Background: Metabolic acidosis refers to any process that elevates the concentration of hydrogen ions in the body, and is commonly encountered in critical illness. It may impair cardiac function, and sodium bicarbonate can be used to normalise blood pH. Despite being in common clinical usage, the clinical efficacy of sodium bicarbonate is still uncertain. Previous studies exploring the effects of sodium bicarbonate therapy have been limited and of variable quality.

Aim: This trial aims to assess if, among adults in the ICU with metabolic acidosis, an infusion of sodium bicarbonate diluted in 5% dextrose, compared with an infusion of 5% dextrose, reduces Major Adverse Kidney Events within 30 days of randomization.

Study Design: Phase 3, international, multicentre, double-blind, randomised clinical trial.

Participants: Adult patients (above 18 years old), admitted to the ICU within 48 hours in. select ICUs internationally, receiving a continuous infusion of a vasopressor drug to maintain a mean arterial pressure above 65 mmHg (or a mean arterial pressure target set by the treating clinician), a dedicated line (central or peripheral) is available (or is about to be made available within 1 hour after randomisation), and within two hours prior to randomisation the participant has metabolic acidosis, defined as: 1) pH less than7.30; 2) BE less than -4 mEq/L; and 3) PaCO2 less than 45 mmHg.

Intervention: Patients will be randomly allocated in a 1:1 ratio to receive two treatments that are commonly used either an infusion of 5% dextrose (D5W) + sodium bicarbonate, or D5W alone, as a comparator. Study drug will be continuously infused targeting a pH 7.30 - 7.35 and a BE more than 0 mEq/L. The infusion will be maintained until this target is achieved and continued by titration thereafter for a maximum of 5 hours (to maintain target pH and base excess levels). All other aspects of care will be determined by the treating clinical team, including the use of additional fluid therapy, vasopressors, and other organ support modalities. Open-label sodium bicarbonate bolus infusion is allowed in both groups if clinically indicated.

Primary outcome: The primary outcome is the proportion of patients who meet one or more criteria for a major adverse kidney event within 30 days (MAKE 30). MAKE 30 is a composite of death, new receipt of renal-replacement therapy, or persistent renal dysfunction (defined as a final inpatient creatinine value ≥ 200% of the baseline value). All components of MAKE30 will be censored at hospital discharge or 30 days after enrollment, whichever comes first.