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.