Is venous blood gas performed in the Emergency Department predictive of outcome during acute on chronic hypercarbic respiratory failure?

BackgroundDuring acute on chronic hypercarbic respiratory failure (AHRF), arterial pH is associated with non-invasive ventilation (NIV) failure and mortality. Venous blood gas (VBG) has been proposed as a substitute for arterial blood gas, based on a good agreement between venous and arterial values. We assessed the predictive value of admission VBG on intubation rate, NIV failure and mortality during AHRF. MethodsRetrospective chart review of inpatients admitted between 2009 and 2015 with AHRF who had VBG performed on admission. Demographic, clinical and biological data were collected throughout the hospital course. Results196 patients were included and hospital survival was not significantly associated with initial venous pH, PCO2 or HCO3-. Patients requiring intubation had significantly lower venous pH [7.29 (7.24-7.33) vs 7.31 (7.28-7.36), P=.04] while venous PCO2 and HCO3- did not differ as compared to non-intubated patients. Intubation within 48 h of admission was associated with significantly lower venous pH [7.28 (7.24-7.30) vs 7.32 (7.28-7.37), P=.002] and higher PCO2 [72 (63-92) mm Hg vs 62 (52-75) mm Hg, P=.04]. Among 69 patients receiving NIV, there were no differences in venous pH [7.29 (7.25-7.31) vs 7.30 (7.27-7.35), P=.3] or PCO2 [68 (44-74) mm Hg vs 70 (55-97) mm Hg, P=.23] associated with subsequent intubation. Using c statistics, we observed poor performances of venous pH, PCO2 or HCO3- for prediction of NIV failure, intubation or hospital mortality. ConclusionsOur results do not support the use of VBG on admission as a predictor for NIV failure, intubation and mortality during AHRF.