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An evaluation of the contributions by fresh gas flow rate, carbon dioxide concentration and desflurane partial pressure to carbon monoxide concentration during low fresh gas flows to a circle anaesthetic breathing system

Published online by Cambridge University Press:  01 August 2008

S.-Z. Fan ,
Y.-W. Lin ,
W.-S. Chang  and
C.-S. Tang
S.-Z. Fan
Affiliation:
National Taiwan University, College of Medicine, Department of Anesthesiology, Taiwan, ROC
Y.-W. Lin
Affiliation:
Fu-Jen Catholic University, College of Medicine, Department of Public Health, Taiwan, ROC
W.-S. Chang
Affiliation:
National Taiwan University, College of Medicine, Department of Anesthesiology, Taiwan, ROC
C.-S. Tang*
Affiliation:
Fu-Jen Catholic University, College of Medicine, Department of Public Health, Taiwan, ROC
*
Department of Public Health, College of Medicine, Fu-Jen Catholic University, 510 Chung Cheng Road, Hsinchuang, Taipei County 24205, Taiwan, ROC. E-mail: tangcs@mail.fju.edu.tw; Tel: +886 2 29053433; Fax: +886 2 29056385
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Summary

Background and objective

Numerous in vitro studies have shown that volatile anaesthetics react with desiccated carbon dioxide (CO2) absorbents to produce carbon monoxide (CO). The effects of anaesthetic concentration, fresh gas flow rate, and the hydration of absorbent or the excretion of CO2 by patients on CO production have also been investigated. This work aims to identify the most significant one of these factors on CO concentration in a low-flow anaesthesia system, without control of the hydration of the absorbents.

Methods

A simulated clinical circle anaesthetic breathing system was used to study the CO concentration under various conditions. Desflurane was used at three different concentrations. Two CO2 flow rates and three fresh gas flow rates were used. The absorbent temperatures and hydration were measured simultaneously.

Results

Desflurane degraded to produce CO in the breathing tube, when the CO2 absorbents were not dried beforehand. In this imitation clinical low-flow setting, fresh gas flow affected the CO production more than the CO2 did (31.7% vs. 9.5%). The actual desflurane partial pressure was not a significant factor. The CO2 flow rate explained 18.2% and 54.0% of the variation of the absorbent hydration changes (%) and temperature, respectively.

Conclusions

In clinical practice, the CO2 production varies among patients and is uncontrollable, but markedly affects CO production. The only controllable factor is the fresh gas flow rate if the ultimate goal is to reduce the undesirable exposure of patients to CO from the breathing tube according to this bench model without counting the oxygen consumption.

Keywords

INHALATION ANAESTHETICS, desfluraneCARBON MONOXIDEVENTILATION, fresh gas flow
Type
Original Article
Information
European Journal of Anaesthesiology , Volume 25 , Issue 8 , August 2008 , pp. 620 - 626
Copyright
Copyright © European Society of Anaesthesiology 2008

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