Respiratory Care Equipment, Medical Gas Therapy, and Airway Management
Oxygen delivery devices
Low-flow systems (nasal cannula, simple mask) provide variable FiO2 because room air is entrained. High-flow systems (Venturi mask, air-entrainment nebulizer, HFNC) provide a more stable FiO2 when flow exceeds peak inspiratory demand. A 40% Venturi mask uses an air:O2 ratio of about 3.2:1; total flow = oxygen flow × 4.2. Oxygen cylinder duration (min) = (gauge psi × cylinder factor)/flow. E cylinder factor 0.28 L/psi; H cylinder 3.14 L/psi.
Airway management
Oropharyngeal airways are for unconscious patients without a gag; nasopharyngeal airways are better tolerated but avoid in basilar skull fracture. Confirm ETT depth, secure it, and verify with continuous capnography plus auscultation. Suction only as needed, limit to 10–15 seconds, and preoxygenate. Humidify high-flow oxygen and bypassed airways.
Worked example
An E cylinder reads 1,500 psi and delivers 5 L/min. Duration = (1,500 × 0.28)/5 = 84 minutes. A 40% air-entrainment mask at 6 L/min O2 gives total flow ≈ 6 × 4.2 = 25 L/min, enough for many adults but not all; increase flow if the reservoir or mask lacks mist.
Traps
Nasal cannula FiO2 is not fixed at 2 L = 28% for every patient. Do not use an oxygen flowmeter for helium mixtures without a calibrated correction. Never rely on auscultation alone to confirm tube position.