How a Bag Valve Mask Delivers Oxygen Without Supplemental Oxygen
When you squeeze a bag valve mask (BVM) without it being connected to an oxygen source, the self-inflating bag draws in room air (approximately 21% oxygen) through its one-way inlet valve and delivers this to the patient—which is sufficient for effective ventilation during resuscitation. 1
The Mechanism of Self-Inflating Bags
The BVM works through a simple but elegant design:
- The bag automatically refills with ambient room air after each squeeze through a non-jam inlet valve that opens when the bag re-expands, allowing atmospheric air to enter 2
- Room air contains 21% oxygen, which is the same concentration we all breathe normally and is adequate for maintaining oxygenation during emergency ventilation 1
- The one-way valve system prevents exhaled air from re-entering the bag while allowing fresh room air to enter with each refill 2
Oxygen Delivery Concentrations
The oxygen concentration delivered varies significantly based on whether supplemental oxygen is attached:
- Without oxygen connection: ~21% oxygen (room air only) 1
- With oxygen at 10 L/min: 30-80% oxygen 1
- With oxygen reservoir bag at 10-15 L/min: 60-95% oxygen 1, 3
Clinical Effectiveness
The American Heart Association confirms that bag-mask devices can provide effective "mask ventilation with room air or oxygen", validating that both options are clinically viable 4, 1
Key points about effectiveness:
- Room air ventilation is sufficient for resuscitation when supplemental oxygen is unavailable 1
- Never delay rescue breathing while searching for oxygen equipment—begin ventilation with room air immediately 1
- Proper technique matters more than oxygen concentration for initial resuscitation, including maintaining adequate mask seal and delivering appropriate tidal volumes 2
Critical Technical Requirements
Regardless of oxygen availability, effective BVM ventilation requires:
- Deliver approximately 600 mL tidal volume for adults to produce visible chest rise 1, 2
- Give each breath over 1 second and watch for chest rise 1, 2
- Use two-person technique when possible: one rescuer maintains airway and mask seal with both hands while the other squeezes the bag 1, 2
Common Pitfall to Avoid
Avoid excessive ventilation—use only enough force to make the chest visibly rise, as excessive ventilation increases intrathoracic pressure, impedes venous return, and decreases cardiac output 1, 2