Obstructive sleep apnea syndrome (OSAS) is characterized by fruitless respiratory efforts after repetitive airway occlusion during drowsiness and sleep, determining respiratory pauses longer than 10 seconds that may be accompanied by oxygen desaturation. Medullary respiratory centers and ascendant reticular system are activated, with concomitant awakening and resumption of airflow. Obstruction relieve is usually accompanied by loud snoring.1

Clinical case: important contact loss presented by an 81 yo patient in ICU. EEG showed alternating periods of drowsiness accompanied by loud snoring and short wakefulness.  Oronasal thermocouple confirmed apnea (OSAS). (Figures 1 & 2)

Sleep specialist was consulted and clear improvement occurred after CPAP installation. EEG is no polysomnography substitute, but may raise the question, and orient the necessity of evaluation. It is important to consider this diagnosis, especially in old aged patients. Besides, alternating EEG rhythms from drowsiness to wakefulness was nicely explained.


Figure 1. 30 seconds page from top to bottom: 18 EEG channels (montage on the left), sensitivity 7 µV/mm, filters 0,5 – 70 Hz, 1 channel for respiration (oronasal thermocouple) and 1 for EKG. Respiration channel during drowsiness shows a flat line for 30 seconds; the apnea lasted longer. Right side figure shows slow waves predominance on 4 CSA (Compressed Spectral Array) channels comparing left x right and anterior x posterior regions, and video recording below.


Figure 2. Same patient showing that after 25 seconds respiration resumes, accompanied by loud snoring.


Broughton RJ. Polysomnography: Principles and Applications in Sleep and Arousal Disorders. in Nierdermeyer E, Silva FL editors. Electroencephalography: Basic Principles, Clinical Applications, and Related Fields. 4th ed. Philadelphia: Lippincott Williams & Wilkins, 1999. p. 858-895.