26.6e Oxygen Delivery Devices

Oxygen delivery to patients is measured in liters of flow per minute (L/min).

A number of delivery devices are available; the patient’s condition dictates which method you use.

You must continually reassess the patient who requires oxygen therapy to be certain that the delivery method and flow rate are adequate.

Some patients require positive-pressure ventilation rather than a passive delivery device.

A nasal cannula is a catheter placed at the nares.

It provides an optimal oxygen supplementation of up to 40 percent when set at 6 L/min flow.

At flow rates above 6 L/min, the nasal mucous membranes become very dry and easily break down.

Patients generally tolerate the nasal cannula well.

It is indicated for low-to-moderate oxygen requirements and long-term oxygen therapy.

A Venturi mask is a high-flow face mask that uses a Venturi system to deliver relatively precise oxygen concentrations regardless of the patient’s rate and depth of breathing.

(A Venturi system has a constriction within the pipe—an hourglass shape—that varies the flow characteristics of a liquid or gas.

As the velocity of administered oxygen in in the patient’s throat increases, pressure decreases to even out the flow.) As oxygen passes into the Venturi mask through a jet orifice in the base of the mask, it entrains room air.

The device then delivers the resulting mixture to the patient.

Some Venturi masks have dial selectors to control the amount of ambient air taken in; others have interchangeable caps.

Either type can deliver concentrations of 24 percent, 28 percent, 35 percent, and 40 percent oxygen.

The liter flow depends on the oxygen concentration desired.

The Venturi mask is particularly useful for COPD patients who benefit from careful control of inspired oxygen concentration.

These masks are rarely placed by EMS practitioners, but you might encounter them during transfers.

A simple face mask is indicated for patients requiring moderate oxygen concentrations.

Side ports allow room air to enter the mask and dilute the oxygen concentration during inspiration.

Flow rates generally range from about 6 to 10 L/min, providing 40 to 60 percent oxygen at the maximum rate depending on the patient’s respiratory rate and depth.

Delivery of volumes beyond 10 L/min does not enhance oxygen concentration.

These devices are rarely carried by EMS practitioners but can be encountered during transfers.

A partial rebreather mask is indicated for patients requiring moderate-to-high oxygen concentrations when the simple face mask does not obtain satisfactory clinical results.

One-way disks that cover the partial rebreather mask’s side ports prevent the inspiration of room air.

Minimal dilution occurs with inspiration of residual expired air along with the supplemental oxygen.

Maximal flow rate is 10 L/min.

A nonrebreather mask has one-way side ports as well as an attached reservoir bag to hold oxygen ready to inhale.

It provides the highest oxygen concentration of all oxygen delivery devices available, about 80 percent when set at 15 L/min of oxygen and the mask is fit tightly to the face.

EMS commonly uses these masks for initial management of patients with high oxygen requirements.

Any patient who requires a nonrebreather should be closely monitored for refractory hypoxemia that requires invasive or noninvasive positive-pressure ventilation.

Nebulizer chambers containing 3 to 5 mL of fluid are attached to a face mask that allows for delivery of medications in aerosol form (nebulization) that is more likely to pass through the upper airway to the lower airways.

Pressurized oxygen or air enters the chamber to create a mist, which the patient then inspires.

Oxygen is the usual carrier but air is occasionally used for COPD patients, and a helium–oxygen mixture can be used in patients with upper airway obstruction.

You can provide humidified oxygen to the patient by attaching a sterile water reservoir to the oxygen outlet.

Humidified oxygen is often given to pediatric patients with upper airway problems such as croup, although there is no evidence that it improves outcomes.

Humidification is also useful for patients receiving long-term oxygen therapy to prevent the complications of drying out the mucous membranes.

Humidification is rarely necessary in the EMS setting.

Positive airway pressure (PAP) is delivered via a face mask to maintain a constant level of pressure within the airway; it assists a patient in breathing by preventing collapse of the airway during inhalation.

Continuous positive airway pressure (CPAP) maintains a steady level of pressure during both inhalation and exhalation.

Bilevel positive airway pressure (BiPAP) maintains a higher level of pressure during inhalation and a lower level during exhalation.

CPAP and BiPAP devices can be used to administer oxygen in conjunction with increased airway pressures.

Positive end-expiratory pressure (PEEP) is an adjunct to ventilation methods (bag-valve mask, extraglottic airways, and endotracheal intubation).

It is delivered by a simple valve attached between the ventilatory device and the face mask or advanced airway (Figure 22-41).

PEEP valves can provide adjustable levels of pressure added to the end of expiration.

They can improve oxygenation by recruiting and maintaining additional alveoli that might have been closed due to atelectasis.

High levels of PEEP can also increase intrathoracic pressure and can depress cardiac output, so their use must be titrated as needed for oxygenation.

Think of PEEP for ventilated patients as doing the same thing that CPAP and BiPAP do for spontaneously ventilating patients.

All of them—PEEP, CPAP, BiPAP—create back-pressure to help keep alveoli open and improve oxygenation.

High-flow nasal cannula (HFNC) devices can deliver humidified oxygen noninvasively at a much higher flow rate (typically between 40 and 60 lpm) than by a standard nasal cannula.

These are special devices that differ from the nasal cannulas typically used by EMS.

(Figure 22-42).

They are often well tolerated and used in patients who cannot tolerate mask-dependent devices such as CPAP or BiPAP.