How is required positive airway pressure determined for the treatment of sleep-disordered breathing (SDB)?

Updated: Feb 13, 2020
  • Author: Vittorio Rinaldi, MD; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
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The criterion standard for determining the amount of pressure required to restore upper-airway patency is traditionally determined during polysomnography (PSG) by trained technicians. In some centers, this is performed as a split-night study, with data from the first half of the night used for diagnosis of SDB. Once this diagnosis is made, if the RDI is high enough to suggest benefit from initiation of n-CPAP (usually ≥20), the second half of the night’s study is used to determine the optimal amount of pressure.

The disadvantage of the split-night approach is that the second half of a full-night study often reveals more severe sleep apnea, and thus a diagnostic study limited to the first half of the night can underestimate disease severity.

The amount of pressure delivered is reported in centimeters of water. An average starting point for CPAP would be 8-10 cm H2O. Patients report that pressures at these levels feel odd but are tolerable even at the beginning of treatment and become more tolerable as the patients become accustomed to treatment. Higher levels (>15 cm H2O) are often not well tolerated.

When a second overnight study is logistically difficult, some clinicians empirically start a patient on n-CPAP with a pressure of 8-10 cm H2O. Newer n-CPAP machines can sense, on the basis of the patterns of inspiratory airflow, the amount of pressure needed to overcome upper-airway resistance. Patients are sometimes started on these machines without a prior titration study. [80, 81]

Alternatively, an autotitrating machine can be used for several nights, the record of amount of pressure required to suppress apneas and hypopneas can be downloaded and studied, and a suitable nightly pressure can be determined in this fashion. Also, the amount of pressure required to suppress snoring can be used as an audible guide to appropriate pressures.

A patient who routinely takes sedatives or ingests alcohol during the evening and does not intend to change this should probably be tested after continuing their usual nightly routine. n-CPAP titration without sedatives or alcohol is likely to lead to undertreatment of the SDB at home, when such patterns are resumed.

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