Canadian Journal of Anaesthesia

, Volume 39, Issue 6, pp 617–632 | Cite as

Capnometry and anaesthesia

  • K. Bhavani-Shankar
  • H. Moseley
  • A. Y. Kumar
  • Y. Delph
Review Article

Abstract

In the last decade, capnography has developed from a research instrument into a monitoring device considered to be essential during anaesthesia to ensure patient safety. Hence, a comprehensive understanding of capnography has become mandatory for the anaesthetist in charge of patients in the operating room and in the intensive care unit. This review of capnography includes the methods available to determine carbon dioxide in expired air, and an analysis of the physiology of capnograms, which are followed by a description of the applications of capnography in clinical practice. The theoretical backgrounds of the effect of barometric pressure, water vapour, nitrous oxide and other factors introducing errors in the accuracy of CO2 determination by the infra-red technique, currently the most popular method in use, are detailed. Physiological factors leading to changes in end-tidal carbon dioxide are discussed together with the clinical uses of this measurement to assess pulmonary blood flow indirectly, carbon dioxide production and adequacy of alveolar ventilation. The importance of understanding the shape of the capnogram as well as end-tidal carbon dioxide measurements is emphasized and its use in the early diagnosis of adverse events such as circuit disconnections, oesophageal intubation, defective breathing systems and hypoventilation is highlighted. Finally, the precautions required in the use and interpretation of capnography are presented with the caveat that although no instrument will replace the continuous presence of the attentive physician, end-tidal carbon dioxide monitoring can be effective in the early detection of anaesthesia-related intraoperative accidents.

Key words

carbon dioxide: end-tidal, measurement, monitoring measurement techniques: capnometry monitoring: carbon dioxide 

Résumé

La capnographie est maintenant un élément essentiel du monitorage des patients pendant l’anesthésie générate et tout anesthésiste doit comprendre les principes de fonctionnement de cette technique. La présente révision décrit les méthodes disponibles de mesure de gaz carbonique (CO2) expiré, ainsi qu ’une analyse de la physiologie associée aux différents capnogrammes. Une description des applications cliniques de la capnographie fait suite à ces énoncés théoriques. Les effets de la pression barométrique, de la vapeur d’eau, du protoxide d’azote et de plusieurs autres facteurs affectant la mesure du CO2 a l’aide d’infra-rouge sont décrits. La capnographie permet une mesure indirecte de la circulation pulmonaire, de la production de CO2 et de la ventilation alveolaire. Ces mesures sont influencees par de nombreux facteurs physiologiques qu ’il importe de bien connaître afin de déterminer les limites de ce monitorage. Une bonne interprétation de la forme des cburbes de capnographie est nécessaire afin de permettre la détection précoce d’incidents dangereux tels un défaut ou débranchement du circuit anesthésique, une intubation oesophagienne ou une hypoventilation. Le présent travail permet à l’anesthésiste de revoir toutes ces notions et rappelle que même si la capnographie ne remplace pas la vigilance du clinicien, elle peut permettre la détection rapide d’événements qui pourraient mener à des complications anesthésiques.

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Copyright information

© Canadian Anesthesiologists 1992

Authors and Affiliations

  • K. Bhavani-Shankar
    • 1
  • H. Moseley
    • 1
  • A. Y. Kumar
    • 1
  • Y. Delph
    • 1
  1. 1.Department of AnaesthesiaQueen Elizabeth Hospital, University of West IndiesBarbadosWest Indies

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