Continuous positive airway pressure
Positive airway pressure (PAP) is a mode of respiratory ventilation
Modes of mechanical ventilation
Modes of mechanical ventilation are one of the most important aspects of the usage of mechanical ventilation. The mode refers to the method of inspiratory support. Mode selection is generally based on clinician familiarity and institutional preferences since there is a paucity of evidence...

 used primarily in the treatment of sleep apnea
Sleep apnea
Sleep apnea is a sleep disorder characterized by abnormal pauses in breathing or instances of abnormally low breathing, during sleep. Each pause in breathing, called an apnea, can last from a few seconds to minutes, and may occur 5 to 30 times or more an hour. Similarly, each abnormally low...

, for which it was first developed. PAP ventilation is also commonly used for those who are critically ill in hospital with respiratory failure
Respiratory failure
The term respiratory failure, in medicine, is used to describe inadequate gas exchange by the respiratory system, with the result that arterial oxygen and/or carbon dioxide levels cannot be maintained within their normal ranges. A drop in blood oxygenation is known as hypoxemia; a rise in arterial...

, and in newborn infants (neonates). In these patients, PAP ventilation can prevent the need for tracheal intubation
Tracheal intubation
Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic or rubber tube into the trachea to maintain an open airway or to serve as a conduit through which to administer certain drugs...

, or allow earlier extubation. Sometimes patients with neuromuscular diseases use this variety of ventilation as well. CPAP is an acronym for "continuous positive airway pressure", which was developed by Dr. George Gregory and colleagues in the neonatal intensive care unit at the University of California, San Francisco. A variation of the PAP system was developed by Professor Colin Sullivan at Royal Prince Alfred Hospital
Royal Prince Alfred Hospital
The Royal Prince Alfred Hospital is a major public teaching hospital in Sydney, Australia, located on Missenden Road in Camperdown...

 in Sydney, Australia, in 1981.


The main indications for positive airway pressure are congestive heart failure
Congestive heart failure
Heart failure often called congestive heart failure is generally defined as the inability of the heart to supply sufficient blood flow to meet the needs of the body. Heart failure can cause a number of symptoms including shortness of breath, leg swelling, and exercise intolerance. The condition...

 and chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease , also known as chronic obstructive lung disease , chronic obstructive airway disease , chronic airflow limitation and chronic obstructive respiratory disease , is the co-occurrence of chronic bronchitis and emphysema, a pair of commonly co-existing diseases...

. There is some evidence of benefit for those with hypoxia
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...

 and community acquired pneumonia.

PAP ventilation is often used for patients who have acute type 1 or 2 respiratory failure
Respiratory failure
The term respiratory failure, in medicine, is used to describe inadequate gas exchange by the respiratory system, with the result that arterial oxygen and/or carbon dioxide levels cannot be maintained within their normal ranges. A drop in blood oxygenation is known as hypoxemia; a rise in arterial...

. Usually PAP ventilation will be reserved for the subset of patients for whom oxygen delivered via a face mask is deemed insufficient or deleterious to health (see CO2 retention
CO2 retention
CO2 retention is a pathophysiological process in which too little carbon dioxide is removed from the blood by the lungs. The end result is hypercapnia, an elevated level of carbon dioxide dissolved in the bloodstream. Various diseases may lead to this state; disturbed gas exchange may lead to...

). Usually, patients on PAP ventilation will be closely monitored in an intensive care unit
Intensive Care Unit
thumb|220px|ICU roomAn intensive-care unit , critical-care unit , intensive-therapy unit/intensive-treatment unit is a specialized department in a hospital that provides intensive-care medicine...

, high dependency unit, coronary care unit
Coronary care unit
A coronary care unit is a hospital ward specialized in the care of patients with heart attacks, unstable angina, Cardiac dysrhythmia and various other cardiac conditions that require continuous monitoring and treatment.-Characteristics:...

 or specialist respiratory unit.

The most common conditions for which PAP ventilation is used in hospital are congestive cardiac failure and acute exacerbation of obstructive airway disease
Airway obstruction
Airway obstruction is a respiratory problem caused by increased resistance in the bronchioles that reduces the amount of air inhaled in each breath and the oxygen that reaches the pulmonary arteries...

, most notably exacerbations of COPD and asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...

. It is not used in cases where the airway
The pulmonary airway comprises those parts of the respiratory system through which air flows, conceptually beginning at the nose and mouth, and terminating in the alveoli...

 may be compromised, or consciousness is impaired. CPAP is also used to assist premature babies with breathing in the NICU setting.

The mask required to deliver CPAP must have an effective seal, and be held on very securely. The "nasal pillow" mask maintains its seal by being inserted slightly into the nostrils and being held in place by various straps around the head. Some full-face masks "float" on the face like a hover-craft, with thin, soft, flexible "curtains" ensuring less skin abrasion, and the possibility of coughing and yawning. Some people may find wearing a CPAP mask uncomfortable or constricting. Breathing out against the positive pressure resistance (the expiratory positive airway pressure component, or EPAP) may also feel unpleasant to some patients. These factors lead to inability to continue treatment due to patient intolerance in about 20% of cases where it is initiated. Some machines have pressure relief technologies that makes sleep therapy more comfortable by reducing pressure at the beginning of exhalation and returning to therapeutic pressure just before inhalation. The level of pressure relief is varied based on the patient’s expiratory flow, making breathing out against the pressure less difficult. Those who suffer an anxiety disorder
Anxiety disorder
Anxiety disorder is a blanket term covering several different forms of abnormal and pathological fear and anxiety. Conditions now considered anxiety disorders only came under the aegis of psychiatry at the end of the 19th century. Gelder, Mayou & Geddes explains that anxiety disorders are...

 or claustrophobia
Claustrophobia is the fear of having no escape and being closed in small spaces or rooms...

 are less likely to tolerate PAP treatment. Sometimes medication will be given to assist with the anxiety caused by PAP ventilation.

Unlike PAP used at home to splint the tongue
The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...

 and pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

, PAP is used in hospital to improve the ability of the lungs to exchange oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, and to decrease the work of breathing (the energy expended moving air into and out of the alveoli). This is because:
  • During inspiration, the inspiratory positive airway pressure, or IPAP, forces air into the lungs—thus less work is required from the respiratory muscles.
  • The bronchioles and alveoli are prevented from collapsing at the end of expiration. If these small airways and alveoli are allowed to collapse, significant pressures are required to re-expand them. This is because of the Young–Laplace equation
    Young–Laplace equation
    In physics, the Young–Laplace equation is a nonlinear partial differential equation that describes the capillary pressure difference sustained across the interface between two static fluids, such as water and air, due to the phenomenon of surface tension or wall tension, although usage on the...

     (which explains why the hardest part of blowing up a balloon is the first breath).
  • Entire regions of the lung that would otherwise be collapsed are forced and held open. This process is called recruitment. Usually these collapsed regions of lung will have some blood flow (although reduced). Because these areas of lung are not being ventilated, the blood passing through these areas is not able to efficiently exchange oxygen and carbon dioxide. This is called ventilation–perfusion (or V/Q) mismatch. The recruitment reduces ventilation–perfusion mismatch.
  • The amount of air remaining in the lungs at the end of a breath is greater (this is called the functional residual capacity
    Functional residual capacity
    Functional Residual Capacity is the volume of air present in the lungs, specifically the parenchyma tissues, at the end of passive expiration...

    ). The chest and lungs are therefore more expanded. From this more expanded resting position, less work is required to inspire
    Inhalation is the movement of air from the external environment, through the air ways, and into the alveoli....

    . This is due to the non-linear compliance
    Pulmonary compliance
    Pulmonary compliance can refer to either dynamic or static lung compliance. Static lung compliance is the change in volume for any given applied pressure...

    –volume curve of the lung.


A major issue with CPAP is non-compliance
Compliance (medicine)
In medicine, compliance describes the degree to which a patient correctly follows medical advice...

. Studies showed that some users either abandon the use of CPAP, and/or use CPAP for only a fraction of the nights.

Prospective PAP candidates are often reluctant to use this therapy, since the nose mask and hose to the machine look uncomfortable and clumsy. Airflow required for some patients can be vigorous. Some patients will develop nasal congestion while others may experience rhinitis
Rhinitis , commonly known as a stuffy nose, is the medical term describing irritation and inflammation of some internal areas of the nose. The primary symptom of rhinitis is nasal dripping. It is caused by chronic or acute inflammation of the mucous membrane of the nose due to viruses, bacteria or...

 or a runny nose. Some patients adjust to the treatment within a few weeks, others struggle for longer periods, and some discontinue treatment entirely. However, studies show that cognitive behavioral therapy at the beginning of therapy dramatically increases compliance—up to 148%. While PAP side effects are a nuisance, serious side effects such as eustacian tube infection, or pressure build up behind the cochlea are very uncommon. Furthermore, research has shown that PAP side effects are rarely the reason patients stop using PAP. There are reports of dizziness, sinus infections, bronchitis, dry eyes, dry mucosal tissue irritation, ear pain, and nasal congestion secondary to CPAP use.

PAP manufacturers frequently offer different models at different price ranges, and PAP masks have many different sizes and shapes, so that some users need to try several masks before finding a good fit. These different machines may not be comfortable for all users, so proper selection of PAP models may be very important in furthering adherence to therapy.

Beards, mustaches, or facial irregularities may prevent an air-tight seal. Where the mask contacts the skin must be free from dirt and excess chemicals such as skin oils. Shaving before mask-fitting may be necessary.

The CPAP mask can act as an orthodontic headgear and move the teeth and the upper and/or lower jaw backward. This effect can increase over time and may or may not cause TMD
Temporomandibular joint disorder
Temporomandibular joint disorder , or TMJ syndrome, is an umbrella term covering acute or chronic inflammation of the temporomandibular joint, which connects the mandible to the skull. The disorder and resultant dysfunction can result in significant pain and impairment...

 disorders in some patients. These facial changes have been dubbed "Smashed Face Syndrome".

Fixed-pressure CPAP

A continuous positive airway pressure (CPAP) machine was initially used mainly by patients for the treatment of sleep apnea at home, but now is in widespread use across intensive care units as a form of ventilation. Obstructive sleep apnea
Obstructive sleep apnea
Obstructive sleep apnea or obstructive sleep apnea syndrome is the most common type of sleep apnea and is caused by obstruction of the upper airway. It is characterized by repetitive pauses in breathing during sleep, despite the effort to breathe, and is usually associated with a reduction in...

 occurs when the upper airway becomes narrow as the muscles relax naturally during sleep. This reduces oxygen in the blood and causes arousal from sleep. The CPAP machine stops this phenomenon by delivering a stream of compressed air via a hose to a nasal pillow, nose mask, full-face mask, or hybrid, splinting the airway (keeping it open under air pressure) so that unobstructed breathing becomes possible, therefore reducing and/or preventing apnea
Apnea, apnoea, or apnœa is a term for suspension of external breathing. During apnea there is no movement of the muscles of respiration and the volume of the lungs initially remains unchanged...

s and hypopneas. It is important to understand, however, that it is the air pressure, and not the movement of the air, that prevents the apneas. When the machine is turned on, but prior to the mask being placed on the head, a flow of air comes through the mask. After the mask is placed on the head, it is sealed to the face and the air stops flowing. At this point, it is only the air pressure that accomplishes the desired result. This has the additional benefit of reducing or eliminating the extremely loud snoring
Snoring is the vibration of respiratory structures and the resulting sound, due to obstructed air movement during breathing while sleeping. In some cases the sound may be soft, but in other cases, it can be loud and unpleasant...

 that sometimes accompanies sleep apnea.

The CPAP machine blows air at a prescribed pressure (also called the titrated pressure). The necessary pressure is usually determined by a sleep physician after review of a study supervised by a sleep technician during an overnight study (polysomnography
Polysomnography , also known as a sleep study, is a multi-parametric test used in the study of sleep and as a diagnostic tool in sleep medicine. The test result is called a polysomnogram, also abbreviated PSG...

) in a sleep laboratory. The titrated pressure is the pressure of air at which most (if not all) apneas and hypopneas have been prevented, and it is usually measured in centimetres of water (cmH2O). The pressure required by most patients with sleep apnea ranges between 6 and 14 cmH2O. A typical CPAP machine can deliver pressures between 4 and 20 cmH2O. More specialised units can deliver pressures up to 25 or 30 cmH2O.

CPAP treatment can be highly effective in treatment of obstructive sleep apnea. For some patients, the improvement in the quality of sleep and quality of life due to CPAP treatment will be noticed after a single night's use. Often, the patient's sleep partner also benefits from markedly improved sleep quality, due to the amelioration of the patient's loud snoring.

Given that sleep apnea is a chronic health issue which commonly doesn't go away, ongoing care is usually needed to maintain CPAP therapy. Based on the study of cognitive behavioral therapy (referenced above), ongoing chronic care management
Chronic care management
Chronic care management encompasses the oversight and education activities conducted by health care professionals to help patients with chronic diseases and health conditions such as diabetes, high blood pressure, lupus, multiple sclerosis and sleep apnea learn to understand their condition and...

 is the best way to help patients continue therapy by educating them on the health risks of sleep apnea and providing motivation and support.

Automatic positive airway pressure

An automatic positive airway pressure device (APAP, AutoPAP, AutoCPAP) automatically titrates, or tunes, the amount of pressure delivered to the patient to the minimum required to maintain an unobstructed airway on a breath-by-breath basis by measuring the resistance in the patient's breathing, thereby giving the patient the precise pressure required at a given moment and avoiding the compromise of fixed pressure.

Bi-level pressure devices

"VPAP" or "BPAP" (variable/bilevel positive airway pressure) provides two levels of pressure: inspiratory positive airway pressure (IPAP) and a lower expiratory positive airway pressure (EPAP) for easier exhalation. (Some people use the term BPAP to parallel the terms APAP and CPAP.) Often BPAP is incorrectly referred to as "BiPAP". BiPAP® is the name of a portable ventilator manufactured by Respironics Corporation, it is just one of many ventilators that can deliver BPAP.
  • Modes
    • S (Spontaneous) – In spontaneous mode the device triggers IPAP when flow sensors detect spontaneous inspiratory effort and then cycles back to EPAP.
    • T (Timed) – In timed mode the IPAP/EPAP cycling is purely machine-triggered, at a set rate, typically expressed in breaths per minute (BPM).
    • S/T (Spontaneous/Timed) – Like spontaneous mode, the device triggers to IPAP on patient inspiratory effort. But in spontaneous/timed mode a "backup" rate is also set to ensure that patients still receive a minimum number of breaths per minute if they fail to breathe spontaneously.


  • Flow generator (PAP machine) provides the airflow
  • Hose connects the flow generator (sometimes via an in-line humidifier) to the interface
  • Interface (nasal or full face mask, nasal pillows, or less commonly a lip-seal mouthpiece) provides the connection to the user's airway

Optional features

  • Humidifier adds moisture to low humidity air
    • Heated: Heated water chamber that can increase patient comfort by eliminating the dryness of the compressed air. The temperature can usually be adjusted or turned off to act as a passive humidifier if desired. In general, a heated humidifier is either integrated into the unit or has a separate power source (i.e. plug).
    • Passive: Air is blown through an unheated water chamber and is dependent on ambient air temperature. It is not as effective as the heated humidifier described above, but still can increase patient comfort by eliminating the dryness of the compressed air. In general, a passive humidifier is a separate unit and does not have a power source.
  • Mask liners: Cloth-based mask liners may be used to prevent excess air leakage and to reduce skin irritation and dermatitis.
  • Ramp may be used to temporarily lower the pressure if the user does not immediately sleep. The pressure gradually rises to the prescribed level over a period of time that can be adjusted by the patient and/or the DME provider.
  • Exhalation pressure relief: Gives a short drop in pressure during exhalation to reduce the effort required. This feature is known by the trade name C-Flex or A-Flex in some CPAPs made by Respironics
    Respironics, Inc.
    Respironics, Inc. is a medical supply company that specializes in products that improve respiratory functions. It is based in the Pittsburgh suburb of Murrysville.-History:...

     and EPR in ResMed
    Founded in Australia, ResMed is now a global manufacturer of products for the treatment of sleep disorders, particularly obstructive sleep apnea . ResMed employs about 2700 employees worldwide, it has direct operations in 18 countries and distribution in more than 50 countries...

  • Flexible chin straps may be used to help the patient not breathe through the mouth (full-face masks avoid this problem), thereby keeping a closed pressure system. The straps are elastic enough that the patient can easily open his mouth if he feels that he needs to. Modern straps use a quick-clip instant fit. Velcro-type adjustments allow quick sizing, before or after the machine is turned on.
  • Data logging records basic compliance info or detailed event logging, allowing the sleep physician (or patient) to download and analyse data recorded by the machine to verify treatment effectiveness.
  • Automatic altitude adjustment versus manual altitude adjustment.
  • DC power source versus AC power source.

Such features generally increase the likelihood of PAP tolerance and compliance.

Care and maintenance

As with all durable medical equipment, proper maintenance is essential for proper functioning, long unit life and patient comfort. The care and maintenance required for PAP machines varies with the type and conditions of use, and are typically spelled out in a detailed instruction manual specific to the make and model.

Most manufacturers recommend that the end user perform daily and weekly maintenance. Units must be checked regularly for wear and tear and kept clean. Poorly connected, worn or frayed electrical connections may present a shock or fire hazard; worn hoses and masks may reduce the effectiveness of the unit. Most units employ some type of filtration, and the filters must be cleaned or replaced on a regular schedule. Sometimes HEPA filters may be purchased or modified for asthma or other allergy clients. Hoses and masks accumulate exfoliated skin, particulate matter, and can even develop mold. Humidification units must be kept free of mold and algae. Because units use substantial electrical power, housings must be cleaned without immersion.

In cold climates, humidified air may require insulated and/or heated air hoses. These may be bought ready-made, or modified from commonly available materials (aluminium foil and bubble-wrap insulation. Noisy machines may be distanced from the sleeper by extension hoses between the machine and the sleeping person).

Modifications are usually needed by the end-user. Straps are easily twisted wrongly (add hot-melt glue or silicone rubber on the "wrong" side). Fittings and buttons are invisible or without adequate sensation in the darkness of the night, so use bright tape or other fittings (self-adhesive children's earrings, masking tape, etc.) to help prevent mistakes.


Since continuous compliance is an important factor in the success of treatment, it is of importance that patients who travel have access to portable equipment. Progressively, PAP units are becoming lighter and more compact, and often come with carrying cases. Dual-voltage power supplies permit many units to be used internationally.

Long-distance travel or camping presents special considerations. Most airport security inspectors have seen the portable machines, so screening rarely presents a special problem. Increasingly, machines are capable of being powered by the 400-Hz power supply used on most commercial aircraft and include manual or automatic altitude adjustment. Machines may easily fit on a ventilator tray on the bottom or back of a power wheelchair with an external battery. Some machines allow power-inverter and/or car-battery powering.

Some patients on PAP therapy also use supplementary oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

. When provided in the form of bottled gas, this can present an increased risk of fire
Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....

 and is subject to restrictions. (Commercial airlines generally forbid passengers to bring their own oxygen.) As of November 2006, most airlines permit the use of oxygen concentrator
Oxygen concentrator
An oxygen concentrator is a device providing oxygen therapy to a patient at minimally to substantially higher concentrations than available in ambient air. They are used as a safer, less expensive, and more convenient alternative to tanks of compressed oxygen. Common models retail at around US$800...



In many countries, PAP machines are only available by prescription. A sleep study at an accredited sleep lab is usually necessary before treatment can start. This is because the pressure settings on the PAP machine must be tailored to a patient's treatment needs. A sleep medicine doctor, who may also be trained in respiratory medicine
In medicine, pulmonology is the specialty that deals with diseases of the respiratory tract and respiratory disease. It is called chest medicine and respiratory medicine in some countries and areas...

, psychiatry, neurology, paediatrics, family practice or otolaryngology (ear, nose and throat), will interpret the results from the initial sleep study and recommend a pressure test. This may be done in one night (a split study with the diagnostic testing done in the first part of the night, and CPAP testing done in the later part of the night) or with a follow up second sleep study during which the CPAP titration may be done over the entire night. With CPAP titration (split night or entire night), the patient wears the CPAP mask and pressure is adjusted up and down from the prescribed setting to find the optimal setting.
  • In the United States
    United States
    The United States of America is a federal constitutional republic comprising fifty states and a federal district...

    , PAP machines are often available at large discounts online, but a patient purchasing a PAP personally must handle the responsibility of securing reimbursement from his or her insurance or Medicare. Many of the internet providers that deal with insurance such as Medicare will provide upgraded equipment to a patient even if he or she only qualifies for a basic PAP. In some locations a government programme, separate from Medicare, can be used to claim a reimbursement for all or part of the cost of the PAP device.
  • In the United Kingdom
    United Kingdom
    The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

    , PAP machines are available on National Health Service
    National Health Service
    The National Health Service is the shared name of three of the four publicly funded healthcare systems in the United Kingdom. They provide a comprehensive range of health services, the vast majority of which are free at the point of use to residents of the United Kingdom...

     prescription after a diagnosis of sleep apnea or privately from the internet provided a prescription is supplied.
  • In Australia
    Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

    , PAP machines can be bought from the Internet or physical stores. There is no requirement for a doctor's prescription, however many suppliers will require a referral. Low-income earners who hold a Commonwealth Health Care Card should enquire with their state's health department about programmes that provide free or low-cost PAP machines. Those who have private health insurance may be eligible for a partial rebate on the cost of a CPAP machine and the mask. Superannuation may be released for the purchase of essential medical equipment such as PAP machines, on the provision of letters from two doctors, one of whom must be a specialist, and an application to the Australian Prudential Regulation Authority (APRA).
  • In Canada
    Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

    , CPAP units are widely available in all provinces. Funding for the therapy varies from province to province. In the province of Ontario, the Ministry of Health's Assistive Devices Program will fund a portion of the cost of a CPAP unit based on a sleep study in an approved sleep lab showing Obstructive Sleep Apnea Syndrome and the signature of an approved physician on the application form. This funding is available to all residents of Ontario with a valid health card once every 5 years.
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