Introduction When both severe metabolic acidemia (pH equal or less than 7.20; PaCO2 equal or less than 45 mm Hg and bicarbonate concentration equal or less than of 20 mmol/L) and moderate-to-severe acute kidney injury are observed, day 28 mortality is approximately 55%–60%. A multiple centre randomised clinical trial (BICARICU-1) has suggested that sodium bicarbonate infusion titrated to maintain the pH equal or more than 7.30 is associated with a higher survival rate (secondary endpoint) in a prespecified stratum of patients with both severe metabolic acidemia and acute kidney injury patients. Whether sodium bicarbonate infusion may improve survival at day 90 (primary outcome) in these severe acute kidney injury patients is currently unknown. Methods and analysis The sodium bicarbonate for the treatment of severe metabolic acidosis with moderate or severe acute kidney injury in the critically ill: a randomised clinical trial (BICARICU-2) trial is an investigator-initiated, multiple centre, stratified, parallel-group, unblinded trial with a computer-generated allocation sequence and an electronic system-based randomisation. After randomisation, the intervention group will receive 4.2% sodium bicarbonate infusion to target a plasma pH equal or more than 7.30 while the control group will not receive sodium bicarbonate. The primary outcome is the day 90 mortality. Main secondary outcomes are organ support dependences. Ethics and dissemination The trial has been approved by the appropriate ethics committee (CPP Nord Ouest, Rouen, France, 25 April 2019, number: 19.03.15.72446). Informed consent is required. If sodium bicarbonate improves day 90 mortality, it will become part of the routine care. Trial registration number NCT04010630.