ER Basics for Rookies

For rookies, the oxygen wall outlet and the pile of masks, cannulas, and tubing on the airway cart can feel overwhelming. Which device should you grab first? Which one actually delivers 100% oxygen? Which is best for the crashing patient? Understanding the basics of oxygen delivery devices is essential to making quick, safe decisions in the emergency department.

Why Oxygen Delivery Matters

• Oxygen is the first drug in resuscitation.
• The device you choose affects how much oxygen (FiO₂) the patient receives, how comfortable they are, and whether you buy enough time for further interventions.
• Misuse (e.g., using low-flow when high-flow is needed) can delay stabilization and worsen outcomes.

1. Nasal Cannula (NC)

Description

• Small prongs that rest in the nares, connected to oxygen tubing.
• Delivers low-flow oxygen.

Flow Rate & FiO₂

• 1–6 L/min.
• ~24% (1 L/min) → ~44% (6 L/min).

Pros

• Comfortable, patients can eat and talk.
• Easy to apply, cheap.
• Useful for mild hypoxemia or chronic oxygen supplementation (COPD, CHF).
• Can be used for apneic oxygenation during intubation.

Cons

• Limited FiO₂ delivery—never achieves >45%.
• Ineffective in severe hypoxemia.
• Mouth breathing reduces efficacy.

2. Non-Rebreather Mask (NRB)

Description

• Face mask with reservoir bag and one-way valves.
• Often called “the 100% mask” (but in reality, usually delivers 60–70%).

Flow Rate & FiO₂

• 10–15 L/min.
• FiO₂: ~60–90% (depending on seal, fit, and patient’s inspiratory flow).

Pros

• Best simple mask for moderate–severe hypoxemia.
• Easy, fast to apply.
• Useful as preoxygenation for stable patients awaiting intubation.

Cons

• Leaks easily if seal is poor.
• Claustrophobic for some patients.
• Doesn’t provide positive pressure—alveoli can still collapse in shunt physiology.
• If O₂ flow <10 L/min, risk of CO₂ rebreathing.

3. High-Flow Nasal Cannula (HFNC)

Description

• Heated, humidified oxygen delivered at very high flow rates via wide-bore nasal prongs.
• Provides a continuous washout of dead space and mild PEEP effect.

Flow Rate & FiO₂

• 30–60 L/min.
• FiO₂: up to 100% (precisely titratable).

Pros

• Excellent for severe hypoxemia (pneumonia, ARDS, COVID).
• Improves comfort compared to NRB or NIV.
• Allows patient to eat, talk, and clear secretions.
• Provides mild PEEP (3–6 cm H₂O), improving oxygenation.
• Can be used for preoxygenation and apneic oxygenation before RSI.

Cons

• Requires special equipment (not always in smaller EDs).
• Takes 1–2 minutes to set up.
• Not effective in hypercapnia (e.g., COPD exacerbations) compared to NIV.
• Can delay escalation if overused in crashing patients.

Quick Comparison Table

Choosing the Right Device in the ED

• Stable, mild hypoxemia (SpO₂ 88–92%) → Nasal cannula.
• Moderate hypoxemia (SpO₂ 75–90%) → NRB, escalate if not improving.
• Severe hypoxemia, tachypnea, impending fatigue → HFNC (if available) or NIV.
• Crash situations → NRB or BVM while preparing for intubation.

Rookie Mistakes

• Using NRB at low flow rates (<10 L/min) → CO₂ rebreathing.
• Expecting NC to fix severe hypoxemia.
• Delaying intubation while “waiting to see” if low-flow oxygen helps in a crashing patient.
• Forgetting that oxygen delivery ≠ oxygenation: if lungs are shunted (ARDS, pulmonary edema), FiO₂ alone won’t fix the problem—positive pressure may be needed.

Rookie Pearls

• Always check SpO₂ response within minutes of applying oxygen—if no improvement, escalate.
• For preoxygenation before RSI: use NRB at 15 L/min + nasal cannula at 15 L/min (“double oxygen setup”).
• HFNC is your friend for the sick but still breathing patient—it buys you time.

Take-Home Message

Every rookie needs to know the strengths and weaknesses of oxygen delivery devices. In the ED:

• Nasal cannula is your gentle helper.
• NRB is your workhorse.
• HFNC is your game-changer for severe hypoxemia.

Choose wisely, escalate early, and never forget that oxygenation is your first priority in every resuscitation.