Continuous positive airway pressure (CPAP) is non-invasive positive pressure ventilation (NIPPV) that helps improve the work of breathing and oxygenation for individuals with different cardiopulmonary complaints related to primary respiratory or cardiovascular complaints. The concept of positive pressure ventilation started in the 1930s and gained momentum in the 1950s during the polio epidemic. It was not until the 1980s that noninvasive forms of CPAP were adopted to help patients with obstructive sleep apnea and chronic obstructive pulmonary disease. Using CPAP in the prehospital setting gained traction in the late 90s as the primary form of non-invasive positive pressure ventilation as an alternative to endotracheal intubation or supraglottic devices. Over the past several years has become the standard of care of patients with acute respiratory distress in the prehospital setting. Meta-analysis performed by Goodacre et al. shows that there is a reduction in mortality and intubation rates with comparison to standard care.
Initial models of CPAP used a control unit (flow generator) attached to the oxygen source to produce the necessary positive pressure. Newer models of CPAP devices deliver a specific amount of pressure based on either adjustment of a control valve (PEEP valve) or by adjusting the amount of flow that is delivered to produce the necessary positive end-expiratory pressure (PEEP). These newer models have all the necessary parts built into the device and subsequently, have a significantly reduced cost versus the original devices. The newer devises are smaller, cheaper and more intuitive to use.
With each breath a person takes, the negative intrathoracic pressure causes the alveoli and distal pulmonary structures to collapse (similiar to deflating a balloon) but with patients that have stiff lungs [chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis patients] there is an abnormal residual pressure due to air trapping referred to as auto-PEEP (positive end-expiratory pressure).Usage of continuous positive airway pressure allows for a constant pressure throughout the ventilatory cycle (inspiration and expiration phases) and does not allow for the alveoli to completely collapse during the exhalation phase. This positive pressure will reduce the surface tension on the walls of the alveoli by increasing the intrathoracic pressure which helps to reduce the work of breathing. Similarly, there is also an increase in the surface area of the alveoli which allows for an increase in gas exchange. The positive pressure from CPAP allows for individuals to overcome the auto-PEEP and will help reduce the work-of-breathing. With the increase in intrathoracic pressure, there is also a reduction in preload coming back to the heart which allows for a fluid shift out of the lungs and back into the pulmonary vasculature.
Individuals that can breathe spontaneously throughout the complete respiratory cycle can use CPAP. The primary function of non-invasive positive-pressure ventilation is to improve pulmonary compliance, improve alveoli aeration by recruiting and stabilizing collapsed alveoli, and ultimately improve ventilation-perfusion mismatches. Continuous positive airway pressure increases intrathoracic pressure which in turn reduces venous return (preload), transmural pressure, and afterload. This ultimately allows for enhancement in cardiac function and reduces pulmonary edema.
Common indications for CPAP include
Absolute contraindications for non-invasive, positive-pressure ventilation include cardiac arrest, respiratory arrest, coma, or any condition requiring immediate intubation.
Relative contraindications for non-invasive, positive-pressure ventilation include:
There are multiple commercial grade devices available for the prehospital providers that combine the flow generator with the face mask as a disposable product. The major brand of devices includes the Pulmodyne and Flow-Safe II. The Pulmodyne CPAP device has an attached PEEP valve that can be adjusted for a maximum of 10 cm of water. The Flow-Safe II was created using a venturi effect where an increase in airflow turbulence causes an increase in pressure. Both of these devices have a closed circuit nebulization features. Philips Respironics created a nasal CPAP device (ComfortFusion Nasal) that is supposed to be more comfortable for patients.
Common settings for prehospital NIPPV include an inspiratory pressure of 5 to 10 cm water with an expiratory pressure of 5 cm water. Patients with asthma, bronchitis, COPD usually start with a pressure of 5 cm water versus those with congestive heart failure (CHF), severe pneumonia and pulmonary edema due to near-drownings at 10 cm water. With these levels, the work of breathing can be reduced by as much as 60% and have an improvement of inspiratory muscle endurance up to 95%.
The scope of practice for emergency management service (EMS) providers over the years have changed with the 2018 National EMS Scope of Practice Model introduced by the National Highway Traffic Safety Administration further delineates the roles of the prehospital providers. Due to the advances with CPAP, EMT's have lost some of their skills in relation to intubation and the need to perform invasive airway techniques. The original 2007 Practice Model for EMS providers had CPAP/BiPAP as paramedic skills. With the 2018 National EMS Scope of Practice Model, the use of CPAP has been transferred to the level of an emergency medical technician. Further more, in most states, the emergency management technician (EMT) is allowed to use a CPAP device with appropriate training and approval from their medical director.
Most patients who have used a noninvasive positive-pressure ventilation device before need a little education about the device. It is the patient who has never used the device before or the ones that are anxious who will need help to ensure that they do not "fight" the device. The full face mask devices can cause some claustrophobe feelings for patients. Education and coaching from the medical provider are important for the patient to become comfortable and use the device. When dealing with a patient that is in an acute respiratory distress situation the prehospital provider will need to assemble the NIPPV device quickly. Ensure that the device is attached to a properly filled oxygen source because the majority of the devices will use a large amount of oxygen (refer to specific manufacturers devices) in a short period of time. Initially, just apply the mask to the face of the patient and coach them to take in deep breaths. Once the patient can tolerate the mask, then you can apply the head strap. Reassess the patient frequently for improvement in their respiratory status, lung sounds and how well they are tolerating the device.
Apply the mask to the face of the patient and coach them to take in deep breaths. Once the patient can tolerate the mask, then you can apply the head strap. Reassess the patient frequently for improvement in their respiratory status, lung sounds and how well they are tolerating the device.
Complications of NIPPV include patient discomfort, anxiety, and agitation, pulmonary barotrauma (ie pneumothorax), hypotension (secondary to increased intrathoracic pressure and reduced preload) gastric distention (usually with elevated inspiratory positive airway pressure greater than 20 cm water) leading to abdominal compartment syndrome. Most of these problems can be alleviated by using the lowest, safest setting that provides results. Hypotension can be treated with either administration of intravenous (IV) fluids.
Non-invasive positive pressure ventilation and continuous positive pressure ventilation provides clinical significance with patients in acute respiratory distress from a number of etiologies, but the mainstay treatment for prehospital providers has been for those individuals with congestive heart failure and COPD. In the 1998 article from Pang et al., they performed a literature review that demonstrated a reduction in the need for invasive ventilation with the use of CPAP devices.  Ucgun et al. demonstrated that the most important predictor of mortality in the COPD patient pertains to invasive ventilation and complications related to mechanical ventilation.  Nielsen et al. showed through a regional observational study that the use of CPAP improved SpO2 and reduced respiratory rate from arrival at the scene to arrival at the hospital. 
Continuous Positive Airway Pressure (CPAP) was originally intended to be used for the patients with polio and then sleep apnea, but since the 1990s the use of CPAP was introduced into the prehospital setting and has changed the outcome of several disease processes. Since the original Scope of Practice Model for EMS providers, prehospital providers and physicians have been conducting research to show the efficacy of non-invasive ventilation in the prehospital setting. The research conducted has been overwhelming positive where the 2018 EMS Scope of Practice Model concludes to use CPAP at the EMT level and above.
The EMS Scope of Practice Model along with the EMS Agenda for the future shows the value and need for prehospital providers to be educated to perform the skills with most training programs being accredited by the Commission on Accreditation of Allied Health Education Programs (CAAHEP), then certified as competent with most states requiring an initial certification through the National Registry of EMT, and the majority of states allowing prehospital providers to perform non-invasive ventilation as a minimum scope of practice with medical directors credentialling the prehospital providers to perform this skill. The trend for use of non-invasive ventilation in the prehospital setting has since pushed emergency medicine physicians, nurses, respiratory therapist and hospitals to adopt a similar practice method of use of non-invasive ventilation in the hospital setting. Education on the use of non-invasive ventilation has become a collegial endeavor between prehospital and hospital providers.