Prospective study, unicenter - Intensive Care Unit - HNSC. Period: May/2010 to June/2011. Serial assessment of GapCO2 of ScvO2 Clac and the first 72 hours post-PCR. Excluded under 18, survival of less than 6HS, pregnant women, traumatized, post-operative hypothermia and liver disease. T-student test, 95% (p <0.05).