Figure 17-40 Schematic diagram of the causes of hypercapnia during anesthesia. An increase in carbon dioxide (CO₂ ) production (V̇CO₂ ) will increase PaCO₂ with a constant minute ventilation (V̇E). Several events can increase alveolar dead space: a decrease in pulmonary artery pressure (Ppa), the application of positive end-expiratory pressure (PEEP), thromboembolism, and mechanical interference with pulmonary arterial flow (ligatures and kinking of vessels). A decrease in V̇E causes an increase in PaCO₂ with a constant V̇CO₂ . It is possible for some anesthesia systems to cause rebreathing of CO₂ . Finally, the anesthesia apparatus may increase the anatomic dead space, and inadvertent switching off of a CO₂ absorber in the presence of low fresh gas flow can increase PaCO₂ . (Redrawn with modification from Benumof JL: Anesthesia for Thoracic Surgery, 2nd ed. Philadelphia, WB Saunders, 1995, Chapter 8.)