The role of arterial blood gas analysis (ABG) in amyotrophic lateral sclerosis respiratory monitoring

There is still a lack of consensus among different guidelines about the right timing for starting non-invasive mechanical ventilation (NIMV) in amyotrophic lateral sclerosis (ALS).1–3 The importance of spirometry as a reliable prognostic factor in ALS has been widely recognised; conversely, very few studies investigated the role of arterial blood gas analysis (ABG). With respiratory failure being the main cause of death in ALS, we aimed at investigating the role of ABG as proxy for pulmonary function tests (PFTs) in a large cohort of patients with ALS, identifying the best cut-off values for forced vital capacity (FVC%), carbon dioxide (pCO2), carbonate (HCO3-) and standard base excess (SBE) to predict NIMV starting and survival. We included 488 patients with concomitant ABGs, PFTs and Amyotrophic Lateral Sclerosis Functional Rating Scale - revised (ALSFRS-r) score, followed up in the Turin ALS Center, resident in Piemonte and Valle d’Aosta, diagnosed between 2000 and 2015, excluding patients with severe pulmonary and kidney comorbidities. Descriptive statistic of the population is shown in the online supplementary material 1. Two-hundred and seventy-four patients (56.1%) underwent NIMV. Median time between ABG/PFT and NIMV initiation was 5.0 months (IQR 1.0–12.0). NIMV was started at a median FVC% value of 57.4% (IQR 44.2–73.6). Median overall survival after NIMV initiation was 225 days (IQR 104–491). Patients who did not undergo NIMV (n=214) were significantly older (68.6 years vs 64.9 years, p<0.001) and had a shorter overall median survival (2.3 years, IQR 1.5–3.5 vs 2.6 years, IQR 1.9–4.0, p=0.003).### Supplementary data [jnnp-2020-323810supp001.pdf] ABG parameters showed a significant correlation with ALSFRS-r respiratory subscore (for pCO2 r=−0.301; for HCO3- r=−0.290; for SBE …