Metabolic acidosis is common in critically ill patients and is associated with increased risk of organ dysfunction, need for renal replacement therapy, and death. Despite its frequency and clinical relevance, the optimal treatment approach remains uncertain. Sodium bicarbonate is often used to correct acidosis, but its risk-benefit profile in this setting is unclear.To describe the study protocol and statistical analysis plan for the sodium bicarbonate for metabolic acidosis in the intensive care unit (SODa-BIC) trial.Protocol for an international, multicentre, randomised, double-blind, parallel-group, superiority adaptive clinical trial. Five hundred (n = 500) adults with metabolic acidosis and receiving a continuous infusion of a vasopressor will be randomly assigned to sodium bicarbonate or placebo in a 1:1 ratio. SODa-BIC started recruiting in April 2023. It is anticipated that recruitment will be completed in 2026.The primary outcome will be major adverse kidney events within 30 days (MAKE30). Secondary and tertiary outcomes include 30- and 90-day mortality, receipt of renal replacement therapy, and vasopressor-free and ICU-free days at day 30. All analyses will be conducted on an intention-to-treat basis.SODa-BIC will evaluate whether sodium bicarbonate improves clinically meaningful outcomes in critically ill patients with metabolic acidosis. The trial has the potential to inform international practice guidelines and provide robust evidence to guide the treatment of a common and severe condition in the intensive care unit.Clinicaltrials.gov (NCT05697770).