Oxygen Delivery Devices: Mask Types and Uses

Oxygen therapy is a critical intervention, but the appropriate choice of device is essential for effective patient management and safety. Choosing the correct oxygen delivery system—from low-flow cannulae to high-flow therapy—depends entirely on the patient’s condition, the required FiO₂​ (Fraction of Inspired Oxygen), and their risk of carbon dioxide (CO₂​) retention (hypercapnia).

Room air provides 21% O_2​ and 78% N₂​. Even small increases in inspired O₂​ concentration can produce large gains in tissue oxygenation.

1. Low-Flow Systems: Variable FiO₂​

These systems use low flow rates of oxygen and the final FiO₂​ is diluted by the patient’s own inspired room air. This makes the delivered FiO₂​ highly variable and dependent on the patient’s respiratory rate and depth.

A. Nasal Cannula (NC)

• Description: A thin tube with two small nozzles inserted into the nostrils.
• Flow Rate & FiO₂​ Range: 1–6 L/min, delivering 24%–44% FiO₂​.
• Clinical Use: Used for non-critically ill patients. Well-tolerated and often preferred over a facemask.
• Caution: High flow rates (>6 L/min) can cause nasal mucosal drying and nosebleeds.

B. Simple Facemask

• Description: Fits over the nose and mouth. Open side ports allow room air to enter and dilute the O₂​, and also allow exhaled CO₂​ to leave.
• Flow Rate & FiO₂​ Range: 2–12 L/min, delivering 24%–65% FiO₂​.

2. Fixed-Performance & High-FiO_2​ Systems

These systems are necessary when precise FiO₂​ control is needed or when a very high concentration of oxygen must be delivered.

A. Venturi Mask (High-Flow Air-Entrainment Mask)

• Description: A system with specific flow rate settings and air ports designed to precisely entrain room air. External ports must remain open to ensure accurate air entrainment.
• Key Feature: Delivers a variable but FIXED amount of FiO₂​ regardless of the patient’s breathing pattern. The maximum practical FiO_2​ is 50%.
• Clinical Gold Standard for COPD: The Venturi mask is the device of choice for managing patients with COPD and known CO₂​ retention. Clinicians typically start with a 24-28% mask. Subsequent management is guided by ABG monitoring.
• FiO_2​ Settings (Examples): 24% (2–4 L/min), 28% (4–6 L/min), 40% (10–12 L/min).

B. Non-Rebreather (NRB) Mask with reservoir

• Description: Similar to a simple mask but features three one-way valves and a reservoir bag. The valves prevent 21% room air from diluting the mix and prevent exhaled air from entering the reservoir.
• Key Feature: Delivers the highest possible FiO_2​ without intubation.
• Flow Rate & FiO_2​ Range: Flow must be sufficient to keep the reservoir bag inflated on inspiration (typically 15 L/min), delivering 85%–90% FiO₂​.
• Indications: Used for critically ill patients when a high FiO_2​ is urgently required.

3. Advanced and Emergency Support

Safety in Practice: Target Saturation and Monitoring

• General Target: For most non-critically ill patients, the SaO2​ target is typically 94%–98%.
• Hypercapnic Risk (COPD): For patients at risk of CO2​ retention, the target SaO2​ is deliberately lower: 88%–92%. This practice ensures adequate oxygenation while minimizing the risks of worsening hypercapnia (Type II respiratory failure). This occurs partly due to the Haldane Effect, where excess oxygen binding to hemoglobin causes CO2​ to be released into the blood, increasing PaCO2​.

References and Further Reading

1. O’Driscoll, B. R., et al. “BTS guideline for oxygen use in healthcare and emergency settings.” Thorax, vol. 72, no. 5, 2017, pp. i1–i90.DOI : 10.1136/thoraxj-2016-209040
2. Global Initiative for Chronic Obstructive Lung Disease (GOLD): Global Strategy for the Diagnosis, Management, and Prevention of COPD. (Latest Annual Report) URL: https://goldcopd.org/
3. Jones, B., & Bell, L. “The physiological basis for the management of acute exacerbations of chronic obstructive pulmonary disease.” Continuing Education in Anaesthesia, Critical Care & Pain, vol. 18, no. 4, 2018, pp. 110–115. DOI : 10.1093/bjaed/mky013
4. Roca, O., et al. “High-flow nasal cannula in acute respiratory failure.” Critical Care, vol. 20, no. 1, 2016, 291. DOI : 10.1186/s13054-016-1473-z
5. American Thoracic Society (ATS) / European Respiratory Society (ERS). “Standards for the Diagnosis and Management of COPD.” (Relevant section on Oxygen Therapy).
6. Simonds, A. K. “Home mechanical ventilation: an overview.” European Respiratory Journal, vol. 46, no. 5, 2015, pp. 1530–1536. DOI : 10.1183/13993003.00344-2015

Learn more about the acute management of COPD

Dr Kunal Varma Bheecarry

Dr. Kunal Varma Bheecarry, MD is a GMC registered substantive Consultant Physician in the UK, specializing in Internal Medicine. With more than 15 years of experience on the clinical frontlines in both General Internal Medicine and Acute Medicine, he is passionate about translating complex medical topics, common problems and clinical guidelines into clear, actionable knowledge for healthcare professionals and patients alike. Every article is written and rigorously reviewed by him and other registered medical professionals to ensure clinical accuracy, guideline compliance, evidence-based reliability, authoritativeness and trustworthiness.

Disclaimer: All content is purely educational and does not constitute personal medical advice. It is not a substitute for professional clinical advice and readers must consult their own primary team. All views and interpretations are mine and not related to the work place.