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

Background: During 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. Methods: Retrospective 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. Results: 196 patients were included and hospital survival was not significantly associated with initial venous pH, PCO₂ or (Formula presented.). 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 (Formula presented.) 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 (Formula presented.) for prediction of NIV failure, intubation or hospital mortality. Conclusions: Our results do not support the use of VBG on admission as a predictor for NIV failure, intubation and mortality during AHRF.