Contribution of Transcutaneous P_CO2 in Obesity Hypoventilation Syndrome

Background: More and more patients have obesity-hypoventilation syndrome (OHS) because of the increasing prevalence of obesity. The accuracy of transcutaneous P_CO2 (P_tcCO2 ) has recently been validated. However, no study evaluated the interest of measuring systematically nocturnal P_tcCO2 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_tcCO2 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_aCO2 > 45 mm Hg or bicarbonate ≥ 27 mmol/L, S_pO2 < 90% for ≥ 10% of the night, or P_tcCO2 > 49 mm Hg for ≥ 10% of the night.

Results: A total of 32 subjects were included. Twenty-nine subjects with nocturnal P_tcCO2 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 with transcutaneous capnography. Only one subject presented with hypoventilation symptoms (asthenia).

Conclusions: The assessment of P_tcCO2 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.