This is a prospective, observational study to investigate molecular mechanisms mediating the systemic inflammatory process, and changes to metabolism, and their impact on brain injury, survival, and functional outcomes after cardiac arrest. Investigators have shown that cardiac arrest induces changes in the numbers and properties of circulating immune cells, shifting the balance towards a pro-inflammatory phenotype and there is increased interest in the inflammatory pathways and the signaling mechanisms through which they are modulated. Participants will undergo blood sampling during 7 days following cardiac arrest, and analyses performed. Patient characteristics, clinical circumstances, and outcomes will be recorded and their associations with these inflammatory pathways characterized.