Monitoring of Pulmonary Capillary Blood Flow and Alveolar Dead Space Using the Combined Methods of Volumetric Capnography and “Partial CO₂ Rebreathing” (NiCO₂)

Abstract

Data available in all operating theaters and intensive care units make it possible to obtain important information about the adequacy of the ventilation perfusion ratio (V/Q). This ratio, which is normally 0.8, decreases and increases in two specific conditions. It decreases in the case of poorly ventilated but perfused alveoli (increased shunt QS/QT) and it increases with well-ventilated but poorly perfused alveoli (increased alveolar dead space VD ALV). In both of these cases, it is difficult for the pulmonary capillary to eliminate CO₂, in the first case due to inadequate ventilation and in the second because of inadequate perfusion. Thus, arterial CO₂ (p_aCO₂) increases and alveolar pCO₂ (pet CO₂ of traditional capnography) decreases in both situations.