Extreme acidosis in hospitalised patients: A 10-year single-centre, retrospective analysis

Acidaemia is a commonly occurring abnormality of acid-base balance. The literature assessing extreme acidosis (pH ≤ 7) is limited and is largely focused on those admitted to intensive care. Therefore, we sought to review the demographics, aetiologies, and outcomes of all hospitalised patients with extreme acidosis.

This was a retrospective cohort study conducted at a single centre, tertiary hospital in Melbourne, Australia Participants: Patients with acidosis were identified using the hospital pathology database. Exclusion criteria included hospital readmissions or samples taken in a non-inpatient setting. Main Outcome Measures: The primary outcome was 30-day mortality. Secondary outcomes included 90-day mortality and the association of mortality with type and aetiology of acidosis. Data were analysed using a Cox proportional hazards model.

Between June 2015 and June 2025, 162,697 patients had 451,788 multi-day admissions. Five hundred eighty-six admissions were identified, in which a patient had a measured pH ≤ 7.0. The final cohort consisted of 493 first admission episodes. Three hundred twenty-four (68.5 %) were male with a median age of 59.3 (interquartile range: 41.2-71.7). By day 30, 226 (45.8 %) of patients had died. Mixed acidosis (321, 65.1 %) and cardiorespiratory arrest (160, 32.5 %) were the most frequently occurring type and aetiology of acidosis. Relative to metabolic acidosis, both mixed acidosis (adjusted hazard ratio (aHR): 2.25, 95 % CI: 1.55-3.27) and respiratory acidosis (aHR: 2.08, 95 % CI: 1.01-4.27) had a higher hazard of 30-day mortality. Causes associated with the highest risk of 30-day mortality were vascular (aHR: 31.2, 95 % CI: 9.60-101) and cardiorespiratory arrest (aHR: 27.0, 95 % CI: 9.17-79.4). One hundred nine (22.1 %) patients did not require intensive care unit admission; however, 37 (33.9 %) of these patients still had died by day 30.

Extreme acidosis is extremely rare in hospitalised inpatients. Mortality varies according to type and aetiology of the cause of acidosis and therefore careful consideration as to the implications of extreme acidosis when considering cessation of treatment is crucial.