Arterial blood gas analysis: base excess and carbonate are predictive of noninvasive ventilation adaptation and survival in amyotrophic lateral sclerosis

Objective: To investigate the role of arterial blood gas (ABG) analysis parameters (blood carbon dioxide, pCO2; oxygen, pO2; carbonate, HCO3^-; standard base excess, SBE) in monitoring respiratory function and ventilation compliance after noninvasive mechanical ventilation (NIV) adaptation, predicting survival in ALS patients. Methods: We selected the first ABG performed after NIV start in ALS patients followed from 2000 to 2015 in Turin ALS Center. 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. Results: 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. Conclusions: HCO3^- and SBE blood levels are markers of ventilation compliance, tolerance and efficacy, being able to predict survival after NIV start in ALS.