Although frequently mentioned as a problem, there is no convincing evidence that the CPAP pressure level actually impairs adherence. Some patients may complain of initial increased resistance to exhalation or the sensation of too much pressure in the nose. For these patients, a CPAP unit with a pressure ramp may be considered. Ramp is a standard feature on most contemporary CPAP devices. The ramp allows the pressure to increase gradually over a set time interval (usually 5-30 minutes) to the optimal CPAP pressure. No studies have been performed to show that a ramp feature improves acceptance or adherence with CPAP; however, interestingly, a case of "ramp abuse" has been reported where continuous patient application of the ramp function led to undertreatment of sleep apnea (65). Alternatively, a BPAP system, in which inspiratory and expiratory positive airway pressure (PAP) can be adjusted independently, may be used, as this approach lowers mean airway pressure and resistance to expiration. Again, it is not clear whether these approaches will improve adherence. Limited data indicate that use of bilevel devices does not affect positive pressure usage in OSA patients (66) (see also Chapter 7). More recently, a novel type of CPAP with reduced expiratory compared to inspiratory pressure has been marketed (C-Flex™, Respironics, Inc., Murrysville, Pennsylvania, U.S.) with no evidence in one study for increased patient adherence using this modality at one month compared to conventional CPAP (67). The researchers report some adherence and other modest advantage in another study at three months follow-up (68). Interim reports [published as abstracts at the Associated Professional Sleep Societies (APSS) Meeting in 2005] of further studies of this device suggest equivalence or marginally better outcomes compared to conventional CPAP (69-73). Further large-scale clinical trials are necessary to determine any definite advantage.
Patients occasionally find the air generated by the CPAP unit too warm or too cold. Initial correction attempts may involve moving the machine from the floor to a bedside table, heating the bedroom, placing tubing under the blankets or the use of a specifically-designed insulated wrap. If these do not correct the problem, incorporating a heated humidifier into the circuit may help. Bed partners may also experience cold air on their bodies from the expiratory port of the device. Employment of an alternative mask or interface may help redirect the stream of air away from the bed partner. Another complaint, also usually from the bed partner is that the CPAP machine generates too much noise. With the newest generation of CPAP devices, the majority of noise is aerodynamic, being generated either through the tubing, or at the patient interface. However, for noisy machines, removing the machine from the bedside or placing it in a closet may remedy the problem. Extra tubing may be needed but it is important to recheck pressures if nonstandard tubing is used. Excessive noise, or a changing level of noise intensity or quality may be a problem in some auto-CPAP devices, as well as in CPAP with expiratory pressure relief, due to the nature of their motor control.
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