Oxygen Therapy Delivery Systems

Oxygen Reservoir Devices (Low Flow)

Some low-flow devices utilize a reservoir to collect oxygen-rich gas during exhalation, which is then inhaled during the next breath. This can provide a bolus of 100% oxygen (20–40 ml) and helps decrease the total flow rate required to maintain a specific $\mathrm{SpO}_{2}$.

• Reservoir Cannula (Oxymiser): A specialized cannula that traps oxygen during exhalation.
• Simple Mask: Delivers a moderate $\mathrm{FiO}_{2}$ of 0.40–0.60. It requires a minimum flow of 5–6 L/min to ensure exhaled $\mathrm{CO}_{2}$ is flushed out of the mask.
• Partial Rebreather Mask: A mask with a reservoir bag but no valves. It captures the first third of exhalation (anatomic deadspace) and provides an $\mathrm{FiO}_{2}$ of 0.40–0.70.
• Non-Rebreather Mask (NRB): This device uses one-way valves to prevent the patient from rebreathing exhaled gas or inhaling room air. It provides a high $\mathrm{FiO}_{2}$ of 0.60–0.80 (or higher theoretically). Clinically, it should be started at 10 L/min to keep the reservoir bag inflated.

High-Flow Oxygen Delivery Systems

High-flow systems provide a flow rate that meets or exceeds the patient's inspiratory flow demand. This allows for a fixed, precise $\mathrm{FiO}_{2}$ (0.24 to 1.0) that remains constant regardless of the patient's breathing pattern.

Rule of Thumb: Determining High Flow To qualify as a high-flow device, the system should provide at least 60 L/min total flow. This is based on the fact that average adult peak inspiratory flow is approximately three times the minute volume.

Venturi Masks and Air Entrainment

Venturi masks and Air Entrainment Nebulizers (AEM) provide a fixed $\mathrm{FiO}_{2}$ by mixing oxygen with a specific amount of ambient air through an orifice or entrainment port.

• Venturi Mask: Uses different orifice sizes to achieve precise air dilution.
• Air Entrainment Nebulizer (LVN): Delivers both oxygen and aerosol. Common applications include aerosol masks, face tents, trach collars, and T-pieces (Briggs adapters).

High-Flow Specialized Systems

• Oxygen Blenders: These devices take pressurized air and oxygen (50 psig) and mix them to achieve a specific, precise $\mathrm{FiO}_{2}$.
• High-Flow Nasal Cannula (HFNC): Unlike standard low-flow cannulas, these use a blender system to provide flows up to 40 L/min, meeting most patients' inspiratory needs while providing high relative humidity.
• Oxygen Adder: If an LVN cannot provide enough flow for an $\mathrm{FiO}_{2} > 0.40$, two nebulizers can be used in an "oxygen adder" setup.

Specialized Gas Therapies

Heliox Therapy

Heliox is a mixture of Helium and Oxygen. Because Helium is less dense than Nitrogen or Oxygen, it diffuses more easily through restricted airways. It is used for asthma exacerbations, airway obstructions (like post-extubation stridor), and croup.

When using Heliox, the flowmeter must be adjusted using a correction factor based on the ratio:

• 80:20 Ratio: $1.8 \times \text{liter flow}$
• 70:30 Ratio: $1.6 \times \text{liter flow}$
• 60:40 Ratio: $1.4 \times \text{liter flow}$

Carbogen Therapy

Carbogen is a mixture of $\mathrm{CO}_{2}$ and $\mathrm{O}_{2}$ (typically 5%/95% or 7%/93%) used for CO poisoning or as a respiratory stimulant. It is administered via a snug NRB mask for no more than 5–10 minutes.

Warning: Carbogen Complications Monitor the patient closely for hypoxemia, PVCs, muscle twitching, and hypertension. If any adverse effects occur, STOP treatment immediately.