Evaluation of respiratory insufficiency in patients with amyotrophic lateral sclerosis through transcutaneous carbon dioxide monitoring

Introduction: Nocturnal hypoventilation is a frequent and early manifestation of respiratory involvement in Amyotrophic Lateral Sclerosis (ALS), a progressive neurodegenerative disease with variable onset and evolution. Objectives: This study investigates the use of transcutaneous carbon dioxide (TcCO₂) monitoring as a non-invasive tool for early detection of nocturnal hypoventilation in ALS patients, to optimize the timing of non-invasive ventilation (NIV) initiation and potentially improve prognosis. Methods: Forty ALS patients (22 males, 18 females; age range 52–80 years) underwent cardio-respiratory monitoring, pulmonary function tests, arterial blood gas analysis and overnight TcCO₂ monitoring. Results: The prevalence of hypoventilation varied depending on the criteria used. Only 2.5% of patients (1/40) had daytime arterial CO₂ (PaCO₂) >45 mmHg, while 35.3% (12/40) showed a peak TcCO₂ ≥49 mmHg during the night. Notably, one-third of patients with normal daytime CO₂ levels exhibited nocturnal hypoventilation detectable only via TcCO₂ monitoring. Conclusions: Early identification of nocturnal hypoventilation in ALS is essential to initiate NIV before daytime respiratory failure ensues. Transcutaneous carbon dioxide monitoring is a sensitive, non-invasive method to detect early nocturnal respiratory insufficiency, even in patients with normal daytime gas exchange. Although a universally accepted definition of nocturnal hypoventilation is still lacking, TcCO₂ monitoring may play a key role in guiding clinical decisions and improving patient outcomes.