The choice of delivery devices depends on the patient’s oxygen requirement, efficacy of the device, reliability, ease of therapeutic application and patient acceptance. An arterial blood gas (ABG) or oximetry is advised upon switching delivery devices. Frequent monitoring is highly advisable in the unstable patient [2-5].
The first-line options and the second-line options for oxygen delivery are presented here.
Standard nasal cannula
The standard nasal cannula delivers an inspiratory oxygen fraction (FI,O2) of 24-40% at supply flows ranging from 1-5 L·min-1. The formula is FI,O2 = 20% + (4 × oxygen litre flow). The FI,O2 is influenced by breath rate, tidal volume and pathophysiology. The slower the inspiratory flow the higher the FI,O2 .
A Venturi mask mixes oxygen with room air, creating high-flow enriched oxygen of a settable concentration. It provides an accurate and constant FI,O2. Typical FI,O2 delivery settings are 24, 28, 31, 35 and 40% oxygen. The Venturi mask is often employed when the clinician has a concern about CO2 retention .
Simple face mask
The volume of the face mask is 100-300 mL. It delivers an FI,O2 of 40-60% at 5-10 L·min-1. The FI,O2 is influenced by breath rate, tidal volume and pathology. The face mask is indicated in patients with nasal irritation or epistaxis. It is also useful for patients who are strictly mouth breathers. However, the face mask is obtrusive, uncomfortable and confining. It muffles communication, obstructs coughing and impedes eating .
Nonrebreathing face mask with reservoir and one-way valve
The nonrebreathing face mask is indicated when an FI,O2 >40% is required. It may deliver FI,O2 up to 90% at high flow settings. Oxygen flows into the reservoir at 8-10 L·min-1, washing the patient with a high concentration of oxygen. Its major drawback is that the mask must be tightly sealed on the face, which is uncomfortable. There is also a risk of CO2 retention .
Reservoir cannulas improve the efficiency of oxygen delivery. Hence, patients may be well oxygenated at lower flows. Litre flows of =8 L·min-1 have been reported to adequately oxygenate patients with a high flow requirement [7, 8].
High-flow transtracheal catheters
Transtracheal catheters deliver oxygen directly into the trachea. There are wash-out and storage effects that promote gas exchange as well as providing high-flow oxygen. High-flow transtracheal catheters may reduce the work of breathing and augment CO2 removal. Patients who have been extubated may benefit from an interim of high-flow transtracheal oxygen to better ensure weaning success [9, 10].
High-flow warmed and humidified nasal oxygen
Nasal oxygen has been administered at lows ranging from 10-40 L·min-1. When this oxygen is warmed to body temperature and saturated to full humidity, it is comfortable. Early clinical and bench studies have demonstrated Sa,CO2 equivalent to or surpassing nonrebreathing face masks at the same supply flow setting. Definitive recommendations about high-flow nasal oxygen will await more definitive studies .