Feasibility of Longitudinal Home Monitoring of Nocturnal Transcutaneous CO 2 and Relationship to Standard Respiratory Measures in Patients With ALS : A Pilot Cohort Study

ABSTRACT Introduction/Aims Amyotrophic lateral sclerosis (ALS) results in respiratory muscle weakness causing hypoventilation, retention of carbon dioxide (CO 2 ), and chronic hypercapnic respiratory failure. In this pilot study, we performed a 12‐month assessment of daytime and home nocturnal CO 2 to track respiratory progression, determine relationships with surrogate respiratory measures, and assess the impact of non‐invasive ventilatory support. Methods Adults with forced vital capacity (FVC) less than 90% predicted secondary to ALS were recruited from two sites in the northeast US. Participants were followed up at standard visits every 3 months for up to five visits. Spirometry, functional scores, and patient‐reported outcomes of dyspnea were recorded. Each visit included a 15‐min, seated measurement of transcutaneous CO 2 (PtcCO 2 ) while in clinic, followed by 3 nights of home overnight PtcCO 2 monitoring. Linear mixed‐effects models were employed to describe the changes that occurred longitudinally and resulting from the initiation of non‐invasive ventilation (NIV). Results Sixteen subjects were enrolled, with nine completing the full study. Strength and FVC declined over time, while daytime PtcCO 2 remained stable. Five individuals demonstrated nocturnal hypercapnia that preceded FVC < 50% predicted normal. Transition to NIV was associated with a 7 mmHg decrease in nocturnal PtcCO 2 . Discussion Home nocturnal PtcCO 2 assessment in ALS may identify respiratory insufficiency prior to FVC. Transcutaneous CO 2 may play a role in the respiratory management of patients as a biomarker for hypoventilation risk and NIV titration. However, equipment availability and data quality limitations would benefit from professional assistance rather than independent in‐home use.