RST common mistakes
RST · Understand the traps and how to avoid them.
Calculating the apnea-hypopnea index by dividing the total number of respiratory events by the total recording time instead of by the total sleep time.
Candidates default to the time the patient was in the lab or the total recording time because it is easier to track, forgetting that AHI is defined per hour of sleep and that sleep time is shorter than recording time.
What to do instead
Before any index calculation, write down total sleep time in hours separately and use only that denominator for AHI, and reserve recording time for the respiratory disturbance index; practice converting stage totals into TST first.
Scoring hypopneas without applying a consistent amplitude-drop threshold and associated desaturation or arousal criterion across the whole record.
Candidates drift between criteria mid-study or apply one rule to one portion of the night and another elsewhere, often because the rule set was memorized incompletely.
What to do instead
State the scoring rule being used at the top of the record and apply a single amplitude threshold plus a single associated-event criterion to every candidate event; recheck borderline events in a second pass.
Mixing up sleep stage scoring rules, such as assigning stage N1 when a K-complex or sleep spindle is present, or misplacing the transition to stage R.
Stage definitions share overlapping features and candidates rely on visual impression rather than verifying the defining criteria for each stage.
What to do instead
For each epoch, verify the defining feature explicitly (spindle or K-complex for N2, low-amplitude mixed-frequency with slow eye movements for N1, rapid eye movements with low chin tone for R) before assigning a stage, and score the epoch according to the majority rule.
Misidentifying arousals by counting movement or artifact as cortical arousal, or missing arousals that follow respiratory events.
Arousals are brief and easily obscured by artifact, and candidates look only at the EEG without correlating chin EMG and respiratory channels.
What to do instead
Require an abrupt shift in EEG frequency lasting at least three seconds with ten seconds of stable sleep preceding it, and confirm with chin EMG increase during REM; scan the two to three seconds after each respiratory event specifically for arousals.
Failing to verify and correct sensor signal quality, such as a loose oximetry probe or a displaced thermistor, before interpreting the study.
Candidates treat artifacts as findings and score events from unreliable channels rather than recognizing signal failure.
What to do instead
Perform a systematic channel-by-channel quality check at the start and end of scoring, document artifact, and exclude or flag periods with unreliable signals instead of scoring events from them.
Confusing obstructive and central respiratory events, especially central events during transition or with Cheyne-Stokes pattern.
Both present as reduced airflow, and candidates rely on the presence of effort without checking whether effort is absent or paradoxical.
What to do instead
Compare thoracic and abdominal effort channels against airflow for every event; absence of effort with airflow reduction indicates central, while continued or increasing effort with airflow reduction indicates obstructive, and note periodic breathing patterns explicitly.
Recommending or interpreting PAP therapy without confirming adherence and residual event data, or ignoring the difference between compliance and efficacy.
Candidates focus on the device being prescribed rather than on whether it is being used and whether it is controlling events.
What to do instead
Always review both usage hours per night and residual AHI or leak data together; treat adequate usage and adequate event control as separate questions before concluding therapy is effective.
Overlooking comorbid conditions and medications that alter sleep, such as untreated depression, thyroid disease, or sedating agents, when interpreting a study.
Candidates interpret the polysomnogram in isolation and do not integrate the clinical history, so they miss contributors to insomnia or daytime sleepiness.
What to do instead
Build a standard intake checklist covering mood, medications, substance use, and medical conditions, and explicitly link each to the sleep findings before forming a clinical impression.
Misapplying the multiple sleep latency test or maintenance of wakefulness test interpretation, such as averaging sleep latencies incorrectly or ignoring REM onset criteria.
Candidates memorize a single cutoff number without understanding the scoring of each nap and the conditions that invalidate a nap.
What to do instead
Score each nap individually, compute mean sleep latency only across valid naps, and apply the REM onset criterion consistently; check that the preceding overnight study and medication washout conditions were met.
Failing to distinguish insomnia disorder from insufficient sleep or another cause of daytime impairment, leading to an incorrect diagnosis.
Candidates equate reported poor sleep with insomnia without checking duration, frequency, opportunity to sleep, and resulting daytime impairment.
What to do instead
Verify the required duration and frequency of difficulty sleeping plus daytime consequences, and rule out inadequate sleep opportunity and other sleep disorders before assigning the diagnosis.