Early assessment of Nocturnal Hypoventilation in ALS patients

Background and Objective: Nocturnal hypoventilation (NH) is a respiratory complication in Amyotrophic Lateral Sclerosis (ALS) patients. The correct timing to start non-invasive ventilation (NIV) is crucial to treat alveolar hypoventilation, prevent acute diurnal hypercapnia crises, prolong tracheostomy-free time, and lengthen patient survival. This study aims to detect NH with daytime normocapnia evaluated with capnometry. Methods: We performed Transcutaneous carbon dioxide monitoring (TcCO2) to assess NH in 31 non-ventilated normocapnic ALS patients. NH was defined as peak TcCO2 > 49 mmHg. Concomitant pulmonary function tests, morning blood gas analysis, and polygraphy data were collected. Results: Twelve of 31 daytime normocapnic ALS patients showed NH. Data were analyzed to determine whether nocturnal oxygen desaturation (SpO2 88% for ≥ 5% of monitoring time), BMI, FVC, Apnea Hypopnea Index (AHI), and daytime blood gas analysis could predict the presence of NH. The T-test between the group with NH (12 patients) and without NH group (19 patients) showed that HCO3- is significantly different. Linear regression between TcCO2 and HCO3- showed a significant correlation. Conclusions: ALS patients can develop NH in the absence of daytime hypercapnia. Bicarbonate is confirmed to be a good indicator of NH. On the contrary, oxygen desaturation, BMI, FVC, and AHI were poor predictors of NH. Therefore, monitoring of NH should be included among nocturnal respiratory assessments of these patients as an additional tool to determine when to commence non-invasive ventilation.