Background: Obesity-hypoventilation syndrome (OHS) is associated with significant morbidity and mortality compared to obstructive sleep apnea syndrome (OSAS) without hypercapnia; and is often under-diagnosed. The aim of this study was to determine possible differences of OHS and to assess long term prognosis of those patients compared to normocapnic obese with OSAS.
Methods: Retrospective study on 107 obese (BMI >30 kg/m2) patients with apnea-hypopnea syndrome (AHI >15/h) under long term observation in a specialized outpatient clinic. At observation onset, 49 were hypercapnic in awake and were characterized as OHS patients after excluding other diseases, while the rest 58 OSAS patients served as controls. Anthropometric characteristics were recorded, as well as medical history, pulmonary function tests, arterial blood gases, daytime sleepiness [assessed by Epworth Sleepiness Scale (ESS)], apnea hypopnea index (AHI), mean SpO2 during sleep, mode of non-invasive mechanical ventilation (NIV), kind of interface, long term oxygen therapy conditions, patients’ compliance with therapy over time and survival.
Results: Significant differences were observed in terms of BMI (46.36±8.64 vs. 42.03±8.28 kg/m2, P<0.05), PaO2 (62.6±9.37 vs. 67.83±7.52 mmHg, P<0.05) and HCO3 concentration (31.35±3.86 vs. 25.22±3.33 mmol/lt, P<0.05). On the contrary, no significant difference was observed in age, gender, spirometric results, AHI, mean nocturnal SpO2 and ESS. Coronary heart disease was more prevalent in OHS (22.2% vs. 4.9%, P<0.05). The majority of patients with OHS used biphasic mechanical ventilation modes, via full face mask, received oxygen therapy, nocturnal and during daytime with a statistically important correlation. The majority of patients in both groups continued mechanical ventilation therapy, but discontinuation was more likely to occur in men, younger patients, and patients with lower ESS. Survival curves did not differ between the two patient groups (P=0.788).
Conclusions: OHS should be suspected in OSAS patients with increased BMI and HCO3 concentration, low daytime PaO2 levels and a medical history of coronary heart disease. However, compliance to long term therapy and survival of OHS patients under NIV does not differ from those of normocapnic obese patients.
