This is an investigator-initiated, multicenter, randomized, placebo-controlled, parallel group, double-blind, superiority trial of sodium bicarbonate during adult in-hospital cardiac arrest. There will be 22 enrolling sites in Denmark. 778 adult patients with in-hospital cardiac arrest receiving at least one dose of adrenaline will be enrolled. The primary outcome is return of spontaneous circulation and key secondary outcomes include survival at 30 days and survival at 30 days with a favorable neurological outcome.

Inclusion Criteria:

1. In-hospital cardiac arrest
2. Age ≥ 18 years
3. Received at least one dose of adrenaline during cardiopulmonary resuscitation (CPR)

Exclusion Criteria:

1. Clearly documented "do-not-resuscitate" order prior to the cardiac arrest
2. Prior enrollment in the trial
3. Invasive mechanical circulatory support at the time of the cardiac arrest
4. Known or suspected pregnancy at the time of the cardiac arrest
5. Known objection by the patient to participate in the trial
6. Clinical indication for bicarbonate administration

Six months after the publication of the last results, all de-identified individual patient data will be made available for data sharing. Procedures, including re-coding of key variables, will be put in place to allow for complete de-identification of the data. Data will be completely anonymized according to Danish law.

All relevant trial-related documents, including the protocol, data dictionary, and the main statistical code, will be shared along with the data. There will be no predetermined end date for the data sharing.

Data will be available for any research purpose to all interested parties who have approval from an independent review committee and who have a methodological sound proposal as determined by the steering committee of the current trial. Only the methodological qualities and not the purpose or objective of the proposal will be considered. Interested parties will be able to request the data by contacting the principal investigator. Authorship of publications emerging from the shared data will follow standard authorship guidelines from the International Committee of Medical Journal Editors and might or might not include authors from the steering committee depending on the nature of their involvement.