Title: 
Initial blood pH as an independent predictor of neurological outcome in patients with out-of-hospital cardiac arrest 

Purpose: 
Metabolic acidosis is observed in 98% of patients with Out-of-hospital cardiac arrest (OHCA). The longer the no-flow or low-flow duration, the more severe the acidosis is in these patients. This study aim to demonstrate the blood pH on arrival at emergency department (ED) could be an independent predictor of neurological prognosis in patients with OHCA. 
Material and Methods 
We retrospectively recruited patients with OHCA from January 2012 to June 2017. Patients with blood gas analyses performed upon arrival at the ED simultaneously with CPR were enrolled into this study. Those aged younger than 20 years, those who with cardiac arrest consecutive to trauma, and those with do-not-resuscitate orders were excluded. Patient’s data were collected according to the Utstein-style template. The primary outcome of this study was neurological status at hospital discharge.
Results
A total of 1711 patients with OHCA were enrolled into this study. The majority was males (61.89%) with an average age of 67.8 ± 17.0 years. OHCA was witnessed in 458 cases, and CPR was performed before the arrival of the paramedics in 371 (22.3%) cases. 207 (12.1%) patients had a shockable rhythm. Age, shockable rhythm, witness, and pH from initial ED blood gas analysis remained independent predictors of neurological outcome after multivariate regression. (Table 1)

Conclusions: 
Initial blood pH on arrival of ED, age, shockable rhythm and witness of collapse were independent prognostic factors of neurological outcome after OHCA. Blood gas analysis upon arrival of ED may provide additional information about prognosis of patients with OHCA.

4 - Initial blood pH as an independent predictor of neurological outcome in patients with out-of-hospital cardiac arrest