Study of Microcirculation During Extracorporeal Circulation in Cardiac Surgery

The aim of the proposed study is to evaluate microcirculatory alterations in patients undergoing open heart surgery under extracorporeal circulation. Microcirculatory changes during cardiac surgery have been investigated mainly during coronary procedures using the conventional extracorporeal circulation. There is no single study in the literature investigating microcirculatory alterations using a perioperative strategy of "physiologic" perfusion. Positive clinical results evidenced with goal-directed perfusion and cerebral oximetry monitoring could be attributed to preserved microcirculation at tissue level.

All patients will follow the same anaesthetic and perfusion protocol. The protocol for the evaluation of microcirculation will be based on:

• Cerebral near-infrared spectroscopy (rScO2) measurements (INVOS, Covidien-Medtronic Inc.).
• NIRS-Based Cerebral Autoregulation Monitoring: Analog arterial blood pressure signals will be digitized and then processed with the digital NIRS signals using a personal computer and a special ICM software (University of Cambridge, Cambridge, UK). Monitoring cerebral autoregulation ensures adequate renal perfusion. Hence, brain can be used not just as a target but also as an index organ indicating adequacy of perfusion.
• Somatic near-infrared spectroscopy (rSsO2) measurements (INVOS, Covidien-Medtronic Inc.).
• Sublingual mucosal microcirculation measurements during surgery using side dark field (SDF) imaging (MicroScan, Microvision Medical, Amsterdam, The Netherlands).

All measurements will be performed at the following time points:

T0: after induction of anaesthesia T1: after initiation of cardiopulmonary bypass T2: 10 minutes after cross- clamping the aorta T3: 10 minutes before removing the aortic cross-clamp T4: after weaning from extracorporeal circulation

Inclusion criteria

• patients aged > 18 and < 85 years with coronary artery disease and/or aortic valve disease undergoing open heart surgery with accepted indications

Exclusion criteria

• patients undergoing emergency surgery
• patients in preoperative cardiogenic shock with evidence of tissue malperfusion
• patients > 85 years of age
• patients with severe peripheral vascular disease