Analyser position for end-tidal carbon dioxide monitoring in a rebreather circuit

作者：Ineson Alastair; Henderson Kaylene; Teubner David; Mitchell Simon^*

来源：Diving and Hyperbaric Medicine, 2010, 40(4): 206-209.

• Carbon dioxide
• hypercapnia
• rebreathing
• rebreathers/semi-closed circuit
• rebreathers/closed circuit
• physiology
• simulation

(Meson A, Henderson K, Teubner D, Mitchell S Analyser position for end-tidal carbon dioxide monitoring in a rebreather circuit Diving and Hyperbaric Medicine 2010,40(4) 206-9)
Introduction A diving rebreather currently nearing release incorporates an infra-red CO(2) analyser at the end of the exhale hose and uses the expired gas CO(2) measurement made at this position to detect hypercapnia This configuration may allow exhaled anatomic and mouthpiece dead space gas to mix with alveolar gas in the exhale hose thus falsely lowering the CO(2) measurement, especially at low tidal volumes
Methods A test circuit was constructed using a typical rebreather mouthpiece and exhale hose connected into an anaesthetic machine breathing loop True end-tidal PCO(2) was measured in gas sampled from the mouth and compared breath-by-breath to the PCO(2) measured in gas sampled at the end of the exhale hose Two subjects each completed 60 breaths at tidal volumes of 500, 750, 1000, 1500 and 2000 ml
Results There was a small (<= 0 21 kPa) mean difference between true end-tidal CO(2) and end-of-hose CO(2) at tidal volumes of 1000 ml or more However, at lower tidal volumes, the mean difference increased and, at 500 ml, it was 1 04 kPa and 0 70 kPa in subjects 1 and 2 respectively
Conclusion Measurement of the peak exhaled PCO(2) at the end of a rebreather exhale hose may provide a reasonable estimation of the true end-tidal CO(2) at large tidal volumes, but may significantly underestimate the true end-tidal CO(2) at low tidal volumes

• 出版日期2010-12