Neutrophil Gelatinase-associated Lipocalin as a Marker of Postoperative Acute Kidney Injury Following Cardiac Surgery in Patients with Preoperative Kidney Impairment.

INTRODUCTION: Acute kidney injury (AKI) is a serious complication of cardiac surgery. The current 'gold standard' for determining AKI is change in serum creatinine and urine output, however, this change occurs relatively late after the actual injury occurs. Identification of new biomarkers that detect early AKI is required. Recently, new biomarkers, such as the NephroCheck® Test and AKIRisk have also been tested and found to be good indicators of AKI. Neutrophil gelatinase-associated lipocalin (NGAL) has shown promise in paediatric patients but has displayed varied results in adult populations, particularly post cardiac surgery. The aim of this study was to assess the value of urinary NGAL as a biomarker of AKI in patients with pre-existing renal impairment (eGFR >15ml/min to eGFR<60ml/min). METHODS: A post-hoc analysis of urinary NGAL concentrations from 125 patients with pre-existing kidney impairment, who participated in a randomised trial of haemofiltration during cardiac surgery, was undertaken. Urinary NGAL was measured using ELISA at baseline, post-operatively and 24 and 48 hours after surgery, and serum creatinine was measured pre and postoperatively and then at 24, 48, 72 and 96 hours as routine patient care. NGAL concentrations were compared in patients with and without AKI determined by changes in serum creatinine concentrations. A Kaplan-Meier plot compared survival for patients with or without AKI and a Cox proportional hazards analysis was performed to identify factors with the greatest influence on survival. RESULTS: Following surgery, 43% of patients developed AKI (based on KDIGO definition). Baseline urinary NGAL was not found to be significantly different between patients that did and did not develop AKI. Urinary NGAL concentration was increased in all patients following surgery, regardless of whether they developed AKI and was also significant between groups at 24 (p=0.003) and 48 hours (p<0.0001). Urinary NGAL concentrations at 48 hours correlated with serum creatinine concentrations at 48 hours (r=0.477, p<0.0001), 72 hours (r=0.488, p<0.0001) and 96 hours (r=0.463, p<0.0001). Urinary NGAL at 48 hours after surgery strongly predicted AKI (AUC=0.76; P=0.0001). A Kaplan- Meier plot showed that patients with postoperative AKI had a significantly lower 7-year survival compared with those without AKI. Postoperative urinary NGAL at 48 hours >156ng/mL also strongly predicted 7-year survival. However, additive EuroSCORE, age, current smoking and post-operative antibiotics usage were distinctly significantly more predictive of 7-year survival as compared with postoperative urinary NGAL at 48 hours >156ng/mL. CONCLUSIONS: Our study demonstrated that postoperative urinary NGAL levels at 48 hours postsurgery strongly predicts the onset or severity of postoperative AKI based on KDIGO classification in patients with preoperative kidney impairment and were also strongly related to 7-year survival.

The impact of continuous haemofiltration with high-volume fluid exchange during cardiopulmonary bypass surgery on the recovery of patients with impaired renal function: a pilot randomised trial.

BACKGROUND: There is widespread variability in clinical practice within cardiac surgery units worldwide on the use of haemofiltration. The clinical impact and safety of this modality is, however, unknown. OBJECTIVES: The primary pilot trial objectives were as follows: to assess the feasibility of randomising 60 patients with impaired kidney function undergoing on-pump coronary artery bypass graft (CABG) surgery within 6 months; to assess the suitability and reliability of our chosen outcome measures; to explore issues that may impact on recruitment into a definitive trial; and to undertake an exploratory economic evaluation. DESIGN: A pilot, single-centre, open-label randomised trial. SETTING: Liverpool Heart and Chest Hospital NHS Foundation Trust between November 2010 and March 2012. PARTICIPANTS: Men and women, aged > 18 years of age, undergoing on-pump CABG surgery, who had pre-operative impaired kidney function indicated by an estimated glomerular filtration rate (eGFR) of < 60 ml/minute adjusted for 1.73 m(2) of body surface area. INTERVENTIONS: Group 1: patients who received haemofiltration during bypass (experimental group). Group 2: patients who did not receive haemofiltration during bypass (control group). MAIN OUTCOME MEASURES: (1) Feasibility outcome measures: barriers to recruitment to a larger trial were documented as observations made during the recruitment period of the trial. Reliability of data collection methods was monitored using a 13-point case record form validation check for data entry against the patient clinical notes and the trial database. (2) The main clinical outcomes were frequency of intensive care unit (ICU) stay of duration > 3 days and the length of ICU stay days. (3) Other clinical outcomes were the need for postoperative haemofiltration in the ICU, mechanical ventilation time, hospital stay, composite of outcome of unfavourable perioperative events and eGFR values at 6 weeks' follow-up. (4) Secondary health economic feasibility outcomes. RESULTS: Recruitment into the pilot trial was from 21 November 2010 to 30 March 2012. Thirty-seven eligible patients were consented and successfully randomised into the trial arms (30%). The main issues impacting on recruitment were the high volume of off-pump CABG surgery within the centre; recruitment being restricted to research nurses' working hours of the week; issues arising associated with the screening process for identifying prospective eligible patients based on eGFR values; protocol deviations/treatment crossovers; and unexpected outbreaks of pandemic influenza and other infectious conditions. The data collection process was sufficiently robust, with few errors detected. The length of ICU stay days was deemed a suitable primary outcome. There was an overall trend towards reduction in the length of ICU stay for patients who were given intraoperative haemofiltration, more so for those with diabetes. The economic evaluation estimated that the incremental costs per person were £1744 lower for the intraoperative haemofiltration group, while the incremental benefits per person increased by 0.11. CONCLUSION: Given sufficient resources and broadening of the inclusion criteria, the recruitment into a larger multicentre trial is feasible and may demonstrate potential clinical and cost benefits of using intraoperative haemofiltration in this group of patients. However, owing to the small sample size in this pilot trial, no firm conclusions can be drawn from the findings at this stage. The outcomes of this pilot study are very encouraging and suggest that it is feasible to design a continuous superiority trial with the length of ICU stay days or time to tracheal extubation as the primary outcome measure, provided that guidelines for avoiding bias are implemented. An alternative primary outcome measure that avoids bias is mortality. The inclusion criteria should also be widened to include all cardiac surgery patients with impaired renal function. TRIAL REGISTRATION: ISRCTN49513454. FUNDING: This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 17, No. 49. See the HTA programme website for further project information.

A pilot randomised controlled trial in intensive care patients comparing 7 days' treatment with empirical antibiotics with 2 days' treatment for hospital-acquired infection of unknown origin.

BACKGROUND: Management of cardiac intensive care unit (ICU) sepsis is complicated by the high incidence of systemic inflammatory response syndrome, which mimics sepsis but without an infective cause. This pilot randomised trial investigated whether or not, in the ICU, 48 hours of broad-spectrum antibiotic treatment was adequate to safely treat suspected sepsis of unknown and unproven origin and also the predictive power of newer biomarkers of sepsis. OBJECTIVE: The main objective of this pilot study was to provide preliminary data on the likely safety and efficacy of a reduced course of antibiotics for the treatment of ICU infections of unknown origin. DESIGN: A pilot, single-centre, open-label randomised trial. SETTING: This study was carried out in the ICU of a tertiary heart and chest hospital. PARTICIPANTS: Patients being treated within the ICU were recruited into the trial if the intensivist was planning to commence antibiotics because of evidence of systemic inflammatory response syndrome and a strong suspicion of infection but there was no actual known source for that infection. INTERVENTIONS: Broad-spectrum antibiotic treatment administered for 48 hours (experimental) compared with treatment for 7 days (control). MAIN OUTCOME MEASURES: The primary outcome was a composite outcome of the rate of death or initiation of antibiotic therapy after the completion of the treatment schedule allocated at randomisation. Secondary outcomes included the duration of mechanical ventilation and ICU and hospital stay; the incidence of infection with Clostridium difficile (B. S. Weeks & E. Alcamo) Jones & Bartlett International Publishers, 2008, or methicillin-resistant Staphylococcus aureus (MRSA) (B. S. Weeks & E. Alcamo) Jones & Bartlett International Publishers, 2008; resource utilisation and costs associated with each of the two pilot arms; the ratio of patients screened to patients eligible to patients randomised; the incidence of crossover between groups; and the significance of newer biomarkers for sepsis for predicting patients' need for further antibiotics. RESULTS: A total of 46 patients were recruited into the trial, with 23 randomised to each group. There was no significant difference between the two groups in terms of the composite primary outcome measure. The risk difference was 0.12 [95% confidence interval (CI) 0.11 to 0.13; p = 0.3]. In the 2-day group, four patients (17.4%) required further antibiotics compared with three (13%) in the 7-day group. Four patients died within the trial period and the deaths were not trial related. Patients who died during the trial period received no additional antibiotics in excess of their trial allocation. There were no documented incidences of MRSA or C. difficile infection in either group. No significant differences in adverse events were observed between the groups. Key economic findings were mean antibiotic costs per patient of £168.97 for the 2-day group and £375.86 for the 7-day group. The potential per annum cost saving for the ICU of 2-day treatment was estimated to range from £108,140 to £126,060. Patient screening was considered the biggest barrier to recruitment. There was no crossover between the two randomised groups. Data verification ascertained > 98% accuracy in data collection. Baseline procalcitonin was found to be predictive of the composite outcome (death and needing further antibiotics) (odds ratio 1.79, 95% CI 1.20 to 2.67; p = 0.005). Analysis of baseline procalcitonin also indicated a trend towards it being a predictor of restarting antibiotics, with an odds ratio of 1.45 (95% CI 1.04 to 2.02; p = 0.01). CONCLUSIONS: Data from this pilot study suggest that there could be significant benefits of reducing broad-spectrum antibiotic use in the ICU without it undermining patient safety, with a potential cost saving in our unit of over £100,000 per year. Evidence from this pilot trial is not definitive but warrants further investigation using a large randomised controlled trial. TRIAL REGISTRATION: Current Controlled Trials ISRCTN82694288. FUNDING: This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 16, No. 36. See the HTA programme website for further project information.

Issues in online patient self-reporting of health status.

Patient self-reporting of symptoms and quality of life following surgical interventions is generally delivered in the form of paper-based questionnaires to be completed in the outpatient clinic or at home. A commonly used tool for patient self-reporting of quality of life is the EQ5D health status questionnaire which, while limited in scope, has general applicability across a range of health interventions. In this article we examine the issues relating to online patient self-reporting using this questionnaire and the wider implications for the online reporting of health status.

Free radicals in blood: evolving concepts in the mechanism of ischemic heart disease.

There has been a considerable debate over past decade on how reactive oxidant species (ROS) in blood augment the cell signaling processes involved in the pathogenesis of coronary heart disease. In particular, it is not clear whether ROS is an important component of the cross-talk between blood and elements of the vasculature during the initial and latter stages of vascular injury and development of atherosclerotic lesions. Features like the recruitment of the circulating activated monocytes, T cells and granulocytes occur extensively in patients with acute coronary syndromes. It is not known what drives the infiltration of these cells into the vessel wall in the active stages of atherosclerosis and whether ROS plays an intermediate part. Currently, the thinking is that although inflammatory processes may be prompted by different etiological factors from that of coronary heart disease, the presence of ROS in circulating blood is the key intermediary related to vascular injury and organ dysfunction. We review, the clinical and experimental data of the mechanisms involved, and evaluate the wider implications of this concept.

Effect of diabetes on nitric oxide metabolism during cardiac surgery.

The metabolism of nitric oxide (NO) during cardiac surgery is unclear. We studied the effect of diabetes on NO metabolism during cardiac surgery in 40 subjects (20 with diabetes and 20 without diabetes). The patients were randomized to receive an infusion of physiological saline or nitroglycerin (GTN) at 1 microg. kg(-1). min(-1) starting 10 min before the initiation of cardiopulmonary bypass and then continuing for a period of 4 h. Blood and urine samples were collected at several time points for up to 8 h. NO metabolites were determined by the measurement of nitrate/nitrite (NOx, micromol/mmol creatinine) and cyclic guanosine monophosphate (cGMP, nmol/mmol creatinine) in plasma and urine. Plasma insulin levels were also determined at selected time points. Plasma NOx levels before surgery were significantly elevated in the group with diabetes compared with the group without diabetes (P < 0.001), and values were further increased during surgery in the former (P = 0.005) but not in the latter (P = 0.8). The greater plasma NOx values in patients with diabetes were matched by commensurate elevations in plasma cGMP levels (P = 0.01). Interestingly, infusion of GTN, an NO donor, significantly reduced plasma NOx (P < 0.001) and its urine elimination (P < 0.001) in patients with diabetes without reducing plasma cGMP levels (P = 0.89). Cardiac surgery increased plasma insulin in patients with and without diabetes; this increase was delayed by the infusion of GTN, but it was not related to the changes in NO production. In conclusion, NO production during cardiac surgery is increased in patients with diabetes, and this elevation can be blunted by the infusion of GTN in a rapid and reversible manner.

Cardiopulmonary bypass exacerbates oxidative stress but does not increase proinflammatory cytokine release in patients with diabetes compared with patients without diabetes: regulatory effects of exogenous nitric oxide.

BACKGROUND: Cardiopulmonary bypass induces oxidative stress and a whole-body inflammatory reaction that are believed to increase surgical morbidity. OBJECTIVES: Our goal was to investigate the effect of nitric oxide supplementation on bypass-induced oxidative stress and inflammatory reaction in patients with and without diabetes undergoing elective coronary bypass graft surgery. METHODS: Patients with and without diabetes were randomized to receive an infusion of saline solution or the nitric oxide donor nitroglycerin at 1 microg. kg(-1). min(-1) starting 10 minutes before the initiation of cardiopulmonary bypass and then maintained for 4 hours (n = 10 per group). Serial blood samples were taken at various intervals and plasma was analyzed for markers of oxidative stress (lipid hydroperoxides, protein carbonyls, and protein nitrotyrosine) and inflammation (complement C3a, elastase, interleukin 8, and tumor necrosis factor alpha). RESULTS: Cardiopulmonary bypass significantly increased lipid hydroperoxides, protein carbonyls, protein nitrotyrosine, complement C3a, elastase, soluble E-selectin, interleukin 8, and tumor necrosis factor alpha in both groups. Infusion of nitroglycerin significantly reduced the increase in lipid hydroperoxides and protein carbonyls in patients who have diabetes without affecting levels in patients without diabetes. Nitroglycerin infusion markedly reduced protein nitrotyrosine and tumor necrosis factor alpha levels in both groups. In contrast, nitroglycerin infusion significantly increased C3a in patients without diabetes and increased elastase and interleukin 8 levels in patients with diabetes. CONCLUSIONS: Cardiopulmonary bypass induces a greater oxidative stress in patients with diabetes than in those without diabetes, and the inflammatory reaction is qualitatively different in the 2 groups of patients. In addition, nitroglycerin reduces oxidative stress in patients with diabetes and differentially affects the inflammatory response to bypass both in patients with and in those without diabetes. The results have important implications with respect to the use of nitric oxide donors during cardiopulmonary bypass.

Off-pump bypass graft operation significantly reduces oxidative stress and inflammation.

BACKGROUND: This study investigated whether off-pump coronary bypass graft operations on the beating heart under normothermic conditions reduces the systemic oxidative stress and inflammatory reaction seen in patients operated under cardiopulmonary bypass (CPB). METHODS: A cardiac stabilizer (Octopus Tissue Stabilizer; Medtronic Inc, Minneapolis, MN) was used to perform the coronary anastomoses on the normothermic beating heart with or without CPB. Serial blood samples were taken at various intervals. Plasma was analyzed for several oxidative stress and inflammatory markers. RESULTS: Significant increases from prior anesthesia values of lipid hydroperoxides (190% at 4 hours), protein carbonyls (250% at 0.5 hours) and nitrotyrosine (510% at 0.5 hours) were seen in the CPB group, but they were abolished or significantly reduced in the off-pump group. Complement C3a and elastase levels were rapidly increased upon the institution of CPB, and this was followed by increases in IL-8, TNF-alpha, and sE-selectin. In contrast, the rise of these factors was blunted in patients operated without CPB. CONCLUSIONS: Off-pump coronary bypass graft operation on a beating heart significantly reduces oxidative stress and suppresses the inflammatory reaction associated with the use of CPB.

Ex vivo complement protein adsorption on positively and negatively charged cellulose dialyser membranes.

An ex vivo test system was used to measure complement protein C3 and factor B adsorption onto small dialyser modules made from regenerated and modified cellulosic hollow fibre membranes in which positive diethylaminoethyl (DEAE) or negative carboxymethyl (CM) groups were introduced into the cellulose matrix. The extracorporeal system, which included test-dialysers and the dialysis environment, allowed the use of labelled proteins without contaminating the blood donors which were connected in an open-loop fashion to the extracorporeal test system. The modules were removed at selected time points from the extracorporeal system for radioactivity counting. The results were used to evaluate the mechanisms involved in complement reactions to foreign surfaces. The system therefore allowed the analysis of complement protein adsorption occurring in the dialyser modules and its relationship to the complement generation rate in the extracorporeal system to be evaluated. It was possible to demonstrate that significant complement C3 and factor B adsorption occurred in the test modules made of cellulosic membranes. Complement adsorption as a function of the pH and the release reaction of the adsorbed C3 and factor B after membrane blood perfusion were therefore found to be variable according to the cellulosic membrane type and the presence of positive or negative charged groups within the cellulose matrix. The data obtained from the ex vivo model therefore provided additional evidence on the discussion of the mechanisms involved in the increased complement activation by regenerated cellulose and in its attenuation by DEAE- or CM-modified cellulose.

Effect of glucose and pyruvate in acidic and non-acidic peritoneal dialysis fluids on leukocytes cell functions.

A new peritoneal dialysate containing pyruvate anions has been tested for its effects on cell functions and compared with conventional lactate and bicarbonate based solutions. The dialysate has a final pH of 5.4 to 5.6 and is composed of 1.36 to 3.86% glucose-monohydrate, 132 mmol/liter sodium, 1.75 mmol/liter calcium, 0.75 mmol/liter magnesium, 102 mmol/liter chloride and 35 mmol/liter pyruvate. For cytotoxicity testing peritoneal macrophages and peripheral blood mononuclear cells (PBMC) were exposed to conventional lactate dialysate, pyruvate dialysate, bicarbonate dialysate and a control medium RPMI 1640 (Biochrom KG, Berlin, Germany), followed by activation with different bacterial stimuli. In addition, the study further investigated the effect of varying glucose concentration in the different dialysates ranging from 0 to 3.86% and pH changes between 5.2 and 7.4 on the cytotoxicity effect on the selected cells. Mononuclear cells exposed to pyruvate-based dialysate before stimulation with endotoxin exhibited a tumor necrosis factor (TNF)-mRNA signal comparable to those of cells exposed to RPMI. In contrast, exposure to lactate-based dialysate completely inhibited TNF-mRNA synthesis. In addition, cytokine synthesis in macrophages and PBMCs after exposure to pyruvate was less inhibited when compared to the corresponding levels measured after exposure to lactate. The chemotactic response of polymorphonuclear cells and O-2 generation in all tested cell types after exposure to pyruvate was found not to be inhibited, whereas a complete inhibition was observed after exposure to lactate. The results demonstrate that cytotoxicity effects of peritoneal dialysate on cell lines can be minimized by using a new dialysate formulation containing pyruvate anions instead of lactate.

In vitro blood compatibility evaluation of hollow fibre membrane using a controlled flow system: a comparative study.

A procedure has been established for the in vitro assessment of hollow fibre haemodialysis membranes. A 30 ml syringe containing 20 ml of fresh non-anticoagulated blood was mounted onto a non-pulsatile syringe pump and blood was perfused through minimodules constructed from 80 fibres retrieved from Cuprophan (Baxter ST15), cellulose acetate (M57-12, JMS Co Ltd, Hiroshima, Japan), and AN69HF (Filtral 20, Hospal, France) dialysers. Samples were collected before perfusion, 3, 6, 9 and 12 minutes. The modules were clamped vertically to minimise the effect of red cell pooling and the dialysate compartment was filled with 0.9% saline to minimise ultrafiltration. After sample processing, complement C3a, thrombin-antithrombin III complexes, prothrombin F1 + 2, and factor XII-like activity were evaluated. The results indicated that the system could discriminate between the membranes evaluated and therefore was a relevant procedure for the assessment of hollow fibre haemodialysis membranes.

The influence of biomaterials on inflammatory responses to cardiopulmonary bypass.

The nature of cardiopulmonary bypass and the complexity of the inflammatory response make the detection and interpretation of a biomaterial influence difficult. However, if mediation of the inflammatory response is considered to be an appropriate clinical goal, alteration to the biomaterial influence merits further investigation.

Determination of contact phase activation by the measurement of the activity of supernatant and membrane surface-adsorbed factor XII (FXII): its relevance as a useful parameter for the in vitro assessment of haemodialysis membranes.

We investigated hemodialysis membrane biocompatibility with respect to contact phase activation by determination of FXII-like activity (FXIIA) on the membrane surface and in the supernatant phase, during plasma contact with various hemodialysis membranes using an in vitro incubation test cell. The results were compared to the influence of these membranes on the activation of purified FXII. A time course for the generation of activated FXII using purified FXII solution at physiologic concentrations on two similar negatively charged polymers was performed. The membranes assessed were regenerated cellulose (Cuprophan; Akzo Faser AG, Germany), modified cellulosic (Hemophan; Akzo Faser AG), acrylonitrile-sodium methallyl copolymer-based membrane AN69S (Hospal, France), and SPAN, a new polyacrylonitrile-based copolymer (akzo Nobel AG). The plasma FXIIA at the membranes surface was significantly different between the membranes, while the supernatant phase FXIIA exhibited no significant differences. In contrast, activation of purified FXII in a plasma-free system with respect to supernatant activity indicated significant differences between the materials. A similar finding for the membrane-bound factor XIIA was also observed when purified factor XII was used. The membrane-bound FXIIA values observed in the plasma system containing heparin were significantly greater than in citrated plasma. This demonstrated the strong influence of heparin and the interaction of other plasma components to the membrane surface on the activation of contact phase of coagulation.

In vitro contact phase activation with haemodialysis membranes: role of pharmaceutical agents.

Contact phase activation was investigated in vitro using flat sheet type of haemodialysis membranes, Cuprophan (Akzo, Faser, Germany) and AN69S (Hospal, France), and a negatively charged polyamide Ultipor NR 14225 membrane as a control. The investigation focussed on the determination of factor XII-like activity (FXIIA) as an indicator of contact phase activation in the supernatant phase and at the membrane surface after plasma-membrane contact using an incubation test cell. The findings were compared with the observations from a plasma-free system utilizing purified unactivated factor XII. The plasma FXIIA bound to the membrane surface was significantly different between the membranes, while the supernatant phase FXIIA exhibited no significant differences. In contrast, the plasma-free system exhibited significant differences in the supernatant FXIIA and membrane-bound FXIIA for all the materials used and the magnitude of the activity was significantly greater for negatively charged materials. This finding demonstrated the strong influence of the interaction of other plasma constituents on the membrane surface and as such the binding and subsequent activation of factor XII may be altered possibly due to competitive binding and steric hindrance. On the addition of anticoagulants such as heparin, low-molecular-weight heparin, citrate and hirudin, no significant differences were observed in plasma supernatant phase FXIIA. However, each anticoagulant appears to have a distinct influence on the magnitude of plasma membrane-bound FXIIA. On the addition of aprotinin (a kallikrein inhibitor), no significant differences were observed in the plasma supernatant FXIIA. In contrast, aprotinin appears to significantly reduce membrane-bound FXIIA on Cuprophan and polyamide NR, but significantly increase the magnitude of the membrane-bound FXIIA on AN69S.

Biomaterials in cardiopulmonary bypass.

The improved utilization of biomaterials in cardiopulmonary bypass is dependent on polymer science and technology, procedures for blood compatibility assessment, optimization of biomaterial/antithrombotic agent combinations and the interpretation of clinical data.