Oxygen Delivery & Respiratory Support Calculator

Understanding Oxygen Delivery, FiO2, and Respiratory Support

Oxygen therapy is one of the most fundamental medical interventions, used to treat hypoxemia (low blood oxygen) and support patients with respiratory failure. Understanding oxygen delivery methods, how they deliver different concentrations of oxygen (FiO2—fraction of inspired oxygen), and appropriate targets for different patient populations is critical for healthcare providers and educational understanding. This calculator provides an educational overview of oxygen delivery systems, their FiO2 ranges, and SpO2 (blood oxygen saturation) targets for different patient types. This is an educational tool and should never replace clinical judgment or direct medical supervision.

Oxygen delivery systems vary in complexity and FiO2 delivery. Room air contains 21% oxygen; without supplemental oxygen therapy, healthy people maintain SpO2 around 95–100%. When supplemental oxygen is needed, the goal is typically to achieve SpO2 of 94–98% in most patients, though specific targets vary by condition. COPD patients, for example, may have lower targets (88–92%) to avoid suppressing respiratory drive and causing CO2 retention.

Nasal cannula is the most commonly used oxygen delivery system. It delivers oxygen at 1–6 liters per minute, providing FiO2 of approximately 24–44%. A general formula is: FiO2 = 21% + (4% × flow rate in L/min). So, 3 L/min nasal cannula provides approximately 21% + (4% × 3) = 33% FiO2. The advantage of nasal cannula is comfort (patients can eat, talk, etc.) and ease of use. The disadvantage is that it cannot deliver high FiO2 concentrations, and actual FiO2 depends on the patient's breathing pattern.

Simple face masks deliver 5–8 L/min, providing FiO2 of approximately 40–60%. The formula is similar: FiO2 ≈ 20% + (3.5% × flow rate). Face masks provide higher FiO2 than nasal cannula but are less comfortable. Non-rebreather masks are sealed masks with a reservoir bag, delivering 10–15 L/min and providing FiO2 of 60–95%. The reservoir bag must remain at least one-third full during inspiration, ensuring high-concentration oxygen is delivered. Non-rebreather masks are used for severe hypoxemia and acute respiratory distress.

High-flow nasal cannula (HFNC) is a newer technology delivering heated, humidified oxygen at 20–60 L/min. Because of the high flow, it provides FiO2 up to 50–100% (depending on flow rate) and offers several physiologic advantages: washout of dead space (anatomic airways that don't participate in gas exchange), improved secretion clearance, and reduced work of breathing. HFNC has become increasingly popular for moderate-to-severe hypoxemia and can sometimes prevent intubation.

Mechanical ventilation is used when non-invasive methods fail. Intubation allows direct control of FiO2 (up to 100%), tidal volume, respiratory rate, and positive end-expiratory pressure (PEEP), which improves oxygenation. Ventilator settings are highly individualized based on lung mechanics, cause of respiratory failure, and patient physiology. Lung-protective ventilation strategies (lower tidal volumes, permissive hypercapnia) are standard in most conditions to prevent ventilator-induced lung injury.

MathML Formula for FiO2 Delivery from Nasal Cannula:

This formula assumes normal atmospheric pressure and that the patient is breathing spontaneously with a normal breathing pattern.

Worked Example: A 65-year-old patient with pneumonia presents with SpO2 of 88% on room air. Their respiratory rate is 24 (elevated). A nasal cannula is placed at 4 L/min, providing approximately 21% + (4% × 4) = 37% FiO2. Within an hour, their SpO2 improves to 92%, and respiratory rate decreases to 20. If it had remained below 90%, the next step would be a simple face mask or high-flow nasal cannula. If FiO2 delivery still failed to achieve target SpO2 above 88%, intubation and mechanical ventilation might be considered, especially if the patient shows signs of respiratory distress or fatigue.

Comparison table of oxygen delivery methods and typical FiO2 ranges:

Appropriate SpO2 targets vary by patient population. Healthy patients and most hospitalized patients target SpO2 of 94–98%. COPD patients, particularly those with chronic CO2 retention (hypercapnia), target lower SpO2 (88–92%) to avoid suppressing respiratory drive. Patients with acute coronary syndrome (heart attack) may target slightly higher SpO2 (94–98%). Septic patients often target higher SpO2 (94–98%) to maximize oxygen delivery to tissues. Premature infants have special considerations, targeting lower SpO2 (85–95%) to avoid retinopathy of prematurity (eye damage from excessive oxygen).

Limitations and Disclaimers: This calculator is an educational tool and should never be used for actual clinical decision-making. Oxygen therapy must always be prescribed and monitored by qualified healthcare professionals. Individual patient factors (lung disease, cardiac function, anemia, shunting, etc.) dramatically affect oxygen delivery and oxygenation. FiO2 formulas provided are approximations; actual FiO2 delivered varies based on breathing pattern, mask fit, and other factors. SpO2 targets should be individualized based on clinical assessment and underlying conditions. This calculator does not account for mechanical ventilation settings, PEEP, lung protective strategies, or complex physiology. Always follow institutional protocols and clinical guidelines for oxygen therapy. Complications of oxygen therapy (oxygen toxicity, absorption atelectasis, suppression of respiratory drive in hypercapnic patients) are not addressed here but are important clinically. Consult with respiratory therapists, intensivists, or pulmonologists for complex cases.