Biocompatibility of three different membrane oxygenators: effects on complement, neutrophil and monocyte activation

Evaluation of cytokine response to extracorporeal membrane oxygenation

RATIONALE

Increased cytokine response is common in patients receiving extracorporeal life support and is often a poor prognostic indicator. There is interest in using adjunctive cytokine adsorption technologies to reduce inflammatory burden, However, it is debated whether extracorporeal membrane oxygenation (ECMO) itself provides therapeutic benefit beyond gas exchange. Thus, we sought to characterize the inflammatory profile of ECMO in the first 72-96 h of and quantify its effect on cytokine levels in a case series of patients undergoing ECMO.

METHODS

Eight patients initiating ECMO were studied. Of these, we measured cytokines pre- and post-oxygenator over 96 h. Comparisons of cytokine levels were made across the oxygenator and over time.

RESULTS

The average age of patients was 64.3 years with 62% being male. Centrally cannulated patients had higher IL-6 levels (820.43 vs. 6907.53 pg/ml, p < 0.03), whereas peripherally cannulated patients had higher IL-12p70 levels (7.73 vs. 2.59 pg/ml, p < 0.05). Cytokine levels on day one included IL-12p70 (4.17 ± 2.56), IL-6 (4971.23 ± 8569.88), TNF (undetected), IL-8 (346.68 ± 670.18), IL-1B (undetected), and IL-10 (72.27 ± 87.9). Cytokine levels increased over 96 h; however, no significant differences were appreciated despite blood product transfusion. On day 3, IL-12p70 levels were significantly lower post-oxygenator (p < 0.05).

CONCLUSION

The inflammatory profile of ECMO does not change significantly over the early course of illness when accounting for transfusion. However, the decrease in IL-12p70 specifically at day 3 of ECMO may indicate adsorption of specific inflammatory markers by the oxygenator although the clinical significance of this is still unknown. Further investigation of the oxygenator on cytokine response is warranted.

Clinical Evaluation of Five Commercially Available Adult Oxygenators in Terms of Pressure Drop during Normothermic and Hypothermic Cardiopulmonary Bypass

Background

It is well documented that trans-membrane pressure drop (TMPD) of hollow-fiber membrane oxygenators (HFMO) may lead to hemolysis, damage to platelets, and systemic inflammatory response. The purpose of this study was to evaluate five commercially available adult oxygenators in terms of pressure drop during normothermic and hypothermic cardiopulmonary bypass (CPB).

Materials and Methods

In a clinical setting, 5 different adult HFMOs were tested in terms of TMPDs. Forty patients scheduled for cardiac surgery were enrolled in the study and were divided into 5 groups according to the type of oxygenator used during CPB: group J (Maquet Quardox n=8), group A (Affinity NT n=8), group P (Polystan Safe Maxi n=8), group T (Terumo Capiox SX 18 n=8) and group C (COBE APEX-TM n=8). Clinical parameters were collected during CPB, including mean arterial pressure (MAP), pump flow, temperature, hematocrit, duration of CPB, cross-clamp time and bypass time. TMPDs of pre-oxygenator and post-oxygenator pressures were recorded at the start of systemic cooling (T1), 10 min after stable hypothermia at 30°C (T2), and at termination of rewarming before the end of CPB (T3).

Results

There were no significant differences among the 5 groups in pump-flow rate, temperature, hematocrit, and mean arterial pressure during CPB. TMPDs of group J were the lowest at different time-points (T1, 30.71 ± 8.42mmHg; T2, 25.71 ± 5.41 mmHg; T3, 27.42 ± 13.01 mmHg). Compared to the other 3 groups (P, C and T groups), TMPDs of groups J and A at various time-points were lower (J group compared with the other three groups (p<0.001). Although TMPDs in groups A, P and T during hypothermia were higher than during normothermia and post-rewarming, there was no significant statistical difference (p> 0.05).

Conclusions

These results suggest that the HFMOs in groups J and A produced significantly lower TMPDs and pre- and post-oxygenator extracorporeal circuit pressures during normothermic and hypothermic CPB.

180 ml and less: Cardiopulmonary bypass techniques to minimize hemodilution for neonates and small infants

Objective. To determine the efficacy of decreasing cardiopulmonary bypass (CPB) prime volume for neonates and small infants by using low prime oxygenators, small diameter polyvinyl chloride (PVC) tubing and removing the arterial line filter (ALF) in an effort to reduce intraoperative exposure to multiple units of packed red blood cells (PRBC). Methods. Two retrospective database studies comparing neonatal CPB prime volume were undertaken: Study 1 — A CPB circuit consisting of a 1/8 inch arterial line, a 3/16 inch venous line and a low prime oxygenator with 172 ml total circuit prime ( n = 74) was compared to a circuit with a 3/16 inch arterial line, a 1/4 inch venous line and a higher prime oxygenator with a 350 ml total circuit prime ( n = 74). Study 2 — The 172 ml circuit ( n = 389) was compared to a circuit that included an ALF and had a total circuit prime volume of 218 ml ( n = 389). Results. Study 1— of the 74 neonates and small infants whose CPB prime volume was 350 ml, 19 were exposed to two or more intraoperative exogenous PRBC units while only 3 neonates and small infants in the 172 ml prime group ( n = 74) received two or more units ( p = 0.0002). Study 2 — of the 389 neonates and small infants where an ALF was used (prime volume 218 ml), 54 were exposed to two or more exogenous PRBC units while only 36 of the 389 patients where an ALF was not used (prime volume 172 ml) received two or more units of intraoperative PRBCs ( p = 0.0436). Conclusion. Decreasing the neonatal and small infant extracorporeal circuit prime volume by as little as 46 ml resulted in significantly fewer multiple exposures to exogenous PRBC units. Perfusion (2007) 22, 327—331.

Miniature cardiopulmonary bypass — the Hammersmith experience

The decision to embark on a miniature cardiopulmonary bypass programme requires careful planning. The objective of this paper is to present our experience and initial findings for consideration by our multidisciplinary peers, who may wish to implement this technology at their own hospitals. The paper reviews the evolution of our programme over the first 150 clinical cases and our current position on the advantages and disadvantages of miniature cardiopulmonary bypass. Perfusion (2007) 22, 161—166.

Cardiac compression of lung lower lobes after coronary artery bypass graft with cardiopulmonary bypass

Background

Atelectasis is a major cause of hypoxemia after coronary artery bypass grafting (CABG) and is commonly ascribed to general anesthesia, high inspiratory oxygen concentration and cardiopulmonary bypass (CPB). The objective of this study was to evaluate the role of heart-induced pulmonary compression after CABG with CPB.

Methods

Seventeen patients without pre-operative cardiac failure who were scheduled for coronary artery bypass graft underwent pre- and postoperative thoracic computed tomography. The cardiac mass, the pressure exerted on the lungs by the right and left heart and the fraction of collapsed lower lobe segments below and outside of the heart limits were evaluated on a computed tomography section 1 cm above the diaphragmatic cupola.

Results

In the postoperative period, cardiac mass increased by 32% (117±31 g versus 155±35 g, p<0.001), leading to an increase in the pressure that was exerted on the lungs by the right (2.2±0.6 g.cm⁻² versus 3.2±1.2 g.cm⁻², p<0.05) and left heart (2.4±0.7 g.cm⁻² versus 4.2±1.8 g.cm⁻², p<0.001). The proportion of collapsed lung segments beneath the heart markedly increased [from 6.7% to 32.9% on the right side (p<0.001) and from 6.2% to 29% on the left side (p<0.001)], whereas the proportion of collapsed lung segments outside of the heart limits slightly increased [from 0.7% to 10.8% on the right side (p<0.001) and from 1.5% to 12.6% on the left side (p<0.001)].

Conclusion

The pressure that is exerted by the heart on the lungs increased postoperatively and contributed to the collapse of subjacent pulmonary segments.

Inhibition of biomaterial-induced complement activation attenuates the inflammatory host response to implantation

Although complement is a known contributor to biomaterial-induced complications, pathological implications and therapeutic options remain to be explored. Here we investigated the involvement of complement in the inflammatory response to polypropylene meshes commonly used for hernia repair. In vitro assays revealed deposition of complement activation fragments on the mesh after incubation in plasma. Moreover, significant mesh-induced complement and granulocyte activation was observed in plasma and leukocyte preparations, respectively. Pretreatment of plasma with the complement inhibitor compstatin reduced opsonization >2-fold, and compstatin and a C5a receptor antagonist (C5aRa) impaired granulocyte activation by 50 and 67%, respectively. We established a clinically relevant mouse model of implantation and could confirm deposition of C3 activation fragments on mesh implants in vivo using immunofluorescence. In meshes extracted after subcutaneous or peritoneal implantation, the amount of immune cell infiltrate in mice deficient in key complement components (C3, C5aR), or treated with C5aRa, was approximately half of that observed in wild-type littermates or mice treated with inactive C5aRa, respectively. Our data suggest that implantation of a widely used surgical mesh triggers the formation of an inflammatory cell microenvironment at the implant site through complement activation, and indicates a path for the therapeutic modulation of implant-related complications.

Computed tomography assessment of lung structure in patients undergoing cardiac surgery with cardiopulmonary bypass

Hypoxemia is a frequent complication after coronary artery bypass graft (CABG) with cardiopulmonary bypass (CPB), usually attributed to atelectasis. Using computed tomography (CT), we investigated postoperative pulmonary alterations and their impact on blood oxygenation. Eighteen non-hypoxemic patients (15 men and 3 women) with normal cardiac function scheduled for CABG under CPB were studied. Hemodynamic measurements and blood samples were obtained before surgery, after intubation, after CPB, at admission to the intensive care unit, and 12, 24, and 48 h after surgery. Pre- and postoperative volumetric thoracic CT scans were acquired under apnea conditions after a spontaneous expiration. Data were analyzed by the paired Student t-test and one-way repeated measures analysis of variance. Mean age was 63 ± 9 years. The PaO2/FiO2 ratio was significantly reduced after anesthesia induction, reaching its nadir after CPB and partially improving 12 h after surgery. Compared to preoperative CT, there was a 31% postoperative reduction in pulmonary gas volume (P < 0.001) while tissue volume increased by 19% (P < 0.001). Non-aerated lung increased by 253 ± 97 g (P < 0.001), from 3 to 27%, after surgery and poorly aerated lung by 72 ± 68 g (P < 0.001), from 24 to 27%, while normally aerated lung was reduced by 147 ± 119 g (P < 0.001), from 72 to 46%. No correlations (Pearson) were observed between PaO2/FiO2 ratio or shunt fraction at 24 h postoperatively and postoperative lung alterations. The data show that lung structure is profoundly modified after CABG with CPB. Taken together, multiple changes occurring in the lungs contribute to postoperative hypoxemia rather than atelectasis alone.

Modulation of systemic inflammatory response after cardiac surgery

Cardiac surgery and cardiopulmonary bypass initiate a systemic inflammatory response largely determined by blood contact with foreign surfaces and the activation of complement. It is generally accepted that cardiopulmonary bypass initiates a whole-body inflammatory reaction. The magnitude of this inflammatory reaction varies, but the persistence of any degree of inflammation may be considered potentially harmful to the cardiac patient. The development of strategies to control the inflammatory response following cardiac surgery is currently the focus of considerable research efforts. Diverse techniques including maintenance of hemodynamic stability, minimization of exposure to cardiopulmonary bypass circuitry, and pharmacologic and immunomodulatory agents have been examined in clinical studies. This article briefly reviews the current concepts of the systemic inflammatory response following cardiac surgery, and the various therapeutic strategies being used to modulate this response.

Induction and detection of disturbed homeostasis in cardiopulmonary bypass

During cardiopulmonary bypass (CPB) haemodynamic alterations, haemostasis and the inflammatory response are the main causes of homeostatic disruption. Even with CPB procedures of short duration, the homeostasis of a patient is disrupted and, in many cases, requires intensive postoperative treatment to re-establish the physiological state of the patient. Although mortality is low, disruption of homeostasis may contribute to increased morbidity, particularly in high-risk patients. Over the past decades, considerable technical improvements in CPB equipment have been made to prevent the development of the systemic inflammatory response syndrome (SIRS). Despite all these improvements, only the inflammatory response, to some extent, has been reduced. The microcirculation is still impaired, as measured by tissue degradation products of various organs, indicating that CPB may still be considered as an unphysiological procedure. The question is, therefore, whether we can detect the pathophysiological consequences of CPB in each individual patient with valid bedside markers, and whether we can relate this to determinant factors in the CPB procedure in order to assist the perfusionist in improving the adequacy of CPB. The use of these markers could play a pivotal role in decision making by providing an immediate feedback on the determinant quality of perfusion. Therefore, we suggest validating the proposed markers in a nomogram to optimize not only the CPB procedure, but also the patient's safety.

Perfusing and ventilating the patient's lungs during bypass ameliorates the increase in extravascular thermal volume after coronary bypass grafting

BACKGROUND

To test the hypothesis that bilateral extracorporeal circulation (ECC) (Drew technique) ameliorates the increase in extravascular thermal volume (ETV) observed after conventional cardiopulmonary bypass (CPB) in patients undergoing coronary artery bypass grafting.

METHODS

Thirty-four consecutive patients underwent either bilateral ECC (n = 24, additional cannulation of pulmonary artery and left atrium and lungs perfused and ventilated during bypass) or conventional CPB (n = 10, right atrial and aortic cannulation, lungs statically inflated to 4 mbar (0.41 cm H(2)O) with oxygen, 500 mL/min). Determinations of ETV (thermodye dilution technique) and intraoperative fluid balance were made before surgery, at the end of surgery, and 4 hours thereafter. In addition, interleukin (IL)-8, thromboxane B2 (TxB(2)), and endothelin (ET)-1 concentrations were measured in the right atrium and pulmonary vein at specified time points.

RESULTS

Comparisons of ETV made at the start of surgery, after aortic declamping, and after termination of ECC, respectively, revealed an increase from 4.8 +/- 0.2 mL/kg (mean +/- SEM) to 6.7 +/- 0.4 mL/kg, and 6.3 +/- 0.3 mL/kg with conventional CPB but ETV remained unchanged at 5.2 +/- 0.3 mL/kg, 5.1 +/- 0.2 mL/kg, and 4.9 +/- 0.3 mL/kg with bilateral ECC. Priming volume (1,580 +/- 10 mL versus 2,213 +/- 77 mL, p < 0.001) and intraoperative fluid balance (+1,955 +/- 233 mL versus +2,654 +/- 210 mL, p < 0.05) were less with conventional CPB. Concentrations of IL-8, TxB(2), and ET-1 were not different between groups.

CONCLUSIONS

Despite a significantly greater prime volume and a more positive intraoperative fluid balance, ETV did not change with bilateral ECC but increased with conventional CPB. Thus, using the patient's lungs as an oxygenator during bypass mitigates the increase in extravascular pulmonary fluid.

Comparison of three commercially available hollow fiber oxygenators: gas transfer performance and biocompatibility

The new generation of oxygenators have improved blood flow pathways that enable reduction in priming volume and, thus, hemodilution during cardiopulmonary bypass (CPB). We evaluated three oxygenators and two sizes of venous reservoirs in relation to priming volume, gas transfer, and blood activation. To compare priming volume, gas transfer, and biocompatibility of three hollow fiber oxygenators and two different size venous reservoirs, 60 patients were randomly allocated in groups to undergo cardiopulmonary bypass. In each group, an oxygenator with a different surface area and priming volume was used: 1.8 m2 and 220 ml (group 1, n = 23), 2.2 m2 and 290 ml (group 2, n = 20), and 2.5 m2 and 270 ml (group 3, n = 17). In groups 1 and 3, a large soft shell (1900 ml) venous reservoir was used, whereas in group 2, a smaller soft shell (600 ml) venous reservoir was used. Gas transfer was assessed by calculating the oxygen transfer rate for each group and per square meter for each oxygenator group. Partial arterial oxygen pressure (paO2) and partial arterial carbon dioxide pressure (paCO2) between the groups were assessed with forward stepwise regression analysis. Biocompatibility was evaluated through measurement of platelet numbers, complement activation products (C3b/c), coagulation (thrombin anti-thrombin III complex), and fibrinolysis (plasmin anti-plasmin complex). No differences were found in oxygen transfer rate per group. However, when correcting the oxygen transfer rate for surface area, group 1 demonstrated a higher oxygen transfer rate compared with group 2 (p < 0.05) at an FiO2 of 40 and 60% and compared with group 3 at an FiO2 of 60 and 70%. The regression analysis showed that the average arterial PO2 was the highest in group 3, i.e., 79.2 mm Hg higher than in group 1 (p < 0.001) and 73.5 mm Hg higher than in group 2 (p < 0.001). Group 3 also had the lowest average arterial pCO2, 0.57 mm Hg lower than in group 1 (p = 0.004) and 0.81 mm Hg lower than in group 2 (p < 0.001). During CPB, platelet numbers decreased significantly in all groups (p < 0.001), without differences between the groups. C3b/c levels increased in all groups during CPB. At cessation of CPB the C3b/c level in group 2 (398 nmol/L(-1)) was significantly higher compared to group 1(251 nmol/L(-1); p < 0.05) and group 3 (303 nmol/L(-1); p < 0.05). Thrombin anti-thrombin III complexes and plasmin anti-plasmin complex complexes increased during CPB to significantly high levels at cessation of CPB, but there were no differences between the groups. The oxygenator with the smallest surface area and lowest priming volume (group 1) had the highest oxygen transfer rate per square meter and showed the least blood damage, as depicted by complement activation. The oxygenator with the largest blood contact surface area and improved geometric configuration (group 3) showed the lowest oxygen transfer rate per square meter. However, this oxygenator elevated oxygen partial pressure the most and reduced carbon dioxide partial pressure the most. In group 2, where a smaller venous reservoir was used, the highest blood activation was observed.

Inflammatory response to cardiopulmonary bypass using two different types of heparin-coated extracorporeal circuits

Previous reports have highlighted the disparity in biocompatibility of two differently engineered heparin coatings during the cardiopulmonary bypass (CPB) procedure. The aim of this prospective study was to evaluate the impact of the difference in haemocompatibility provided by either the Duraflo II equipment or the Carmeda equipment in the terminal inflammatory response observed after coronary artery surgery. Thirty patients were randomly allocated to two groups to be operated on using either Duraflo II equipment (group I) or Carmeda equipment (group 2) for extracorporeal circulation (ECC). Initial inflammatory response was assessed by terminal complement complex activation (SC5b-9). The late inflammatory response observed in the postoperative period was assessed by measuring cytokine production (tumour factor necrosis (TNF alpha), interleukin IL-6, interleukin IL-8) and circulating concentrations of adhesion molecules (ELAM-1, ICAM-1). The release of SC5b-9 after CPB and after protamine administration was lower in group 2 than in group 1 (p = 0.0002 and p = 0.006, respectively). A significant production of cytokines was detected in both groups with peak values observed within the time range of 4-6 h after the start of CPB.