Low arterial pH links to higher ICU mortality in older adults
In a study of 324,806 ICU admissions, lower arterial blood pH within 24 hours showed a stronger link to mortality in patients aged 65 and older.
Journal of Intensive Care
In a nationwide retrospective study of 324,806 adult intensive care unit admissions in Japan, researchers examined whether patient age influences the prognostic value of arterial blood pH. Using data from the Japanese Intensive Care Patient Database between 2018 and 2023, the authors evaluated the lowest arterial blood pH recorded within the first 24 hours of admission. Overall ICU mortality across the cohort was 4.4%, and 215,880 patients (66.5%) were 65 years or older.
Lower arterial blood pH was nonlinearly associated with higher ICU mortality. This association was significantly modified by age, showing a stronger effect in patients aged 65 and older than in patients aged 18 to 64 years.
Why it matters
The findings suggest that older individuals are more susceptible to severe consequences from acidemia, consistent with age-related reductions in physiological reserve during critical illness.
Caveats
The study was observational and retrospective, and the authors note that prospective studies must evaluate whether age-specific acid-base interpretation actually improves prognostic accuracy.
The paper
St. Luke's International Hospital
Journal of Intensive Care · 29 Sep 2026