**1. Introduction**

Coronary artery bypass grafting (CABG) using a cardiopulmonary bypass (CPB) is a routine therapeutic method in the surgical treatment of ischemic heart disease. Although CPB is suc‐ cessfully used thousands of times each day worldwide it is still associated with some unan‐ swered questions [1].

One of the basic questions that arise with the use of this technology is an adequate blood flow during surgery [1,2]. There are no standards for optimal pump flow during CPB and institutional practices are largely based on empirical experience. Optimal blood flow rate has not been definitively established by large-scale randomized trials carried out on animal models more than fifty years ago and proved by clinical experiences [1,3]. Initial flow is cal‐ culated based upon the body surface area and a temperature management strategy. The flow rate most commonly used during hypothermic CPB is 2.2 - 2.4 l.min-1.m-2 and during normothermic CPB 2.5 - 2.8 l.min-1.m-2 [3].

Despite progress, cardiopulmonary bypass predominantly used during coronary operations is still associated with profound physiological reactions and changes. In the majority of cas‐ es these reactions are caused by contact of blood with artificial material within the system and by other sources such as coronary suction, blood-air contact, non-turbulent flow, hemo‐ dilution and hypothermia.

A large number of advancements in the technology, equipment and techniques have been introduced to decrease the negative impact of CPB. One of the latest complex innovations is miniaturized CPB (mini CPB). The use of more biocompatible materials and minimization of equipment and internal surface of the system can reduce pathological reactions [4-8].

© 2013 Mandak; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Volume constant perfusion (perfusion without a reservoir) is a major advantage of mini CPB, but it can be associated with significant problems. The calculated blood flow (pump flow) must often be reduced to compensate for the volume in case of lower venous return during perfusion. Other reasons for reduction in pump flow are an increase in arterial pres‐ sure and flooding of the operating field with blood.

an emergency procedure, patients with local, systemic infection or inflammation, severe left ventricular dysfunction (ejection fraction < 25%), renal failure (serum creatinine >180 μmol

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

Perfusion Monitoring Study) http://dx.doi.org/10.5772/54300 101

The patients were randomized to two groups. Group A, consisting of 20 patients who un‐ derwent the conventional myocardial revascularization, coronary artery bypass grafting (CABG) using standard CPB and Group B, consisting of 20 patients who underwent coro‐

l


nary surgery using miniaturized CPB (Figure 1).

**Figure 1.** Coronary artery bypass grafting using cardiopulmonary bypass

tion the patients were randomly assigned to the study (n = 40).

Patient preoperative characteristics (Table 1), operative (Table 2) and postoperative data (Ta‐ ble 3) were prospectively recorded. The differences between groups (age, accompanying dis‐ ease) were not statistically significant (Table 1). All routine therapeutic and monitoring steps commonly used with this diagnosis were performed. After clinical and angiographic evalua‐

Delivery of oxygen to the tissues is equally dependent on blood flow and the O2 content of blood. Reduction of blood flow can decrease optimal tissue oxygenation. Inadequate oxy‐ genation and perfusion can be associated with severe pathological peripheral tissue changes associated with clinical complications [1,9,10].

It is difficult to assess local changes in perfusion or blood circulation in the periphery. The direct measurement of blood flow through separate organs or skeletal muscles during car‐ diac surgery is both technically difficult and ethically unacceptable. Evaluation of the stand‐ ard biochemical and hemodynamic parameters (blood pressure, blood lactate, heart rate, O2 saturation in the capillary bed, diuresis, etc.) yields for general results but not for regional changes [1,3,9].

For this purpose, direct continuous measurement of interstitial tissue oxygen tension (ptO2) of a skeletal muscle, as a typical peripheral tissue, was used in this study. Tissue oxygen ten‐ sion reflects the adequacy of regional tissue oxygenation and perfusion [11,12].

Oxygen tension was measured with a special optical multiparametric sensor inserted into the patient´s deltoid muscle. The sensor is based upon the principle of fluorescence quench‐ ing whereby the intensity of a fluorescent optical emission form, an indicator, is quenched (reduced) in the presence of oxygen. Oxygen from the surrounding blood equilibrates with the sensor materials and quenches the fluorescent light. This method was introduced into brain and liver perfusion measurement but it has not been used in connection with cardio‐ pulmonary bypass until now.

The present study was designed to evaluate changes in peripheral tissue (skeletal muscle) oxygenation during cardiac surgery and to compare tissue perfusion in relation to blood flow during standard CPB versus mini CPB.
