Assessment of dCA during CPB General anaesthesia was induced using weight-related dosing of sufentanil and etomidate, and muscle relaxation was achieved with pancuronium bromide. General anaesthesia was maintained during surgery using propofol. An initial dose of heparin, 300 IU/kg of body weight (Leo Pharmaceutical Products®, Ballerup, Denmark), was injected into a central venous catheter before the initia- tion of CPB. When a target activated clotting time exceeded 400 seconds CPB was started. At the end of CPB heparin was reversed by protamine chloride (Valeant Pharmaceuticals®, Eschborn, Germany) at a 1:1 ratio of the total loading dose before CPB. An extracorporeal circuit optimized (ECCo) for CPB system (Sorin Group Italia®, Mirandola, Italy) was used consisting of a revolution dis- posable centrifugal pump (Sorin Group Italia®, Mirandola, Italy), a phosphoryl- choline coated 1.1 m2 hollow fiber oxygenator (Sorin Group Italia®, Mirandola, Italy), a cell-saving device (Dideco Electa, Sorin Group Italia®, Mirandola, Italy), 3/8” arterial and venous lines and an intermittently isolated hard-shell reservoir (D 790, Sorin Group Italia®, Mirandola, Italy). For dynamic assessment of CA and cerebral carbon dioxide reactivity during CPB, ABP, middle cerebral artery blood flow velocity, paCO2, absolute cerebral tissue oxygenation and CPB pump flow were continuously recorded. ABP was recorded from an intra-arterial pressure module (Philips Medical®, The Nether- lands), CBFV recordings of both left and right middle cerebral artery via two 2MHz TCD probes mounted on a head frame (ST3, Spencer Technologies®, Seattle, USA) at a depth between 45 and 56 mm, in-line arterial paCO2 measure- ment via an optical fluorescence and reflectance-based system (CDI-500, Te- rumo®, Japan), absolute cerebral tissue saturation (SctO2) via near-infrared spectroscopy (ForeSight, Casmed®, USA) with the electrodes placed on the right and left forehead, whereas pump flow was recorded by an ultrasonic flow moni- tor (Transonic Systems Europe BV®, Maastricht, The Netherlands). All data were sampled at 250 Hz and stored using an 8-channel acquisition system (IDEEQ, Maastricht Instruments®, Maastricht, the Netherlands), and were subsequently down sampled to 5 Hz by averaging over 0.2 s intervals. Similar to Diehl et al (7) who assessed CA in awake patients using triggered 6/min deep breathing to vary cardiac output, our method uses three level cyclic changes of indexed pump flow from a lower level of 2.0 l/min/m2 to a base level of 2.4 l/min/m2 and to an upper level of 2.8 l/min/m2, with a frequency of 6 cycles/min (2.5 s per indexed flow rate). All measurements were performed after CPB (constant hematocrit, constant arterial blood temperature, constant arterial oxygen tension, and constant pump 105
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