In the early days of the COVID-19 pandemic, most physicians treated critically ill coronavirus patients with mechanical ventilation to support damaged lungs. When it became apparent that many mechanically ventilated patients were dying in spite of these measures, research began showing that some patients recovered more quickly using noninvasive positive airway pressure devices, including single-level, continuous positive airway pressure (CPAP) and bi-level (BiPAP) units. This article provides an overview of these technologies, along with safety and purchase considerations.
Noninvasive positive airway pressure units are specialized devices designed to apply continuous, bi-level, intermittent or expiratory positive airway pressure to non-intubated adult, pediatric or neonatal patients. They are commonly utilized on spontaneously breathing patients who require short-term mechanical assistance; however, they are not designed to be life support devices and are not intended to replace basic or advanced mechanical ventilators.
These devices are also referred to by a variety of names, such as bi-level positive airway pressure units, BiPAP units, continuous positive airway pressure units, CPAP units, EPAP units, expiratory positive airway pressure units, intermittent positive air pressure units, intermittent positive pressure breathing units or IPPB units.
CPAP units deliver air or a mixture of air and oxygen (O2) at high flow rates through tubing to a nasal or oral-nasal mask affixed to the patient’s face. These devices use an airflow generator to deliver a continuous supply of gas to the patient at a set pressure, typically between 3 and 20 cm H2O. CPAP units are commonly used to treat patients with obstructive sleep apnea (OSA) or sleep apnea/hypopnea syndrome (SAHS).
Hospitals use specialized CPAP units with advanced functions and features to treat patients with other types of breathing problems, such as acute asthma, cardiogenic pulmonary edema, cystic fibrosis, chronic lung disease and, most recently, COVID-19. When exacerbations of these conditions make breathing more difficult and decrease blood oxygen levels, CPAP with supplemental oxygen may be utilized to facilitate the opening of small airways and improve oxygenation.
While CPAP units deliver pressure continuously at a single previously set level throughout the period of use, BiPAP units can deliver two different levels of pressure during the inspiratory and expiratory phases of a breath. BiPAP allows clinicians to adjust pressures more precisely for maximal benefit.
For most patients, a slightly lower pressure is set during the expiratory phase to reduce the effort required to exhale. By adjusting inspiratory and expiratory time variables, BiPAP units can also synchronize with the patient’s breathing. This can significantly reduce the work of breathing for patients who are struggling.
In hospitals, BiPAP is commonly used as a first-line treatment for patients who need temporary ventilatory support. When effective, BiPAP can noninvasively improve both oxygenation (delivery of oxygen to the blood) and ventilation (removal of CO2 from the blood). If treatment with BiPAP is not effective, intubation and mechanical ventilation is usually necessary.
Principles of Operation
CPAP and BiPAP devices consist of a flow generator or “blower,” a length of tubing and a patient interface (typically a tight-fitting mask). Masks come in three varieties: those that seal against the nostrils, those that cover the entire nose and those that cover both the nose and mouth. Elastic bands that go around the patient’s head hold the masks in place. Commercially available CPAP face masks are pre-formed and available in various sizes and contours. They are made of a hard plastic outer shell with a soft inner-flap seal of vinyl or silicone. Most CPAP and BiPAP units can be used with a variety of mask types as long as the mask allows for passive ventilation of exhaled CO2 through some form of vent. Non-invasive ventilation masks are not safe to use with CPAP or BiPAP since they do not allow for passive venting. Masks may be included with the equipment purchase or sold separately. The mask is attached to plastic tubing, which runs to the flow generator. High flow from the generator acts as a pneumatic airway splint by using gentle pressure, ranging from about 3 to 20 cm H2O.
Most CPAP units are simple to operate and only have controls to set pressure levels. Some CPAP units offer a “pressure ramp” option that starts pressures at a low level (which is more comfortable for the patient), then slowly increases the pressure to the final prescribed level over a period of time (e.g., 15 to 30 minutes) as the patient falls asleep. BiPAP units are more complex than CPAP units. Most have controls to set inspiratory time and pressure, expiratory time and pressure, cycle rate and trigger sensitivity. These settings are specifically prescribed by a physician. Common accessories for CPAP and BiPAP units include humidifiers, O2 analyzers and tubing support arms or stands.
Noninvasive positive airway pressure devices are generally considered safe. No serious problems with long-term use have been documented. Many of the reported problems involving CPAP and BiPAP units arise from air leakage that can cause a lack of pressure, discomfort or irritation related to the fit of the mask, nasal congestion or dryness and loud noise coming from the unit.
Nasal obstruction, increased age, higher body mass index (BMI), central fat distribution and male sex are associated with increased risk of air leakage. Full-face masks are more likely to leak air than nasal masks due to the increased size of the seal. Air leaks are typically fixed by changing the mask type or size and adjusting it properly.
For infection control, CPAP units and masks require regular cleaning and microbiological monitoring. These units can accumulate bacteria and viruses from the patient’s face, hands and environment, which can cause respiratory infections, especially in high-risk populations like low birth-weight infants. Proper cleaning includes cleaning the interface, humidifier and tubing as well as changing water and filters.
Nasal trauma is a frequent complication of CPAP, especially in preterm infants. Nose injuries can range from skin irritation to septal necrosis. They are increasingly common with low gestational age, low birth weight and longer CPAP use.
Stage of Development
Newer generations of CPAP units have built-in software that can monitor usage patterns and patient compliance. Some modern devices monitor the time the devices are used each night and transmit the data to the cloud. At least one manufacturer offers a CPAP device that is completely self-contained and will function without the need for an external power or water source.
Some manufacturers offer facemasks constructed from either cloth or leather that are designed to be more comfortable. Additionally, at least one manufacturer offers a mask that allows the cushion and frame to move independently, to adapt to a user as they change position in sleep and avoid air leaks. Masks with quick release clips are becoming more available; these are designed to make it easier to remove the mask should the patient need to use the restroom or leave their bed during the night. Latex-free masks are now also readily available, as many potential users may be allergic to the material.
This article is adapted from ECRI’s searchable database of technology overviews and product specifications for capital medical equipment. The source article is available online to ECRI members. Learn more at www.ecri.org/components/HPCS. Many additional resources are available through ECRI’s COVID-19 Resource Center, a free public resource to help hospitals protect healthcare workers and patients during the COVID-19 pandemic. Access that site at www.ecri.org/coronavirus-covid-19-outbreak-preparedness-center. To learn more about ECRI’s technology decision support solutions, visit https://www.ecri.org/solutions/technology-decision-support, or contact ECRI at (610) 825-6000, ext. 5891, or by e-mail at email@example.com.
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