 Latest international guidelines recommend the use of therapeutic hypothermia in patients who have had cardiac arrest and remain in coma after return of spontaneous circulation. This is recommended essentially to limit the cerebral injury caused by cardiac arrest and possibly amplified upon reperfusion. At times, although a spontaneous circulation has returned, cerebral oxygenation may remain inadequate due to inadequate perfusion pressure, and hypothermia, by reducing cardiac output and cerebral blood flow could actually aggravate this phenomenon. The rewarming period is thought to be at greatest risk of inadequate oxygenation for the increase in metabolic demand. With this study we aim to understand what happens to cerebral oxygenation and metabolism during therapeutic hypothermia for cardiac arrest through cerebrovenous oxygen saturation monitoring and in particular, to see whether through this type of monitoring we could recognize otherwise unnoticed periods of inadequate cerebral oxygenation. 