Bag-Mask Ventilation After Pre-Oxygenation
Bag-mask ventilation after pre-oxygenation is used to maintain oxygenation and prevent desaturation during the apneic period between induction and successful intubation, particularly when intubation is delayed or difficult. 1
Primary Purpose: Bridging the Apneic Gap
Pre-oxygenation creates an oxygen reservoir in the lungs by replacing nitrogen with oxygen, extending the safe apneic time before desaturation occurs. 1 However, this reservoir is finite and depletes during the intubation attempt. Bag-mask ventilation actively delivers oxygen during this critical apneic period to prevent hypoxemia, which is particularly important when:
- Intubation attempts are prolonged or multiple attempts are required 1
- Advanced airway placement is delayed or unsuccessful 1
- The patient has reduced oxygen reserves (obesity, pregnancy, critical illness) 1
Evidence Supporting Bag-Mask Ventilation Over Passive Oxygenation
Recent high-quality research demonstrates that bag-mask ventilation is superior to apneic oxygenation alone. A 2022 randomized trial analysis found that bag-mask ventilation resulted in a median lowest oxygen saturation of 96% compared to 92% with apneic oxygenation (nasal cannula at 15 L/min), with an adjusted mean difference of 4.2% higher oxygen saturation. 2 The incidence of severe hypoxemia (SpO2 <80%) was 6.6% with bag-mask ventilation versus 15.6% with apneic oxygenation alone. 2
Clinical Context: When Pre-Oxygenation Alone Is Insufficient
Despite optimal pre-oxygenation, only 20% of critically ill patients requiring intubation maintain adequate oxygenation without additional ventilatory support. 1 This is because:
- Pre-oxygenation extends safe apneic time but does not eliminate oxygen consumption
- High-risk patients (obese, critically ill, pregnant) desaturate rapidly even after adequate pre-oxygenation 1
- Intubation attempts often take longer than anticipated, exceeding the safe apneic window
Proper Technique to Maximize Effectiveness
Bag-mask ventilation is most effective when performed by two trained providers using the following approach: 1
- One provider opens the airway with jaw thrust and creates a tight mask seal using both hands
- Second provider squeezes the bag to deliver breaths
- Deliver 600 mL tidal volume (sufficient to produce visible chest rise) over 1 second 1
- Use 100% oxygen at 10-15 L/min flow rate 1
- During CPR: Give 2 breaths during brief pauses after every 30 compressions 1
Critical Pitfalls to Avoid
Excessive ventilation causes harm by increasing intrathoracic pressure, reducing venous return and cardiac output, and increasing aspiration risk. 1 Specifically:
- Avoid hyperventilation: Use only enough force to produce chest rise 1
- Single-provider bag-mask ventilation is not recommended during CPR—use mouth-to-mask instead 1
- Gastric insufflation risk: Excessive pressure or volume causes gastric distension, diaphragm elevation, and aspiration 1
- Mask leak compromises effectiveness: Even with flush-rate oxygen (50 L/min), a simulated mask leak reduced FiO2 from 76% to 30% 3
Device Performance Variability
Not all bag-valve-mask devices perform equally. A 2023 laboratory study found that 8 of 40 BVM devices failed to deliver FiO2 >0.85 during spontaneous breathing, with three delivering FiO2 <0.55. 4 Devices with duckbill non-rebreather valves and without dedicated expiratory valves performed worst. 4 Clinicians must be familiar with their specific device's characteristics and limitations.
Alternative Approaches in Specific Contexts
For spontaneously breathing patients with adequate respiratory effort, a non-rebreather mask at flush-rate oxygen (40-60 L/min) is noninferior to bag-mask ventilation and simpler to use. 5, 3 However, this only applies to pre-oxygenation, not the apneic period after induction.
In hypoxemic patients requiring intubation, non-invasive ventilation (NIV) during pre-oxygenation and the peri-intubation period prevents desaturation episodes more effectively than standard pre-oxygenation alone. 1