When it comes to choosing a CPAP device, there are a host of designs and options available.
1 _ Type of flow
CPAP devices are one of two types: those that run constantly and those that flow only when the pressure drops below a certain level. The constant-flow devices provide CPAP by ensuring that there’s more air/oxygen flow than the circuit and mask can accommodate. The excess is vented through the PEEP valve.
Constant-flow devices require that the system has no leaks in the circuit or at the mask/face seal. Otherwise, flow escapes through the leak and the predetermined level of pressure may not be attained.
Demand-type CPAP devices generate air/oxygen flow only when the pressure within the breathing circuit drops below a set threshold. This occurs when the system has a leak and, of course, when the patient breathes in.
2 _ Oxygen consumption
The rate of oxygen consumption will affect how long you’ll be able to provide CPAP on a cylinder. It also will affect your budget. The rate at which a CPAP device consumes O2 depends on its design. Constant-flow devices consume oxygen at a faster rate than demand-type devices. In addition, some constant-flow devices, such as the Bousignac and OxyPeep, the desired CPAP pressure depends on the oxygen flow rate from the cylinder.
Some constant-flow and demand-type devices can be set to provide less than 100% oxygen, which will result in decreased oxygen consumption.
3 _ Oxygen concentration
The primary benefit of CPAP is that it improves ventilation, which is dependent on work of breathing and not on oxygen delivery. Choosing a device that provides less than 100% oxygen is acceptable as it’s always possible to administer additional supplemental oxygen to the patient by applying a nasal cannula under the mask.
4 _ Pressures
CPAP devices deliver pressure through one of two means. Either the flow rate is in excess of the patient’s need—in which case a PEEP valve is attached to the exhalation port—or the desired amount of pressure is selectable from a control and flow is generated until that level of pressure is reached.
Devices in the first group may use a single valve or include an additional PEEP valve to ensure the pressure listed on them won’t be exceeded. Devices in the second group have a variable PEEP selector that allows for titration of the desired amount of pressure.
There’s no magic number for the proper amount of PEEP, although adverse events tend to occur with pressures exceeding 20 cm H2O. Some patients may tolerate and even improve clinically at levels of 2 cm H2O.
The ability to titrate the amount of pressure provides greater flexibility in CPAP use. Devices that allow variable pressures should include an accurate pressure gauge to allow appropriate monitoring of CPAP pressures.
5 _ Circuits
Some CPAP devices use proprietary circuits that only function with a specific device, while others allow the circuit to be interchanged with other systems. This issue has caused many agencies to choose the non-proprietary circuits.
However, there are two reasons to favor proprietary circuits. First, these circuits are most often used with demand-type CPAP devices. Demand-type devices usually require some form of pressure monitoring within the circuit, and the circuits are specifically designed for this reason.
Second, although it may be tempting to think that non-proprietary circuits will be used on other systems, the reality is that once most patients arrive at the hospital, the respiratory therapist will most likely switch out the entire circuit for one designed for the hospital’s CPAP/BiPAP machine.
Another issue to consider when examining CPAP circuits is whether a filter can be placed on the exhalation port. This is essential when using CPAP on a patient with a suspected infectious condition, such as influenza or tuberculosis. This filter shouldn’t alter the CPAP dynamics of the pressures generated.
6 _ Masks
The key to successful CPAP application is to not have leaks in the system. Tight-fitting straps can help, but they may be uncomfortable for the patient, increasing their anxiety. When evaluating CPAP masks, make sure the mask will provide a comfortable—yet effective—fit to the patient’s face.
7 _ In-line nebulization of bronchodilators
CPAP use with COPD and asthma patients should be combined with the administration of bronchodilators. To facilitate the process, the CPAP circuit and/or mask should allow for the easy introduction of a T-piece nebulizer set that doesn’t require significant and time-consuming modifications.
8 _ CPAP/ventilator Combinations
The number of inexpensive transport ventilators that also provide CPAP is growing. The same issues regarding the CPAP component apply. However, agencies can realize significant cost savings by combining the two functions.
Excellent data is available to support the use of transport ventilators during and following cardiac arrest resuscitation. For more information, see the 2010 AHA Guidelines on CPR and ECC at http://static.heart.org/eccguidelines/2010-guidelines-for-cpr.html
9 _ Ease of use
It’s important for a CPAP device to be easily assembled and used in the field. Involve your providers in field testing prospective units.
10 _ Funding options
Cheaper isn’t always better. If a device doesn’t meet your clinical criteria for reliable CPAP delivery, any savings are offset by the fact that more patients might require intubation and ICU admission.
Some hospitals have agreed to purchase CPAP units and/or generators for all EMS services. Although one such program in Houston cost the hospital system more than $250,000 to implement, they were able to recoup this cost within six months by decreasing ICU admissions.(1)
1. Hewitt MJ, Persse DE. A CPAP partnership that makes sense: Hospital and EMS system form a unique agreement. JEMS. 2009;1:S20–S21.
Memorial Hermann Hospital. Largest hospital system in Texas and local EMS launch unique partnership to provide non-invasive intervention in congestive heart failure patients: Memorial Hermann healthcare system and Houston Fire Department EMS collaboration to serve as a model for the nation. www.memorialhermann.org/newsroom/content.aspx?id=268
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This article originally appeared in the January 2011 JEMS supplement “CPAP: The push for rapid relief” as “Purchasing Power: Consider these 10 tips when choosing a CPAP device.”