Background The optimal choice of fluid therapy for patients with diabetic ketoacidosis (DKA) is uncertain, though preliminary data suggest that buffered crystalloid solutions (Plasma-Lyte® 148) may offer some advantages over 0.9% saline.

Objective To describe the study protocol for the ‘Balanced Electrolyte Solution versus Saline Trial for Diabetic Ketoacidosis’ (BEST-DKA) trial.

Design, setting and participants BEST-DKA is a Phase 3 cluster-crossover, blinded, pragmatic, randomised, controlled trial comparing the effects of saline or buffered crystalloid solution in patients with moderate to severe DKA treated in the emergency department and/or intensive care unit at twenty hospitals in Australia. Each hospital will be randomised to use either saline or buffered crystalloid solution for a period of 12 months before crossing over to the alternate fluid for the next 12 months. The blinded study fluid will be used for all resuscitation and maintenance purposes for included patients.

Main outcome measures This cluster-randomised, crossover randomised controlled trial (RCT) has been designed with the aim of enrolling a minimum of 400 patients, which will provide >91.4% power to detect a 2-day increase in the primary outcome, days alive and out of hospital to day 28, chosen with consumer representation. Secondary outcomes include quality of life and fatigue scores at day 28, intensive care unit and hospital lengths of stay, acute kidney injury, and time to resolution of DKA. All analyses will be conducted on an intention-to-treat basis. A prespecified statistical analysis plan will be developed prior to interim analysis.

Results and conclusion The BEST-DKA trial commenced enrolment in March 2024 and should generate results that will determine whether treatment with Plasma-Lyte® 148, compared with saline, results in increased days alive, and out of hospital to day 28 for patients with moderate or severe DKA.