Contribution of Transcutaneous P CO 2 in Obesity Hypoventilation Syndrome

BACKGROUND: Increasing numbers of patients have obesity-hypoventilation syndrome (OHS) because of the increasing prevalence of obesity. The accuracy of transcutaneous P CO 2 ( P tcCO 2 ) has recently been validated. However, no study evaluated systematically measuring nocturnal P tcCO 2 in the follow-up of patients with OHS and home mechanical ventilation to detect residual nocturnal hypoventilation. We aimed to evaluate the contribution of nocturnal P tcCO 2 to assess nocturnal hypoventilation compared with current routine examinations, that is, daytime arterial blood gases and nocturnal pulse oximetry. METHODS: A prospective monocentric pilot study was conducted from August 2018 to November 2019. Patients with stable OHS and who were treated with home noninvasive ventilation for at least 6 months were eligible to participate. After oral consent, we performed both diurnal arterial blood gases and combined home oximetry and capnography. The primary end point was the presence of residual nocturnal hypoventilation, defined as P aCO 2 > 45 mm Hg or bicarbonate ≥ 27 mmol/L, S pO 2 < 90% for ≥ 10% of the night, or P tcCO 2 > 49 mm Hg for ≥ 10% of the night. RESULTS: A total of 32 subjects were included. Twenty-nine subjects with nocturnal P tcCO 2 were analyzed. Eighteen of the 29 subjects showed residual nocturnal hypoventilation. The association of diurnal arterial blood gases and nocturnal pulse oximetry revealed nocturnal hypoventilation in only 9 subjects. Among the 19 subjects with both normal blood gases and normal nocturnal pulse oximetry, 11 had nocturnal hypoventilation detected with transcutaneous capnography. Only one subject presented with hypoventilation symptoms (asthenia). CONCLUSIONS: The assessment of P tcCO 2 in comparison with nocturnal pulse oximetry and arterial blood gases provides important information for the diagnosis of residual nocturnal hypoventilation in the subjects with OHS who were ventilated at home.