Nocturnal hypercapnia in the patients with idiopathic interstitial pneumonia registered for lung transplantation.

BACKGROUND

Respiratory failure in idiopathic interstitial pneumonia (IIP) is mainly non-hypercapnic hypoxia, although hypercapnia also occurs in advanced stages. Although sleep-disordered breathing in IIPs is drawing attention, the role of nocturnal hypercapnia remains largely unknown. In this study, we aimed to clarify whether nocturnal hypercapnia in patients with advanced IIPs is associated with the clinical characteristics.

METHODS

We retrospectively analyzed 41 patients with IIPs who underwent nocturnal transcutaneous carbon dioxide partial pressure (PtcCO2) monitoring during the evaluation for lung transplantation eligibility. Nocturnal hypercapnia was diagnosed according to the American Academy of Sleep Medicine criteria. Associations between nocturnal hypercapnia and clinical features including comorbidities such as PH, radiographic features, and pulmonary function tests were assessed.

RESULTS

Fourteen patients (34.1%) met the criteria for nocturnal hypercapnia, exhibiting decreased normal lung volume and frequent use of long-term oxygen therapy (LTOT) during sleep. Lower percent predicted vital capacity (%VC) correlated with mean PtcCO2 and PtcCO2>55 mmHg time during sleep. Nocturnal hypercapnia was significantly associated with increased PH complications, higher pulmonary vascular resistance (PVR), and higher mean pulmonary artery pressure (P = 0.010, P = 0.023, and P = 0.045, respectively). Pleuroparenchymal fibroelastosis-like CT features were associated with daytime hypercapnia; however, the frequency of nocturnal hypercapnia among these patients was not significantly higher compared with other patients.

CONCLUSION

Nocturnal hypercapnia is prevalent in advanced IIPs and is linked to reduced normal lung volume, LTOT during sleep, and low %VC. PH was observed more frequently in these patients. Further studies should elucidate the therapeutic potential of nocturnal hypercapnia in IIPs.