Positive airway pressure
From Wikipedia, the free encyclopedia
Positive airway pressure (PAP) is a method of respiratory ventilation used primarily in the treatment of sleep apnea, for which it was first developed.
PAP ventilation is also commonly used for critically ill patients in hospital with respiratory failure, and in newborn infants (neonate). In these patients, PAP ventilation can prevent the need for endotracheal intubation, or allow earlier extubation.
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[edit] Machine
A PAP machine is used mainly by patients at home for the treatment of sleep apnea. Obstructive sleep apnea occurs when the patient's airway becomes restricted as the muscles relax naturally during sleep. This restricts breathing and causes arousal from sleep. The PAP machine stops this phenomenon by delivering a stream of compressed air via a face mask and hose, splinting the airway (keeping it open under air pressure) so that unobstructed breathing becomes possible, reducing and/or preventing apneas and hypopneas.
The PAP machine blows air at a prescribed pressure (also called the titrated pressure). The necessary pressure is usually determined by a physician after review of a study supervised by a sleep technician during an overnight study (polysomnography) 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 (cm H2O). A typical PAP machine can deliver pressures between 4 and 20 cm H2O. More specialized units can deliver pressures up to 25 or 30 cm H2O.
PAP treatment can be highly effective in treating obstructive sleep apnea. For some patients, the improvement in the quality of sleep due to PAP treatment will be noticed after a single night's use.
Prospective CPAP candidates can be reluctant to use this therapy, since the face mask and hose to the machine look uncomfortable and clumsy, and the airflow required for some patients can be vigorous. Some patients adjust to the treatment within a few weeks, others struggle for longer periods, and some discontinue treatment entirely.
Therapy compliance on the part of the patient can be improved with support from a durable medical equipment (DME) provider,[citation needed] including allowing the patient his or her choice of PAP devices. 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.
[edit] Types
- CPAP (Continuous Positive Airway Pressure) provides one constant pressure to the patient
- APAP or AutoPAP (Automatic Positive Airway Pressure) 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.
- VPAP™ or BiPAP® (Variable/Bilevel Positive Airway Pressure) provides two levels of pressure: one for inhalation (IPAP) and a lower pressure during exhalation (EPAP)
- xPAP ST (Spontaneous Time) is a machine that forces a number of set breaths per minute and is used to treat patients with central apneas.
[edit] Components
- Flow generator (PAP machine) provides the compressed air
- Hose connects the flow generator (sometimes via a humidifer) to the inferface
- Interface (mask) provides the connection to the user's airway
[edit] Optional features
- Humidifier adds moisture to the 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.
- 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 can increase patient comfort by eliminating the dryness of the compressed air.
- Ramp is used to temporarily lower the pressure to allow the user to fall asleep more easily. 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® in some PAPs made by Respironics and EPR™ in ResMed machines.
- Data logging records basic compliance info or detailed event logging, allowing the sleep physician (or patient) to download and analyze data recorded by the machine to verify treatment effectiveness.
Such features generally increase the likelihood of PAP tolerance and compliance.
[edit] 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 weekly maintenance. Units must be checked regularly for wear and tear and kept clean. 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. 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.
[edit] Portability
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, nPAP units are becoming lighter and more compact, and often come with carrying cases. Dual-voltage power supplies permit many units to be used internationally.
Air travel 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.
Some patients on PAP therapy also use supplementary oxygen. When provided in the form of bottled gas, this can present an increased risk of fire and is subject to restrictions. As of November, 2006, most airlines permit the use of oxygen concentrators.
[edit] Availability
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The examples and perspective in this article or section may not represent a worldwide view of the subject. Please improve this article or discuss the issue on the talk page. |
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 doctor, who may be a Respiratory Medicine, Ear Nose and Throat (ENT) or Neurology specialist, will interpret the results from the initial sleep study and estimate the correct pressure from experience. This is later confirmed with a follow up sleep study during which 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, 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 Medicaid. 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 program, 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, PAP machines are available on National Health Service prescription after a diagnosis of sleep apnea or privately from the internet provided a prescription is supplied.
- In Australia, PAP machines can be bought from internet or physical stores on the provision of a prescription from a doctor. Low-income earners who hold a Commonwealth Health Care Card should enquire with their state's health department about programs that provide free or low-cost PAP machines. Those who have private health insurance are usually eligible for a partial rebate on the cost of a CPAP machine. 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 your specialist, and an application to the Australian Prudential Regulation Authority (APRA).
[edit] In a hospital setting
PAP ventilation is often used for patients who have acute type 1 or 2 respiratory failure. Usually PAP ventilation will be reserved for the subset of patients for whom oxygen delivered via a face mask is deemed to be insufficient or deleterious to health (see CO₂ retention). Usually, patients on PAP ventilation will be closely monitored in an intensive care, high dependency, coronary care unit 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 airways disease, most notably exacerbations of COPD and asthma. It is not used in cases where the airway may be compromised, or consciousness is impaired.
The mask required to deliver CPAP must have a tight seal, and be held on very firmly. Most people find wearing the mask uncomfortable. Breathing out against the positive pressure resistance (the expiratory positive airway pressure component, or EPAP) is also unpleasant. These factors lead to inability to continue treatment due to patient intolerance in about 20% of cases where it is initiated. Obviously those who suffer an anxiety disorder or claustrophobia are more likely to be unable 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 and pharynx, PAP is used in hospital to improve the ability of the lung to exchange oxygen and carbon dioxide, 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 be required to re-expand them. This is because of the law of Laplace (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). The chest and lungs are therefore more expanded. From this more expanded resting position, less work is required to inspire. This is due to the non-linear compliance-volume curve of the lung.
[edit] The neonate
CPAP is commonly used in the term and preterm neonate with respiratory disease or with recurrent apnea. Often this form of PAP is referred to as bubble cpap, because bubbles are used to generate a high frequency oscillation in the expiratory phase (EPAP). These bubbles dramatically aid ventilation by establishing bidirectional flow of air in the smaller airways. Other differences to CPAP in the adult include lower pressures (usually around 5cm of water), and the use of snug fitting nasal prongs (a mouth component is not required as neonates are obligate nasal breathers).
Respiratory diseases for which CPAP is commonly used include infant respiratory distress syndrome, meconium aspiration syndrome and Transient tachypnea of the newborn. Sometimes it is used for the treatment of bronchiolitis in the older neonate or younger infant. It is not known how CPAP prevents recurrent neonatal apneas.
PAP is used to prevent premature infants from going into respiratory failure thereby preventing the need for intubation. [1]
When compared to ventilation via an endotracheal tube, CPAP seems to result in less barotrauma (although it by no means eliminates the risk of barotrauma) and in the extreme preterm, CPAP reduces the risk of developing Bronchopulmonary dysplasia when compared to mechanical ventilation via an endotrachea tube.
