To investigate the role of arterial blood gas analysis (ABG) parameters (blood carbon dioxide, pCO2; oxygen, pO2; carbonate, HCO3-; standard base excess, SBE) in monitoring respiratory function and ventilation compliance after NIV adaptation, predicting survival in ALS patients.

Non-invasive mechanical ventilation (NIV) is the treatment of choice for impending symptoms and signs of respiratory failure in Amyotrophic Lateral Sclerosis (ALS), improving patients’ quality of life and survival. Patients’ compliance to NIV and adequate ventilator settings are crucial for improving long-term NIV efficacy.

We selected the first ABG performed after NIV start in ALS patients followed from 2000 to 2015 in Turin ALS Centre. Correlations between ABG parameters and survival were calculated. Risk for death/tracheostomy was computed at modifying ABG parameters by using Cox regression models, adjusted for the main prognostic factors. Kaplan-Meier curves were then performed and compared.

A total of 186 post-NIV ABGs were included. HCO3- and SBE showed a significant correlation with survival after NIV (respectively R= -0.183, p=0.018 and R= -0.200, p=0.010). Risk for death/tracheostomy after NIV was significantly higher at increasing HCO3- and SBE blood levels, especially when HCO3- was >29 mmol/L and SBE >4 mmol/L (respectively HR 1.466, 95% CI 1.068-2.011, p=0.018 and HR=1.411, 95% CI 1.030-1.32, p=0.032). Survival in NIV was higher in patients with HCO3- <29.0 mmol/L and SBE <4.0 mmol/L in comparison with those with both parameters increased (0.69 years, IQR 0.33-1.37 vs 0.37 years, IQR 0.12-0.77; p=0.013).

HCO3- and SBE blood levels are not only useful for NIV initiation, but they can be used as markers of ventilation compliance, tolerance and efficacy, being able to predict survival in NIV.