Simple Face Mask 

1. Definition

A Simple Face Mask (SFM) is a low-flow oxygen delivery device ,The term “Hudson mask” originated from the company

2. Principle of Oxygen Delivery

The simple face mask functions as a variable performance oxygen device.(FiO₂ delivered = 35–60%.)

Mechanisms involved:

1. Oxygen Flow Into Mask

Oxygen enters the mask from the oxygen tubing.

2. Mixing With Room Air

Room air enters through side ports during inspiration.

3. Reservoir Effect

A small amount of oxygen accumulates inside the mask between breaths.

4. Rebreathing Prevention

Continuous oxygen flow flushes exhaled CO₂ out of the mask.

3. Oxygen Flow Rate

Minimum required flow: 5 L/min

Reason:

If flow is <5 L/min, exhaled CO₂ accumulates inside the mask, leading to CO₂ rebreathing.

Typical flow rates:

Thus, simple face mask typically delivers:

FiO₂ = 35–60%

4. Factors Affecting Delivered FiO₂

FiO₂ delivered by a simple face mask is variable and depends on several factors:

1. Oxygen Flow Rate

Higher flow → Higher FiO₂

2. Patient Inspiratory Flow

High inspiratory demand → more room air entrainment → lower FiO₂

3. Respiratory Rate

Rapid breathing decreases delivered FiO₂

4. Mask Fit

Poor seal → room air dilution

5. Tidal Volume

Large tidal volume → dilution with ambient air.

5. Advantages

1. Higher FiO₂ than nasal cannula

Nasal cannula delivers only 24–40% FiO₂, whereas SFM provides up to ~60%.

2. Simple and inexpensive

Widely available.

3. Easy to apply

No specialized equipment required.

4. Useful for mouth breathers

Unlike nasal cannula.

6. Disadvantages

1. Variable FiO₂

Cannot provide fixed oxygen concentration.

2. CO₂ Rebreathing Risk

If oxygen flow <5 L/min.

3. Poor Tolerance

Patients may feel:

• Claustrophobia
• Heat
• Pressure on face

4. Interferes With

• Eating
• Speaking
• Oral suctioning

5. Risk of Aspiration

Mask must be removed for vomiting.

7. Complications

1. CO₂ Retention

If oxygen flow is inadequate.

2. Oxygen Toxicity

If prolonged high FiO₂.

3. Skin Pressure Injury

From mask straps.

4. Dryness of Airways

Due to non-humidified oxygen.

5. Gastric Distension

Rare but possible.

8. Simple Face Mask vs Venturi Mask vs Non-Rebreather Mask