Blinding

Due to the nature of the intervention, the clinicians performing the intervention cannot be blinded. Patients along with any surrogate will be blinded. As it is common to note vascular access during cardiac arrest in the patient’s medical records, clinicians involved in post-resuscitative care will not necessarily be blinded either. Due to the same reason, investigators involved in data entry will also not be blinded meaning that outcomes such as return of spontaneous circulation and mortality are entered without blinding. However, there is little – if any – subjectivity in evaluating these outcomes and blinding is therefore of minor importance. Outcome assessors performing the follow-up interviews will be blinded as this involves outcomes with some degree of subjectivity.

Randomization

Patients will be randomized in a 1:1 ratio to either intravenous or intraosseous vascular access. The intraosseous group will be further randomized to the humeral and the tibial site in a 1:1 ratio. The full allocation ratio will therefore be 2:1:1 for intravenous access, tibial intraosseous access, and humeral intraosseous access

To ensure allocation concealment up until the patient meets the criteria for inclusion, randomization will be performed by opening of an opaque envelope. We estimate that the randomization procedure will take approximately 5-10 seconds.