Single breath tracing for carbon dioxide in septic patients with tissue hypoxia

Abstract

We investigated whether tissue hypoxia in sepsis produces substantial modifications of convective airway washout and consequently of CO 2 transit time. Single breath tracing for carbon dioxide (SBT-CO 2) was analysed in 18 ICU septic patients. Nine patients had tissue hypoxia events. Using the Hill formula, all tracings were analysed point by point to obtain the time required for CO 2 to achieve 50% maximal value and the Fractional Expiratory Time 50 (FET 0.5) . Hypoxic patients FET 0.5 and CO 2 clearance were compared with non-hypoxic patients data. In hypoxic group CvCO 2 , CO 2 clearance and FET 0.5 values were higher than in non hypoxic group. During the recovery from hypoxia capnographic parameters did not differ from those recorded in the hypoxic period. CO 2 clearance, but not FET 0.5 , correlated with arterial lactate and base excess either in hypoxic or in recovery period. In conclusion in septic patients tissue hypoxia influences CO 2 elimination, modifying SB-CO 2 tracing and lengthening FET 0.5 . © 2008 Springer Science+Business Media, LLC.