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Title: A modal definition of ideal alveolar oxygen.
Austin Authors: Peyton, Philip J 
Affiliation: Department of Critical Care, Anaesthesia, Perioperative and Pain Medicine Program, Melbourne Medical School, University of Melbourne, Melbourne, Victoria, Australia.
Institute for Breathing and Sleep
Issue Date: Aug-2023
Publication information: Physiological Reports 2023-08; 11(16)
Abstract: In the three-compartment model of lung ventilation-perfusion heterogeneity (VA/Q scatter), both Bohr dead space and shunt equations require values for central "ideal" compartment O2 and CO2 partial pressures. However, the ideal alveolar gas equation most accurately calculates mixed (ideal and alveolar dead space) PAO2 . A novel "modal" definition has been validated for ideal alveolar CO2 partial pressure, at the VA/Q ratio in a lung distribution where CO2 elimination is maximal. A multicompartment computer model of physiological, lognormal distributions of VA and Q was used to identify modal "ideal" PAO2 , and find a modification of the alveolar gas equation to estimate it across a wide range of severity of VA/Q heterogeneity and FIO2 . This was then validated in vivo using data from a study of 36 anesthetized, ventilated patients with FIO2 0.35-80. Substitution in the alveolar gas equation of respiratory exchange ratio R with modalR=R-1-PEtCO2/PaCO2$$ \kern0.5em \mathrm{modalR}=\mathrm{R}\hbox{--} \left(1\hbox{--} \mathrm{PEtC}{\mathrm{O}}_2/\mathrm{P}{\mathrm{aCO}}_2\right) $$ achieved excellent agreement (r2  = 0.999) between the calculated ideal PAO2 and the alveolar-capillary Pc'O2 at the modal VO2 point ("modal" Pc'O2 ), across a range of log standard deviation of VA 0.25-1.75, true shunt 0%-20%, overall VA/Q 0.4-1.6, and FIO2 0.18-1.0, where the modeled PaO2 was over 50 mm Hg. Modal ideal PAO2 can be reliably estimated using routine blood gas measurements.
DOI: 10.14814/phy2.15787
ORCID: 0000-0003-1185-2869
Journal: Physiological Reports
Start page: e15787
PubMed URL: 37612050
ISSN: 2051-817X
Type: Journal Article
Appears in Collections:Journal articles

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