Childhood Adenotonsillectomy Trial

6.6.6 PSG Scoring Process

Following initial review by the CP, each study will be assigned to one of two scorers for scoring of sleep and breathing on an epoch by epoch basis, visualizing each epoch on a high resolution monitor, using customized software that allows flexibility in choosing specific signals for visualization. Assignments will vary so that each scorer is presented equal numbers of studies from each site. During this phase, the scorer completes quality code assessments (Signal Quality form) assigning each data channel a quality code grade according to the duration and quality of signals collected, and each study will be given an aggregate quality grade based on the overall interpretability and duration of artifact-free signals. Other data are coded that are not captured in the computerized scored report (e.g., periodic breathing, alpha intrusion, etc.). This form will be data entered and available for the site and DCC to access using assigned passwords.

Detailed criteria as well as algorithms for sleep staging, arousal detection, and marking of hypopneas and apneas, with example tracings and events, have been developed for various studies supported by the PRC, including pediatric sleep studies. Sleep/wake sleep stages are scored as recommended with the appropriate modification for children. Arousals are scored using published guidelines. All respiratory events (obstructive, mixed, and central apneas and hypopneas) must have a clear beginning and end, are marked from trough to trough and must last the equivalent of at least two respiratory cycles and a minimum duration of 5 secs. Obstructive apneas are identified as absence of airflow on the thermistor channel. Mixed apnea will be scored when the airflow is flat (or nearly flat) and the event has central apnea portion followed by an obstructive apnea portion. Hypopneas are scored when there is ≥ 50% decrease in the summed respiratory inductance signal or in a reliable nasal pressure signal. Central apneas are scored when the amplitude of both effort and airflow signals are flat (or nearly flat). SpO2 measurements associated with a poor pulse waveform and P_ETCO₂ values from waveforms with poor plateaus are marked as artifact. After apneas and hypopneas are identified, software links each event to data from the saturation and EEG channels. Although the primary sleep apnea outcome is the AHI based on pediatric ATS criteria, software provides additional indices that allow assessment of events characterized according to various degrees of associated desaturation and arousal.

The customized software provides summary measures: Respiratory events: Summarized by respiratory event type, duration, associations with level of desaturation, arousal, position, and sleep stage. Dividing the total number of specific events by sleep duration provides the: obstructive apnea index; obstructive apnea hypopnea index, central apnea index; Percent time in apnea or hypopnea. Oximetry: The SpO2 nadir, mean SpO2, and percent of total sleep time during which SpO2 is < 95%, 92%, 90%, 85%, 80%, 75%, 70%. All discrete oxygen desaturations of ≥ 2%, 3%,4%, and 5% from baseline, or any values < 95%, 90%, 85% and 80% are tabulated by stage and position. Capnography: The mean, peak and the percent of total sleep time during which P_ETCO₂ are ≥ 45 and ≥ 50 mm Hg are tabulated by stage and position; Sleep Architecture: Time in each sleep stage; Sleep efficiency (% of the sleep period that the subject was asleep) and latency (time to onset of sleep); REM latency (onset of sleep to first REM); Leg movements: Identified as 0.5-10 sec. bursts of increased amplitude. A periodic limb movement index is calculated based on the number and pattern of limb movements (≥ 4 movements, each separated by 5-90 secs.). EEG arousals: Arousal index (number/sleep hour), number of upward stage shifts (from deeper to lighter) and wake shifts (number of sleep to wake transitions), expressed as total per hour of sleep and by sleep stage (REM vs non-REM) and body position. Arousals will be identified according to whether they followed a respiratory event (within 3 secs. of the event termination); Heart Rate (HR) Maximum, minimum and mean HR in sleep, associated with respiratory events and/or with arousals (REM vs non-REM). Note on scoring and archiving: After studies are scored and initial reports and processing are completed, studies are archived in duplicate at the PRC and DCC (i.e., removed from the individual computers of scoring staff.) Since repeat studies will occur 7 months after the original study, there is virtually no chance that any given scorer will recall the scores of the initially scored study.