**4. Discussion**

The technology of miniinvasive systems has been in development since the beginning of the 1990s.

The benefits of using miniinvasive systems have been clearly proven in many publications. Studies show that the use of miniinvasive systems result in a decrease in quantity of admin‐ istered blood derivatives, a decrease in blood loss, lower incidence of postoperative neuro‐ logic complications, a shorter stay in the ICU, period of artificial ventilation and total hospital stay [4-8].

On the other hand some studies do not entirely confirm the positive clinical effect of using minisystems [13], even though the laboratory tests of these studies lean towards miniinva‐ sive systems compared to standard CPB.

**Group A (n=20)**

**pO2 [mm Hg]**

**pCO2 [mm Hg]**

**BE**

**Lactate [mmol/l]**

signs of general infection or sepsis in either group.

B) (Table 3).

112 Artery Bypass

**4. Discussion**

hospital stay [4-8].

1990s.

**1. postoper. day** 7,40 ± 0,07 7,39 ± 0,05 n.s.

**I.C.U. admission** 98 ± 48 97 ± 60 n.s. **I.C.U after 6 h** 171 ± 25.9 170 ± 50 n.s. **1. postoper. day** 135 ± 39 141 ± 28 n.s.

**I.C.U. admission** 30 ± 5 32 ± 4 n.s. **I.C.U after 6 h** 35 ± 4 39 ± 6 n.s. **1. postoper. day** 36 ± 5 35 ± 4 n.s.

**I.C.U. admission** - 2.93 ± 2.34 - 3.28 ± 2.31 n.s. **I.C.U after 6 h** - 1.8 ± 1,71 - 2.16 ± 2.0 n.s. **1. postoper. day** - 2.61 ± 1.83 - 3.15± 1.91 n.s.

**I.C.U. admission** 1.9 ± 0.7 2.1 ± 1.3 n.s. **I.C.U after 6 h** 1.8 ± 0.5 2.4 ± 1.7 n.s. **1. postoper. day** 2.1± 0.9 2.3 ± 0.8 n.s.

No death, acute renal failure, or stroke occured during the postoperative course either group. The only differences were postoperative atrial fibrillation (6 in Group A, 2 in Group

There were no cases of local complications at the site of inserted sensors, and there were no

The technology of miniinvasive systems has been in development since the beginning of the

The benefits of using miniinvasive systems have been clearly proven in many publications. Studies show that the use of miniinvasive systems result in a decrease in quantity of admin‐ istered blood derivatives, a decrease in blood loss, lower incidence of postoperative neuro‐ logic complications, a shorter stay in the ICU, period of artificial ventilation and total

**Table 5.** Postoperative laboratory characteristics of perfusion (arterial blood gases, lactate)

**Group B**

**(n=20) p-value**

One discussed question while using CPB is the constant value of blood flow during the op‐ eration [1,2]. Preoperative calculated value of optimal blood flow using mini CPB is the same as standard CPB.

Nevertheless adequate and optimal blood flow during CPB is still an important question. There are no standards for optimal pump flow during CPB. Initial flow is calculated on the basis of body surface area and a temperature management strategy. The calculated blood flow often has to be decreased during perfusion using mini CPB.

The reason for the necessary decrease in pumped blood flow is the increase in arterial blood pressure during the operation most likely as a result of increased blood in the vascular bed (an absence of a CPB reservoir).

Another reason for decreased flow could be the flooding of the operating field during wors‐ ened venous return.

Decreased venous return could be another reason. The flow of a centrifugal pump during mini CPB is fully dependent upon adequate venous return with resultant filling of the ve‐ nous bed of the patient.

In an effort to achieve the calculated blood flow the centrifugal rotational velocity is in‐ creased resulting in increased suction pressure within the venous part of the system and thus suction of the artifact with the venous cannulas. The ability to control flow via a cardi‐ otomy reservoir is missed in this case. A possible solution is an increase of blood in the body (patient´s body position in space, application of vasopressors, filling of the circulatory sys‐ tem) or decreasing blood flow in the system. The "antitrendelenburg" position (head up), during which the filling of the lower half of the body is partly increased and consequently an increased venous flow (return), is of some advantage. Further, in this position the heart chambers are adequately emptied. The trendelenburg position described in the literature as a means to increase venous return has typically no effect when mini CPB is applied. In the case of a closed system the patient´s own body is the reservoir.

It is necessary during the procedure to have a coordinated approach between the surgeon, anesthesiologist and perfusionist.

During an acute case of a decrease in the pumped blood flow, in the presence of an impaired venous return, filling was supplemented by blood collected in a collapsible bag at the begin‐ ning of the operation. To restore satisfactory parameters usually a sufficient volume of less than 100ml was required.

The perfusion pressure in both groups was maintained at levels between 50-70 mmHg [1,3,9,10]. In the case of mini CPB this did not fall below 50 mmHg while on the other hand there was a tendency for higher levels of pressure.

Different results in comparison with both groups after analysis of ptO2, MAP and blood flow during CPB and postoperative course were found to our greatest surprise.

In a comparison of monitored parameters of the clinical course we can suggest that lower values of blood flow during perfusion in group B (mini CPB) were sufficient and had no

Peripheral Tissue Oxygenation During Standard and Miniaturized Cardiopulmonary Bypass (Direct Oxymetric Tissue

Perfusion Monitoring Study) http://dx.doi.org/10.5772/54300 115

Tolerance to decreased flow in mini CPB, with maintained sufficient blood pressure, is in our opinion due to a higher hematocrit. Decrease in volume of priming fluid together with technique of RAP ensures a decreased perioperative hemodilution and thus an increase in

Another improtant postive aspect of using mini CPB is also a decrease in microcirculatory dysfunction. The system design (closed loop, biocompatible surface area, centrifugal pump, and elimination of cardiotomy suction) and decreased contact with artificial surfaces (short‐ ened tubing system and absence of cardiotomy reservoir) during lower flow decreases the negative impact on the organism. A lower intensity in the inflammatory reaction results in a decreased dysfunction of the endothelium and subsequent malperfusion. To verify this im‐ pact of the minisystem on the microcirulation it is necessary to perform further studies.

A miniaturized system of CPB enables perfusion with relatively low flow and in normother‐ mic conditions. Monitoring perfusion of skeletal muscle during the operation and our expe‐

Our work experience and the results of this pilot study suggest that a flow decrease in mini

Department of Cardiac Surgery, Charles University in Prague, Faculty of Medicine and Uni‐

[1] Murphy GS, Hessel EA, Groom RC. Optimal perfusion during cardiopulmonary by‐

pass: An evidence-based approach. Anesth Analg 2009; 108:1394-417.

negative impact in the postoperative course.

rience shows that it is a safe method of perfusion.

The chapter was supported by PRVOUK P 37/04/440.

Address all correspondence to: jiri.mandak@centrum.cz

versity Hospital in Hradec Kralove, Hradec Kralove, Czech Republic

CPB is well tolerated by the organism.

blood oxygen carrying capacity.

**5. Conclusion**

**Author details**

Jiri Mandak

**References**

A direct correlation between mean arterial pressure (MAP) and ptO2 was observed in Group A during CPB. Pumped blood flow was continuously maintained at the same calcu‐ lated level. On the other hand, direct correlation between pumped blood flow and MAP was found during mini CPB in Group B. The value of ptO2 was continuous, higher and inde‐ pendent at this time.

So far, we have no clear explanation for these differences in both groups. The main reason could most likely be due to differences in the amount of circulating blood volume, the possi‐ bility of using a cardiotomy reservoir, and the subsequent need to use catecholamines dur‐ ing perfusion.

A decrease in the ptO2 levels not correlated with MAP were analysed during CPB, after CPB and in the postoperative course in both groups. This is the most likely cause of decreased circulatory volume resulting in the use of vasopressors (catecholamines). A decrease in body temperature during this phase of the operation leading to peripheral vasoconstriction can al‐ so contribute equally to this phenomenon.

The lower level of acquired hemodilution (higher hematocrit) during the operation, deter‐ mined by a lower filling volume and retrograde autologous priming are major advantages of using perfusion by mini CPB.

Supply of oxygen to the tissues during reduced flow of the bypass machine is therefore safe in the case of an increased hematocrit. In the mini CPB group, only 2/3 of the priming fluid was used as opposed to classical CPB and another 1/3 of this fluid was replaced by the pa‐ tient's blood using retrograde autologous priming. The hematocrit provides sufficient ca‐ pacity to supply oxygen in normothermia. A combination of decreased primary filling and a shortened tubing system resulted in an increased hematocrit and concentration of hemoglo‐ bin as expected in Group B (mini CPB).

In our study a closed integrated system coated with phosphorylcholine was used. The tub‐ ing system was shortened to a minimum, by placing it as close as possible to the patient, to minimalize priming. The system used allowed for partial back-flow of the patient´s own blood (retrograde autologous priming). Coronary suction was not used and neither was a venous reservoir. No cell saver device was used.

There were no technical perfusion linked complications.

In comparison to the perfusion parameters of both groups there were no differences during surgery. The monitored values of arterial blood gases were comparable and showed optimal perfusion management in both groups. Likewise, the values in both groups were compara‐ ble in the early postoperative course.

No death, acute renal failure, or stroke occurred in the postoperative course of either group. The only difference noted was in the incidence of postoperative atrial fibrillation with group B (mini CPB) showing better results. This study was limited by a small number of patients.

In a comparison of monitored parameters of the clinical course we can suggest that lower values of blood flow during perfusion in group B (mini CPB) were sufficient and had no negative impact in the postoperative course.

Tolerance to decreased flow in mini CPB, with maintained sufficient blood pressure, is in our opinion due to a higher hematocrit. Decrease in volume of priming fluid together with technique of RAP ensures a decreased perioperative hemodilution and thus an increase in blood oxygen carrying capacity.

Another improtant postive aspect of using mini CPB is also a decrease in microcirculatory dysfunction. The system design (closed loop, biocompatible surface area, centrifugal pump, and elimination of cardiotomy suction) and decreased contact with artificial surfaces (short‐ ened tubing system and absence of cardiotomy reservoir) during lower flow decreases the negative impact on the organism. A lower intensity in the inflammatory reaction results in a decreased dysfunction of the endothelium and subsequent malperfusion. To verify this im‐ pact of the minisystem on the microcirulation it is necessary to perform further studies.
