LAUSR

Hypoventilation is a spectrum of respiratory disorders that is frequently found in patients with chronic obstructive pulmonary disease, restrictive lung disease (eg obesity, neuromuscular, severe interstitial lung disease, and chest wall disease), chronic sedative use, and hypothyroidism. Rapid eye movement (REM) sleep hypoventilation may be the first manifestation of hypoventilation prior to development of non-REM sleep hypoventilation and eventual awake alveolar hypoventilation. We present a case of hypoventilation during REM sleep with mild restriction on pulmonary function testing, prior to the development of obesity hypoventilation syndrome (OHS). 68-year-old male with past medical history of diastolic heart failure, class Ill obesity (BMI 46), hypertension, chronic kidney disease lllb, and diabetes mellitus underwent split night polysomnography for evaluation of snoring, witnessed apneas and excessive daytime sleepiness. The study was significant for an apnea hypopnea index of 105/hour, and REM sleep sustained desaturation to a nadir of 72% without apneas or hypopneas, suspicious for hypoventilation. The derangements during REM sleep did not correct during PAP titration despite CPAP and supplemental oxygen. End tidal capnography was not available for the study. Follow up PFT demonstrated normal spirometry, mild restrictive lung volumes, ERV 27%, and severely depressed DLCO which corrected for alveolar volume. Daytime arterial blood gas did not reveal hypercapnia or hypoxemia (7.37/39/78/23). He underwent successful nocturnal titration with average volume assured pressure support with the final settings of IPAP 24-30, EPAP 20, VT 560 (8 ml/kg IBW), rate of 12 breaths per minute and no supplemental oxygen. This patient demonstrates REM sleep hypoventilation without overt OHS during all stages of sleep, which likely would progress to OHS over time. OHS is associated with increased rates of chronic heart failure, pulmonary hypertension, hospitalizations for respiratory failure, and mortality. Early recognition and treatment are important in improving morbidity and mortality.