From the Guidelines
An oxygen mask works by delivering supplemental oxygen to patients who need higher oxygen concentrations than what's available in ambient air, with the most effective type being the Venturi mask for precise oxygen delivery. The mask fits over the nose and mouth, creating a seal that allows oxygen from an attached tank or wall supply to flow directly to the respiratory system. Oxygen masks typically deliver between 24% to 90% oxygen concentration depending on the flow rate (measured in liters per minute) and the specific mask design, as noted in the BTS guideline for oxygen use in adults in healthcare and emergency settings 1. Common types include simple face masks (delivering 35-50% oxygen at 5-10 L/min), non-rebreather masks (delivering up to 90% oxygen with a reservoir bag), and Venturi masks (delivering precise oxygen percentages).
The mask works by increasing the partial pressure of oxygen in the lungs, which enhances diffusion of oxygen into the bloodstream, helping to treat hypoxemia (low blood oxygen) by increasing oxygen saturation in hemoglobin. For proper function, the mask should fit snugly but comfortably, and flow rates should be adjusted according to the patient's needs and oxygen saturation levels, typically monitored via pulse oximetry. According to the BTS guideline 1, for many patients, 24–28% Venturi masks can be substituted with nasal cannulae at low-flow rates (1–2 L/min) to achieve the same target range.
Key considerations for the use of oxygen masks include:
- The flow rate from simple face masks should be adjusted between 5 and 10 L/min to achieve the desired target saturation, as flows below 5 L/min may cause carbon dioxide rebreathing and increased resistance to inspiration 1.
- Patients with COPD with a respiratory rate of >30 breaths/min should have the flow rate set to above the minimum flow rate specified for the Venturi mask and/or packaging, as increasing the oxygen flow rate into a Venturi mask increases the total gas flow from the mask but does not increase the concentration of oxygen delivered 1.
- High-flow nasal cannulae (HFNC) are well tolerated and may be used as an alternative in hypoxic adult patients requiring medium-concentration to high-concentration oxygen therapy and who are not at risk of hypercapnia 1.
Side effects may include skin irritation at contact points, claustrophobia, or dryness of mucous membranes, which can be managed with proper fit adjustments and humidification. Overall, the choice of oxygen mask and flow rate should be guided by the patient's specific needs and clinical condition, with a focus on achieving optimal oxygen saturation levels while minimizing the risk of adverse effects.
From the Research
How an Oxygen Mask Works
- An oxygen mask is a device used to deliver supplemental oxygen to patients who require high oxygen concentrations 2, 3.
- The mask works by providing a flow of oxygen that is inhaled by the patient, with the oxygen concentration depending on the type of mask and the flow rate used 2, 4.
- There are different types of oxygen masks, including simple face masks, Venturi masks, and non-rebreathing masks, each with its own characteristics and uses 3, 5.
Key Components of an Oxygen Mask
- The mask itself, which fits over the patient's nose and mouth 3.
- A reservoir bag, which stores oxygen and helps to maintain a consistent flow rate 5.
- A valve or safety vent, which helps to regulate the flow of oxygen and prevent rebreathing of exhaled air 5.
- A tube or hose, which connects the mask to an oxygen source, such as a tank or wall outlet 2.
Factors Affecting Oxygen Delivery
- Flow rate: increasing the flow rate can increase the oxygen concentration delivered to the patient 2, 4.
- Mask fit: a tight-fitting mask can help to improve the delivery of oxygen by reducing leakage and ensuring a consistent flow rate 5.
- Type of mask: different types of masks can deliver different concentrations of oxygen, with Venturi masks being able to deliver precise concentrations of oxygen 3.
- Breathing pattern: the patient's breathing pattern, including tidal volume and frequency, can affect the oxygen concentration delivered by the mask 2.