Data are collected on past medical illnesses, medication, type of surgery, abnormalities on pre-operative transesophageal echocardiogram and localisation of arterial line.
Before induction of anesthesia, an arterial line is installed. The agents of induction of anesthesia and doses are left to the discretion of the attending anesthesiologist. The trachea is intubated, anesthesia circuit and sidestream CO2 sensor were connected to the endotracheal tube and positive pressure ventilation begins with standardized parameters: control assisted mode with no inspiratory effort, tidal volume of 6-8 mL/kg, respiratory rate of 8-10/minute and PEEP of 5 mmHg. Modification of the ventilation parameters is not permitted before and during the PLR maneuvers. Isoflurane and propofol are used for the maintenance of anesthesia. A PA catheter (Paceport, Edwards Lifesciences, Irvine, California, USA) is inserted in the right internal jugular vein. If a femoral line is installed, the FloTrac/EV1000 is connected to the femoral line, if not, the radial line is used for mini-invasive continuous cardiac output monitoring. The a and v wave aspect and ratio of CVP waveform is noted. The RV waveform is inspected for signs of abnormalities such as a non-horizontal slope restrictive pattern (Figure xx)18. The transducers are all placed at the midthoracic level and a "flush test" is performed prior to CO measurements with the FloTrac/EV1000 to ensure absence of resonance or damping of the system.
At baseline, in the operating room before the first PLR maneuver, the heart rate, systolic, diastolic and mean arterial pressure, CVP value, CI measured in triplicate with the thermodilution method and the FloTrac derived variables are recorded. These variables include the CO indexed CO and SVV measured by the FloTrac/EV1000. The same variables are recorded at 1, 3 and 5 minutes after the beginning of PLR except CI by thermodilution which is measured again only once, at 3 minutes and EtCO2 which is recorded every 12 seconds. The EtCO2 curve is inspected at baseline and during the PLR maneuver to ensure the changes in EtCO2 were not related to changes in inspired CO2, ventilator or circuit malfunction or increase in airway resistance.
After weaning from CPB, the same measures are taken twice: with chest opened, when hemodynamic stability is achieved, and CPB canulas taken out and with chest closed.
In the ICU, two additional PLR maneuvers were executed with a 30 minutes interval in between. The set of measurements previously described are recorded. The use of an epicardial temporary pacemaker, vasopressors (doses and type), vasodilators (doses and type) are also recorded.