Incidence of hypo- and hypercarbia during induced hypothermia after cardiac arrest is high. The original report from HACA-group reported that hypothermia treated patients had improved survival and neurological outcome. Suprisingly, in that trial normocarbia was not achieved even though the aim was set for ventilatory support as normoventilation. This study aims to investigate the effects of mild hypo- and hypercarbia on cerebral perfusion (blood flow, intracranial pressure) and metabolism (microdialysate metabolites). We hypothesize that uncontrolled ventilatory suppport may render the patients in risk of exacerbation of neuronal damage, conversely, further improvement in outcome may be achieved with succesfull ventilatory management. We intend to enroll 10 out-of-hospital cardiac arrest patients succesfully resuscitated and subsequently treated with controlled hypothermia for 24 hours. The patients in need of anticoagulation are excluded. We plan to induce mild hypocarbia and hypercarbia during and after induced hypothermia. Metabolic and perfusion data are collected with clinically used methods such as transcranial doppler, intracranial pressure measurement, near infrared spectroscopy, jugular bulb, intracerebral microdialysis).