Among the listed devices, which generally delivers oxygen with the least precise FiO2 control?

Among the listed devices, which generally delivers oxygen with the least precise FiO2 control?

• A. Venturi mask
• B. Simple face mask
• C. Reservoir mask
• D. Nasal cannula

Answer: (B)

The main idea is that how precisely a device fixes the amount of oxygen you deliver depends on how much the device controls or isolates the inspired air from room air. The venturi mask is designed to deliver a specific FiO2 by using calibrated jets and entrainment ports, so for a given adapter you get a stable, known oxygen concentration. A nasal cannula provides oxygen directly, and while the exact FiO2 depends on flow and breathing pattern, it tends to be more predictable than something without any mechanism to regulate mixing. A reservoir mask can deliver fairly high FiO2 because the reservoir bag supplies a pool of oxygen, but the actual FiO2 still varies with bag inflation and how the patient breathes. The simple face mask, however, has no reservoir and no fixed FiO2. Oxygen pours into the mask and mixes with ambient air as the patient breathes out and in, with leaks around the mask and differences between mouth and nasal breathing all causing wide variation in the amount of air with oxygen that actually reaches the lungs. Because there’s no built-in way to regulate that mixing, the FiO2 can vary quite a bit from breath to breath and patient to patient, making it the least precise option among the listed devices.

The main idea is that how precisely a device fixes the amount of oxygen you deliver depends on how much the device controls or isolates the inspired air from room air. The venturi mask is designed to deliver a specific FiO2 by using calibrated jets and entrainment ports, so for a given adapter you get a stable, known oxygen concentration. A nasal cannula provides oxygen directly, and while the exact FiO2 depends on flow and breathing pattern, it tends to be more predictable than something without any mechanism to regulate mixing. A reservoir mask can deliver fairly high FiO2 because the reservoir bag supplies a pool of oxygen, but the actual FiO2 still varies with bag inflation and how the patient breathes.

The simple face mask, however, has no reservoir and no fixed FiO2. Oxygen pours into the mask and mixes with ambient air as the patient breathes out and in, with leaks around the mask and differences between mouth and nasal breathing all causing wide variation in the amount of air with oxygen that actually reaches the lungs. Because there’s no built-in way to regulate that mixing, the FiO2 can vary quite a bit from breath to breath and patient to patient, making it the least precise option among the listed devices.