Systemic recirculation assessed in apnoeic anaesthetized patients using carbon dioxide concentration measurements during stepwise expiration

This method allows adequate time for full response of sidestream analysers. Recirculation is an important early feature affecting breath-hold estimates of mixed venous carbon dioxide. Carbon dioxide accumulation during apnoea or rebreathing will have prompt effects on arterial carbon dioxide values and a constant mixed venous composition cannot be assumed when methods based on partial rebreathing are used over this time period.