Which of the following are essential components of a continuous positive airway pressure (CPAP) flow system?

1. Blended source of pressurized gas
2. Nonrebreathing circuit with reservoir bag
3. Low-pressure or disconnect alarm
4. Expiratory threshold resistor
a. 3 and 4 only
b. 1, 2, and 4 only
c. 1 and 4 only
d. 1, 2, 3, and 4

ANS: D
A breathing gas mixture from an oxygen blender flows continuously through a humidifier into the inspiratory limb of a breathing circuit. A reservoir bag provides reserve volume if the patient's inspiratory flow exceeds that of the system. The patient breathes in and out through a simple valveless T-piece connector. A pressure alarm system with manometer monitors the CPAP pres-sure at the patient's airway. The alarm system can warn of either low (usually due to a disconnec-tion) or high system pressure. The expiratory limb of the circuit is connected to a threshold resis-tor, in this case a water column (H).