Role of leucocytes in free radical production during myocardial revascularisation

Strategies to attenuate maladaptive inflammatory response associated with cardiopulmonary bypass

Cardiopulmonary bypass (CPB) initiates an intense inflammatory response due to various factors: conversion from pulsatile to laminar flow, cold cardioplegia, surgical trauma, endotoxemia, ischemia-reperfusion injury, oxidative stress, hypothermia, and contact activation of cells by the extracorporeal circuit. Redundant and overlapping inflammatory cascades amplify the initial response to produce a systemic inflammatory response, heightened by coincident activation of coagulation and fibrinolytic pathways. When unchecked, this inflammatory response can become maladaptive and lead to serious postoperative complications. Concerted research efforts have been made to identify technical refinements and pharmacologic interventions that appropriately attenuate the inflammatory response and ultimately translate to improved clinical outcomes. Surface modification of the extracorporeal circuit to increase biocompatibility, miniaturized circuits with sheer resistance, filtration techniques, and minimally invasive approaches have improved clinical outcomes in specific populations. Pharmacologic adjuncts, including aprotinin, steroids, monoclonal antibodies, and free radical scavengers, show real promise. A multimodal approach incorporating technical, circuit-specific, and pharmacologic strategies will likely yield maximal clinical benefit.

Preoperative hydroperoxide concentrations are associated with a risk of postoperative complications after cardiac surgery

This study aimed to assess whether preoperative oxidative stress levels can predict postoperative complications in patients undergoing cardiac surgery. Ninety-five cardiac surgery patients received an assessment of preoperative oxidative stress by measurement of hydroperoxide values in blood via the d-Rom test. Area under the receiver operating characteristic curve and also multivariate logistic regression were used to evaluate the prognostic significance of preoperative hydroperoxide concentrations in predicting the occurrence of major organ morbidity and mortality (MOMM). MOMM included death, deep sternal infection, reoperation, stroke, renal failure requiring haemodialysis and prolonged ventilation (>48 hours). The ability of preoperative hydroperoxide concentrations to predict MOMM was not significantly different from that of the European system for cardiac operative risk evaluation (EuroSCORE) (area under the receiver operating characteristic curve 0.822 versus 0.821 respectively, P=0.983). The optimal threshold value of hydroperoxide concentration to differentiate between patients with and without MOMM was 450 UCarr (sensitivity, 87.0%; specificity, 81.9%). Duration of intensive care unit stay, mechanical ventilation time and hospital stay were significantly longer in patients with preoperative hydroperoxide concentrations ≥450 UCarr (H group) compared to those patients with preoperative hydroperoxide concentrations <450 UCarr (L group). An increase in preoperative hydroperoxide concentrations remained associated with an increased risk of MOMM (odds ratios: 1.01, 95% confidence interval: 1.00 to 1.03) and prolonged intensive care unit stay (odds ratio 1.01, 95% confidence interval: 1.00 to 1.02), after adjusting for age, gender and EuroSCORE. In conclusion, an increased hydroperoxide concentration before cardiac surgery is an independent risk factor for severe postoperative complications.

The appearance of L-selectin(low) polymorphonuclear leukocytes in the circulating pool of peripheral blood during myocardial infarction correlates with neutrophilia and with the size of the infarct

BACKGROUND

It is assumed that not only leukocytosis, but also the activation of white blood cells (WBC) may play a role in the pathogenesis and prognosis of patients with myocardial infarction (MI). Activation of WBC includes upregulation of CD11b/CD18 and downregulation of CD62L (L-selectin) antigens.

HYPOTHESIS

The activation of WBC is associated with the appearance of a larger MI.

METHODS

CD11b/CD18 and CD62L were measured on the surface of WBC on Day 1 and Day 3 from the onset of MI. The size of the infarct with estimated by calculating the area under the curve of the creatine kinase enzyme, which was measured every 6 h.

RESULTS

A negative correlation was noted between the absolute polymorphonuclear count and the availability of the CD62L on these cells during Day 1 (r = -0.46, p = 0.003) and Day 3 (r = -0.35, p = 0.05). There was a positive correlation between the size of MI and the WBC count (r = 0.46, p = 0.004) and a negative correlation with CD62L on polymorphonuclears (r = -0.35, p = 0.03). During Day 3, the CD11b/CD18 on the polymorphonuclears increased despite a decrement in the absolute number of these cells.

CONCLUSION

The neutrophilia during the early phases of acute MI correspond to the appearance of the L-selectin(low) population of polymorphonuclear leukocytes. There is a correlation between the appearance of this population and the size of the infarct.

Glutathione suppresses increase of serum creatine kinase in experimental hypoglycemia

Inhibitory effects of reduced glutathione (GSH) on serum enzymes including alanine aminotransferase (AST), lactate dehydrogenase (LDH) and creatine kinase (CK) were investigated in the hypoglycemic rabbits. Hypoglycemia lasting for 60 min was induced by intravenous injection of insulin (10U/kg) and then recovered by intravenous glucose injection. Serum levels of ALT, AST, LDH and CK increased significantly (p<0.05) at 6h after the induction of hypoglycemia. Plasma GSH, oxidized glutathione (GSSG) and total glutathione (TGSH) began to increase significantly (p<0.05) at 1h after the insulin injection, and GSSG/TGSH ratio rose significantly (p<0.05) at 6h after the induction of hypoglycemia. GSSG contents and GSSG/TGSH ratio in quadriceps significantly increased during hypoglycemia. Administration of GSH significantly decreased plasma GSSG levels, GSSG/TGSH ratio (p<0.05) and suppressed the rise of serum enzymes induced by hypoglycemia. These results suggest that GSH administration may play a preventive role for increases of serum enzymes by experimental hypoglycemia.

What is the Role of Leukocyte Depletion in Cardiac Surgery?

Leukocytes play an important pathogenic role in ischaemia-reperfusion injury. During cardiopulmonary bypass, leukocyte filters have the potential to remove leukocytes, thereby reducing contact of activated leukocytes with the endothelium of target organs. Improvement in the safety and efficacy of commercially available leukocyte filters in recent years has led to their increasing use in cardiac surgery. However, the benefits have been inconsistent. Current evidence suggests that leukocyte depletion may not have a significant impact in low risk elective coronary artery bypass grafting but may be beneficial in valve surgery and high-risk cardiac surgery. High-risk surgical groups that may benefit from leukocyte filtration are those with left ventricular hypertrophy (LV mass>300 g), poor ejection fraction (EF<40%), chronic obstructive airways disease (predicted FEV1<75%), prolonged ischaemia (cross clamp time>120 min or cardiac transplantation), paediatric cardiac surgery and patients in cardiogenic shock requiring emergency coronary artery bypass grafting. Future trials should be powered to detect important clinical end points and be designed to avoid premature exhaustion of the filter.

The effects of various leukocyte filtration strategies in cardiac surgery

It is known that cardiopulmonary bypass causes an inflammatory reaction with an associated morbidity and mortality. Several anti-inflammatory strategies have been implemented to reduce this response, including leukocyte removal from the circulation using specialised filters. The aim of this study is to systematically review the available evidence on leukocyte filtration in cardiac surgery, focusing on its effect on systemic inflammation and whether this has influenced clinical outcomes. Five electronic databases were systematically searched for studies reporting the effect of leukocyte filtration at any point within the cardiopulmonary bypass circuit in humans. Reference lists of all identified studies were checked for any missing publications. Two authors independently extracted the data from the included studies. Whilst systemic leukodepleting filters do not appear to consistently lower leukocyte counts, they may preferentially remove activated leukocytes. Small improvements in early post-operative lung function in patients receiving systemic leukodepletion have been reported, but this does not lead to reduced hospital stay or decreased mortality. There is substantial evidence that cardioplegic leukocyte filtration attenuates the reperfusion injury at a cellular level, but this has not been translated into clinical improvements. Finally, whilst various strategies involving multiple leukocyte filters, or the incorporation of pharmacological agents into leukocyte-depleting protocols have been evaluated, the current available results are not conclusive. Our study suggests that there is not enough high quality or consistent evidence to draw guidelines regarding the use of leukocyte-depleting filters within routine cardiac surgical practice.

Total leukocyte control for elective coronary bypass surgery does not improve short-term outcome

BACKGROUND

Despite early promise as a means of reducing the inflammatory response to surgery and subsequent organ damage, the evidence of the clinical value of leukocyte filtration remains equivocal.

METHODS

Three hundred patients presenting for routine coronary artery bypass surgery were randomized to a total leukocyte filtration group (filters in five different locations) and a control group with a standard 40-mum filter in the bypass return line only. Data on efficacy and safety of leukocyte filtration were collected by research and postoperative care staff who were blinded to the mode of filtration.

RESULTS

Leukofiltration achieved a transient fall in white cells immediately after surgery (p = 0.07) and a sustained fall in platelets, which was still significant on the second postoperative day (p = 0.0001). However, there were no significant differences in postoperative hospital stay, the primary outcome variable (p = 0.35), in ICU stay (p = 0.92), or mortality (p = 1.0). There were no differences in postoperative cardiac status including cardiac output (p = 0.16), inotrope (p = 0.93) or balloon pump (p = 0.48) requirement, or 24-hour troponin (p = 0.60). Similarly there were no differences in pulmonary or renal function (intubation time (p = 0.83), respiratory index (p = 0.19) rise in creatinine (p = 0.13) or hemofiltration (1.0)). Leukofitration was not associated with a statistically significant increase in bleeding or requirement for blood or blood products. It was associated with a decrease approaching significance (p = 0.1) in number and severity of postoperative wound infections. Three filters were blocked during use but were changed without incident or compromise to patient safety.

CONCLUSIONS

Leukocyte filtration is safe but not efficacious in improving short-term outcome.

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.

Deferoxamine infusion during coronary artery bypass grafting ameliorates lipid peroxidation and protects the myocardium against reperfusion injury: immediate and long-term significance

AIMS

Previous reports have demonstrated enhanced myocardial protection and better post-ischaemic recovery using the oxygen free radical scavenger deferoxamine (DEF) during cardioplegia. The aim of this study was to test whether, in patients undergoing coronary artery bypass grafting (CABG), DEF i.v. infusion can reduce reperfusion injury on a short- and long-term basis.

METHODS AND RESULTS

Forty-five consecutive male patients were randomly allocated to two groups: in group D (n=25, age 60.8+/-8.6 years), 4 g of DEF were infused for 8 h starting immediately after the induction of anaesthesia; in group C (n=20, age 62.2+/-6.4 years) dextrose solution was given for the same time as placebo. Haemodynamic monitoring and measurement of oxygen free radical production [by measuring thiobarbituric acid reactive substances (TBARS)] were carried out before and after CABG. Left ventricular ejection fraction (EF) and wall motion score index (WMSI) were measured before and after CABG and 12 months later. Haemodynamic measurements were similar in both groups before and after CABG. TBARS peaked at 4.8+/-1.1 nmol/mL in group C, but remained unchanged (2.4+/-0.9 nmol/mL) in group D (P=0.01). At baseline, both the EF and WMSI were similar between the groups. Following CABG, EF increased more in group D (8.8+/-8.4%) than in group C (1.3+/-6.7%), P=0.008, while WMSI decreased more in group D (-0.7+/-0.3) than in group C (-0.2+/-0.2), P=0.0001. Dividing group D according to the pre-operative median EF value (38%), we observed that after 1 year follow-up, DEF infusion conferred more protection in patients with a lower EF (EF increased by 19.3+/-6.2%, WMSI decreased by -1.1+/-0.2) than in those with a higher EF (EF increased by 7.7+/-4.5%, WMSI decreased by -0.8+/-0.2), P=0.001, respectively.

CONCLUSION

In patients undergoing CABG, DEF i.v. infusion ameliorates oxygen free radical production and protects the myocardium against reperfusion injury. Patients with a lower EF seem to benefit more by DEF i.v. infusion.

Blood cardioplegia filtration

The introduction of blood cardioplegia has been proven to limit ischaemia and reperfusion injury in cardiac surgery. But the presence of activated neutrophils in the capillary bed may cause further damage. Leukocyte filters have been shown to be very effective in reducing the leukocytes in blood cardioplegia to less than 10%. Leukocyte depletion of blood cardioplegia provides an excellent approach to minimizing myocardial injury, predominantly in high-risk cardiac surgery.

Inflammation After Cardiopulmonary Bypass: Therapy for the Postpump Syndrome

Cardiopulmonary bypass (CPB) is used in most, but not all, complex heart operations. CPB is associated with a systemic inflammatory response in adults and children. Many materials-dependent (exposure of blood to non- physiologic surfaces and conditions) and materials-in dependent (surgical trauma, ischemia-perfusion to the organs, changes in body temperature, and release of endotoxin) factors during CPB have been implicated in the etiology of this complex response. The mechanisms involved may include complement activation, release of cytokines, leukocyte activation with expression of ad hesion molecules, and production of various vasoactive and immunoactive substances. Postpump inflamma tion may lead to postoperative complications and may result in respiratory failure, renal dysfunction, bleeding disorders, neurologic dysfunction, altered liver func tion, and ultimately multiple organ failure. Significant efforts are being made to decrease the generation and effects of postpump inflammation. Interventions to this end have included avoiding CPB when possible, im proving the biocompatibility of the involved mechani cal devices, and administering medications that main tain cellular integrity. This article provides an overview of the etiology, pathophysiology, and treatment of postpump inflammation. Perhaps with additional in sight into this syndrome, CPB can be made a safer and more efficacious modality of cardiorespiratory support. Copyright© 2001 by W.B. Saunders Company.

The effect of leukocyte-depleted blood cardioplegia in patients with severe left ventricular dysfunction: a randomized, double-blind study

BACKGROUND

The propensity for leukocytes to cause reperfusion injury in patients undergoing heart surgery is widely accepted. Reperfusion injury may result in myocardial damage and unfavorable operative outcome, especially in patients with severely reduced ejection fractions. This study was performed to evaluate the impact of leukocyte filtration on the postoperative course of patients undergoing coronary bypass surgery.

METHODS

Thirty-two patients with coronary artery disease and left ventricular ejection fraction less than 35% were included in this double-blind, randomized study. Two serial leukocyte removal filters (Pall BC1B filter [Pall Biomedical, Portsmouth, England], group F, 15 patients) or two dummy filters (group C, 17 patients) were connected to the blood cardioplegia line. Leukocyte count, hemodynamic measurement, and transesophageal echocardiography were performed before and after cardiopulmonary bypass. Cardiac-specific enzymes were analyzed from arterial blood during the first 72 hours and from coronary sinus blood 30 and 60 minutes after aortic unclamping.

RESULTS

Patient characteristics were similar in the two groups (ejection fraction 20.9% +/- 4.3% in group C and 21.1% +/- 4.8% in group F; P =.773). No early death or perioperative myocardial infarction occurred. Leukocyte count, hemodynamic parameters, cardiac troponin T, cardiac troponin I, and creatine kinase MB mass levels in arterial blood were similar in the two groups. Group F showed lower release of cardiac troponin T from the coronary sinus 30 minutes after unclamping of the aorta (group F, 0.263 +/- 0.12 ng/mL; group C, 0.6 +/- 0.32 ng/mL; P =.005). Lower doses of dopamine were necessary after cardiopulmonary bypass (group F, 0.36 +/- 0.11 mg x kg(-1) x min(-1); group C, 0.49 +/- 0.14 mg x kg(-1) x min(-1); P =.003). A moderate increase in ejection fraction was observed at 30 minutes in both groups (group F, 30.3% +/- 6.2%; group C, 28.0% +/- 6.3%; P =.239) and a significant increase at 60 minutes in group F (group F, 32.5% +/- 6.0%; group C, 27.4% +/- 7.5%; P =.012).

CONCLUSIONS

These results indicate that serial leukocyte filters connected to the blood cardioplegia line decrease myocardial cell injury and may therefore help to improve outcome of patients with severely depressed ejection fractions undergoing coronary artery bypass grafting.

Oxidized proteins as a marker of oxidative stress during coronary heart surgery

The measurement of the degree of oxidative stress in patients often causes problems because of the lack of useful parameters. Therefore, we used an ELISA technique to evaluate serum protein carbonyls as a parameter of oxidative stress in patients during coronary heart surgery. Protein carbonyls were detected in serum samples of 14 patients undergoing coronary surgery and cardiopulmonary artery bypass grafting. A clear 2- to 3-fold increase in protein carbonyls in serum samples taken from human venous coronary sinus could be detected in the reperfusion period of the heart. We compared these data with markers of oxidative stress previously used, such as the glutathione status and the lipid peroxidation product malondialdehyde (MDA). Strong correlations of the protein carbonyl formation with MDA (r2 = 0.86) and oxidized glutathione (r2 = 0.81) were found in the early reperfusion stage. Increased levels of oxidized glutathione and MDA were detected only in the early reperfusion period. In contrast, the serum protein carbonyl content remained elevated for several hours, indicating a considerably slower serum clearance of oxidized proteins compared with that of lipid peroxidation products and the normalization of the glutathione status. We therefore concluded that the measurement of serum carbonyls by this ELISA technique is suitable to detect oxidative stress in serum samples of patients. The relative stability of the parameter makes the protein carbonyl detection even more valuable for clinical purposes.

Relation between left ventricular function and oxidative stress in patients undergoing bypass surgery

OBJECTIVE

To determine whether preoperative left ventricular ejection fraction (LVEF) is related to the degree of myocardial oxidative stress during bypass surgery in man.

DESIGN

Observational study.

SETTING

Tertiary care centre.

PATIENTS AND INTERVENTIONS

31 patients (LVEF range was 20% to 68%) undergoing elective coronary bypass surgery with blood cardioplegic reperfusion were studied. Arterial and coronary sinus blood was collected before aortic cross clamping (T0) and at 0 (T1), 15 (T2), and 30 (T3) minutes after unclamping. Transmural left ventricular biopsies were also obtained from 15 patients at T0 and at T1.

MAIN OUTCOME MEASURES

Glutathione and adenine nucleotides were measured in myocardial biopsies, while coronary sinus-artery differences for glutathione, nucleotides, and products of lipid peroxidation were calculated from blood specimens. Creatine kinase (myocardial band; CK-MB) was measured in plasma at four and 12 hours after operation.

RESULTS

Myocardial glutathione and adenine nucleotides were correlated (p < 0.02) with preoperative LVEF both at T0 (r = 0.909 and 0.672) and T1 (r = 0.603 and 0.605). Oxidised glutathione released from the heart during reperfusion was inversely correlated with LVEF (r = -0.448, -0.466, and -0461 at T1, T2, and T3, p < 0.01), while reduced glutathione (r = 0.519 and 0.640 at T1 and T2) and glutathione redox ratio (r = 0.647, 0.714, 0.645, and 0.702 at T0, T1, T2, and T3) showed a direct correlation (p < 0.01). Lipid peroxidation at T1 was negatively related to LVEF (r = -0.492). CK-MB was also negatively related to LVEF (r = -0.440 at 4 h and -0.462 at 12 h).

CONCLUSIONS

The capacity to counterbalance oxidative burst following ischaemia and reperfusion appears to be related to the functional ability of the heart.