You are connecting a nasal cannula to a patient who requires Oxygen. You are setting the oxygen flow to 5 L/min. How much of FiO2 (Fraction of inspired Oxygen Concentration) will be delivered to the patient?

1. A

   24%

2. B

   28%

3. C

   36%

4. D

   40%

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2019

Explanation

• A nasal cannula is a low-flow oxygen delivery device where the final inspired oxygen concentration is an estimate because it mixes with room air.
• The fraction of inspired oxygen (FiO2) can be estimated using a standard rule: start with room air (21% O2) and add approximately 4% for each liter per minute of oxygen flow.
• For a flow rate of 5 L/min, the calculation is: 21% + (5 L/min × 4%) = 21% + 20% = 41%, which is clinically rounded to 40%.

Why Other Options Were Wrong

• Option A: This FiO2 corresponds to a much lower oxygen flow rate.
• Option B: This FiO2 corresponds to a lower oxygen flow rate than what is specified in the question.
• Option C: This FiO2 is delivered at a flow rate of 4 L/min, not 5 L/min.

Related Visual

Clinical Relevance

• Nursing practice connection: Use the key finding related to Calculation of FiO2 for a low-flow nasal cannula to guide bedside assessment, documentation, and the next nursing action.
• When administering oxygen at flow rates of 4 L/min or higher via nasal cannula, it is crucial to attach a humidifier to prevent drying of the nasal mucosa, which can cause discomfort and nosebleeds.
• Nurses must regularly assess the patient's nares and the skin over the ears for signs of pressure injury or irritation from the cannula tubing.
• Continuously monitor the patient's oxygen saturation (SpO2) and respiratory status to ensure the prescribed oxygen therapy is effective and titrate as ordered.

How to Approach the Question

• Identify the core question: It asks for the FiO2 delivered at a specific flow rate (5 L/min) using a specific device (nasal cannula).
• Recall the clinical rule of thumb for nasal cannulas: FiO2 increases by about 4% for every 1 L/min of oxygen flow, starting from the 21% oxygen in room air.
• Apply the formula: FiO2 (%) ≈ 21% + (L/min × 4%).
• Calculate for 5 L/min: 21 + (5 × 4) = 41%. Find the closest answer among the options.
• Select the option that matches the calculation, which is 40%.

Concept Tested & Keywords

• Concept Tested: Calculation of FiO2 for a low-flow nasal cannula.
• Stem keywords: nasal cannula, oxygen flow, 5 L/min, FiO2, Fraction of inspired Oxygen Concentration
• Lead-in keywords: How much

Question ID

QFxZrJq5Tr-kHbdkahIM6a

Copy ID

Reference Book

E6 Nursing Fundamentals Taylor p. 731-733

E6 Nursing Fundamentals Potter Perry 12e Part 5 p. 7-9

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 663-665