the development of cardiopulmonary bypass ( cpb ) has been an ongoing process since its first clinical use . today , this technology is used in more than one million cases annually worldwide . the optimal technical characteristics of a cpb system for any given patient as well as the optimal operative strategy are still under debate . recently , an array of articles on best practices and guidelines for the conduct of cpb has been published . according to a widely used definition , the term biocompatibility refers to  ... the ability of a material to perform with an appropriate host response in a specific application  . the extent of body reactions to the exposure to non - physiologic materials is a function of the characteristics of foreign materials and the nature , location and length of time in use . however , questions in conjunction with biomaterials are whether it is possible to synthesize biomaterial with reliable predictability of its properties ( appropriate host response ) , and whether this material has any effect on increased patient safety during cpb . biocompatibility refers to the ability of a biomaterial to perform its desired function with respect to a medical therapy , without eliciting any undesirable local or systemic effects in the recipient or beneficiary of that therapy , but generating the most appropriate beneficial cellular or tissue response in that specific situation , and optimising the clinically relevant performance of that therapy  . physiologically , several mechanisms prevent the organism from blood loss due to injured blood vessels : the coagulation system , endothelium and regulatory proteins , platelets and fibrinolysis . this hemostatic system of a patient is activated during cardiac surgery with and without cpb . furthermore , the so - called systemic inflammatory response syndrome ( sirs ) is triggered . surgical trauma , blood contact with cpb surfaces , endotoxemia and ischemia trigger mediators , transcription factors and adhesion molecules , leading to leukocyte extravasation , lipid peroxidation , edema and eventually cell death . clinically , sirs can lead to coagulopathy , arrhythmias , endothelial dysfunction , neurological manifestations and end organ failure . in order to improve the above scenario , first of all , use of the heart - lung machine could be avoided , whenever feasible . however , activation of the hemostatic system is still detectable in off - pump cardiac surgery . a second strategy would be to use more advanced perfusion circuits , such as minimized perfusion circuits ( mpcs ) , for those operations where conventional circuits are not necessary . the biomarker profile measured during the use of mpcs is comparable to the profile measured when conventional circuits are in use . minimized perfusion circuits minimized perfusion circuits are usually comprised of venous and arterial tubings , a centrifugal pump , a membrane oxygenator ( optionally with integrated arterial line filter ) and cannulae . a venous reservoir and suction devices ( vent and field suction ) all components of the circuits are either heparin coated or treated with alternative coating agents .   the use of centrifugal arterial pumps is advocated . further , low priming volume of mpcs in contrast to conventional circuits , the use of cell salvage devices instead of intraoperative retransfusion of untreated suction blood as well as venous line air handling devices are characteristics of these miniaturized systems . initial concerns about a lack of safety in air - handling or cases of major blood loss could be refuted by the results of studies focusing on that matter . even demonstrated superiority in the handling of air in an mpc compared to conventional bypass . modular concepts of mpcs allow the quick integration of additional suckers and reservoirs if major bleeding occurs . a variety of studies was undertaken in order to determine differences in patient outcomes when conventional cpb circuits were compared to minimized perfusion circuits . to date , a number of studies with prospective randomized design and a cohort of more than 40 patients have been published   ( table 1 ) . clinical experience and findings with mpcs . describe the effect of minimized circuits on inflammatory markers and end - organ effects . although a reduction in the amount of circulating inflammatory markers can be measured , the authors state that survival rates of patients operated upon with conventional cpb do not differ from those of patients operated on with mpc . in contrast , anastasiadis et al . in their metaanalysis found that so - called minimal extracorporeal circulation improved short - term patient outcome by reducing the mortality and morbidity associated with conventional systems . the requirement for blood transfusion is today regarded as a risk factor for adverse long - term outcome in cardiac surgery . avoiding transfusion by reducing hemodilution , caused by excessive priming volume of conventional cpb circuits , is recommended . the use of mini - circuits is advocated especially in patients with high risks for adverse effects of hemodilution . mpcs are associated with significantly reduced hemodilution and higher hematocrit at the end of the extracorporeal circulation , as compared with conventional cpb .   a retrospective study on transfusion requirements in 285 coronary artery bypass grafting ( cabg ) patients compared off - pump procedures , conventional circuits ( with cold hydroxyethyl starch cardioplegia ) and mpcs ( with warm blood cardioplegia ) . the authors stated that significantly fewer blood transfusions were needed in the mpc group than in the off - pump and conventional cpb groups . for the conventional cpb group , the use of thrombocyte concentrates was higher on the day of operation than in the mpc group . however , the results of this study may be questionable , since the type of cardioplegia differed between the on - pump groups . a metaanalysis of randomized controlled studies , which included pooled data from 1051 patients , found that mpcs decreased the risk of red blood cell transfusion and the amount of red blood cells transfused per patient when compared with conventional cpb in cabg patients .   in a prospective randomized multicenter study ( 6 hospitals ) , five hundred patients were included ; 252 patients were assigned to the same type of mpc , 248 patients were assigned to the standard open cpb system of the respective hospital . in this study , favorable results were noted for the mpc procedures regarding transfusion requirements , incidence of atrial fibrillation and the incidence of major adverse events ( death , myocardial infarction , major cerebrovascular accidents , re - operation ) . furthermore , an optimal outcome , defined as freedom from blood transfusion or any adverse event , was clearly in favour of the mpc group ( 52% vs. 41% ; p = 0.02 ) . this study also showed significant differences regarding biochemical parameters in favour of the mpc group . beside platelets , red and white blood cells , granulocytes and lymphocytes , plasma free hemoglobin , creatinine and ldh were measured . miniaturized cpb in pediatric surgery in analogy to the developments in adult cardiac surgery , interest in reducing hemodilution and the subsequent necessity for transfusion of homologous blood components in pediatric cardiac surgery has increased recently . alongside the potential for transmission of infection , the use of fresh whole blood for priming heart lung machines for children and the use of blood components are triggers for altered immunologic function . for this reason , avoiding blood components for priming of the cpb circuit may have beneficial effects . miniaturization of conventional cpb has been achieved in experimental surgery and in clinical practice . the asanguineous priming fluid in the animal model described by hickey et al . was found to improve postoperative right ventricular function , pulmonary compliance , alveolar gas exchange , recovery of cerebral perfusion and the inflammatory cytokine load . initial experiences with blood - free priming of a conventional cpb circuit for a neonatal cardiac operation   showed that this approach was possible . subsequently , neonates in several series were operated on without the use of blood prime [ 30 , 31 ] . in a retrospective analysis on 288 children from the same institution , children weighing from 1.7 to 15.9 kg were divided into the three categories no transfusion , postoperative transfusion only , and intraoperative as well as postoperative transfusion .   of these children , 24.7% did not require any form of blood transfusion during their hospital stay , 23.6% received transfusions postoperatively , and 51.7% received intra- and postoperative transfusion . it was noted that this achievement was only possible because of the concerted efforts of the surgeon , anaesthesiologist and perfusionist in addition to the availability of the appropriate equipment . conduct and monitoring of cpb while the conduct of cpb was referred to as  experience based  in contrast to based on evidence only a short while ago , a number of publications have subsequently dealt with this issue . shann et al . gathered available evidence on the practice of cpb in adults , mainly focusing on neurologic injury , glycemic control , hemodilution and the inflammatory response . one of the recommendations of this paper was to avoid direct retransfusion of unprocessed blood exposed to pericardial and mediastinal surfaces . also , hemodilution should be minimized to avoid subsequent allogeneic blood transfusion .   in a following paper , murphy et al . focused on management of physiologic parameters during cpb , namely on determinants of tissue oxygen supply and demand , such as mean arterial pressure , systemic bypass flow rates , hematocrit values , oxygen delivery , systemic temperatures , pulsatility and acid - base management . the authors addressed these topics extensively , but also concluded that since there is limited high quality data on perfusion - related issues , evidence - based guidelines are of uncertain reliability .   the term  goal - directed perfusion management  was created by the working group of ranucci et al . one of the key findings of a recent publication is the statement that oxygen delivery should be preserved by reducing hemodilution and maintaining high pump flows , since a nadir oxygen delivery of 262ml / min / m during cpb is associated with acute kidney failure .   in the future , more patient - targeted pharmaceutical strategies , including genetic risk profiles for hemostatic activation , will make it possible to select the appropriate cpb technology for a given patient . the combined strategies of avoiding excessive hemodiluion , decreasing cpb circuit size , avoiding blood transfusion , limiting the use of cardiotomy suction , and the use of re - engineered and optimized perfusion circuits may make cardiopulmonary bypass more patient - friendly .   the knowledge base for cardiopulmonary bypass related technologies has expanded , and evidence - based guidelines have been established in some areas . well - controlled studies on the effect of interventions are warranted to help in choosing the right technology for the right patient .
the development and improvement of cardiopulmonary bypass technology is an ongoing process . during the past decade , 
 a number of publications on improvements and best practices have appeared , especially in the areas of biocompatibility , materials sciences , instrumentation , monitoring of physiological parameters and knowledge base ( education and evidence - based medicine ) . 
 biocompatibility may be defined not only as an inherent property of a particular composition of matter , but also as a set of properties concerning shape , finish , fabrication techniques and choice of application . materials in use for cardiopulmonary bypass have changed and coated components have been used frequently . 
 improvements in the area of instrumentation were achieved by adaptation of conventional cardiopulmonary bypass circuits . 
 miniaturization and re - design of cardiopulmonary bypass circuits ( so - called minimized perfusion circuits or minimal extracorporeal circulation circuits ) have made cardiopulmonary bypass technology less traumatic . 
 a team approach , including the cardiac surgeon , the anesthesiologist and the cardiovascular perfusionist , was deemed beneficial in order to achieve further improvements . 
 next to choice of technology and material for a given operation , adjunct measures such as pharmaceutical treatment and blood conservation strategies need to be taken into consideration . 
 monitoring of variables during cardiopulmonary bypass has made some progress , while the knowledge base has expanded due to studies on best practices . 
 for the immediate future , sound scientific knowledge and intelligent monitoring tools will allow cardiopulmonary bypass to be tailored to individual patients needs .