Patients with nocturnal hypoventilation are at risk of developing daytime ventilatory failure. As a result, this finding has therapeutical implications. Currently, assessment of nocturnal hypoventilation is performed using nocturnal oximetry (NO) coupled to diurnal arterial blood gases (ABG). Even if theoretically useful, transcutaneous PCO2 (TcPCO2) monitoring is not routinely used. Therefore, its role should be defined. Objectives: To compare NO coupled to ABG versus TcPCO2 for detecting alveolar hypoventilation in a cohort of chronic respiratory failure patients. Methods: We performed 153 NO coupled to a TcPCO2 recording (91 under non invasive ventilation and 62 during spontaneous breathing) in 98 patients. In addition, ABG were performed during spontaneous breathing. Aetiologies of respiratory failure were: neuromuscular disorder (97 traces), thoracic cage abnormalities (35 traces) and lung disease (21 traces). Nocturnal hypercapnia was defined by a nightime mean PtcCO2 ≥ 50 mmHg, nocturnal hypoxemia as ≥30% of the night spent with a SaO2 45 mmHg. Results: Combined normal NO and normal ABG underestimated nocturnal hypercapnia in >50% of both spontaneously breathing and ventilated patients. Conversely, nocturnal hypoxemia was associated with nocturnal hypoventilation in 100% of non ventilated patients but only in 50% of ventilated ones. Conclusion: Normal values of nocturnal oximetry and/or ABG do not allow to exclude nocturnal hypoventilation. Our results underline the interest of performing nocturnal TcPCO2 monitoring to evaluate patients at risk of nocturnal hypoventilation.
Nguyen-Baranoff et al. (Thu,) studied this question.