Partial Rebreather Mask 

Overview & Basic Structure

A Partial Rebreather Mask (PRM) is a high-flow oxygen delivery device with a reservoir bag that allows partial rebreathing of exhaled gases (specifically dead space gas), thereby increasing delivered FiO₂.

 It is intermediate between a simple face mask and a non-rebreather mask (NRBM).

Components

1. Face Mask

• Covers nose and mouth
• Loose-fitting (no airtight seal)

2. Reservoir Bag

• Capacity: 600–1000 mL
• Stores oxygen + first portion of exhaled gas

3. Side Ports (Open)

• Unlike Non-rebreather mask
• No one-way valves → allows room air entrainment

4. Oxygen Tubing

• Connected to central oxygen source

Principle of Functioning

Key Concept: Rebreathing Dead Space Gas

During expiration:

• First portion of exhaled gas = anatomical dead space gas
  • High O₂, low CO₂
• This gas enters reservoir bag

During inspiration:

• Patient inhales:
  • Oxygen from flow
  • Oxygen from reservoir bag
  • Minimal room air

 Hence:

• ↑ FiO₂ compared to simple mask
• No significant CO₂ retention (if properly used)

Oxygen Delivery Characteristics

Indications (ICU-Oriented)

Moderate Hypoxemia

• SpO₂ not improving with nasal cannula/simple mask

Acute Conditions

• Pneumonia
• Early ARDS
• Pulmonary edema
• Trauma patients

 Pre-oxygenation (selected cases)

• When NRBM not available

Step-up oxygen therapy

• Between:
  • Simple mask → PRM → NRBM → HFNC → NIV → Intubation

 Contraindications

Absolute

• None (relative device)

 Relative

• Severe hypoxia needing high FiO₂ → use NRBM/HFNC
• Hypercapnic respiratory failure (e.g., COPD exacerbation)
• Poor respiratory effort
• Facial trauma (mask fit issues)