Autoadjusting Continuous Positive Airway Pressure
What Can We Expect?

Patrick Lévy and Jean-Louis Pépin

Sleep Laboratory and Respiratory Disease Department, University Hospital and Joseph Fourier University, Grenoble, France

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Since 1996, there have been technologies that allow automatic adjustment of continuous positive airway pressure (CPAP) for treatment of obstructive sleep apnea (OSA) (1). There are many factors that influence overnight pressure needs in a given individual, including sleep structure, sleeping position, physiological changes in nasal resistance, and fluctuations in body weight. Moreover, it has been assumed that a significant reduction in CPAP pressure may improve compliance with treatment due to a reduction in side effects or improvement in comfort, although there are nearly no data to support such an hypothesis until now (1).

Several parameters have been used to drive autoadjust CPAP, using either pressure or flow signals available inside the machine that allow the detection of apneas, hypopneas, snoring, and flow limitation. The forced oscillation technique (FOT) is a very promising concept allowing a continuous measure of upper airway (UA) impedance. A single threshold of impedance may be used to drive the device without any need to identify specific respiratory events (5).

In the first March issue of the Journal (pp. 652-657), Randerath and coworkers evaluated an original autoadjusting CPAP system based on FOT (6). In a randomized crossover study, they compared the effects of autoadjusting positive airway pressure (APAP) and constant CPAP on sleep-disordered breathing, sleep structure, and treatment compliance in more than 50 patients over a 6-wk period.

Identification of sleep-disordered breathing was based on thermistors placed under the CPAP mask, as a pneumotachometer inserted in the CPAP line might have altered the application of FOT. This method of measurement and a desaturation criterion of 4% make the scoring of hypopneas very insensitive (7)specifically when looking at residual events while using CPAP. Scoring of respiratory events, however, was equally insensitive under both constant CPAP and APAP conditions.

Overall, APAP, driven by FOT, was effective in correcting respiratory disturbances and improving sleep structure (6), and it was comparable with published data on other intelligent CPAP systems (1, 8). The reduction in microarousals while using APAP also supports its efficacy. There is a need, however, for additional information on whether residual hypopneas and upper airway resistance events occur while using APAP based on FOT. There was no difference in treatment compliance between the fixed CPAP or APAP. This confirms previous results regarding CPAP compliance using an autoadjusting system (1), apart from one study showing a significant improvement in a small subset of patients with OSA (3). It does not support the suggestion that an autoadjusted system would improve compliance with CPAP. That compliance did not decrease with APAP suggests that relatively long-term use is possible without major technical or medical problems (9). A lack of significant improvement in compliance with CPAP was expected in a nonselected sample of patients with OSA because use of CPAP is relatively high when all published data are taken into account (2, 10) and cannot be easily further improved.

When APAP was initially introduced, the main objective was to achieve a significant reduction in the pressure required to abolish apneas and hypopneas and restore sleep microstructure. However, the changes in pressure found overnight in a population of patients with OSA are variable. The variability in pressure is not systematic and the proportion of patients displaying significant variability remains unknown. This variability is not necessarily associated with a significant reduction in mean pressure when using APAP systems. In the present study, a reduction in mean pressure was observed, although the 95% percentile in pressure was not reduced; this suggests that the variability in pressure was high, especially toward high levels of pressure. This was also found in several studies in which a reduction in mean pressure was limited or absent (1).

For patients compliant with constant CPAP, the data confirm that there is probably little or no advantage for use of an APAP device. If the preference data are explained at least in part by the prolonged periods of low pressure, patients with the greatest variability in pressure would be the best candidates for such a device. This has already been suggested by us (11) and others, but never demonstrated. It would be helpful to evaluate the benefit of APAP in patients who comply poorly. If an optimal educational and technical intervention has already been achieved, a reduction in mean airway pressure with use of an APAP device might increase compliance by improving comfort.

The limitations of any autoadjusting CPAP device are relatively well known. Occurrence of mouth or mask leaks above a given threshold, rapid alternation between sleep and wake periods, or occurrence of central hypopneas all lead to partial or ineffective adjustment of pressure. This usually results in prolonged periods of high pressure that aggravate both leaks and sleep instability. None of these conditions appeared to occur frequently in the present study, but this concern requires further investigation.

This raises the question of the limitations of FOT in driving autoadjusted CPAP. It is necessary to determine whether FOT should be used in isolation or in combination with pressure or flow signal analysis. A systematic evaluation of the efficacy of an FOT autoadjusting device on respiratory events and sleep structure in large studies of unselected OSA patientswhich has never been done for any available APAP systemis required before advocating its routine use. In a recent review, APAP systems were recommended for patients with uncomplicated OSA and for those unable to tolerate standard CPAP (2), although further safety data are required (2). Any APAP system needs to be tested under conditions of normal breathing, central sleep apnea, periodic breathing, rapid eye movement (REM) hypoventilation, and positional OSA. In patients demonstrating a significant number of central events, increases in pressure are often inadequate and typically these patients are usually not good candidates for APAP (1, 2). Subjects with respiratory insufficiency are at risk of prolonged REM hypoventilation, which is not usually detected by APAP devices (1). The reactions of a given APAP system cannot be predicted, and it has to be studied under all conditions to ensure safe use for both titration and long-term treatment.

The traditional approach when diagnosing OSA and prescribing CPAP is to devote a full night polysomnogram both to the diagnostic study and to manual CPAP titration. Costs might be reduced by using APAP to perform titration, which could be done either in the ward or at home (12), and then used for 1 or 2 wk at home with systematic clinical follow-up (2, 11). This would allow selection of patients with the highest variability on the basis of more than a single test night. These patients may represent the best candidates for long-term use of an autoadjusted device. Most patients who do not exhibit significant overnight pressure variability may conversely use a constant pressure, that is, close to the 95 percentile maximum pressure. The preference of the patient can also be further tested. This will never replace careful educational, technical, and medical follow-up, which is the key for success with CPAP treatment. But optimal adjustment to individual needs can be expected.

	Footnotes

	References

TOP ARTICLE REFERENCES

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