. have you ever administered albuterol to a ventilated patient and witnessed the anaesthetic gas analyzer detect halothane instead. in this gas analyzer functionality and how your gas analyzer can mistake albuterol and halothane, two fundamentally different molecules. the
Gas analyzer on your anaesthetic machine is an underappreciated technological marvel found in paramagnetic analyzer to detect oxygen and a gas phase infrared spectrometer for all other gases. because oxygen does not absorb infrared light, it cannot be analyzed by infrared spectroscopy and requires its own analyzer. for
This discussion we will concentrate on infrared spectroscopy. note that this discussion applies to all modern anaesthetic gas analyzers, as all major companies that offer analyzers utilize ir technology. as you will recall from your introductory chemistry classes, infrared spectroscopy is a method of molecular
Identification that, in its most common implementation, uses the absorption pattern of infrared light to identify molecules. techniques exists to identify solid, liquid, and gas phase compounds. in a simplified model of an anesthetic detection chamber, transparent to infrared light, infrared light source, and
An infrared camera to detect transmitted light. the gas sample will flow from the patient’s circuit into the detection chamber and back to the patient’s circuit. as the gas flows through the detection chamber, the infrared light will pass into the detection chamber where some of the light is absorbed and
Camera where it is recorded by the gas analyzer a simplified version of an ir spectrometer; real-life implementations would include various mirrors, filters, and prisms depending on the application. under research conditions, as in a chemistry lab, the recorded wavelengths and intensity of transmitted infrared light
Will be used to generate a characteristic graph and the the absorption peaks to functional groups known to absorb at that specific wavelength and identify the molecule. in a chemistry lab we may be trying to identify an unknown molecule from a possible list of thousands of molecules. in the operating room we
Are only concerned with about five molecules. instead of scanning the whole spectrum and identifying all possible peaks, an anaesthetic gas analyzer only scans two 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 absorption peaks, this allows for a rapid you administer interoperative albuterol via the inspiratory limb of the breathing circuit or directly via endotracheal tube. you then see an abrupt increase in mac value followed by the hasn’t been a bottle of halothane in
Your being detected? albuterol and halothane have importantly, albuterol’s structure contains produce unique infrared absorption peaks not found in halothane. let’s look at the absorption even from a lay person’s point of view, these are very different absorption spectra. perhaps we need to take into
Account the limited spectrum of which the computer is analyzing; however, as you can see with these overlays the absorption peaks simply don’t match. 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 by nebulized solution will not. perhaps the inhaler contains an extra ingredient that is similar to halothane and perhaps that ingredient is listed right on the front of the package? hfa. hfa, the propellant and most albuterol inhalers stands for (h)ydro
(F)luoro (a)lkane. conveniently halothane contains the components of a hydro fluoro alkane. if we reference the albuterol hfa package insert, we see that the specific hfa used is hfa 134a, which looks like this. 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. now let’s look at the halothane and here’s hfa 134a. with both of the molecules major absorption peaks overlapping, there’s little doubt that it is hfa 134a and not albuterol which is causing the anesthetic gas analyzer to
Read as halothane. a final question the same region as all the other halogenated for halothane and not any other anaesthetic? to answer that question we can narrow our detection range even more and look only at the region where halothane’s major peaks occur. we can clearly see that only hfa 134a and halothane share
Two indistinguishable to the gas analyzer’s algorithm. in conclusion, i have concisely shown here that when an albuterol metered dose inhaler is administered to a patient in the operating room, it is not the albuterol molecule itself, the gas analyzer’s detection of halothane. this video, thanks for watching.
Transcribed from video
Why Your Anesthetic Gas Analyzer Detects Halothane When You Administer Albuterol By Marc Rodriguez MD