Around 184,000 critically ill adults are admitted to critical care each year in the UK. Around half have a sudden worsening in kidney function that happens as part of their illness defined as acute kidney injury (AKI). This rapid decline in kidney function frequently causes more acid to build up in the blood (known as acidosis) which can cause further harm.

Critically ill patients with acidosis in the context of also having AKI have a very poor prognosis, with a 90-day mortality of 59%. In these patients, kidney replacement therapy (KRT) is the most commonly used treatment. Another option is to treat the acidosis directly by administering “buffer” solutions (e.g. sodium bicarbonate), with the aim of raising extracellular pH to restore cardiovascular function and oxygen delivery to tissues. This has the potential to both increase survival and avoid KRT, which is invasive and resource-intensive.

A recent trial evaluating the use of sodium bicarbonate in critically ill patients with acidosis found a significant reduction in 28-day mortality (46% sodium bicarbonate vs. 63% control) and use of KRT in a subgroup of patients with AKI. However, such sub-group analyses must be treated with caution, and the authors rightly called for a larger RCT to address this question. Currently, there is uncertainty among critical care clinicians as to whether sodium bicarbonate should be used for routine treatment of acidosis in patients with AKI, and there is little high-quality evidence for the use of sodium bicarbonate in patients with acidosis and AKI which likely leads to varied use in critical care units worldwide.


The Multicentre evaluation Of Sodium bicarbonate in Acute kidney Injury in Critical Care (MOSAICC) RCT will address the clinically important question of whether treatment with IV sodium bicarbonate is superior to no IV sodium bicarbonate in critically ill adults with metabolic acidosis and AKI. This will be measured in terms of all-cause mortality at 90 days (clinical effectiveness) and incremental costs, quality-adjusted life years (QALYs) and net monetary benefit at 90 days (cost-effectiveness).

This evaluation will have a large and immediate impact on clinical practice and on patient outcomes in the NHS and worldwide.

Key information

Chief investigator(s)

Professor Lui Forni, University of Surrey

Professor Nick Selby, University of Nottingham


University Hospitals of Derby and Burton NHS Foundation Trust


National Institute for Health and Care Research (NIHR) – Health Technology Assessment (HTA) Programme 

(Project Number: NIHR129617)

Trial registration(s)

ISRCTN Registry: ISRCTN14027629

NIHR Central Portfolio Management System: 49697

Contact information

Trial Manager – Catherine Oversby


Phone: 020 7831 6878

Trial protocol