2.2 Oxygenation & Ventilation
Key Takeaways
- A nasal cannula delivers roughly 24-44% oxygen at 1-6 liters per minute (L/min), while a non-rebreather mask delivers up to about 90% at 10-15 L/min for hypoxic patients with adequate breathing.
- Bag-valve-mask (BVM) ventilation for an adult in respiratory arrest is delivered at about 10-12 breaths per minute (one breath every 5-6 seconds) with only enough volume to produce visible chest rise.
- Continuous positive airway pressure (CPAP) is within the AEMT scope for awake, spontaneously breathing patients in respiratory distress from pulmonary edema or COPD, and is contraindicated in apnea, hypotension, or vomiting.
- Waveform capnography normal end-tidal carbon dioxide (EtCO2) is about 35-45 mmHg; a rising value suggests hypoventilation and a sudden drop can indicate airway dislodgement or loss of perfusion.
- Pulse oximetry can read falsely high in carbon monoxide poisoning, so treatment decisions are based on the clinical picture, not the SpO2 number alone.
Oxygenation vs. Ventilation
These terms are tested as distinct concepts:
- Oxygenation is delivering oxygen to the alveoli and bloodstream — measured by pulse oximetry (SpO2).
- Ventilation is the mechanical movement of air in and out, which removes carbon dioxide — measured by waveform capnography (EtCO2).
A patient can be well oxygenated on supplemental oxygen yet still be hypoventilating and retaining carbon dioxide. The AEMT must assess both.
Oxygen Delivery Devices
Match the device to the patient's respiratory effort and need.
| Device | Flow Rate | Approx. FiO2 | Best Use |
|---|---|---|---|
| Nasal cannula | 1-6 L/min | 24-44% | Mild hypoxia, patient who will not tolerate a mask |
| Simple face mask | 6-10 L/min | 35-60% | Moderate hypoxia with adequate tidal volume |
| Non-rebreather mask (NRB) | 10-15 L/min | up to ~90% | Severe hypoxia with adequate breathing |
| Bag-valve-mask (BVM) with reservoir | 15 L/min | up to ~100% | Inadequate or absent breathing (assisted/positive-pressure) |
FiO2 is the fraction of inspired oxygen. A non-rebreather requires the reservoir bag to be inflated before placing it on the patient. If a patient is breathing inadequately, no oxygen mask alone is sufficient — the patient needs positive-pressure ventilation.
Bag-Valve-Mask (BVM) Ventilation
The bag-valve-mask is the core ventilation tool at the AEMT level. Effective technique is more important than the device.
- Maintain a tight mask seal; the two-rescuer E-C clamp technique is preferred for difficult seals.
- Squeeze slowly and smoothly over about one second, delivering only enough volume to see visible, gentle chest rise.
- Over-ventilating (too fast, too much volume) causes gastric distension, raises intrathoracic pressure, and reduces venous return and cardiac output.
Positive-Pressure Ventilation Rates
| Patient | Rate | Notes |
|---|---|---|
| Adult respiratory arrest (pulse present) | ~10-12 / min (1 every 5-6 sec) | Visible chest rise only |
| Infant/child respiratory arrest (pulse present) | ~12-20 / min (1 every 3-5 sec) | Smaller volumes, gentle pressure |
| Adult cardiac arrest with advanced airway | ~10 / min (1 every 6 sec) | Continuous compressions, do not pause |
| Patient breathing inadequately | Assist in synchrony, then increase to a normal rate | Coach with the patient's own effort |
Avoid hyperventilation in all cases; it worsens outcomes by lowering carbon dioxide and impairing perfusion.
CPAP (AEMT Scope)
Continuous positive airway pressure (CPAP) delivers constant pressure that holds alveoli open, improves oxygenation, and reduces the work of breathing. CPAP is within the AEMT scope and can prevent the need for intubation.
- Indications — an awake, cooperative patient who is spontaneously breathing with respiratory distress, classically acute pulmonary edema (CHF) or a COPD/asthma exacerbation.
- Contraindications — apnea or inadequate spontaneous breathing, hypotension, decreased level of consciousness, active vomiting, suspected pneumothorax, or inability to protect the airway or tolerate the mask.
- Coach the patient through the initial mask sensation and reassess vital signs continuously; if the patient deteriorates or stops breathing adequately, switch to BVM ventilation.
Monitoring: Pulse Oximetry and Capnography
Pulse Oximetry (SpO2)
- Normal room-air SpO2 is generally 94-100%.
- Falsely high readings occur with carbon monoxide poisoning (the oximeter cannot distinguish carboxyhemoglobin from oxyhemoglobin). Treat the clinical picture with high-flow oxygen regardless of the number.
- Falsely low or unreliable readings occur with poor perfusion, hypothermia, severe anemia, or nail polish.
Waveform Capnography (EtCO2)
- Normal end-tidal carbon dioxide (EtCO2) is approximately 35-45 mmHg.
- A rising EtCO2 indicates hypoventilation or carbon dioxide retention.
- A falling EtCO2 or low waveform may indicate hyperventilation, airway device dislodgement, or a drop in cardiac output/perfusion.
- Capnography is the most reliable confirmation that ventilations are actually reaching the lungs after an advanced airway is placed.
An AEMT is ventilating an apneic adult with a pulse using a bag-valve-mask. Which rate is most appropriate?
Which patient is the most appropriate candidate for AEMT-applied CPAP?
A patient rescued from a house fire is confused but has a pulse oximetry reading of 99%. What is the best interpretation and action?
After an advanced airway is placed, the patient's waveform capnography shows a sudden drop toward zero. What does this most likely indicate?