**2. Anatomy of the miniaturized extracorporeal circulation system**

Different types of MECC circuits are on the market and although they can have some differences among them in terms of characteristics of blood pump, oxygenator membrane, length of tubing, arterial and venous filters, the principle key is substantially equal for each system: closed circuit without a venous cardiotomy reservoir.

The MECC circuit consists of a closed loop, which includes the oxygenator and the pump. The circuit has not any open venous reservoir. All components of MECC circuit are pretreated with heparin according to different techniques available on the market. The heparin pre-treatment of the circuit minimizes the systemic heparinization dose requirements (usually half dose of conventional ECC: 150IU/Kg instead of 300IU/Kg) (Curtis et al. 2010; Formica et al. 2009, Puheler et al. 2009; Beghi et. 2006) and provides biocompatibility for blood cells (Koivisto et al. 2010; Remadi et al. 2007; Remadi et al. 2004; Fromes et al 2002;)

Miniaturized Extracorporeal Circulation 137

Aortic and atrial cannulation are equal to conventional ECC. Usually an aortic vent is positioned in ascending aorta and a further vent is inserted in the pulmonary main trunk

A cell-saver device can be associated with the MECC with the aim to sucked all the

The very strong difference between the MECC and the standard ECC circuit is the absence of a venous reservoir. In the MECC, the patient is the own venous reservoir and for this reason the straight collaboration among the cardiac surgeon, the anaesthesiologist and the perfusionist is extremely important to guarantee the best outcome. Use of vasodilator and vasoconstrictor drugs, Trendelemburg or anti-Trendelemburg position of the patient, reducing or increasing the centrifugal pump flow are all fundamental keys to manage a MECC system with the aim to avoiding malperfusion syndrome, systemic embolization,

The Systemic Inflammatory Response Syndrome (SIRS) is a complex plurifactorial syndrome often associated with the ECC. The SIRS to ECC is initiated by many aggressive factors including surgical trauma, blood contact with nonendothelial sufaces, cardioplegia, ischemia-reperfusion injury (Raja & Berg, 2007; Larmann & Theilmerr, 2004; Royston, 1997). Several blood elements such as neutrophils, monocytes, endothelial cells, platelets and complement proteins are involved in the SIRS. These blood components when activates, release of cytotoxic and vasoactive substances, produce inflammatory and inhibitory cytokine, express cell receptors interacting with specific cellular substance (Royston 1997). Therefore when SIRS is initiated, several inflammatory mediators, including antiinflammatory and pro-inflammatory cytokines could be associated with a worse

failure of the MECC and rapid conversion to standard ECC.

**3. Systemic inflammatory response** 

Fig. 2. MECC system.

during aortic valve surgery.

pericardial and bloodshed.

postoperative course.

Fig. 1. Miniaturized extracorporeal circuit on the left and conventional extracorporeal circulation on the right

The tubing length is described to be shorter than conventional ECC in different published reports. Tubing length of about 100 cm is frequently reported as well as a smaller tubing section than conventional ECC tubing (3/8" size instead of 1/2" size) (Formica et al 2009; Mazzei et al 2007). These characteristics lead to a circuit prime volume smaller than standard ECC, ranging between 200-650 ml for the MECC against 1200-1600 ml for the standard ECC (Formica et al 2009, Stalder et al. 2007; Remady et al. 2006). The combination of short length tubing, heparin pre-treatment, small size tubing and absence of a venous reservoir, leads to a significant reduction of hemodilution with as well as a reduction in clotting factor consumption ad triggering of SIRS (Vohra et al 2009; Ohata et al. 2007; Wippermann et al. 2005; Fromes et al. 2002). The blood pump included in the circuit is usually a centrifugal pump. The centrifugal pump is a very versatile pump, which reduces the cells trauma on the erythrocytes, and the platelets with possible lower effects on hemolysis. Moreover the centrifugal pump can generate up to 900 mmHg of forward pressure and only 400 mmHg of negative pressure with less cavitation and lower microemboli formation. The oxygenator of the MECC circuit is one of the most important components of the circuit itself. Oxygenators have the oxygenation membrane of either microporous polypropylene (El-Essawi et al. 2010; Wippermann et al. 2005) or polymethylpentene (Anastasiadis et al. 2011; Puehler et al. 2010; Formica et al. 2009; Remady et al 2006; ). In the latter case the membrane is considered as a diffusion membrane Usually the oxygenator has an integrated heat exchanger and one of the largest gas exchange surface areas, reaching about 2.4 m2. In this way the oxygenator can give a full oxygenation also with high blood flow pump up to 7 L/min.

Many MECC circuits include an arterial filter between the oxygenator and the aortic cannula. The filter has a prime ranging between 150-200 ml but its presence is of extreme importance because strongly reduce the risk of cerebral and systemic embolization or air, thrombus and calcium. Moreover some MECC circuits include a venous bubble trap or some similar device with the aim of reducing the big air entrainment in the circuit that could be one of the causes of accidental blockage of the MECC circuit. These devices are located between the venous cannula and the blood centrifugal pump.

Fig. 1. Miniaturized extracorporeal circuit on the left and conventional extracorporeal

The tubing length is described to be shorter than conventional ECC in different published reports. Tubing length of about 100 cm is frequently reported as well as a smaller tubing section than conventional ECC tubing (3/8" size instead of 1/2" size) (Formica et al 2009; Mazzei et al 2007). These characteristics lead to a circuit prime volume smaller than standard ECC, ranging between 200-650 ml for the MECC against 1200-1600 ml for the standard ECC (Formica et al 2009, Stalder et al. 2007; Remady et al. 2006). The combination of short length tubing, heparin pre-treatment, small size tubing and absence of a venous reservoir, leads to a significant reduction of hemodilution with as well as a reduction in clotting factor consumption ad triggering of SIRS (Vohra et al 2009; Ohata et al. 2007; Wippermann et al. 2005; Fromes et al. 2002). The blood pump included in the circuit is usually a centrifugal pump. The centrifugal pump is a very versatile pump, which reduces the cells trauma on the erythrocytes, and the platelets with possible lower effects on hemolysis. Moreover the centrifugal pump can generate up to 900 mmHg of forward pressure and only 400 mmHg of negative pressure with less cavitation and lower microemboli formation. The oxygenator of the MECC circuit is one of the most important components of the circuit itself. Oxygenators have the oxygenation membrane of either microporous polypropylene (El-Essawi et al. 2010; Wippermann et al. 2005) or polymethylpentene (Anastasiadis et al. 2011; Puehler et al. 2010; Formica et al. 2009; Remady et al 2006; ). In the latter case the membrane is considered as a diffusion membrane Usually the oxygenator has an integrated heat exchanger and one of the largest gas exchange surface areas, reaching about 2.4 m2. In this way the oxygenator can give a full oxygenation also

Many MECC circuits include an arterial filter between the oxygenator and the aortic cannula. The filter has a prime ranging between 150-200 ml but its presence is of extreme importance because strongly reduce the risk of cerebral and systemic embolization or air, thrombus and calcium. Moreover some MECC circuits include a venous bubble trap or some similar device with the aim of reducing the big air entrainment in the circuit that could be one of the causes of accidental blockage of the MECC circuit. These devices are located

circulation on the right

with high blood flow pump up to 7 L/min.

between the venous cannula and the blood centrifugal pump.

Fig. 2. MECC system.

Aortic and atrial cannulation are equal to conventional ECC. Usually an aortic vent is positioned in ascending aorta and a further vent is inserted in the pulmonary main trunk during aortic valve surgery.

A cell-saver device can be associated with the MECC with the aim to sucked all the pericardial and bloodshed.

The very strong difference between the MECC and the standard ECC circuit is the absence of a venous reservoir. In the MECC, the patient is the own venous reservoir and for this reason the straight collaboration among the cardiac surgeon, the anaesthesiologist and the perfusionist is extremely important to guarantee the best outcome. Use of vasodilator and vasoconstrictor drugs, Trendelemburg or anti-Trendelemburg position of the patient, reducing or increasing the centrifugal pump flow are all fundamental keys to manage a MECC system with the aim to avoiding malperfusion syndrome, systemic embolization, failure of the MECC and rapid conversion to standard ECC.
