Dyspnea, commonly known as shortness of breath, describes difficult or uncomfortable breathing. This sensation results from an imbalance between the body’s demand for oxygen and the respiratory system’s ability to supply it, leading to hypoxemia, or low blood oxygen levels. The primary objective of oxygen therapy is to enhance tissue oxygenation and reduce the work of breathing. Selecting the correct oxygen delivery device is crucial, as the choice affects both therapeutic effectiveness and patient well-being.
Understanding Basic Principles of Oxygen Delivery
The effectiveness of supplemental oxygen relies on two fundamental concepts: the flow rate and the Fraction of Inspired Oxygen (FiO2). Flow rate is measured in Liters per Minute (LPM) and indicates the speed at which oxygen leaves the delivery device. FiO2 represents the actual concentration of oxygen the patient inhales, where room air is approximately 21%. The goal is to increase the FiO2 above this ambient level to improve oxygen transfer in the lungs.
A client experiencing dyspnea often exhibits an increased respiratory rate and tidal volume, meaning their total inspiratory flow demand is significantly higher than normal. When the oxygen delivery system cannot meet this high demand, the patient automatically draws in ambient room air. This dilution reduces the final inhaled oxygen concentration, making the delivered FiO2 unpredictable and variable. This concept is the basis for classifying systems into either low-flow or high-flow categories, determined by whether they meet or exceed the patient’s inspiratory needs.
Low-Flow Devices and Variable Oxygen Delivery
Low-flow systems deliver oxygen at a rate lower than the patient’s peak inspiratory flow, making the final FiO2 dependent on the client’s breathing pattern. The Nasal Cannula is the most common low-flow device, typically used for flow rates between 1 and 6 LPM. Each liter per minute of flow is estimated to increase the FiO2 by about 4%, resulting in an approximate range of 24% to 44%. This device is suitable for mild hypoxemia or chronic stable conditions.
For clients needing a higher concentration, the Simple Face Mask can deliver oxygen at flow rates between 5 and 12 LPM, providing an FiO2 range of about 35% to 55%. A flow rate of at least 5 LPM is required to ensure adequate flushing of exhaled carbon dioxide (CO2) from the mask space, preventing CO2 rebreathing. If the dyspneic client breathes rapidly or deeply, the effective oxygen concentration they receive drops significantly as they entrain more room air. This variability means the actual dose of oxygen is unknown, which can be inadequate for clients with more severe respiratory distress.
High-Flow Systems for Precise Oxygen Targeting
High-flow systems are engineered to supply a flow rate that meets or exceeds the patient’s total inspiratory demand, ensuring the inhaled oxygen concentration remains fixed and precise, regardless of the patient’s breathing pattern. This mechanism is achieved by mixing 100% oxygen with a specific volume of room air before it reaches the patient. The Venturi Mask uses a jet-mixing principle to deliver an accurate, dialed-in FiO2, typically ranging from 24% to 50%. This precision is important for clients with Chronic Obstructive Pulmonary Disease (COPD), where excessive oxygen can suppress the respiratory drive.
The Non-Rebreather Mask is used when the goal is to deliver the maximum possible oxygen concentration, up to 90% or more, in acute, life-threatening situations. This mask features a one-way valve between the reservoir bag and the mask, preventing exhaled air from entering the bag. Exhalation ports with flaps minimize the entrainment of room air. The flow rate must be high enough, typically 10 to 15 LPM, to keep the reservoir bag inflated during the patient’s inspiration.
The High-Flow Nasal Cannula (HFNC) delivers heated and humidified oxygen at flow rates up to 60 LPM. HFNC systems provide a precise FiO2 from 21% to 100% and generate a slight positive pressure, which helps reduce the work of breathing and improve oxygenation.
Patient Comfort and Monitoring the Client
Beyond the technical specifications of oxygen delivery, patient comfort is a consideration, as discomfort can exacerbate anxiety and worsen dyspnea. High flow rates, particularly those exceeding 4 LPM, can cause drying and irritation of the nasal mucosa, which is why heating and humidification are often necessary with high-flow systems like HFNC. Skin integrity requires close attention, as prolonged use of masks or cannulas can cause pressure injuries over the ears, cheeks, or the bridge of the nose. Addressing potential claustrophobia is also necessary, as being covered by a mask can trigger panic, which further increases respiratory effort; switching to a more open system like a nasal cannula or face tent may be beneficial.
Monitoring the client is an ongoing process to confirm the selected mask is effective and safe. The objective measure is Pulse Oximetry (SpO2), which should be titrated to the target saturation level, typically 92% to 96% for most clients, or 88% to 92% for those at risk of CO2 retention. Signs of success include a reduction in the patient’s respiratory rate, a decrease in the visible use of accessory breathing muscles, and the patient reporting an improved comfort level. If dyspnea and hypoxemia persist despite maximal oxygen delivery, it indicates a need to escalate care, possibly transitioning to Non-Invasive Positive Pressure Ventilation (NIPPV) or mechanical ventilation.