How should I write an oxygen prescription for 2 L per minute delivered via nasal cannula?

How to Write an Oxygen Prescription for 2L Nasal Cannula

Write the oxygen prescription as: "Oxygen 2 L/min via nasal cannula, target SpO2 94-98%" (or 88-92% if the patient has COPD or risk of hypercapnic respiratory failure). 1

Essential Prescription Components

Every oxygen prescription must include 1:

• Delivery device: Nasal cannula
• Flow rate: 2 L/min
• Target oxygen saturation range: This is the most critical element
  • 94-98% for most patients
  • 88-92% for patients with COPD or risk of hypercapnia
• Your signature on the drug chart or electronic prescribing order

Target Saturation Selection Algorithm

For patients WITHOUT risk of hypercapnic respiratory failure 1:

• Target: 94-98%
• This includes: acute hypoxemia, pneumonia, asthma, heart failure, pulmonary embolism, most postoperative patients

For patients WITH risk of hypercapnic respiratory failure 1:

• Target: 88-92%
• This includes:
  • Known COPD
  • Patients >50 years who are long-term smokers with chronic breathlessness
  • Cystic fibrosis exacerbations
  • Neuromuscular disorders with respiratory failure
  • History of previous hypercapnic respiratory failure requiring NIV

Flow Rate Considerations

The 2 L/min flow via nasal cannula typically delivers an FiO2 of approximately 0.28-0.30 (28-30%) in adults with normal breathing patterns 2, 3. However, the actual delivered oxygen concentration varies significantly based on:

• Respiratory rate: Higher rates (>20 breaths/min) decrease FiO2 by approximately 0.012 2
• Mouth breathing: Decreases FiO2 by approximately 0.024 2
• Minute ventilation: Higher ventilation decreases delivered FiO2

The BTS guideline recommends nasal cannula flow rates of 2-6 L/min for medium-concentration oxygen therapy 1, so 2 L/min is appropriate for mild hypoxemia or as a starting point for titration.

Critical Documentation Requirements

You must document 1:

1. The target saturation range on the respiratory section of the observation chart
2. Baseline oxygen saturation before starting therapy (when possible)
3. The prescription should remain active even after oxygen is discontinued, in case of deterioration

Common Pitfalls to Avoid

• Never prescribe oxygen without a target saturation range - this is the single most important element 1
• Don't use flow rates <2 L/min with nasal cannula in general wards - this practice requires pediatric flow meters and is not recommended outside specialist units 1
• Don't assume 2 L/min is always appropriate - if target saturation isn't achieved, you must titrate up to 6 L/min via nasal cannula or escalate to simple face mask (5-10 L/min) or reservoir mask (15 L/min) 1
• Recheck blood gases at 30-60 minutes in patients with COPD or hypercapnia risk, even if initial PCO2 was normal 1

When to Escalate Beyond 2L Nasal Cannula

If SpO2 remains below target on 2 L/min nasal cannula 1:

• Increase to 3-6 L/min via nasal cannula
• If still inadequate, switch to simple face mask at 5-10 L/min
• If SpO2 <85%, use reservoir mask at 15 L/min immediately
• Ensure senior medical review

Monitoring and Titration

After initiating oxygen 1:

• Monitor saturation continuously or frequently
• Lower the oxygen if saturation exceeds target range for 4-8 hours
• Increase oxygen if saturation falls below target range
• Document any changes and clinical response

The prescription format should be standardized in your facility - most hospitals have designated oxygen sections on drug charts or electronic prescribing systems specifically for this purpose 1.