The First Night

Sleeping with a nasal mask applied to the face, along with feeling the pressure sensation of CPAP, although not necessarily uncomfortable, are certainly novel experiences for most patients. Physician explanation, video programs, and mask "acclimatization" sessions prior to commencing CPAP are routine in many centers. Although the benefits of these approaches have not been fully scientifically evaluated, it would seem obvious that patient education about CPAP will reduce anxiety and improve acceptance. Current evidence provides some support for the benefit of more intensive patient education in CPAP usage (17,21). Thus, patient exposure to CPAP actually may begin prior to the first full night of therapy.

On the first night of treatment, it is important to ensure that the CPAP level that is identified as most therapeutically effective is sufficient not only to prevent apnea and oxyhaemoglobin desaturation (Fig. 3) but also to prevent respiratory-related arousals in all sleep stages and postures of sleep. Thus, simple apnea prevention is not the sole endpoint of CPAP titration. It is important to ensure that the airflow-CPAP pressure measurement is competent so as to avoid residual partial airway obstruction (7). An abnormal or technically challenged tracing (e.g., amplifier saturation, clipped signals) presents an opportunity for failure in detection of flow limitation and snoring. It is important to treat residual flow limitation as it may indicate upper airway obstruction, potentially causing arousal (22). Studies have emphasized the importance of proper airflow measurement in CPAP titration using pressure-based airflow transducers rather than thermistors or other more indirect airflow measures (23). Proper airflow measurement could help determine the optimal CPAP level by providing insights regarding the etiology of arousals; whether they are related to respiratory events (respiratory-related arousals) and if increasing pressure has a beneficial effect on sleep continuity. Although acute (one-night) studies suggest that flow limitation correction may be the preferred endpoint of CPAP

FIGURE 3 All-night recordings of arterial hemoglobin saturation in one of the earliest patients to use home continuous positive airway pressure (CPAP). (A) Control night. (B) CPAP trial night. A CPAP of 7 cm H2O was applied at arrow A and continued for the rest of the night. Source: From Ref. 2.

titration, long-term data are sparse (24). Furthermore, pursuing normalization of the RDI may not be the only or even optimal goal in CPAP titration strategies in some OSA patients, who exhibit a cyclic alternating pattern non-rapid eye movement (NREM) sleep stage respiratory instability and who are relatively nonresponsive to CPAP (25). Prediction equations for starting pressures may enhance the success of titration studies (26) and also potentially offer the option of an effective outpatient setting titration strategy for CPAP-providing health services (27-30). Heated humidification appears not to offer any advantages during nasal CPAP titration studies (31).

When the correct CPAP level is reached and the airway is open, sleep should no longer be fragmented by repetitive arousals. There is often substantial "rebound" augmentation of slow-wave and rapid eye movement (REM) sleep (32). This rebound phase of recovery from prior severe sleep fragmentation lasts about a week; the duration and intensity of this rebound decrease quickly after the first night of treatment (32). The improvement in basic aspects of sleep architecture is usually immediate and can be used as a sign of an effective CPAP level. Also, following the time course of more detailed analysis of sleep pattern reorganization beyond the first night of treatment under the influence of CPAP therapy may provide a novel adjunct to conventional CPAP titration (33).

Continued frequent arousals may indicate that a critical level of upper airway resistance persists, especially if associated with flow limitation. Continued snoring is another sign of inadequate CPAP pressure. There are data demonstrating that hysteresis exists in the CPAP-upper airway resistance relationship. In other words, to eliminate inspiratory flow limitation, higher pressures are required during upward titration of CPAP compared with downward titration from higher pressures (34). This means that an OSA patient may actually normalize their breathing during sleep at a lower CPAP level if manual or automatic titration involves both upward titration till airflow is sinusoidal in shape, and downward titration till obstructed events recur. This may be an important concept in patients with complications of CPAP due to higher CPAP levels (such as mask or mouth leak) or a problem if an auto-titrating CPAP does not allow for this "up-then-down" titration approach.

Considering the length of time CPAP has been used to treat patients with sleep apnea, there are surprisingly little published data on the variability in CPAP pressure with posture or sleep stage. Some evidence exists for higher pressure requirements with the supine posture (35) and REM sleep (36). It appears that a CPAP level accurately set on one night is generally effective on subsequent nights (37). Early work and clinical experience suggested this was the case, but the use of auto-titrating CPAP (auto-CPAP) technology in the home has provided the research methodology to support this view (38). Clinically, in patients who respond immediately to CPAP but then report continued daytime sleepiness on home treatment, it may be appropriate to empirically increase CPAP pressure, assuming that the laboratory study underestimated the subsequent "domiciliary" CPAP pressure requirement. However, this has not been specifically studied. There is also a range of factors which may have an impact on the therapeutic efficacy of a given CPAP pressure in the home. Weight gain may lead to a need for a higher CPAP setting (39). Heavy, but not moderate, alcohol consumption may affect CPAP pressure, presumably owing to the effect of alcohol in depressing upper airway neuromuscular tone (40). Nasal congestion, alterations in levels of daily fatigue, or a different posture in the home may also lead to different pressure requirements but this has not been well researched.

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