Review on the multifactorial aspects of bioincompatibility in CPB

Association between cardioplegia and postoperative atrial fibrillation in coronary surgery

OBJECTIVE

The aim of this multicenter study was to evaluated whether cold or warm cardioplegia are associated with postoperative atrial fibrillation (POAF) and the prognostic role of the latter on early stroke and neurological mortality.

METHOD

This was a retrospective analysis of prospective collected data from 9 cardiac centers in Italy and the United States including patients undergoing surgery between 2010 and 2018. From the 9 institutional databases, 17,231 patients underwent isolated CABG on-pump, using either warm cardioplegia (n = 7730) or cold cardioplegia (n = 9501); among the latter group blood and crystalloid cardioplegia were used in 691 and 8810 patients, respectively. After matching, two pairs of 4162 patients (overall cohort 8324) were analyzed.

RESULTS

In matched population, the rate of POAF was 18% (1472 cases), 15% (608) in warm group versus 21% (864) in cold group (p < 0.001). Multivariable analysis confirmed that cold cardioplegia was associated with higher rate of POAF, along with age, hypercholesterolemia, LVEF, reoperation, preoperative IABP, previous stroke, cardiopulmonary and cross-clamp. Moreover, cold cardioplegia as well as POAF increased the rate of postoperative stroke as well as early mortality and neurological mortality Propensity-weighted cohort included 11,830 (70%) patients out of 17,231. After adjustment, both cold blood and cold crystalloid cardioplegia negatively influenced POAF, stroke and neurological mortality.

CONCLUSIONS

Warm cardioplegia may reduce the rate of POAF in CABG patients with respect to cold cardioplegia, either blood or crystalloid. This has a prognostic impact on postoperative stroke and neurological mortality.

Mechanisms of oxidative stress and myocardial protection during open-heart surgery

Cold heart protection via cardioplegia administration, limits the amount of oxygen demand. Systemic normothermia with warm cardioplegia was introduced due to the abundance of detrimental effects of hypothermia. A temperature of 32-33°C in combination with tepid blood cardioplegia of the same temperature appears to be protective enough for both; heart and brain. Reduction of nitric oxide (NO) concentration is in part responsible for myocardial injury after the cardioplegic cardiac arrest. Restoration of NO balance with exogenous NO supplementation has been shown useful to prevent inflammation and apoptosis. In this article, we discuss the "deleterious" effects of the oxidative stress of the extracorporeal circulation and the up-to-date theories of "ideal'' myocardial protection.

Does contemporary oxygenator design influence haemolysis?

Based on their design, all membrane oxygenators generate a certain resistance to flow. In clinical practice, this resistance is calculated by measuring both blood flow and the pressure drop over the oxygenator. Historically, some designs, such as the Kolobow spiral coil oxygenator and the Cobe flat sheet oxygenator, had quite a high pressure drop, but were, nevertheless, considered very haemocompatible. Today, both medium and low pressure drop oxygenators are commercially available. Based on physics and the existing literature, this review aims to investigate whether pressure drop by itself can be considered an independent factor of haemolysis.

Active or passive bio-coating: does it matters in extracorporeal circulation?

Background: Two types of surface coating for cardiopulmonary bypass (CPB) are used: bioactive (heparin, nitric oxide) and biopassive (albumin, polyethyleneoxide (PEO), phosphorylcholine). When haemocompatible coatings are combined with the separation of pleuro-pericardial aspiration, attenuation of both the coagulation and complement cascades, as well as better platelet preservation, has been demonstrated. This study wants to investigate if the combination of a bioactive with a biopassive coating (unfractionated heparin embedded in a phosphorylcholine matrix) combines the beneficial effects of both approaches.

Materials and methods: Thirty patients undergoing elective CABG were prospectively randomized into two groups of 15 patients. The sole exclusion criterion was an ejection fraction of less than 40%. In the control group (PC), the whole CPB circuit was coated with phosphorylcholine (PC). In the study group (XPC), unfractionated heparin was embedded in the PC matrix of the oxygenator and arterial line filter.

Results: No differences were found for haemolytic index, thrombin-anti-thrombin complex (TAT), IL-6, IL-10 and blood loss. PF4 plasma concentration increased from 27.6±22.0 IU/mL to 165.7±43.9 IU/mL (p<0.001) at 15 minutes of CPB in the PC and from 16.0±9.7 IU/mL to 150.9 ± 61.3 IU/mL (p<0.001) in the XPC group. Terminal complement complex (TCC) increased over time in both groups until the end of CPB (Figure 2A). Within each group, TCC generation was statistically significantly higher after the release of the aortic cross-clamp (p<0.001) and at the end of CPB (p<0.001). Total TCC generation was statistically significantly higher in the XPC group compared to the PC group (p=0.026). The difference was statistically significant after the release of the aortic cross-clamp (p=0.005) and at the end of CPB (p=0.001).

Conclusions: Based on our results, there is no additional benefit in combining phosphorylcholine with unfractionated heparin in elective patients undergoing coronary artery bypass grafting (CABG). Massive haemodilution leads to enhanced complement activation.

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.

A review of myocardial normothermia: its theoretical basis and the potential clinical benefits in cardiac surgery

Myocardial protection during cardiac surgery aims to preserve myocardial function while providing a bloodless and motionless operating field to make surgery easier. Myocardial protection is achieved by decreasing the oxygen needs using hypothermia and producing electromechanical cardiac arrest using potassium infusion which allows surgery to be performed on a non-beating heart. The deleterious effects of hypothermia include dysfunction of enzymatic systems, development of acidosis, a decrease in tissue oxygen delivery, an increase in blood viscosity and a decrease in erythrocyte deformability. Ninety percent of the decrease in oxygen consumption is obtained by inducing electromechanical arrest and inducing hypothermia has little additional benefit. Maintenance of systemic and myocardial normothermia reduces problems and provides a more physiological approach for cardiopulmonary bypass (CPB). The current results obtained using normothermic protection are very encouraging, and it is an easier inexpensive option. This review summarizes the current knowledge on the benefits of normothermia, based upon experimental and clinical studies.

Application of a new dynamic flow model for investigating the biocompatibility of modified surfaces

An in vitro model was developed to compare the biocompatibility of four different coating methods (three heparin and one nonheparin) under hemodynamic conditions. Fresh human donor blood (heparin 5 IU/ml) was recirculated in a standardized experimental circuit. All circuit components were either coated or remained uncoated for control purposes. The aim of the study was to investigate a wide spectrum of effects on blood; coagulation parameters (e.g., fibrinogen, ATIII, thrombin-antithrombin-complex), complement parameters (C1rsC1 Inh, C3b(Bb)P, SC5b-9, C5a), differential blood analyses, platelet activation (flow cytometric investigations), PF 4, and PMN-elastase release were examined by showing possible trends. All heparin coated systems reduced platelet stimulation in comparison to untreated biomaterials. Leukocyte activation was reduced to different degrees depending upon the coating method used. Complement activation was markedly reduced by all coated systems. The results obtained indicate that the pump driven, dynamic blood flow model is suitable to characterize the biocompatibility of surface modified biomaterials. Advantages lie in the integration of the different polymers as parts of the circuit, the low priming volume, and the generation of blood flow conditions similar to those that occur in clinical applications.

Synthetic protein treated versus heparin coated cardiopulmonary bypass surfaces: similar clinical results and minor biochemical differences

OBJECTIVE

Complications associated with cardiopulmonary bypass (CPB) have gained more attention due to increased interest in coronary artery bypass grafting without CPB. The impact of heparin coating of CPB circuits has been discussed controversially. The present study examines if the treatment of the oxygenator surface with a synthetic protein may serve as an alternative to a completely heparin coated circuit.

METHODS

Fifty-eight patients undergoing coronary artery bypass grafting with CPB were randomly assigned to completely heparin coated circuits or synthetic protein treated oxygenators in a double blind protocol, focussing on the inflammatory reaction resulting in membrane damage, coagulation changes and markers of cerebral injury or dysfunction. Treatment groups did not differ as to preoperative demographics, and intraoperative clinical data. Patients with any neurologic disease or risk factors for cerebral dysfunction were not included in the study.

RESULTS

Postoperative clinical data did not differ between groups. Both surface treatments resulted in similar coagulation activation, hyperfibrinolysis and disseminated intravascular coagulation. Platelet count displayed a difference in favour of the heparin coated group (P = 0.029). Increased leukocyte activation reflected by rising myeloperoxidase concentrations on CPB was present in both synthetic protein and heparin coating groups. Interleukins 6 and 8 reacted similarly, but interleukin 8 increased significantly more (P = 0.0061) at the end of surgery in patients treated with protein treated oxygenators. The same pattern was observed for complement activation as determined by total complement complex (P = 0.006). Both surface changes resulted in moderately increased S-100B protein and neuron specific enolase, without difference between groups. Both markers did not reach concentrations associated with clinical manifestation of cerebral injury.

CONCLUSIONS

These results in routine patients with short bypass time, imply that protein treated oxygenators are associated with a limited increase of biochemical markers similar to heparin coating. However, significantly lower interleukin 8 release and complement activation can be achieved by heparin coating. The protein treatment is a standard feature of the oxygenator examined in both groups. It is not associated with additional cost and therefore appropriate for use in routine patients.

Heparin-bonded circuits: clinical outcomes and costs

The aim of this study was to use meta-analysis to combine the results of numerous studies and examine the impact of heparin-bonded circuits on clinical outcomes and the resulting costs. Heparin-bonded circuits, both ionically and covalently bonded, are examined separately. The results of the study provide evidence that heparin-bonded circuits result in improved clinical outcomes when compared to the identical nonheparin-bonded circuits. These improved clinical outcomes result in subsequent lower costs per patient with their use. However, differences are apparent in the significance and magnitude of these outcomes between ionically and covalently bonded circuits. Covalently bonded circuits provide a greater magnitude and significance of improvement in clinical outcomes than ionically bonded circuits. Total cost savings can be expected to be three times greater with covalently bonded circuits ($3231 versus $1068). It was concluded that the choice regarding the use of a heparin-bonded circuits and the type of heparin-bonded circuit used has the potential to alter clinical outcomes and subsequent costs. Cost consideration cannot be ignored, but clinical benefits should be the main rationale for the choice of cardiopulmonary bypass circuit. This analysis provides evidence that clinical benefits and cost savings can both be derived from use of the same technology-covalently bonded circuits.