Delivery systems, FiO2 calculations, indications, complications, and oxygen toxicity.
60 min estimated
Oxygen delivery systems are classified as low-flow (do not meet patient's total inspiratory flow demand, air entrainment dilutes FiO2) or high-flow (meet or exceed inspiratory flow, deliver precise FiO2).
Low-flow systems: - Nasal cannula: 1–6 L/min → FiO2 ~24–44%; each liter adds ~4% FiO2 - Simple face mask: 5–10 L/min → FiO2 ~35–55%; minimum 5 L/min to flush CO2 - Partial rebreather mask: 6–10 L/min → FiO2 ~35–60%; bag should not collapse - Non-rebreather mask (NRB): 10–15 L/min → FiO2 ~60–90%; reservoir bag + one-way valves
High-flow systems: - Venturi mask (air-entrainment mask): precise FiO2 24, 28, 31, 35, 40, 50% — reliable for COPD - HFNC (high-flow nasal cannula): 20–60 L/min heated humidified; FiO2 21–100%
Clinical Tip
For COPD patients needing precise O2, use a Venturi mask at 28% or 31% — nasal cannula FiO2 is highly variable with breathing pattern changes.
Oxygen therapy is indicated when PaO2 <60 mmHg or SpO2 <90%, acute MI, CO poisoning, sickle cell crisis, and cluster headaches.
Oxygen toxicity: risk with FiO2 >0.60 for >24–48 hours. Causes absorption atelectasis (nitrogen washout), pulmonary O2 toxicity (free radical injury to type II pneumocytes → ARDS-like picture), retinopathy of prematurity (preterm infants with SpO2 >96%).
Absorption atelectasis: occurs when high FiO2 washes out nitrogen (the structural gas), leaving O2 which is rapidly absorbed, causing distal alveolar collapse.
CO poisoning: 100% O2 (NRB) reduces CO half-life from 4–5 hours to 60–90 minutes. Hyperbaric O2 reduces half-life to 20–30 minutes; used for severe CO poisoning (neurologic symptoms, pregnancy).
Clinical Tip
Pulse oximetry cannot distinguish oxyhemoglobin from carboxyhemoglobin — in CO poisoning, SpO2 will read falsely normal. Use co-oximetry (blood gas) to measure true O2 saturation.
HFNC delivers heated, humidified O2 at flows of 20–60 L/min, providing FiO2 21–100%. Mechanisms of benefit: meets/exceeds inspiratory demand (prevents FiO2 dilution), generates low-level PEEP (~1–2 cmH2O/10 L), reduces anatomic dead space, improves mucociliary clearance with humidification.
Indications: acute hypoxemic respiratory failure, post-extubation, COPD (high flow, controlled FiO2), immunocompromised patients avoiding intubation.
ROX index predicts HFNC success: SpO2/FiO2 ÷ RR. ROX <2.85 at 12 hours predicts HFNC failure and need for intubation.
HFNC is preferred over NIV for pure hypoxemic failure; NIV preferred for hypercapnic failure.
Clinical Tip
On HFNC, if a patient needs FiO2 >0.80 to maintain SpO2 >92%, consider escalating to NIV or intubation — high FiO2 requirement predicts failure.
Choosing the Right O2 Device
A 70-year-old COPD patient (FEV1 38%) is admitted for exacerbation. SpO2 is 84% on room air. What is the best oxygen delivery device?
Which device provides the most controlled FiO2 for this patient?
Venturi mask at 28% or 31% FiO2. Target SpO2 88–92%.
COPD patients with chronic hypercapnia need controlled, precise O2 to avoid worsening hypercapnia. Venturi mask reliably delivers fixed FiO2 regardless of respiratory pattern — nasal cannula FiO2 varies with breathing rate and depth. Start at 28%, titrate to SpO2 88–92%.
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