CPAP or Continuous Positive Airway Pressure, is a method of applying positive pressure to the upper airway to prevent it from collapsing during sleep. 'Positive pressure' is the pressure inside a balloon when it is blown up; it is pressure greater than the surrounding, or ambient air pressure. Air at a higher pressure than ambient will travel to any region that has a lower air pressure; hence when positive air pressure is pushed through the nose, it travels down the throat where the air pressure is lower. As a result, the air flows from the nose down into the lungs and keeps the upper airway from collapsing during sleep.

All this is accomplished via a 'CPAP' mask that fits over the nose, so air can't escape around the nose. The mask is connected via a hose to a small pump -- the CPAP machine -- which plugs into a standard electrical socket. Thus the CPAP machine or "pump" functions like any other small electrical appliance.

CPAP works, and is now the standard therapy for obstructive sleep apnea. For specific medical indications, see Indications for Positive Airway Pressure Treatment of Adult Obstructive Sleep Apnea Patients, in the medical journal Chest, Vol. 115, March 1999, pages 863-866.

The history of CPAP is interesting. It was first reported for sleep apnea in 1981 (Sullivan CE, Issa FG, Berthon-Jones M, Eves L. Reversal of obstructive sleep apnea by continuous positive airway pressure applied through the nares. Lancet 1981;1:862-5.) However, it was not until the mid 1980s that CPAP began to be accepted for sleep apnea. Since then there have been steady technologic improvements in three areas: the CPAP machine itself, the nasal mask and strap arrangements, and humidification. The machines have become much smaller and quieter. The masks have been made far more comfortable for the user, and strap arrangements have improved. Finally, for patients with some nasal problems, heated humidification added to the system has increased compliance.

Another advance is the gradual acceptance among payors that CPAP works, so that now CPAP is usually covered by health insurance. However, there are still issues in this area. One is the amount of coverage; some companies require a co-pay that the patient can't afford. Another issue is the degree of sleep apnea that will trigger insurance reimbursement; mild cases are often not covered. It is also true that some HMO insurance plans will (perversely) pay for a sleep study but not pay for "durable medical equipment," so that the patient is not reimbursed for the machine. Finally, of course, millions of people have no insurance coverage, yet would greatly benefit from CPAP.

In any case, the huge volume of CPAP now in use in the U.S., and the fairly wide insurance coverage, has led to a viable business. Many companies now market CPAP machines. This competition breeds product improvement and better service, all to the patient's benefit. It is now fairly routine for CPAP apparatus to be delivered to the patient's home, and fully set up with hands-on instructions, all within 24 hours of a physician's order.

There is no doubt that nasal CPAP is the "gold standard" for treating obstructive sleep apnea. But to be effective it must be used for most of the night, and every night (or, for shift workers with sleep apnea, whatever part of the day they sleep). According to the ACCP consensus statement, adequate use of CPAP is defined as greater than 4.5 hours per night on a routine basis.

Perhaps 50% of patients quit using CPAP within the first year. The main reasons are inconvenience and discomfort. Most of these problems are solvable by finding a mask that fits properly, a machine with acceptable noise level, and (not least) a patient's understanding of the sleep problem.

Principal advantages of CPAP, besides its benefit for OSA, are that it can give immediate relief, is painless, and can be stopped instantly if not tolerated. This is in contrast to surgery, which is invariably painful, and can't be reversed if the procedure is ineffective.

There are many makes and models of CPAP machines. They are priced from a few hundred dollars to over $2000. The fancier models come with many bells and whistles, and as a rule are quieter than cheaper models.

In the last few years machines have been introduced that can determine the optimum pressure for the patient. These so-called 'auto-CPAP' machines HAVE NOT gained wide acceptance, for several reasons. One reason is that no study has shown them to be more effective than using a set pressure throughout the night. Also, these machines are much more expensive than conventional (fixed pressure) devices. Until there are studies proving the clear superiority of auto CPAP over fixed CPAP machines, the latter will continue to dominate the CPAP market.

The CPAP mask is a critical part of the CPAP treatment. Masks can cost anywhere from $100 to $200 depending on the make and model. If you cannot get comfortable with the mask or the mask does not fit properly, you will not be able to obtain the full benefits of CPAP. The standard CPAP mask is made of silicone and forms a seal over the nose. Some patients find the newer gel-filled masks more comfortable and obtain a better seal with them. Other patients feel too claustrophobic with their nose covered and prefer the "nasal pillows" which has 2 silicone fittings that go directly into the nostrils. The oils in the face will break the silicone down after 6 - 8 months, and the mask must then be replaced. Gel-filled masks tend to be more durable. Newer designs may incorporate features that allow you to replace only the worn out parts.

Problems with CPAP are mainly from intolerance (a feeling of claustrophobia is common). Other problems are facial pressure soreness from too tight a fit, noise (mainly from older, cheaper machines), dryness of mouth and throat (often alleviated with humidity which can be added to the circuit), and, rarely, nasal bleeding and sinus infection.

The three biggest obstacles to effective CPAP are:

	Poor patient tolerance/compliance. The patient is capable of using the machine, but finds it too discomforting or bothersome;
	Inability to use the machine. The patient is willing but simply unable to strap it on every night. This is often a problem with elderly and demented patients;
	Inadequate or no insurance reimbursement. The patient is willing, but because of lack of proper insurance (e.g., requirement of co-pay which the patient can't afford), or no insurance, or loss of insurance, the machine is not available.

Another important aspect of CPAP therapy is the supplier, i.e., the company that delivers the CPAP machine and mask, sets it up in the home, instructs the patient on proper use, and then responds to any problems that may arise. The major equipment problem most patients encounter is the CPAP mask. The mask is like a new pair of shoes; the first pair you try on (or the 2nd or 3rd) may not fit. The patient should be prepared to change the mask, or the strap arrangement (or even the machine if it is too noisy or has some malfunction). The company has to serve the patient. Most companies do this well, but some patients have quit using CPAP because of poor company response to their complaints.