Oxygen delivery devices

Devices in this category are used for oxygen therapy and, in some cases, non-invasive ventilation or respiratory support such as continuous positive airway pressure (CPAP) and non-invasive ventilation (NIV).

Devices delivering high-flow nasal oxygen are dicussed elsewhere

Performance of these devices can be described according to

1. the maximum oxygen concentration achievable to be delivered to the patient,

2. the reliability/ variability with which the devices do that.

Looking at the reliability and variability of oxygen delivery to the patient we can divide these pieces of equipment into fixed performance or variable performance devices. This means that inspired oxygen concentration is either more dependent on the patient's peak inspiratory flow rate (PIFR) (variable performance devices) or less so (fixed performance devices).

Fixed performance devices

These devices deliver a fixed inspired oxygen concentration to the patient, independent of the PIFR. Even at the time of PIFR no random entrainment of room air will occur to unpredictably alter the FiO2 with this equipment.

Devices in this group include:

Venturi masks

There is entrainment of room air with these devices, but it is fixed and not dependent on the patient's PIFR. Therefore the resulting delivered FiO2 is also constant.

Non-rebreather facemasks

A reservoir bag supplies 100% oxygen and makes up for the deficit which occurs during times when the patient's PIFR is higher than the oxygen supply flow to the mask.

Anesthetic facemasks (with a breathing circuit)

These masks form a complete seal around the patient's airway so no entrainment of room air can occur. The delivered oxygen concentration is the same as in the gas mixture supplied to the mask (assuming no rebreathing occurs in the anesthetic breathing circuit).

The Patil-Syracuse and the endoscopy mask also come under this heading. Both of these devices allow instrumentation with a fiberoptic scope or other endoscopic devices while maintaining a seal to the face with the mask.

Variable performance devices

These devices deliver a variable inspired oxygen concentration to the patient, which depends on the PIFR. Depending on a patient's inspiratory effort (tidal volume, 'speed' of inspiration and respiratory rate) the PIFR can often exceed the flow rate at which oxygen or an oxygen/air mixture is supplied by the device, meaning that at the time of PIFR more or less entrainment of room air occurs, altering the resulting FiO2 in an unpredictable fashion.

Devices in this group are:

Nasal cannulas

Nasal cannulas as part of high-flow nasal oxygen delivery systems are discussed in more detail elsewhere [link]

Simple facemasks/ 'Hudson' masks

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