Nocturnal hypercapnia with daytime normocapnia in patients with advanced pulmonary arterial hypertension awaiting lung transplantation.

BACKGROUND: Pulmonary arterial hypertension (PAH) is frequently complicated by sleep disordered breathing (SDB), and previous studies have largely focused on hypoxemic SDB. Even though nocturnal hypercapnia was shown to exacerbate pulmonary hypertension, the clinical significance of nocturnal hypercapnia among PAH patients has been scarcely investigated. METHOD: Seventeen patients with PAH were identified from 246 consecutive patients referred to Kyoto University Hospital for the evaluation of lung transplant registration from January 2010 to December 2017. Included in this study were 13 patients whose nocturnal transcutaneous carbon dioxide partial pressure (PtcCO2) monitoring data were available. Nocturnal hypercapnia was diagnosed according to the guidelines of the American Academy of Sleep Medicine. Associations of nocturnal PtcCO2 measurements with clinical features, the findings of right heart catheterization and pulmonary function parameters were evaluated. RESULTS: Nocturnal hypercapnia was diagnosed in six patients (46.2%), while no patient had daytime hypercapnia. Of note, nocturnal hypercapnia was found for 5 out of 6 patients with idiopathic PAH (83.3%). Mean nocturnal PtcCO2 levels correlated negatively with the percentage of predicted total lung capacity (TLC), and positively with cardiac output and cardiac index. CONCLUSION: Nocturnal hypercapnia was prevalent among advanced PAH patients who were waiting for lung transplantation, and associated with %TLC. Nocturnal hypercapnia was associated with the increase in cardiac output, which might potentially worsen pulmonary hypertension especially during sleep. Further studies are needed to investigate hemodynamics during sleep and to clarify whether nocturnal hypercapnia can be a therapeutic target for PAH patients.

Continuous carbon dioxide partial pressure monitoring in lung transplant recipients.

BACKGROUND: Living-donor lobar lung transplantation (LDLLT) recipients often have hypercapnia preoperatively, which confers a risk of worsened hypercapnia intraoperatively. We reviewed our experience with continuous carbon dioxide partial pressure (PtcCO2) monitoring in LDLLT to evaluate its accuracy and feasibility. We also assessed preoperative and intraoperative carbon dioxide levels in LDLLT recipients. MATERIAL AND METHODS: Twenty-six LDLLT recipients without pulmonary hypertension underwent preoperative nocturnal and intraoperative PtcCO2 monitoring, determined with a TOSCA-500 monitor. RESULTS: Maximal preoperative nocturnal PtcCO2 (72.7 ± 19.3 mmHg) was significantly correlated with preoperative resting arterial carbon dioxide partial pressure (PaCO2; 55.1 ± 11.6 mmHg, r(2)=0.84). PtcCO2 was more correlated with PaCO2 (range, 39-192 mmHg) during LDLLT (r(2)=0.93) than with end-tidal carbon dioxide partial pressure (r(2)=0.38). Intraoperative continuous PtcCO2 monitoring was useful for evaluating real-time carbon dioxide levels. Intraoperative PtcCO2 did not exceed maximal preoperative nocturnal PtcCO2 in 13 recipients (50%) but temporarily exceeded it in 11 recipients (42%). PtcCO2 was further elevated in 2 recipients (8%) requiring the early establishment of cardiopulmonary bypass. There were no complications related to PtcCO2 monitoring. CONCLUSIONS: PtcCO2 monitoring in LDLLT recipients is useful as a means for determining intraoperative carbon dioxide levels, which increase dramatically and can be predicted preoperatively and assessed in a timely manner.