Type of mask of o2

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Here is a complete overview of the types of oxygen (O2) masks used in clinical practice:

Types of Oxygen Masks

1. Nasal Mask

A hybrid of the nasal cannula and a face mask. The lower edge rests on the upper lip, surrounding the external nose. It provides supplemental oxygen equivalent to a nasal cannula under low-flow conditions and is often more comfortable (no sores around the nares, no "jetting" of dry gas into the nasal cavity).

2. Simple Face Mask

A disposable, lightweight plastic device covering both nose and mouth - no reservoir bag.
Minimum flow: ~5 L/min (to flush exhaled CO2 and prevent rebreathing).
Delivered FiO2: ~0.30 to 0.60 at flows of 5-10 L/min; can approach 0.70-0.80 under ideal conditions.
Best suited for short-term oxygen therapy (e.g., transport, post-anesthesia care, ER). Not ideal for profoundly hypoxemic or tachypneic patients.

3. Reservoir Masks (Variable-Performance)

These incorporate a 600-800 mL reservoir bag below the chin, increasing available oxygen per breath.

a) Partial Rebreather Mask

The first ~1/3 of exhaled tidal volume (from anatomic dead space - high O2, low CO2) refills the reservoir bag.
Flow: 8-15 L/min (keep reservoir at least half full).
FiO2: ~0.35 to 0.60 (up to higher with optimal fitting).

b) Non-Rebreather Mask (NRM)

Same as the partial rebreather but adds a one-way valve between the bag and the mask, preventing exhaled air from entering the reservoir.
One-way valves on the side ports also minimize ambient air inhalation.
Flow: ~15 L/min.
FiO2: ~0.60 to 0.80-0.90 in practice (theoretically up to 1.0, but real-world mask fit limits this).
Indicated for significant hypoxemia with relatively normal minute ventilation.

4. Air-Entrainment Mask (Venturi Mask) - Fixed-Performance

Consists of a mask, a jet nozzle, and adjustable entrainment ports.
Oxygen delivered under pressure through the nozzle entrains ambient air in a fixed, predictable ratio - giving a precise, controlled FiO2.
FiO2 range: 0.24, 0.28, 0.31, 0.35, 0.40, 0.50, 0.60 (depending on valve/port setting).
Total gas flow is high, ensuring the FiO2 is stable regardless of breathing pattern.
Best for patients needing precise O2 titration, e.g., COPD patients at risk of hypercapnia from excess oxygen.

5. Bag-Mask-Valve (BVM) / Anesthesia Bag Systems - High-Performance

Self-inflating (~1.5 L) or non-self-inflating anesthesia bags with a mask.
With adequate seal and reservoir flow, FiO2 can approach ~1.0 (100%).
Used for patients with gasping respirations or who need assisted/manual ventilation.

6. High-Flow Nasal Cannula (HFNC)

Not a "mask" in the traditional sense, but increasingly used instead of masks.
Delivers heated, humidified oxygen at 40-60 L/min, providing a nearly constant and high FiO2.
Provides a small degree of PEEP and excellent patient comfort.

Quick Comparison Table

Mask Type	Flow (L/min)	FiO2 Range	Key Feature
Simple Face Mask	5-10	0.30-0.60	No reservoir, short-term use
Partial Rebreather	8-15	0.35-0.60	Reservoir bag, partial CO2 return
Non-Rebreather	10-15	0.60-0.90	One-way valve, highest FiO2 of masks
Venturi (Air-entrainment)	Varies	0.24-0.60	Precise, fixed FiO2
BVM / Anesthesia Bag	High	Up to 1.0	Assisted ventilation
HFNC	40-60	0.21-1.0	Heated/humidified, high comfort

Sources: Morgan & Mikhail's Clinical Anesthesiology, 7e; Fishman's Pulmonary Diseases and Disorders

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