• V H Larsen, T Waldau, and B Oberg.
• Department of Anaesthesiology, Herlev Hospital, University of Copenhagen, Denmark.
• Acta Anaesthesiol Scand Suppl. 1995 Jan 1;107:81-5.

BackgroundContinuous monitoring of O2 and CO2 in the airways of spontaneously breathing patients can be carried out by sampling air to a gas monitor through a catheter placed in the upper airway. The graphical display of O2 (oxygraphy) is a rather new facility.ObjectiveTo describe the photo-acoustic and magneto-acoustic technique for CO2 and O2 monitoring in the open unintubated airway, to evaluate the efficacy of oxygen therapy by oxygraphy and to determine alveolar gas tensions and alveolar-arterial partial pressure gradients.Data SourcesO2 and CO2 fractions in the airways were monitored in 9 healthy subjects. Blood samples were drawn from the radial artery.MethodsThe Multigas Monitor 1,304 (Brüel and Kjaer, Naerum, Denmark) was used; end-expiratory measurements were considered as representative for the alveolar gas composition. Arterial blood was analysed by ABL520 (Radiometer Medical A/S, Copenhagen, Denmark).ResultsReliable tracings of gas fractions (FCO2 and FO2) were obtained during the respiratory cycle in all subjects. When oxygen was supplied, FO2 of the airway varied considerably during the inspiratory phase whereas it remained almost constantly during the expiratory phase. The end-expiratory FO2 increased from 0.15 breathing atmospheric air to 0.41 breathing oxygen 15 L/min through a Hudson mask. Alveolar-arterial partial pressure differences were: pO2(A-a): 1.07 +/- 0.85 kPa and pCO2(A-a): -0.04 +/- 0.33 kPa during normoventilation in atmospheric air.ConclusionContinuous monitoring of CO2 and O2 in the airway gives information about the pulmonary gas exchange and the efficacy of oxygen supply. Combined with arterial blood gas analysis the method allows determination of alveolar-arterial CO2 or O2 gradients.

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