Fig. 5. Rebreathing potential in noninvasive ventilation systems. During normal use, elimination of exhaled carbon dioxide depends on a high rate of gas flow. In the conventional continuous positive airway pressure system (A ), an electrical power-off scenario results in rebreathing of exhaled gas. There is a rapid rise in inspired carbon dioxide and fall in inspired oxygen concentration. Design features that include nonrebreathing valves (B ) mitigate the risk for rebreathing. NIV = noninvasive ventilation. Reproduced with permission from Farréet al.  30