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LETTER TO EDITOR Table of Contents   
Year : 2010  |  Volume : 13  |  Issue : 1  |  Page : 77-78
An anesthetic in use with bronchodilator inhaler: A fact less known

Department of Anesthesia, Christian Medical College and Hospital, Vellore, India

Click here for correspondence address and email

Date of Web Publication11-Jan-2010

How to cite this article:
Kummar P, Korula G, Ninan S, Karthikeyan C. An anesthetic in use with bronchodilator inhaler: A fact less known. Ann Card Anaesth 2010;13:77-8

How to cite this URL:
Kummar P, Korula G, Ninan S, Karthikeyan C. An anesthetic in use with bronchodilator inhaler: A fact less known. Ann Card Anaesth [serial online] 2010 [cited 2023 Feb 2];13:77-8. Available from:

The Editor,

Agent gas monitoring (AGM) is becoming an integral part of intraoperative monitoring. The use of hydrofluoalkane (HFA) pressurized metered dose inhaler (PMDI) during general anesthesia indicates an error in anesthetic gas agent measurement. The analyzer incorrectly identifies the gas as enflurane or halothane or as a mixture of high concentrations [Figure 1]. Literature review to study the effects of inhaler contents on infrared analyzers used in AGM revealed interesting facts.

Infrared (IR) analyzers which are in common use are based on the principle that gases with two or more dissimilar atoms in the molecule (nitrous oxide, CO 2 , and the halogenated agents) have specific and unique IR light absorption spectra. Multiple wavelengths are required to distinguish between different anesthetic gases. The 8-12µm range represents the area of IR spectrum where anesthetic gases show maximum absorbance. [1] One of the most crucial components of PMDI is its propellant. The propellant provides the force to generate the aerosol cloud and is also the medium in which the active component must be suspended or dissolved. It makes up more than 99 % of the delivered dose. Salbutamol/other drugs as such do not cause interference in IR spectra because its quantity is less than that of the propellant and it is in particulate form, not as gas.

After December 2008, in compliance with the UN Environment Program protocol on substances that deplete the ozone layer, [2] use of inhalers containing chlorofluorocarbons (CFCs) as a form of propellant has been discontinued for hydrofluoroalkane-pressurized metered dose inhalers (HFA PMDI's). The 134a HFA, propellant in inhalers, is: 1, 1, 1,2-tetrafluoroethane, also known as Norflurane. From a historical point of view it is interesting to note that 1, 1, 1,2-tetrafluoroethane was developed and tested as an anesthetic agent in animals as early as 1967. [3] It was found to have moderate potency, requiring approximately 50 vol% to induce anesthesia, but was never developed for use in humans. Levin et al. opine that similarities in absorption spectra between HFA 134a and anesthetic gases can, in part, be predicted from the similarity in their molecular structure. The propellant has been shown to be safe and nonanesthetic in doses associated with inhaler use. [4] However, norflurane is an anesthetic. This should caution physicians of anesthetic effect with repeated administration or long term use

   References Top

1.Levin P D, Levin D, Avidan A. Medical aerosol propellant interference with infrared anaesthetic gas monitors. Br J Anaesth 2004;92:865-9.  Back to cited text no. 1      
2. [last accessed on 2009 Dec 30]  Back to cited text no. 2      
3.Shulman M, Sadove MS. 1112- Tetrafluoroethane: an inhalation anesthetic agent of intermediate potency. Anesth Analg 1967;46:629-35.  Back to cited text no. 3  [PUBMED]  [FULLTEXT]  
4.Huchon G, Hofbauer P, Cannizzaro G, Iacono P, Wald F. Comparison of the safety of drug delivery via HFA- and CFC-metered dose inhalers in CAO. Eur Respir J 2000;15:663-9.  Back to cited text no. 4  [PUBMED]  [FULLTEXT]  

Correspondence Address:
Prashant Kummar
Department of Anesthesia, Christian Medical College and Hospital, Vellore
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0971-9784.58847

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1 A perplexing event of propellant masquerading as anesthetic vapors
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[Pubmed] | [DOI]