This study evaluates the usefulness of the ΔvapCO2 / Cav02 ratio to predict complications after elective cardiac surgery, comparing it with others markers such as lactate, arteriovenous CO2 difference (ΔvapCO2) and would try to developed a new predictive score for postoperative complications.

Cardiac surgery is widely used to solve valvular or coronary problems and often requires the use of cardiopulmonary bypass or extracorporeal circulation (EC).

The EC itself produces a series of changes in the macro- and microcirculation hemodynamic and physiological consequences in the hours following surgery that can be difficult to analyze.

During postoperatively management, different monitoring methods are used to optimize different hemodynamic and analytical variables.

Sometimes, monitored variables are corrected but the patient still develops complications such as kidney failure, prolonged mechanical ventilation or even death. In fact, it is not well known either if it is sufficient to correct the variables called "macrodynamics " such as mean arterial pressure (MAP) , stroke volume (SV), pulmonary artery occlusion pressure (PCWP) and cardiac index (CI) or if it is necessary to correct other "micro-dynamics" variables like lactate, to achieve a certain central venous oxygen saturation (ScvO2) or arteriovenous CO2 difference(ΔvapCO2).

In tissue hypoxia, damping of excess protons by bicarbonate increase CO2 production; therefore the relationship between CO2 production and oxygen consumption (VCO2/VO2 ratio or respiratory quotient) increases. This ratio can be simplified relating ΔvapCO2 and O2 content arteriovenous difference (ΔvapCO2 / Cav02 ratio). In shock, anaerobic metabolism is one of the primary energy source. In this situation, ΔvapCO2 / Cav02 is > 1.

The evolution of the ΔvapCO2 / Cav02 ratio and its association with prognosis have nnot been studied yet after cardiac surgery.

The study's objectives are:

• to describe ΔvapCO2 / Cav02 ratios kinetics compared to lactate and other biochemical markers (troponin I, BE) in the first 12 hours after cardiac surgery.
• define if ΔvapCO2 / Cav02 ratio> 1 after 6 hours of adequate postsurgical resuscitation correlates with worse prognosis in patients after cardiac surgery.
• develop a new prognostic score for postoperative complication that includes ΔvapCO2 / Cav02 ratio.

Blood gases and drawn from a central venous and arterial lines. pCO2, O2 content, lactate are analyzed at 0, 2, 6 and 12 hs. Macrodynamic variables are also collected, as well as, the need of extracorporeal support techniques.

Patients would be followed for the next 28 days after surgery.

Inclusion Criteria:

• 18 years old or more
• given informed consent
• elective cardiac surgery
• tip of a central venous catheter correctly positioned (superior vena cava or right atria)
• arterial catheter correctly positioned

Exclusion criteria:

• pregnancy

Patients undergoing elective cardiac surgery in an university hospital that would be followed during the postoperative time in the Cardiovascular Intensive Care Unit.