title: Precise control of end-tidal carbon dioxide levels using sequential rebreathing circuits.
abstract: Anaesthesiologists have traditionally been consulted to help design breathing circuits to attain and maintain target end-tidal carbon dioxide (P(ET)CO2). The methodology has recently been simplified by breathing circuits that sequentially deliver fresh gas (not containing carbon dioxide (CO2)) and reserve gas (containing CO2). Our aim was to determine the roles of fresh gas flow, reserve gas PCO2 and minute ventilation in the determination of P(ET)CO2. We first used a computer model of a non-rebreathing sequential breathing circuit to determine these relationships. We then tested our model by monitoring P(ET)CO2 in human volunteers who increased their minute ventilation from resting to five times resting levels. The optimal settings to maintain P(ET)CO2 independently of minute ventilation are 1) fresh gas flow equal to minute ventilation minus anatomical deadspace ventilation, and 2) reserve gas PCO2 equal to alveolar PCO2. We provide an equation to assist in identifying gas settings to attain a target PCO2. The ability to precisely attain and maintain a target PCO2 (isocapnia) using a sequential gas delivery circuit has multiple therapeutic and scientific applications.
authors.affiliation: University Health Network, Toronto General Hospital, University of Toronto, Department of Physiology, Queen's University, Kingston, Canada.
authors.forename: R B
authors.initials: RB
authors.lastname: Somogyi
authors.forename: A E
authors.initials: AE
authors.lastname: Vesely
authors.forename: D
authors.initials: D
authors.lastname: Preiss
authors.forename: E
authors.initials: E
authors.lastname: Prisman
authors.forename: G
authors.initials: G
authors.lastname: Volgyesi
authors.forename: T
authors.initials: T
authors.lastname: Azami
authors.forename: S
authors.initials: S
authors.lastname: Iscoe
authors.forename: J A
authors.initials: JA
authors.lastname: Fisher
authors.forename: H
authors.initials: H
authors.lastname: Sasano
mesh_terms: D000764:Anesthesia, Closed-Circuit / Q000379:methods*; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000097:blood*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000517:prevention & control; D016857:Hypocapnia / Q000517:prevention & control; D008297:Male; D008991:Monitoring, Physiologic; D011336:Probability; D011659:Pulmonary Gas Exchange; D012016:Reference Values; D012121:Respiration, Artificial; D012126:Respiratory Dead Space / Q000502:physiology*; D015656:Respiratory Mechanics; D012680:Sensitivity and Specificity; D013990:Tidal Volume
chemical_list: D002245:Carbon Dioxide