Clinical heterogeneity among patients with obesity hypoventilation syndrome: therapeutic implications.

BACKGROUND: Obesity hypoventilation syndrome (OHS) can be treated with noninvasive positive pressure ventilation (NIPPV). Once clinical stability is achieved, continuous positive airway pressure (CPAP) can be recommended in many cases. However, some patients respond only partially to CPAP and NIPPV is a better option for them.

OBJECTIVES: To assess treatment effectiveness in 2 groups of patients: those who could be switched to CPAP after polysomnographic titration and those who required NIPPV.

METHODS: A prospective study of 24 OHS patients was conducted, 11 were treated with CPAP and 13 with NIPPV. Morning and evening arterial blood gases were measured. Daytime and overnight oximetric recordings were performed. A post hoc analysis compared both groups.

RESULTS: Neither group exhibited deterioration on morning-to-evening blood gases. All patients in the CPAP group presented SaO(2) of less than 90% (CT90%) for <15% of the time on nocturnal and daytime recordings. In the NIPPV group, 8 patients had either daytime or nocturnal CT90% >or=15%. There were no intergroup differences regarding age, body mass index, Epworth scale values or PaO(2)/PaCO(2) prior to treatment. FVC in the NIPPV group was lower than in the CPAP group (p = 0.01). Apnea-hypopnea index was higher (56 +/- 23 vs. 36 +/- 23, p = 0.049) and baseline CT90% was lower (76 +/- 19% vs. 92 +/- 14%, p = 0.03) in the CPAP group.

CONCLUSIONS: Two patient subtypes can be identified. Those controlled with CPAP have better spirometry and a significantly higher apnea-hypopnea index. None of these patients showed daytime hypoxemia and all exhibited satisfactory overnight oxygenation. However, 61% of the NIPPV group had suboptimal oximetry results. Nocturnal/diurnal oximetries should be made to assess treatment efficacy in stable OHS patients who fail to achieve good control with CPAP.