Patient and Equipment Preparation for Polysomnographic Testing
Before the patient arrives
Preparation starts at scheduling. Confirm the indication, obtain informed consent, and collect a sleep diary (usually 1–2 weeks) plus a full medication list - sedatives, stimulants, opioids, and antidepressants all reshape the tracing (many antidepressants suppress REM and increase chin EMG tone). Ask about caffeine, alcohol, and nicotine, and screen for allergies (latex, adhesive). Instruct the patient to wash and dry the hair, avoid lotions or gels, keep usual sleep–wake habits, and follow the ordering provider's instructions about holding or continuing medications. Document everything; a study whose medication status is unknown may be uninterpretable.
Sensors and the electrode–skin interface
A routine montage includes EEG (F4-M1, C4-M1, O2-M1 with backups), EOG (E1-M2, E2-M1 - referenced to the opposite mastoid), chin EMG (submental, with redundancy), leg EMG (tibialis anterior), modified lead II ECG, nasal pressure and oronasal thermal airflow, thoracic and abdominal effort, pulse oximetry, snore, and body position. Skin preparation is the single biggest determinant of signal quality: mild abrasion plus degreasing, then measure impedance at each electrode. Values below about 5 kΩ are the working target; anything above roughly 10 kΩ should be redone before lights out.
Traps in questions
Distinguish disinfection from sterilization; distinguish DC (calibration) channel checks from physiologic calibration; remember impedance is measured after application, not before. A high-impedance electrode is a preparation problem, not a paste problem.
Rule of thumb
If a channel looks noisy or flat, re-check the electrode–skin interface first - prep and impedance explain more bad channels than amplifier settings do.