Is high flow nasal oxygen safer than low flow nasal oxygen in sedated patients undergoing endoscopy?

High-Flow Nasal Oxygen is Safer Than Low-Flow for Sedated Endoscopy

High-flow nasal oxygen (HFNO) should be used instead of low-flow oxygen during sedated endoscopy procedures, as it dramatically reduces hypoxemia risk from 33.5% to 9.4% and is specifically recommended by the Difficult Airway Society as the technique of choice for procedural oxygenation. 1

Primary Evidence Supporting HFNO

The Difficult Airway Society explicitly recommends HFNO as the technique of choice for procedural oxygenation when available, noting desaturation rates of 12-16% with low-flow oxygen versus only 0-1.5% with HFNO 1. This represents a clinically significant reduction in respiratory complications that directly impacts patient safety.

The most robust clinical trial evidence comes from the 2021 ODEPHI multicenter randomized controlled trial, which demonstrated that HFNO (70 L/min at FiO2 0.50) reduced SpO2 ≤92% events from 33.5% to 9.4% (absolute risk reduction of 23.4%) in high-risk patients undergoing gastrointestinal endoscopy under deep sedation 2. This study specifically targeted patients at elevated risk: those >60 years old, with cardiac/respiratory disease, ASA status >1, obesity, or sleep apnea 2.

Magnitude of Clinical Benefit

HFNO provides multiple layers of safety improvement beyond simple oxygen delivery:

• Eliminates severe hypoxemia: A 2019 multicenter trial of 1,994 patients showed HFNO reduced hypoxemia incidence from 8.4% to 0% and severe hypoxemia from 0.6% to 0% during propofol-sedated gastroscopy 3

• Reduces procedural interruptions: HFNO decreased the need for airway maneuvers from 32.4% to 11.1% 2, and reduced overall procedural interruptions (OR = 0.11) 4

• Maintains higher oxygen saturations: Elderly patients (≥65 years) achieved higher minimum SpO2 values [99% vs 96.5%] and shorter recovery times with HFNO 5

Physiological Mechanisms Explaining Superior Safety

HFNO provides multiple physiological advantages that low-flow oxygen cannot match 1:

• Delivers warm, humidified oxygen at flows up to 60-70 L/min
• Generates modest positive end-expiratory pressure (PEEP effect)
• Reduces anatomical dead space through washout effect
• Improves pulmonary compliance
• Reduces work of breathing
• Provides superior patient comfort compared to masks

Critical Implementation Details

HFNO settings for endoscopy:

• Flow rate: 60-70 L/min 2, 3, 5
• FiO2: 0.50-0.60 2, 5
• These settings should be initiated before sedation begins

Mandatory monitoring regardless of oxygen delivery method 1:

• Continuous pulse oximetry is non-negotiable
• Consider transcutaneous CO2 monitoring for patients at risk of hypercapnia
• Clinical assessment remains essential, as oxygen supplementation may delay recognition of apnea

Special Populations Requiring Caution

For patients at risk of hypercapnia (COPD, obesity hypoventilation) 1:

• Target lower SpO2 of 88-92% rather than 94-98%
• Consider transcutaneous CO2 monitoring
• Exercise caution with any supplemental oxygen, though HFNO remains safer than low-flow

The British Thoracic Society emphasizes that oxygen should only be given to correct hypoxemia, not routinely, particularly in hypercapnia-risk patients 1. However, when oxygen is needed, HFNO's superior safety profile still makes it preferable.

Addressing Guideline Nuances

While the American Gastroenterological Association notes "little evidence that [supplemental oxygen] reduces significant cardiopulmonary complications" 1, this statement predates the high-quality RCT evidence showing HFNO's dramatic reduction in desaturation events. The warning that oxygen may delay recognition of apnea remains valid and reinforces the need for continuous monitoring, but does not negate HFNO's superiority over low-flow oxygen when supplementation is indicated 1.

Practical Considerations

Equipment and training requirements 1:

• HFNO requires additional equipment compared to nasal cannula
• Staff training is necessary but straightforward
• Cost-effectiveness is favorable due to reduced complications and procedural interruptions

Minimal adverse events: The only HFNO-specific adverse event reported was transient nasal dryness/discomfort in 1.7% of patients, resolving within 30 minutes 3. Patient comfort is actually superior to masks 1.

Clinical Algorithm

For all sedated endoscopy patients:

1. Use HFNO at 60-70 L/min, FiO2 0.50-0.60 as first-line 2, 3, 5
2. Initiate before sedation begins
3. Maintain continuous pulse oximetry 1
4. For hypercapnia-risk patients: target SpO2 88-92% and add CO2 monitoring 1

Only use low-flow oxygen (nasal cannula 2-6 L/min) if 1:

• HFNO equipment is unavailable
• Patient refuses HFNO (rare given superior comfort)
• Accept the 3-4 fold higher desaturation risk 2