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Monitoring functional residual capacity (FRC) by quantifying oxygen/carbon dioxide fluxes during a short apnea
Author(s) -
Stenqvist O.,
Olegård C.,
Søndergaard S.,
Odenstedt H.,
Kárason S.,
Lundin S.
Publication year - 2002
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1034/j.1399-6576.2002.460617.x
Subject(s) - functional residual capacity , medicine , apnea , carbon dioxide , anesthesia , oxygen , limits of agreement , ventilation (architecture) , respiration , lung , cardiology , lung volumes , nuclear medicine , chemistry , thermodynamics , physics , organic chemistry , anatomy
Background: Clinically applicable methods for measuring FRC are currently lacking. This study presents a new method for FRC monitoring based on quantification of metabolic gas fluxes of O 2 and CO 2 during a short apnea. Methods: Base line exchange of oxygen and carbon dioxide was measured with indirect calorimetry. End‐tidal (∼alveolar) O 2 and CO 2 concentrations were measured before and after a short apnea, 8–12 s, and FRC was calculated according to standard washin/washout formulas taking into account the increased solubility of CO 2 in blood when the tension is increased during the apnea. The method was tested in a lung model with CO 2 excretion and O 2 consumption achieved by combustion of hydrogen and implemented in six ventilator‐treated patients with acute respiratory failure (ARF). Results: In the lung model the method showed excellent correlation ( r = 0.98) with minimal bias (34 ml) and a good precision, limits of agreement being 160 and ‐230 ml, respectively, compared to the reference method. In six ARF patients changes in FRC induced by increase or decrease in PEEP and measured with the O 2 /CO 2 flux FRC method corresponded well with changes in reference values of FRC ( r = 0.76–0.94). Conclusions: A new method has been proposed in which FRC could be monitored from measurements of physiological fluxes of gases during a short apnea with the use of standard ICU equipment and some calculations. We anticipate that with further development, this technique could provide a new tool for monitoring respiratory changes and ventilator management in the ICU.