Miniaturization in cardiopulmonary bypass

Clinical and Biomaterial Evaluation of a new Condensed Dual-Function Extracorporeal Circuit in Reoperation for Coronary Artery Bypass Surgery

Purpose

This prospective, randomized study compared the clinical performance of three types of circuits: a newly introduced, fully-coated, interchangeable open-closed circuit with a dual configuration (hard shell with a bypass shunt), reduced length, and reduced prime of less than 800 cc (CondECC); a completely coated circuit (ECC); and a similar uncoated, open circuit with standard length and prime (CONT).

Methods

75 patients undergoing reoperation for coronary revascularization were randomly allocated into three groups (N=25): Group 1: CondECC with shortened tubing, components and an open-closed configuration of low priming volume with a centrifugal pump and a shunt which bypassed the reservoir for closed configuration; Group 2: ECC with a roller pump and hard-shell reservoir; Group 3: CONT. Blood samples for CBC, inflammatory mediators [Interleukin-2 (IL-2), Complement-3a (C3a)] and flow cytometry (CD11 b/CD18) were collected after induction (T1) and heparin administration (T2), 15 min after cardiopulmonary bypass (CPB) (T3), before cessation of CPB (T4), 15 min after reversal (T5), and the first postoperative day (T6).

Results

Leukocyte counts demonstrated significant increases at T4, T5 in CONT but remained stable in ECC and CondECC (p<0.05). Platelets were preserved better at T4, T5 in both ECC and CondECC study groups (p<0.05). IL-2 and C3a levels were significantly lower at T3, T4, T5 in CondECC and T4, T5 in ECC (p<0.05). Blood protein adsorption analysis demonstrated increased amount of microalbumin on CONT fibers (p<0.05).

Conclusions

The CondECC is a flexible, dual-function, open/closed configuration system that was easy to use, safe and achieved better biocompatibility when compared to coated and uncoated conventional circuits.

Reduction of hemodilution in small adults undergoing open heart surgery: a prospective, randomized trial

Background. Given that there is an association between the degree of hemodilution during cardiopulmonary bypass (CPB) and postoperative complications, patients-outcome might be improved if the nadir hematocrit concentration is kept within an optimal range. Smaller patients are more likely to have a low hematocrit during CPB: this phenomenon may be related, at least partially, to the extreme hemodilution induced by a large fixed CPB priming volume. Methods. Forty patients with a body surface area (BSA) < 1.7 m2 undergoing open heart operations were randomized to either standard CPB with full prime volume (control group) or reduced prime extracorporeal circuit and vacuum-assisted venous drainage (VAVD) (study group). Results. There were no significant differences between the groups with respect to baseline characteristics, body surface area, hematologic profile and operative data. Clinical outcomes were similar. Nadir hematocrit and hemoglobin on bypass were significantly lower in the control group (22 ± 2.3 vs 24 ± 2.5%, p < 0.02 and 7.4 ± 0.7 vs 8 ± 0.9g/dl, p < 0.04, respectively).

Postoperative chest tube drainage was significantly higher in the control group (272 ± 253vs 139 ± 84ml, p < 0.04). There was no difference in blood transfusion in the two groups (0.5 ± 1.14 v 1.0 ± 1.77 units of packed red blood cells (PRBC), p = 0.29). Conclusions. Lowering CPB priming volume by means of using a small oxygenator and vacuum-assisted venous drainage (VAVD) resulted in a significant decrease of intraoperative hemodilution. This technique should be strongly considered for patients with a small BSA (<1.7 m2) undergoing open heart surgery. Perfusion (2007) 22, 317—322.

Prospective study on cardiopulmonary bypass prime reduction and its effect on intraoperative blood product and hemoconcentrator use

Purpose: Evaluate the feasibility and clinical significance of crystalloid prime reduction during the initiation of cardiopulmonary bypass (CPB) using a modified bridge on the cardioplegia delivery system.

Methods: Prospective trial of crystalloid prime reduction using a standard Duraflow®-coated CPB circuit and Vanguard® 2:1 cardio plegia delivery system. Standard prime volume was 1500 cc of Plasmalyte. Prime was reduced via the bridge in the cardioplegia system during initiation of CPB. Packed red blood cells (PRBC) were transfused for hematocrit (Hct) less than 24% while rewarming. A hemoconcentrator was used if the patient’s circulating blood volume exceeded 150% of calculated. All data were prospectively collected.

Results: Two hundred and twenty-two consecutive patients undergoing cardiac surgery utilizing CPB were evaluated. There were 107 patients with normal prime volume (NPV) and 115 patients with reduced prime volume (RPV). There was no significant difference in sex, mean age, weight, body surface area (BSA), pre-op Hct, procedure time or procedure between the two groups. There was no difference in total crystalloids infused by the anesthetists (average NPV 1205 cc versus RPV 1148 cc). The average RPV was 622 cc (range 400 - 1100 cc) or a 59% reduction. Post-op Hct revealed no difference (NPV 28% versus RPV 29%). There was a 24% reduction in patients requiring PRBC (NPV n=23 versus RPV n=18). The use of hemoconcentrators was reduced by 49% (NPV n=18 versus RPV n=11). The average urine output for both groups exceeded 100 cc/hour while on CPB.

Conclusion: Using a modified cardioplegia delivery system is a safe and effective method of CPB prime reduction. A RPV resulted in fewer patients requiring PRBC transfusions and fewer hemoconcentrators used. Based on our experience, we would recommend attempting to reduce prime volume in all patients undergoing CPB.

[Veno-arterial extracorporeal membrane oxygenation. Indications, limitations and practical implementation]

Due to the technical advances in pumps, oxygenators and cannulas, veno-arterial extracorporeal membrane oxygenation (va-ECMO) or extracorporeal life support (ECLS) has been widely used in emergency medicine and intensive care medicine for several years. An accepted indication is peri-interventional cardiac failure in cardiac surgery (postcardiotomy low cardiac output syndrome). Furthermore, especially the use of va-ECMO for other indications in critical care medicine, such as in patients with severe sepsis with septic cardiomyopathy or in cardiopulmonary resuscitation has tremendously increased. The basic indications for va-ECMO are therapy refractory cardiac or cardiopulmonary failure. The fundamental purpose of va-ECMO is bridging the function of the lungs and/or the heart. Consequently, this support system does not represent a causal therapy by itself; however, it provides enough time for the affected organ to recover (bridge to recovery) or for the decision for a long-lasting organ substitution by a ventricular assist device or by transplantation (bridge to decision). Although the outcome for bridged patients seems to be favorable, it should not be forgotten that the support system represents an invasive procedure with potentially far-reaching complications. Therefore, the initiation of these systems needs a professional and experienced (interdisciplinary) team, sufficient resources and an individual approach balancing the risks and benefits. This review gives an overview of the indications, complications and contraindications for va-ECMO. It discusses its advantages in organ transplantation and transport of critically ill patients. The reader will learn the differences between peripheral and central cannulation and how to monitor and manage va-ECMO.

Oxygenator Is the Main Responsible for Leukocyte Activation in Experimental Model of Extracorporeal Circulation: A Cautionary Tale

In order to assess mechanisms underlying inflammatory activation during extracorporeal circulation (ECC), several small animal models of ECC have been proposed recently. The majority of them are based on home-made, nonstandardized, and hardly reproducible oxygenators. The present study has generated fundamental information on the role of oxygenator of ECC in activating inflammatory signaling pathways on leukocytes, leading to systemic inflammatory response, and organ dysfunction. The present results suggest that experimental animal models of ECC used in translational research on inflammatory response should be based on standardized, reproducible oxygenators with clinical characteristics.

Selection of priming solutions for cardiopulmonary bypass in adults

The issue of choosing the right priming solution for adult cardiopulmonary bypass patients has been studied and argued for at least three decades. However, there is still no general consensus with regard to making the right choice. Basically, priming solutions can be classified into two categories, i.e. crystalloids and colloids. The former consists of dextrose, balanced crystalloid fluids, and mannitol, and the latter consists of albumin, dextrans, gelatins, and hydroxyethyl starch. In general, crystalloids are simple volume expanding solutions that mimic the normal plasma electrolyte concentrations. They can be used as clear priming solutions resulting in effective hemodilution but they lack oncotic activity. On the contrary, colloids have the advantage in maintaining the colloid oncotic pressure and reducing tissue oedema. However, colloids have been associated with increased incidence of anaphylactoid reactions and clinical coagulopathy. In this paper, we will describe the basic characteristics, the clinical efficiency and the safety of different types of priming fluids and make an overview on how to select the ideal priming solution for cardiopulmonary bypass in adults.

The early inflammatory response in a mini-cardiopulmonary bypass system: a prospective randomized study

OBJECTIVE

The aim of this study was to compare the early systemic inflammatory response of the Resting Heart System (RHS; Medtronic, Minneapolis, MN USA), a miniaturized cardiopulmonary bypass (CPB) system, with two groups using a standard extracorporeal circulation system during on-pump coronary artery bypass grafting (CABG) surgery.

METHODS

A total of 60 consecutive patients requiring CABG were prospectively randomized to undergo on-pump CABG using conventional CPB without cardiotomy suction (group A), conventional CPB with cardiotomy suction (group B), or the RHS (group C). Blood samples were collected at five time points: immediately before CPB, 30 minutes into CPB, immediately at the end of CPB, 30 minutes post-CPB, and 1 hour post-CPB. Inflammation was analyzed by changes in (a) levels of plasma proteins, including inflammatory cytokines (interleukin-6 [IL-6], IL-10, and tumor necrosis factor-α), chemokines (IL-8, monokine induced by interferon-γ, monocyte chemotactic protein-1, regulated on activation normal T cell expressed and secreted, and interferon-inducible protein-10), and acute phase proteins (C-reactive protein and complement protein 3); (b) biochemical variables (cardiac troponin I, hematocrit, and immunoglobulin G); and (c) cell numbers (leukocytes, neutrophils, and thrombocytes).

RESULTS

The RHS showed more delayed secretion of the cytokines tumor necrosis factor-α and IL-10, chemokines monokine induced by interferon-γ (P < 0.001); IL-8, and interferon-inducible protein-10; and complement protein 3 than conventional CPB systems did. Median thrombocyte numbers were higher in the RHS group. Levels of cardiac troponin I, monocyte chemotactic protein-1, and IL-6 were lower in both the RHS and conventional CPB without suction than with suction. Levels of C-reactive protein and regulated on activation normal T cell expressed and secreted, plus leukocyte and neutrophil numbers, were similar in all groups.

CONCLUSIONS

The Medtronic RHS may induce less systemic inflammation than conventional CPB systems, particularly when cardiotomy suction was used, but it did not result in improved clinical benefit.

Thirty-day in-vivo performance of a wearable artificial pump-lung for ambulatory respiratory support

BACKGROUND

The purpose of this study was to evaluate the long-term in-vivo hemodynamics, gas transfer, and biocompatibility of an integrated artificial pump-lung (APL) developed for ambulatory respiratory support.

METHODS

The study was conducted in an ovine model by surgically placing the APL between the right atrium and pulmonary artery. Nine sheep were implanted. Heparin was infused as an anticoagulant. The device flow, gas transfer, and plasma free hemoglobin were measured daily. Hematologic data, platelet activation, and blood biochemistry were assessed twice a week. After 30 days, the sheep were euthanized for postmortem examination. The explanted devices were examined for gross thrombosis.

RESULTS

Five sheep survived for 29 to 31 days and were electively terminated. Four sheep died or were terminated early owing to mechanical failure of intravenous lines or device. The APL devices in the 5 long-term animals were capable of delivering an oxygen transfer rate of 148±18 mL/min at a flow rate of 2.99±0.46 L/min with blood oxygen saturation of 96.7%±1.3%. The device flow and oxygen transfer were stable over 30 days. The animals had normal end-organ functions except for surgery-related transient alteration in kidney function, liver function, and cell and tissue injury. There was no hemolysis. The device flow path and membrane surface were free of gross thrombus.

CONCLUSIONS

The APL exhibited the capability of providing respiratory support with excellent biocompatibility, long-term reliability, and the potential for bridging to lung transplant.

A novel wearable pump-lung device: in vitro and acute in vivo study

BACKGROUND

To provide long-term ambulatory cardiopulmonary and respiratory support for adult patients, a novel wearable artificial pump-lung device has been developed. The design features and in vitro and acute in vivo performance of this device are reported.

METHODS

This device features a uniquely designed hollow-fiber membrane bundle integrated with a magnetically levitated impeller that together form one ultracompact pump-lung device, which can be placed like current paracorporeal ventricular assist devices to allow ambulatory support. The device is 117 mm in length and 89 mm in diameter and has a priming volume of 115 ml. In vitro hydrodynamic, gas transfer and biocompatibility experiments were carried out in mock flow-loops using ovine blood. Acute in vivo characterization was conducted in an ovine model by surgically implanting the device between right atrium and pulmonary artery.

RESULTS

The in vitro results show that the device with a membrane surface area of 0.8 m(2) was capable of pumping blood from 1 to 4 liters/min against a wide range of pressures and transferring oxygen at a rate of up to 180 ml/min at a blood flow of 3.5 liters/min. Standard hemolysis tests demonstrated low hemolysis at the targeted operating condition. The acute in vivo results also confirmed that the device can provide sufficient oxygen transfer with excellent biocompatibility.

CONCLUSIONS

Based on in vitro and acute in vivo study findings, this highly integrated wearable pump-lung device can provide efficient respiratory support with good biocompatibility and it is ready for long-term evaluation.

Comparison of two different minimized extracorporeal circulation systems: hematological effects after coronary surgery

Cardiopulmonary bypass induces hemolysis and activation of inflammatory and coagulation systems as a result of a combination of mechanical trauma and biological mechanisms. The aim of our study was to evaluate the performance of two different minimized extracorporeal circulation (ECC) systems and to compare their influence on blood components. From January 2003 to December 2008, 1,218 patients underwent coronary artery bypass grafting with minimized ECC. The PRECiSe system (41%) consists of a microporous capillary membrane oxygenator (MO) and a diagonal pump (DeltaStream DP2). The MECC system (59%) is composed of a polymethylpentene MO with a plasma-tight diffusion membrane and a centrifugal pump (RotaFlow). Serial blood samples were taken preoperatively (T0), on arrival to intensive care unit (T1), 6 hours postoperatively (T2), and at discharge (T3). Demographic data, intraoperative, and technical parameters were similar in both groups. At T1 and T2, the platelet count in the PRECiSe group was significantly lower than that in the MECC group (p < 0.01). Furthermore, at T1, levels of lactate dehydrogenase were significantly higher in the PRECiSe group (p < 0.05). In addition, postoperative blood loss was significantly higher using the PRECiSe system (p < 0.05). In conclusion, cardiac surgery with the MECC system is associated with less postoperative bleeding and improved blood cell preservation.

Perfusion approaches to blood conservation

There are several perfusion techniques that can contribute to blood conservation. Minimizing existing circuit components, using mini-circuits and the maneuver of retrograde autologous priming can be considered steps in prime reduction. Microplegia systems may also reduce systemic as well as cardiac hemodilutional effects. Cell savers can scavenge shed blood, wash the red cells, and may return the red cells to the patient in a concentrated form. When a patient is already hemodiluted, ultrafiltation can be used to hemoconcentrate the patient and to drive their existing hemoglobin levels up. Ultimately, the optimal form of blood conservation comes from team-work, communication, and a combination of efforts.

The Use of a Miniaturized Circuit and Bloodless Prime To Avoid Cerebral No-Reflow After Neonatal Cardiopulmonary Bypass

BACKGROUND

Our miniaturized bloodless prime circuit for neonatal cardiopulmonary bypass (CPB) has previously been shown to elicit significantly reduced systemic inflammation. We studied the effects of this circuit on cerebral reperfusion because the pathophysiology of "no-reflow" is believed to have an inflammatory component.

METHODS

Twenty neonatal piglets were randomized to CPB with miniaturized circuitry using either blood (group 1) or bloodless (group 2) prime. At 18 degrees C, piglets underwent 60 minutes of either (A) deep hypothermic circulatory arrest (DHCA) or (B) continuous low-flow bypass (DHCLF). Analysis of cerebral blood flow (CBF) was undertaken before and after CPB in addition to quantification of circulating tumor necrosis factor-alpha (TNFalpha) and intracerebral TNFalpha messenger RNA (mRNA).

RESULTS

The final hematocrit in group 2 was 22% versus 28% (p < 0.05). The CBF fell in every animal in group 1A, but increased in every animal in group 2A (p < 0.001), despite no overall change in total cardiac output. The use of DHCLF was not associated with pronounced trends in either prime group. Final serum TNFalpha concentrations were significantly higher in group 1B (3166 +/- 843 pg/mL) than group 2B (439 +/- 192 pg/mL; p < 0.05). Irrespective of the CPB strategy used, the use of a blood prime generated significantly higher levels of intracerebral TNFalpha mRNA.

CONCLUSIONS

We attribute the hyperemic cerebrovascular response to reduced inflammation through avoiding allogeneic whole blood. The analysis of circulating and intracerebral TNFalpha in this study suggests that DHCLF in conjunction with a bloodless prime might offer advantages through avoiding ischemia, no-reflow, and in addition, resulting in a significantly reduced cerebral inflammatory response.

Effects of Circuit Miniaturization in Reducing Inflammatory Response to Infant Cardiopulmonary Bypass by Elimination of Allogeneic Blood Products

Conventional neonatal cardiopulmonary bypass requires the use of large volumes of allogeneic blood to prevent unacceptable hemodilution. Evidence is accumulating to suggest that the use of blood products during cardiopulmonary bypass has a negative effect on clinical recovery through inflammatory side effects. This would suggest an advantage for eliminating blood use in infant cardiopulmonary bypass through circuit miniaturization. In this article, we review the data supporting this rationale and provide the results from studies in our laboratory that emphasize the benefits of circuit miniaturization.

Normothermic Beating Heart Surgery with Assistance of Miniaturized Bypass Systems: The Effects on Intraoperative Hemodynamics and Inflammatory Response

The use of miniaturized cardiopulmonary bypass (CPB) circuits and avoidance of cardioplegic arrest are attempts to reduce the inflammatory response to cardiac surgery. We studied the effects of beating heart surgery (BHS) with assistance of simplified bypass systems (SBS) on global hemodynamics, myocardial function and the inflammatory response to CPB. We hypothesized that the use of SBS was associated with less hemodynamic instability after CPB resulting from attenuation of the inflammatory response when compared with surgery performed with a conventional CPB (cCPB) circuit. Forty-five patients undergoing coronary artery bypass grafting were prospectively studied. Fifteen patients were randomized to the use of a cCPB circuit, cold crystalloid cardioplegia, and moderate hypothermia. Two groups of 15 patients underwent BHS during normothermia with assistance of two different SBS consisting of only blood pump and oxygenator. Hemodynamic variables were assessed with transpulmonary thermodilution and transesophageal echocardiography. Plasma levels of proinflammatory and antiinflammatory mediators were measured perioperatively. After CPB, variables of global hemodynamics and systolic ventricular function did not differ among groups. Left ventricular diastolic function was impaired after CPB equally in all groups (P < 0.01 versus pre-CPB). At the end of surgery, there was more need for vasopressor (norepinephrine) support in both SBS groups than in the cCPB group (P < 0.01). After CPB, the release of interleukin (IL)-6 did not differ significantly among groups, whereas plasma levels of IL-10 were higher in the cCPB group (P < 0.01 versus SBS). The extent of myocardial necrosis (Troponin T) was comparable in all groups. We conclude that in our study, miniaturizing bypass systems and avoidance of cardioplegic arrest were not effective in improving hemodynamic performance and in attenuating the proinflammatory immune response after CPB.

The use of Minimized Extracorporeal Circulation System has a Beneficial Effect on Hemostasis--A Randomized Clinical Study

BACKGROUND

Conventional cardiopulmonary bypass (CPB) is associated with increased coagulation and fibrinolytic activity. A closed miniaturized bypass circuit (CorX) features a significantly reduced tubing set, an integrated pump, and an air removal system without a cardiotomy reservoir. In a prospective randomized trial, the effects on hemostasis were investigated while comparing CorX with conventional CPB in patients undergoing coronary artery bypass grafting.

METHODS

Over a period of 1 year, 81 patients were randomly assigned either to the CorX system (n = 39, group A) or standard CPB system (n = 42, group B). Primary endpoints were platelet count, plasmin-antiplasmin complex (PAP), prothrombin fragments 1+2 (F1+F2), D-dimers, and fibrinogen. Secondary end-points were hematocrit, blood loss in the first 12 hours postoperatively, transfused packed red blood cells, and fresh frozen plasma in the first 24 hours postoperatively. In addition, we analyzed partial thromboplastin time, prothrombin time, and antithrombin III.

RESULTS

After aortic declamping, PAP complex and prothrombin F1+F2 were significantly lower in group A than in group B. The difference in D-dimers between groups reached significance at 1 hour post-CPB. Hematocrit values at the end of CPB measured 26 +/- 6% in group A versus 22 +/- 4% in group B (P = .01). The rest of the observed parameters did not significantly differ between groups.

CONCLUSION

Postoperative blood loss was not reduced in the present study. However, the use of the CorX system leads to a significant suppression of activation of coagulation and fibrinolytic cascades compared to conventional CPB, suggesting that miniaturized extracorporeal circuits are a step forward toward reduced imbalance of hemostasis in cardiac surgery.

Initial Experience With a Minimized Extracorporeal Bypass System: Is There a Clinical Benefit?

BACKGROUND

Drawbacks of conventional cardiopulmonary bypass (CPB) are increased inflammatory response, deteriorated coagulation and systemic organ dysfunction. A closed extracorporeal circuit (CorX) features reduced foreign surface area and priming volume. Potential benefits were studied in comparing the CorX system with conventional CPB in arrested heart coronary artery bypass grafting (CABG).

METHODS

Two hundred and four patients were randomly assigned either to CorX system (n = 101, group A) or a standard CPB with cardiotomy reservoir (n = 103, group B). Besides evaluation of perioperative data and routine blood samples, we focused on lung function and perioperative bleeding. Polymorphonuclear elastase (PMNE) and terminal complement complex (TCC) served to assess inflammatory response.

RESULTS

Patient demographics and operative data did not differ between groups. Postoperative lung function was not significantly impaired comparing groups A and B. Intraoperative blood loss was significantly higher in group A compared with group B (1245 +/- 947 mL vs 313 +/- 282 mL, p < 0.0001) as well as the need of fresh frozen plasma. Postoperative chest drainage did not differ significantly between groups. Two patients in each group required re-exploration due to bleeding. One hour after CPB, PMNE as well as TCC were significantly lower in group A compared with group B (PMNE: 76 +/- 44 ng/mL vs 438 +/- 230 ng/mL, p < 0.0001; TCC: 16 +/- 8 IU/mL vs 29 +/- 19 IU/mL, p < 0.0001).

CONCLUSIONS

The CorX system is safe and feasible in patients undergoing CABG. Despite of markedly reduced inflammatory reaction, no clinical benefit was observed.