Objectives The aim of this study was to assess the mortality and predictive factors in patients presenting with a pH<7.0 to the emergency department (ED). Methods A retrospective study of patients presenting to the ED of University Hospital Galway with a pH<7.0 from January 2014 to December 2017 was performed. A pH<7.0 on arrival to the ED from either an arterial or venous sample as measured by the blood gas analyser machine were assessed for inclusion. Results A total of 130 patients presented to ED over a 4-year period, with a mean age of 58 ±20 years. Eighty-one (63%) patients of the total cohort were male. In terms of aetiology of presentation, 66 (51%) cases were from cardiac arrest (CA), while the remaining 64 (49%) cases were non-cardiac arrest (NCA) related. Twenty-eight-day mortality was 69.5% overall, with significant mortality in the CA group (89%) compared to the NCA group (48%) (p<0.00). A modified early warning score (MEWS) (odds ratio [OR] 1.37, 95% CI: 1.18-1.59) and PCO2 ([OR] 1.35, 95% CI: 1.08-1.68.) were predictive of mortality. Conclusion In patients presenting to the ED with a pH of <7.0 the overall mortality was 69.5%, with survival more likely in NCA aetiologies. Mortality was associated with higher pCO2 and MEWS.