Clinical use of heparin-coated cardiopulmonary bypass in coronary artery bypass grafting

Effects of interventions targeting the systemic inflammatory response to cardiac surgery on clinical outcomes in adults

BACKGROUND

Organ injury is a common and severe complication of cardiac surgery that contributes to the majority of deaths. There are no effective treatment or prevention strategies. It has been suggested that innate immune system activation may have a causal role in organ injury. A wide range of organ protection interventions targeting the innate immune response have been evaluated in randomised controlled trials (RCTs) in adult cardiac surgery patients, with inconsistent results in terms of effectiveness.

OBJECTIVES

The aim of the review was to summarise the results of RCTs of organ protection interventions targeting the innate immune response in adult cardiac surgery. The review considered whether the interventions had a treatment effect on inflammation, important clinical outcomes, or both.

SEARCH METHODS

CENTRAL, MEDLINE, Embase, conference proceedings and two trial registers were searched on October 2022 together with reference checking to identify additional studies.

SELECTION CRITERIA

RCTs comparing organ protection interventions targeting the innate immune response versus placebo or no treatment in adult patients undergoing cardiac surgery where the treatment effect on innate immune activation and on clinical outcomes of interest were reported.

DATA COLLECTION AND ANALYSIS

Searches, study selection, quality assessment, and data extractions were performed independently by pairs of authors. The primary inflammation outcomes were peak IL-6 and IL-8 concentrations in blood post-surgery. The primary clinical outcome was in-hospital or 30-day mortality. Treatment effects were expressed as risk ratios (RR) and standardised mean difference (SMD) with 95% confidence intervals (CI). Meta-analyses were performed using random effects models, and heterogeneity was assessed using I2.

MAIN RESULTS

A total of 40,255 participants from 328 RCTs were included in the synthesis. The effects of treatments on IL-6 (SMD -0.77, 95% CI -0.97 to -0.58, I2 = 92%) and IL-8 (SMD -0.92, 95% CI -1.20 to -0.65, I2 = 91%) were unclear due to heterogeneity. Heterogeneity for inflammation outcomes persisted across multiple sensitivity and moderator analyses. The pooled treatment effect for in-hospital or 30-day mortality was RR 0.78, 95% CI 0.68 to 0.91, I2 = 0%, suggesting a significant clinical benefit. There was little or no treatment effect on mortality when analyses were restricted to studies at low risk of bias. Post hoc analyses failed to demonstrate consistent treatment effects on inflammation and clinical outcomes. Levels of certainty for pooled treatment effects on the primary outcomes were very low.

AUTHORS' CONCLUSIONS

A systematic review of RCTs of organ protection interventions targeting innate immune system activation did not resolve uncertainty as to the effectiveness of these treatments, or the role of innate immunity in organ injury following cardiac surgery.

A comparison of low vs conventional-dose heparin for minimal cardiopulmonary bypass in coronary artery bypass grafting surgery

The biocompatibility of minimal extracorporeal circuits has improved; however, anticoagulation is still required. We compared standard high-dose anticoagulation with a low-dose heparin regimen in a retrospective study of patients who underwent coronary bypass surgery using minimal cardiopulmonary bypass. One hundred patients who received 300 IU.kg(-1) heparin were compared with 68 patients who received heparin according to an individually adjusted activated coagulation time target of 300 s, resulting in a mean (SD) heparin dose of 145 (30) IU.kg(-1) . There were no thromboembolic events in either group; however, patients in the low-dose group had lower 24-hour mean (SD) postoperative blood loss than the conventional group (545 (61) vs 680 (88) ml, p=0.001) and a reduced rate of transfusion of allogeneic blood (15% patients transfused vs 32%, p=0.01). An individually tailored low-dose heparin regimen for minimal cardiopulmonary bypass is safe and may be associated with reduced bleeding and lower transfusion requirements.

Plasma protein binding properties to immobilized heparin and heparin-albumin conjugate

Selective adhesion of plasma proteins to immobilized heparin is considered to be beneficial regarding hemocompatibility of foreign materials in contact with blood. Prothrombin, thrombin, antithrombin III (AT3), and fibrinogen were selected for analysis in an experimental model. Biomolecular interaction analysis employing surface plasmon resonance was utilized to record and analyze their binding properties in real time. Biotinylated heparin, heparin-albumin conjugate, and albumin, respectively, were immobilized onto streptavidin-coated sensors as ligands. Prothrombin did not bind to any of the ligand surfaces and no specific binding of any of the plasma proteins to albumin was observed. Binding kinetics of thrombin to heparin and to heparin-albumin conjugate were calculated using two different methods. For heparin, identical K(D)(equilibrium dissociation constant) values of 61 x 10(-9) M were obtained with both methods. For the conjugate, only slightly different K(D) values of 111 x 10(-9) and 104 x 10(-9) M, respectively, were calculated. The affinity of thrombin toward the heparin-coated surface proved to be higher than its affinity toward the heparin conjugate. The binding pattern of AT3 to both heparin and heparin-albumin conjugate, although specific, was biphasic, possibly due to a conformational change during the binding process. Steady-state kinetic analysis revealed a K(D) value of 281 +/- 24 x 10(-9) M for the heparin surface. For the conjugate surface, a K(D) of 53 +/- 5 x 10(-9) M was calculated, indicating a higher affinity toward heparin-albumin conjugate. A high-affinity binding of fibrinogen to high-density surfaces of both heparin and the conjugate was observed. However, as binding to low-density surfaces was considerably reduced, specificity remained uncertain.