|Sleep Apnea - CPAP (BiPAP) therapy|
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CPAP (BiPAP) therapy
Regardless of the mechanism used it is desirable to use the lowest possible pressure to eradicate the sleep apnea. In most cases, positive airway pressure is easier to tolerate at lower pressures. Every patient requires a different pressure. To determine precisely the individual patient's optimum airway pressure, it is necessary to titrate the pressure to each individual patient during a polysomnogram. A polysomnogram will show not only when the respiratory events have ceased, but also when the arousals from the respiratory events occur.
PAP therapy, the more common of the three therapy modes, usually is administered at bedtime through a nasal or facial mask held in place by Velcro straps around the patient's head. The mask is connected by a tube to a small air compressor about the size of a shoe box. The CPAP machine sends air under pressure through the tube into the mask, where it imparts positive pressure to the upper airways. This essentially "splints" the upper airway open and keeps it from collapsing.
Approximately 55% of patients who use CPAP do so on a nightly basis for more than 4 hours. It is the most commonly prescribed treatment for OSA. The advantages of CPAP are that it is very safe and completely reversible. Generally, it is quite well tolerated. The main disadvantage is that it requires active participation every night; that is, patient compliance is necessary for it to work.
Mask fitting is an essential element of a patient's success with positive airway pressure therapy since it affects compliance and effectiveness of treatment. Higher pressures can result in air leak and patient discomfort. Demands on mask stability increase as pressure increases. Higher pressures may also require tighter head gear to maintain an adequate seal contributing to the discomfort. When selecting a CPAP mask the following factors should be considered:
Side effects of CPAP include contact dermatitis, skin breakdown, mouth leaks, nasal congestion, runny nose (rhinorrhea), dry eyes, nose bleeds (rare), tympanic membrane rupture (very rare), chest pain, difficulty exhaling, pneumothorax (very rare), smothering sensation, and excessive swallowing of air (aerophagia).
Nasal congestion often can be reduced or eliminated with nasal steroid sprays and humidification placed into the machine. Rhinorrhea can be eliminated with nasal steroid sprays or ipratroprium bromide nasal sprays. Epistaxis is usually due to dry mucosa and can be combatted with humidification. Dry eyes are usually caused by mask leaks and can be eliminated by changing to a better fitting mask.
Autotitration devices are designed to provide the minimum necessary pressure at any given time and change that pressure as the needs of the patient change. Autotitration devices respond to different parameters and rely on different algorithm so they do not all operate the same.
The AutoSet® by ResMed acts by monitoring the patient's inspiratory flow-time curve. A flattening of the inspiratory flow-time curve typically precedes an upper airway obstruction, which causes apnea, hypopnea, or snoring. Monitoring and responding to the flow-time curve, reduces the number of respiratory events and arousals improving sleep quality.
Bi-level positive airway pressure is a variation of CPAP. Most of the problems patients experience with CPAP are caused by having to exhale against a high airway pressure. Because the air pressure required to prevent respiratory obstruction is typically less on expiration than on inspiration, bi-level positive airway pressure machines are designed to sense when the patient is inhaling and exhaling and to reduce the pressure to a preset level on exhalation. Bi-level positive airway pressure machines usually are used when the patient does not tolerate CPAP or when the patient has more than one respiratory disorder.