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Why Your Anesthetic Gas Analyzer Detects Halothane When You Administer Albuterol

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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