How to be less invasive

Unless cardiac output is reduced, alveolar ventilation can be monitored without arterial blood gas analysis by estimating arterial carbon dioxide tension (PaO2) from rebreathing measurement of mixed venous carbon dioxide tension (PvCO2) (PaCO2 = 0.8 PvCO2). If cardiac output is reduced, the PvCO2 - PaCO2 difference increases, reflecting the increased venoarterial carbon dioxide (CO2) content difference (Fick principle). A reduction in cardiac …