Effect of extracorporeal membrane oxygenation on leukocyte function in neonates

Inflammatory Progression in Patients Undergoing Extracorporeal Membrane Oxygenation

Extracorporeal membrane oxygenation (ECMO) is identified as a novel therapeutic strategy that offers short-term support to the metabolism of the heart and lungs in humans. Recently, the clinical centers, which provide ECMO has increased rapidly worldwide. The indications for the use of ECMO in daily clinical practice were broadened dynamically. However, even with the widespread adoption of ECMO, it still remains significant morbidity and mortality, and the underlying mechanisms are still not elucidated. Notably, one of the vital complications during ECMO was proposed as the inflammatory progression within the extracorporeal circulation. via the development of inflammatory response, patients with ECMO may further suffer from systemic inflammatory response syndrome (SIRS), posing serious risks to human health. Recently, growing evidence confirmed that through exposure of blood into the ECMO circuit could lead to the stimulation of the immune system which also facilitated the inflammatory response and systemic impaired. In the current review, the pathological development of inflammatory progression in patients with ECMO is well-listed. Furthermore, the relationship between immune-related activation and the development of inflammation is also summarized, which may further help us to decide the therapeutic strategies in daily clinical practice.

Clearance of blood stream infections in patients receiving extracorporeal membrane oxygenation: a retrospective single-center cohort study

BACKGROUND

There are limited data on the treatment of blood stream infections (BSIs) in patients receiving extracorporeal membrane oxygenation (ECMO). Current guidance recommends documenting clearance only in fungal and Gram-positive BSIs. This study investigates the incidence and clinical significance of blood stream infections with positive repeat cultures (BSIPRC) in ECMO as well as clinical factors that may predict positive repeat cultures.

METHODS

All BSIs in patients receiving ECMO at Brooke Army Medical Center between September 2012 and October 2021 were included in this study. BSIPRC was defined as re-isolation of the same organism on repeat blood cultures following an initial positive blood culture.

RESULTS

A total of 60 patients developed 87 BSI (38.5 BSI per 1000 ECMO days). Of the 80 (92%) BSIs who had repeat blood cultures drawn, patients had BSIPRC in 35 (44%) of cases. Fever, leukocytosis, and vasopressor requirement on day of repeat culture were not associated with persistent positivity. There was no difference in survival to discharge for patients with BSIPRC as compared to single day BSI (58% vs. 63%, p = 0.78). 19% of patients with Gram-negative bacteremia had BSIPRC, and gram-negative bacteremia in general was associated with an 83% morality.

CONCLUSIONS

There were no clinical findings that differentiated patients with BSIPRC from those who had a single day of positivity. BSI was associated with high mortality in patients with Gram-negative bacteremia. Given high incidence of positive repeat cultures being seen in Gram-negative BSIs, repeat blood cultures have utility for all BSIs in patients receiving ECMO.

Hydrogen gas with extracorporeal cardiopulmonary resuscitation improves survival after prolonged cardiac arrest in rats

BACKGROUND

Despite the benefits of extracorporeal cardiopulmonary resuscitation (ECPR) in cohorts of selected patients with cardiac arrest (CA), extracorporeal membrane oxygenation (ECMO) includes an artificial oxygenation membrane and circuits that contact the circulating blood and induce excessive oxidative stress and inflammatory responses, resulting in coagulopathy and endothelial cell damage. There is currently no pharmacological treatment that has been proven to improve outcomes after CA/ECPR. We aimed to test the hypothesis that administration of hydrogen gas (H₂) combined with ECPR could improve outcomes after CA/ECPR in rats.

METHODS

Rats were subjected to 20 min of asphyxial CA and were resuscitated by ECPR. Mechanical ventilation (MV) was initiated at the beginning of ECPR. Animals were randomly assigned to the placebo or H₂ gas treatment groups. The supplement gas was administered with O₂ through the ECMO membrane and MV. Survival time, electroencephalography (EEG), brain functional status, and brain tissue oxygenation were measured. Changes in the plasma levels of syndecan-1 (a marker of endothelial damage), multiple cytokines, chemokines, and metabolites were also evaluated.

RESULTS

The survival rate at 4 h was 77.8% (7 out of 9) in the H₂ group and 22.2% (2 out of 9) in the placebo group. The Kaplan-Meier analysis showed that H₂ significantly improved the 4 h-survival endpoint (log-rank P = 0.025 vs. placebo). All animals treated with H₂ regained EEG activity, whereas no recovery was observed in animals treated with placebo. H₂ therapy markedly improved intra-resuscitation brain tissue oxygenation and prevented an increase in central venous pressure after ECPR. H₂ attenuated an increase in syndecan-1 levels and enhanced an increase in interleukin-10, vascular endothelial growth factor, and leptin levels after ECPR. Metabolomics analysis identified significant changes at 2 h after CA/ECPR between the two groups, particularly in D-glutamine and D-glutamate metabolism.

CONCLUSIONS

H₂ therapy improved mortality in highly lethal CA rats rescued by ECPR and helped recover brain electrical activity. The underlying mechanism might be linked to protective effects against endothelial damage. Further studies are warranted to elucidate the mechanisms responsible for the beneficial effects of H₂ on ischemia-reperfusion injury in critically ill patients who require ECMO support.

Effects of Steroids and Tocilizumab on the Immune Response Profile of Patients with COVID-19-Associated ARDS Requiring or Not Veno-Venous Extracorporeal Membrane Oxygenation

Veno-venous extracorporeal membrane oxygenation (VV-ECMO) is a life-saving rescue therapy in patients with Acute Respiratory Distress Syndrome (ARDS). ECMO has been associated with development of lymphocytopenia that is also common in COVID-19. Hyperinflammation may complicate SARS-CoV-2 pneumonia, prompting therapy with steroids and immunomodulatory drugs. We aimed to evaluate the association of therapies such as steroids and Tocilizumab with trajectories of the total leukocytes, lymphocyte subpopulation count, and inflammatory and fibrinolysis markers in COVID-19-related ARDS, requiring or not VV-ECMO support. The association of the trajectories of the leukocytes, lymphocyte subpopulation count, and inflammatory and fibrinolysis markers with treatment with steroids (Steroids), Tocilizumab (Tocilizumab), both drugs (Steroids + Tocilizumab), and absence of treatment (No Treatment) were analyzed using mixed effects regression models, where ECMO was considered as a potential effect modifier. One hundred and thirty-nine leukocyte and eighty-one lymphocyte subpopulation counts were obtained from thirty-one patients who required (VV-ECMO, N = 13) or not (no VV-ECMO, N = 18) extracorporeal support. In both groups, treatment with Steroids + Tocilizumab was independently associated with a significant reduction of 46% and 67% in total lymphocytes, 22% and 60% in CD3⁺, and 61% and 91% in CD19⁺ (B lymphocytes) compared to those obtained without treatment, respectively. In the no VV-ECMO group, Tocilizumab was associated with a 79% increase in total lymphocytes and with a reduction in procalcitonin compared to no treatment. CD45⁺, CD3⁺CD4⁺ (Th cell), CD3⁺CD8⁺, CD4⁺/CD8⁺, the NK cell subpopulation, neutrophils, monocytes, and basophils were significantly reduced by Steroids + Tocilizumab without an effect modification by VV-ECMO support. In critically ill COVID-19 patients with ARDS, concomitant therapies with steroids and Tocilizumab, beside mitigating the inflammation and fibrinolysis, could reduce the total leukocyte, lymphocyte, and subpopulation count. Moreover, the effect of Tocilizumab in increasing the total lymphocytes and reducing procalcitonin might be blunted by VV-ECMO.

Analysis of the 2020 EACTS/ELSO/STS/AATS Expert Guidelines on the Management of Adult Postcardiotomy Extracorporeal Life Support

Extracorporeal life support (ECLS), also known as extracorporeal membrane oxygenation (ECMO), increasingly is used in postcardiotomy (PC) shock to facilitate a bridge to sustained recovery, long-term mechanical support, or heart transplantation. Given increasing prevalence and complexity of PC-ECLS, a joint expert consensus guideline was created in 2020 for management of adult PC-ECLS by the European Association for Cardio-Thoracic Surgery (EACTS), the Extracorporeal Life Support Organization (ELSO), the Society of Thoracic Surgeons (STS), and the American Association of Thoracic Surgery (AATS). The aim of this analysis was to comprehensively review the expert consensus guidelines, with particular emphasis on PC-ECLS candidacy, timing, cannula configuration, left ventricular distention, anticoagulation, ECLS weaning, and intensive care unit complications. This analysis finds the expert consensus guideline to be timely, pertinent, and clinically valuable, although there remains the need for larger clinical trials to codify best practices.

Acute Immune Response in Venoarterial and Venovenous Extracorporeal Membrane Oxygenation Models of Rats

Although experimental extracorporeal membrane oxygenation (ECMO) animal models have been reported, there are few studies on the immune response to ECMO. We developed the venoarterial (VA) and venovenous (VV) model in rats and serially investigated the changes in the distribution of immune cells. Forty rats underwent both VA and VV modes of ECMO, and blood samples were collected at 1 day before ECMO (D-1), at the end of ECMO run (D+0), and 3 days after the ECMO (D+3). Flow cytometry was used to characterize surface marker expression (CD3, CD4, CD8, CD43, CD45, CD45R, CD161, and His48) on immune cells. Granulocytes were initially activated in both ECMO types and were further reduced but not normalized until 3 days of decannulation. Monocyte and natural killer cells were decreased initially in VA mode. B lymphocytes, helper T lymphocytes, and cytotoxic T lymphocytes also significantly decreased in VA modes after ECMO, but this phenomenon was not prominent in the VV modes. Overall immune cells proportion changed after ECMO run in both modes, and the immunologic balance altered significantly in the VA than in VV mode. Our ECMO model is feasible for the hemodynamic and immunologic research, and further long-term evaluation is needed.

Current Understanding of Leukocyte Phenotypic and Functional Modulation During Extracorporeal Membrane Oxygenation: A Narrative Review

A plethora of leukocyte modulations have been reported in critically ill patients. Critical illnesses such as acute respiratory distress syndrome and cardiogenic shock, which potentially require extracorporeal membrane oxygenation (ECMO) support, are associated with changes in leukocyte numbers, phenotype, and functions. The changes observed in these illnesses could be compounded by exposure of blood to the non-endothelialized surfaces and non-physiological conditions of ECMO. This can result in further leukocyte activation, increased platelet-leukocyte interplay, pro-inflammatory and pro-coagulant state, alongside features of immunosuppression. However, the effects of ECMO on leukocytes, in particular their phenotypic and functional signatures, remain largely overlooked, including whether these changes have attributable mortality and morbidity. The aim of our narrative review is to highlight the importance of studying leukocyte signatures to better understand the development of complications associated with ECMO. Increased knowledge and appreciation of their probable role in ECMO-related adverse events may assist in guiding the design and establishment of targeted preventative actions.

Incidence of healthcare-associated infections in patients with fever during the first 48 hours after decannulation from veno-venous extracorporeal membrane oxygenation

INTRODUCTION

Fevers following decannulation from veno-venous extracorporeal membrane oxygenation often trigger an infectious workup; however, the yield of this workup is unknown. We investigated the incidence of post-veno-venous extracorporeal membrane oxygenation decannulation fever as well as the incidence and nature of healthcare-associated infections in this population within 48 hours of decannulation.

METHODS

All patients treated with veno-venous extracorporeal membrane oxygenation for acute respiratory failure who survived to decannulation between August 2014 and November 2018 were retrospectively reviewed. Trauma patients and bridge to lung transplant patients were excluded. The highest temperature and maximum white blood cell count in the 24 hours preceding and the 48 hours following decannulation were obtained. All culture data obtained in the 48 hours following decannulation were reviewed. Healthcare-associated infections included blood stream infections, ventilator-associated pneumonia, and urinary tract infections.

RESULTS

A total of 143 patients survived to decannulation from veno-venous extracorporeal membrane oxygenation and were included in the study. In total, 73 patients (51%) were febrile in the 48 hours following decannulation. Among this cohort, seven healthcare-associated infections were found, including five urinary tract infections, one blood stream infection, and one ventilator-associated pneumonia. In the afebrile cohort (70 patients), four healthcare-associated infections were found, including one catheter-associated urinary tract infection, two blood stream infections, and one ventilator-associated pneumonia. In all decannulated patients, the majority of healthcare-associated infections were urinary tract infections (55%). No central line-associated blood stream infections were identified in either cohort. When comparing febrile to non-febrile cohorts, there was a significant difference between pre- and post-decannulation highest temperature (p < 0.001) but not maximum white blood cell count (p = 0.66 and p = 0.714) between the two groups. Among all positive culture data, the most commonly isolated organism was Klebsiella pneumoniae (41.7%) followed by Escherichia coli (33%). Median hospital length of stay and time on extracorporeal membrane oxygenation were shorter in the afebrile group compared to the febrile group; however, this did not reach a statistical difference.

CONCLUSION

Fever is common in the 48 hours following decannulation from veno-venous extracorporeal membrane oxygenation. Differentiating infection from non-infectious fever in the post-decannulation veno-venous extracorporeal membrane oxygenation population remains challenging. In our febrile post-decannulation cohort, the incidence of healthcare-associated infections was low. The majority were diagnosed with a urinary tract infection. We believe obtaining cultures in febrile patients in the immediate decannulation period from veno-venous extracorporeal membrane oxygenation has utility, and even in the absence of other clinical suspicion, should be considered. However, based on our data, a urinalysis and urine culture may be sufficient as an initial work up to identify the source of infection.

Effect of ex vivo extracorporeal membrane oxygenation flow dynamics on immune response

BACKGROUND

Extracorporeal membrane oxygenation is a life-saving support for heart and/or lung failure patients. Despite technological advancement, abnormal physiology persists and has been associated with subsequent adverse events. These include thrombosis, bleeding, systemic inflammatory response syndrome and infection. However, the underlying mechanisms are yet to be elucidated. We aimed to investigate whether the different flow dynamics of extracorporeal membrane oxygenation would alter immune responses, specifically the overall inflammatory response, leukocyte numbers and activation/adhesion surface antigen expression.

METHODS

An ex vivo model was used with human whole blood circulating at 37°C for 6 hours at high (4 L/minute) or low (1.5 L/minute) flow dynamics, with serial blood samples taken for analysis.

RESULTS

During high flow, production of interleukin-1β (p < 0.0001), interleukin-6 (p = 0.0075), tumour necrosis factor-α (p = 0.0013), myeloperoxidase (p < 0.0001) and neutrophil elastase (p < 0.0001) were significantly elevated over time compared to low flow, in particular at 6 hours. While the remaining assessments exhibited minute changes between flow dynamics, a consistent trend of modulation in leukocyte subset numbers and phenotype was observed at 6 hours.

CONCLUSION

We conclude that prolonged circulation at high flow triggers a prominent pro-inflammatory cytokine response and activates neutrophil granule release, but further research is needed to better characterize the effect of flow during extracorporeal membrane oxygenation.

Nosocomial Infections in Neonates Supported by Extracorporeal Membrane Oxygenation: First French Retrospective Study

How to cite this article: Rambaud J, Allioux C, Jean S, Guilbert J, Guellec I, Demoulin M, et al. Nosocomial Infections in Neonates Supported by Extracorporeal Membrane Oxygenation: First French Retrospective Study. Indian J Crit Care Med 2019;23(9):392–395.

Extracorporeal life support and systemic inflammation

Extracorporeal life support (ECLS) encompasses a wide range of extracorporeal modalities that offer short- and intermediate-term mechanical support to the failing heart or lung. Apart from the daily use of cardiopulmonary bypass (CPB) in the operating room, there has been a resurgence of interest and utilization of veno-arterial and veno-venous extracorporeal membrane oxygenation (VA- and VV-ECMO, respectively) and extracorporeal carbon dioxide removal (ECCO₂R) in recent years. This might be attributed to the advancement in technology, nonetheless the morbidity and mortality associated with the clinical application of this technology is still significant. The initiation of ECLS triggers a systemic inflammatory response, which involves the activation of the coagulation cascade, complement systems, endothelial cells, leukocytes, and platelets, thus potentially contributing to morbidity and mortality. This is due to the release of cytokines and other biomarkers of inflammation, which have been associated with multiorgan dysfunction. On the other hand, ECLS can be utilized as a therapy to halt the inflammatory response associated with critical illness and ICU therapeutic intervention, such as facilitating ultra-protective mechanical ventilation. In addition to addressing the impact on outcome of the relationship between inflammation and ECLS, two different but complementary pathophysiological perspectives will be developed in this review: ECLS as the cause of inflammation and ECLS as the treatment of inflammation. This framework may be useful in guiding the development of novel therapeutic strategies to improve the outcome of critical illness.

The Evaluation of Nosocomial Infections in Pediatric Patients with Extracorporeal Membrane Oxygenation Support

Introduction

Extracorporeal membrane oxygenation (ECMO) has become a standard technique over the past few decades in intensive care unit (ICU).

Objective

A review of pediatric patients who received ECMO support in the pediatric cardiac ICU was conducted to determine the incidence, risk factors and causal organisms related to acquired infections and assess the survival rates of ECMO patients with nosocomial infections.

Methods

Sixty-six patients who received ECMO support in the pediatric cardiac ICU between January 2011 and June 2014 were included in the study. Demographic, echocardiographic, hemodynamic features and surgical procedures were reviewed.

Results

Sixty-six patients received a total of 292.5 days of venoarterial ECMO support. Sixty were postoperative patients. Forty-five patients were weaned from ECMO support with an ECMO survival rate of 68.2%. The rate of infection was 116.2/1000 ECMO days. Prolonged ICU stay, duration of ventilation and ECMO were found associated with development of nosocomial infection and only the duration of ECMO was an independent risk factor for nosocomial infections in ECMO patients.

Conclusion

The correction of the underlying process leading to ECMO support and shortening the length of ECMO duration together with stricter application of ECMO indications would improve the infection incidence and hospital surveillance of the patient group.

Oxidative Stress and Neonatal Respiratory Extracorporeal Membrane Oxygenation

Oxidative stress is a frequent condition in critically ill patients, especially if exposed to extracorporeal circulation, and it is associated with worse outcomes and increased mortality. The inflammation triggered by the contact of blood with a non-endogenous surface, the use of high volumes of packed red blood cells and platelets transfusion, the risk of hyperoxia and the impairment of antioxidation systems contribute to the increase of reactive oxygen species and the imbalance of the redox system. This is responsible for the increased production of superoxide anion, hydrogen peroxide, hydroxyl radicals, and peroxynitrite resulting in increased lipid peroxidation, protein oxidation, and DNA damage. The understanding of the pathophysiologic mechanisms leading to redox imbalance would pave the way for the future development of preventive approaches. This review provides an overview of the clinical impact of the oxidative stress during neonatal extracorporeal support and concludes with a brief perspective on the current antioxidant strategies, with the aim to focus on the potential oxidative stress-mediated cell damage that has been implicated in both short and long-term outcomes.

Acquired infection during neonatal and pediatric extracorporeal membrane oxygenation

INTRODUCTION

Our objectives are to (1) describe the pathogens, site, timing and risk factors for acquired infection during neonatal and pediatric ECMO and (2) explore the association between acquired infection and mortality.

METHODS

Secondary analysis of prospective data collected by the Collaborative Pediatric Critical Care Research Network between December 2012 and September 2014. Clinical factors associated with acquired infection were assessed with multivariable Cox regression. Factors associated with mortality were assessed with logistic regression.

RESULTS

Of 481 patients, 247 (51.3%) were neonates and 400 (83.2%) received venoarterial ECMO. Eighty (16.6%) patients acquired one or more infections during ECMO; 60 (12.5%) patients had bacterial, 21 (4.4%) had fungal and 11 (2.3%) had viral infections. The site of infection included respiratory for 53 (11.0%) patients, bloodstream for 21 (4.4%), urine for 20 (4.2%) and other for 7 (1.5%). Candida species were most common. Median time to infection was 5.2 days (IQR 2.3, 9.6). On multivariable analysis, a greater number of procedures for ECMO cannula placement was independently associated with increased risk of acquired infection during ECMO (Hazard Ratio 2.13 (95% CI 1.22, 3.72), p<0.01) and receiving ECMO in a neonatal ICU compared to a pediatric or cardiac ICU was associated with decreased risk (Hazard Ratio pediatric ICU 4.25 (95% CI 2.20, 8.20), cardiac ICU 2.91 (95% CI 1.48, 5.71), neonatal ICU as reference, p<0.001). Acquired infection was not independently associated with mortality.

CONCLUSION

ECMO procedures and location may contribute to acquired infection risk; however, acquired infection did not predict mortality in this study.

The inflammatory response to extracorporeal membrane oxygenation (ECMO): a review of the pathophysiology

Extracorporeal membrane oxygenation (ECMO) is a technology capable of providing short-term mechanical support to the heart, lungs or both. Over the last decade, the number of centres offering ECMO has grown rapidly. At the same time, the indications for its use have also been broadened. In part, this trend has been supported by advances in circuit design and in cannulation techniques. Despite the widespread adoption of extracorporeal life support techniques, the use of ECMO remains associated with significant morbidity and mortality. A complication witnessed during ECMO is the inflammatory response to extracorporeal circulation. This reaction shares similarities with the systemic inflammatory response syndrome (SIRS) and has been well-documented in relation to cardiopulmonary bypass. The exposure of a patient’s blood to the non-endothelialised surface of the ECMO circuit results in the widespread activation of the innate immune system; if unchecked this may result in inflammation and organ injury. Here, we review the pathophysiology of the inflammatory response to ECMO, highlighting the complex interactions between arms of the innate immune response, the endothelium and coagulation. An understanding of the processes involved may guide the design of therapies and strategies aimed at ameliorating inflammation during ECMO. Likewise, an appreciation of the potentially deleterious inflammatory effects of ECMO may assist those weighing the risks and benefits of therapy.

Infections acquired during extracorporeal membrane oxygenation in neonates, children, and adults

OBJECTIVE

To determine current rates, risk factors, and causal organisms related to infections acquired during extracorporeal membrane oxygenation (ECMO).

DESIGN

A descriptive and retrospective case-control study.

SETTING

ECMO centers belonging to the Extracorporeal Life Support Organization.

PATIENTS

The Extracorporeal Life Support Organization Registry was queried for data related to all ECMO cases from 1998 through 2008. All culture-proven infections obtained from any site during ECMO support and not believed preexisting were included. Infection rates were analyzed by age category (i.e., neonatal, pediatric, adult), indication for ECMO (i.e., respiratory, cardiac, cardiopulmonary resuscitation), mode of ECMO (e.g., venovenous), and duration of ECMO support. Infected and noninfected ECMO patients were compared.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 2,418 infections were reported during 20,741 (11.7%) ECMO cases for a rate of 15.4 per 1,000 ECMO days. Rates were highest in the adult vs. the pediatric and neonatal populations (30.6 vs. 20.8 vs. 10.1 infections per 1,000 ECMO days, respectively) and in those necessitating extracorporeal cardiopulmonary resuscitation (24.7 infections per 1,000 ECMO days). In each age category, venoarterial ECMO was the mode of support associated with the highest rate of infection. Prevalence of infection increased with duration of ECMO support from 6.1% of those requiring bypass for ≤ 7 days to 30.3% of those requiring ECMO for >14 days (p < .001). Coagulase-negative staphylococci (15.9%) were the most common organisms cultured followed by species of Candida (12.7%), and Pseudomonas (10.5%). Those with an infection acquired during ECMO support were significantly older, had a longer duration of ECMO, a longer duration of post-ECMO ventilatory support, and a higher prevalence of death than those without.

CONCLUSIONS

Infections acquired during ECMO are common and can have significant associated consequences. Knowledge of high-risk patients and common causal organisms may improve strategies for treatment and prevention, but further work to develop strategies and guidelines for prevention of these infections is urgently needed.

Plasma concentrations of inflammatory cytokines rise rapidly during ECMO-related SIRS due to the release of preformed stores in the intestine

Extracorporeal membrane oxygenation (ECMO) is a life-saving support system used in neonates and young children with severe cardiorespiratory failure. Although ECMO has reduced mortality in these critically ill patients, almost all patients treated with ECMO develop a systemic inflammatory response syndrome (SIRS) characterized by a 'cytokine storm', leukocyte activation, and multisystem organ dysfunction. We used a neonatal porcine model of ECMO to investigate whether rising plasma concentrations of inflammatory cytokines during ECMO reflect de novo synthesis of these mediators in inflamed tissues, and therefore, can be used to assess the severity of ECMO-related SIRS. Previously healthy piglets (3-week-old) were subjected to venoarterial ECMO for up to 8 h. SIRS was assessed by histopathological analysis, measurement of neutrophil activation (flow cytometry), plasma cytokine concentrations (enzyme immunoassays), and tissue expression of inflammatory genes (PCR/western blots). Mast cell degranulation was investigated by measurement of plasma tryptase activity. Porcine neonatal ECMO was associated with systemic inflammatory changes similar to those seen in human neonates. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-8 (IL-8) concentrations rose rapidly during the first 2 h of ECMO, faster than the tissue expression of these cytokines. ECMO was associated with increased plasma mast cell tryptase activity, indicating that increased plasma concentrations of inflammatory cytokines during ECMO may result from mast cell degranulation and associated release of preformed cytokines stored in mast cells. TNF-alpha and IL-8 concentrations rose faster in plasma than in the peripheral tissues during ECMO, indicating that rising plasma levels of these cytokines immediately after the initiation of ECMO may not reflect increasing tissue synthesis of these cytokines. Mobilization of preformed cellular stores of inflammatory cytokines such as in mucosal mast cells may have an important pathophysiological role in ECMO-related SIRS.

Risk factors for nosocomial infection during extracorporeal membrane oxygenation

An increasing number of patients receive extracorporeal membrane oxygenation (ECMO) for life support. This study aimed to investigate the incidence and risk factors for nosocomial infection in adult patients receiving ECMO. We reviewed the medical records of adult patients who received ECMO support for more than 72h at Far Eastern Memorial Hospital from 2001 to 2007. ECMO-related nosocomial infections were defined as infections occurring from 24h after ECMO initiation until 48h after ECMO discontinuation. There were 12 episodes of nosocomial infection identified in 10 of the 114 (8.77%) patients on ECMO, including four cases of pneumonia, three cases of bacteraemia, three surgical site infections and two urinary tract infections. The incidence of ECMO-related nosocomial infection was 11.92 per 1000 ECMO-days. The length of ECMO use and intensive care unit (ICU) stay were significantly different between patients with, and without, nosocomial infection (P<0.001). More than 10 days of ECMO use was associated with a significantly higher nosocomial infection rate (P=0.003). Gram-negative bacilli were responsible for 78% of the nosocomial infections. In the univariate analysis, the duration of ICU stay and duration of ECMO use were associated with nosocomial infection. In the multivariate analysis, only the duration of ECMO was independently associated with nosocomial infection (P=0.007). Overall, the only independent risk factor for ECMO-related nosocomial infection identified in this study was prolonged ECMO use.

Interleukin-6 may predict survival in extracorporeal membrane oxygenation treatment

The cytokine network and its association with complement activation during cardiac surgery with cardiopulmonary bypass (CPB) is complex. Extracorporeal membrane oxygenation (ECMO) differs from CPB in duration of days to weeks rather than hours. However, few studies have analyzed the levels of inflammatory mediators during ECMO treatment. Plasma samples from 22 patients [nine neonates, one infant, four children and eight adults (14 males and eight female)] who underwent ECMO treatment were collected prior to, during and after treatment, and analyzed for concentrations of inflammatory and anti-inflammatory cytokines and parameters of complement activation. Seven children were treated for cardiac and seven for pulmonary failure and, in the adult group, four were treated for cardiac and four for pulmonary failure. ECMO was performed with veno-arterial (VA) bypass in all children and five adults, and with veno-venous (VV) bypass in three adults. Fourteen patients survived (64%) and eight (36%) patients died during follow-up. A marked (approximately 99%) and rapid (i.e., within two days) decrease in IL-6 was seen in survivors. The non-survivors were characterized by persistently high IL-6 levels throughout the observation period (i.e., until death). C-reactive protein (CRP) levels showed a similar pattern as the IL-6, with higher levels in non-survivors throughout the observation period. However, in contrast to IL-6, the differences between survivors and non-survivors reached statistical significance, but only at the end of the observation period. It is possible that early measurements of IL-6 in ECMO patients could give prognostic information beyond that of CRP.

Complement activation by in vivo neonatal and in vitro extracorporeal membrane oxygenation

Complment activation during extracorporeal membrane oxygenation (ECMO) in newborns can be caused by both the underlying disease processes and by blood contact with the ECMO circuit. We investigated the relative importance of these mechanisms by measuring C3a, C5a and sC5b-9 before, during and after neonatal ECMO in six consecutive newborn patients using enzyme-linked immunoassay. In addition complement activation during in vitro ECMO with repeated flow of the same blood volume was measured using blood from healthy adult donors. C3a increased significantly in vivo after 1 h (from 1035+/-193 to 1865+/-419 microg/l) and in vitro ECMO (from 314+/-75 to 1962+/-1062 microg/l). C5a increased during ECMO without significant differences between in vivo and in vitro activation. In neonatal patients, sC5b-9 rose faster than in vitro, but the rapid increase was also significant for in vitro experiments (in vivo: from 328+/-63 to 1623+/-387 microg/l after 2 h; and in vitro: from 78+/-32 to 453+/-179 microg/l after 8 h). After this initial peak at 1-2 h, complement activation decreased gradually until 2-3 days after the initiation of ECMO. We conclude that in newborns the rapid activation of the complement system after the start of ECMO is predominantly caused by contact with artificial surfaces rather than the patient's underlying disease.

Leukocyte and endothelial activation in a laboratory model of extracorporeal membrane oxygenation (ECMO)

An inflammatory response and a capillary leak syndrome frequently develop during the treatment of neonatal respiratory failure by extracorporeal membrane oxygenation (ECMO). The present study was performed to investigate leukocyte activation and endothelial cell dysfunction that are associated with prolonged contact of blood components with synthetic surfaces. Laboratory ECMO was performed with fresh human blood at 37 degrees C for 8 h (n = 6). Leukocyte activation was measured by L-selectin (CD62L) and CD18 integrin surface expression and by neutrophil-derived elastase release. To monitor endothelial activation, endothelial cell ICAM-1 (CD54) expression was measured in cultured endothelial cells from human umbilical veins (HUVEC) after incubation with plasma from the ECMO experiments. CD18 integrin expression was found significantly up-regulated on polymorphonuclear neutrophils and monocytes after 2-4 h of laboratory ECMO. L-selectin was reduced on both cell types during the total duration of the experiments. Soluble L-selectin (sCD62L) and total and differential leukocyte counts remained unchanged during the experiment. Neutrophil-derived elastase content was maximal after 8 h of ECMO. Plasma from the ECMO experiments did not induce ICAM-1 expression of cultured HUVEC. We conclude that prolonged contact with synthetic surfaces during ECMO activates phagocytes, which may contribute to the inflammatory response seen in ECMO-treated patients. Activated phagocytes do not accumulate in the extracorporeal system nor release humoral factors inducing ICAM-1 expression on endothelial cells.

Reduced ventilator pressure and improved P/F ratio during percutaneous arteriovenous carbon dioxide removal for severe respiratory failure

OBJECTIVE

To evaluate the effect of percutaneous arteriovenous carbon dioxide removal (AVCO2R) on ventilator pressures and P/F ratio in a clinically relevant large-animal model of severe respiratory failure.

SUMMARY BACKGROUND DATA

AVCO2R was developed as a simple arteriovenous shunt with a commercially available low-resistance gas exchange device of sufficient surface area for near-total CO2 removal. With an AV shunt 10% to 15% of cardiac output, AVCO2R allows a reduction in ventilator airway pressures without hypercapnia or the complex circuitry and monitoring required for conventional ECMO.

METHODS

AVCO2R was applied to a new, clinically relevant large-animal model of severe respiratory failure created by smoke inhalation and cutaneous flame bum injury. Adult sheep (n = 9, 38+/-6 kg) received a 40% total body surface area, third-deinsufflation. After injury, all animals were placed on volume-controlled mechanical ventilation to achieve PaO2 > 60 mmHg and PacO2 < 40 mmHg. Animals were placed on AVCO2R within 40 to 48 hours of injury when the PaO2/FiO2 was <200. Animals underwent cannulation of the carotid artery and jugular vein with percutaneous 10F arterial and 14F venous cannulas. Shunt flow was continuously monitored using an ultrasonic flow probe and calculated as a percentage of cardiac output.

RESULTS

AVCO2R flows of 800 to 900 ml/min (11% to 13% cardiac output) achieved 77 to 104 ml/min of CO2 removal (95% to 97% total CO2 production) while maintaining normocapnia. Significant reductions in ventilator settings were tidal volume, 421.3+/-39.8 to 270.0+/-6.3 ml; peak inspiratory pressure, 24.8+/-2.4 to 13.7+/-0.7 cm H2O; minute ventilation, 12.7+/-1.4 to 6.2+/-0.8 L/min; respiratory rate, 25.4+/-1.3 to 18.4+/-1.8 breaths/min; and FiO2, 0.88+/-0.1 to 0.39+/-0.1. The P/F ratio increased from 151.5+/-40.0 at baseline to 320.0+/-17.8 after 72 hours.

CONCLUSIONS

Percutaneous AVCO2R allows near-total CO2 removal and significant reductions in ventilator pressures with improvement in the P/F ratio.

Induced cell trauma during in vitro perfusion: a comparison between two different perfusion systems

The purpose of this study was to compare blood cell activation during in vitro long-term perfusion using 2 parallel in vitro extracorporeal membrane oxygenation (ECMO) systems. We compared two substantially different perfusion systems, an assistance respiratoire extra corporelle (AREC) system on one hand, containing an AREC pump, silicon tubing, and a hollow-fiber oxygenator, and a centrifugal pump system, on the other hand, containing a Biomedicus centrifugal pump, PVC tubing, and a membrane oxygenator. We measured the platelet count using an automated blood cell counter. Platelet activation was evaluated using a flow cytometric technique for the platelet membrane expression of glycoproteins and ELISA for the plasma concentration of beta-thromboglobulin (beta-TG), a platelet specific protein released into the blood upon platelet activation. The neutrophil count was assayed using an automated blood cell counter and the plasma concentration of cytokines using an ELISA kit. A significant difference between the two systems was observed in terms of the platelet membrane expression of glycoprotein (GP)Ib (p=0.0001) and GPIIb/IIIa (p=0.0037), indicating a lower degree of platelet activation in the AREC system. The concentration of neutrophils was significantly lower in the centrifugal system (p=0.002) compared to the AREC system. The neutrophil membrane expression of CD11b was significantly lower (p=0.0067) in the AREC system, indicating a lower degree of neutrophil activation compared to the centrifugal pump system. A significantly lower degree of hemolysis, as expressed by plasma hemoglobin, was observed in the AREC pump system (p=0.0491). In conclusion, lower degrees of the platelet membrane expression of GPIb and GPIIb/IIIa and of the neutrophil membrane expression of CD11b were observed in the AREC system, indicating a lower degree of platelet and neutrophil activation in this system. No significant difference between the two systems as to the plasma concentration of interleukin (IL)-1beta, IL-6, or IL-8 could be recorded. Further studies are warranted to specify the role of each individual component of the two systems.

Cytokine release during long-term extracorporeal circulation in an experimental model

The objective of this study was to determine the degree of leukocyte activation, as measured by cytokine release, in circulating blood during experimental extracorporeal circulation. Complete in vitro extracorporeal membrane oxygenation (ECMO) circuits were used, and 9 experiments were performed. Whole blood stored at 37 degrees C was used as the control. Blood samples were withdrawn before the start of perfusion and at 24 h of perfusion. Statistically significant releases of interleukin (IL)-1beta, IL-8, and IL-1 receptor antagonist were observed in the perfusion circuits compared to both the control blood and baseline values. Also, increases in plasma tumor necrosis factor (TNF)alpha and IL-6 were seen after 24 h of perfusion although these changes did not reach statistical significance. These results indicate that extracorporeal circulation induced leukocyte activation and cytokine release. These reactions might, as an additional trauma, deteriorate the situation in an already severely ill patient. A search for methods to counteract this untoward activation seems warranted.

Neutrophil and cytokine activation with neonatal extracorporeal membrane oxygenation

OBJECTIVE

To determine whether extracorporeal membrane oxygenation (ECMO), like cardiopulmonary bypass, produces systemic inflammatory responses that could potentiate organ injury in infants with respiratory failure.

STUDY DESIGN

We evaluated the effects of neonatal ECMO on neutrophil surface adherence proteins, elastase release, and cytokine levels in blood samples from 15 patients before and during ECMO, and from banked blood and ECMO circuit blood before cannulation. Neutrophil elastase, tumor necrosis factor alpha, and interleukin types 1 beta, 6, and 8 were measured. Chest radiographs were evaluated by a radiologist using a lung injury score in blinded fashion.

RESULTS

Primed ECMO circuit blood, in comparison with patient pre-ECMO blood, demonstrated marked up-regulation of CD11b (mean fluorescence intensity 1660 +/- 109 vs 361 +/- 81; p < 0.001 (mean +/- SEM)), shedding of L-selectin (mean fluorescence intensity 10 +/- 2 vs 89 +/- 38; p < 0.01), and elevated elastase levels (349 +/- 76 vs 154 ng/ml +/- 38; p < 0.001), consistent with neutrophil activation. During ECMO, neutrophil CD11b levels increased but L-selectin was not significantly shed. Concentrations of circulating neutrophil elastase increase significantly during ECMO. Corrected circulating quantities of interleukin-8 also rose significantly, but the responses of tumor necrosis factor alpha and interleukin-1 beta were minimal. Radiographic lung injury scores worsened with the initiation of ECMO (median score: 6 before ECMO vs 11 in first hour of ECMO; p = 0.012), in conjunction with indicators of neutrophil activation.

CONCLUSION

Neonates with respiratory failure have activation of the inflammatory cascade. ECMO incites additional neutrophil and cytokine activation in association with early pulmonary deterioration. Routine leukodepletion of blood for circuit priming to remove activated neutrophils may be beneficial.

Inhibition of neutrophil adhesion during cardiopulmonary bypass

Blood contact with synthetic surfaces during cardiopulmonary bypass (CPB) causes a diffuse inflammatory reaction that includes neutrophil activation. The purpose of this study was to determine if inhibition of neutrophil adhesion with a new antiinflammatory agent NPC 15669 (N-(9H-(2,7-dimethylfluorenyl-9-methoxy)-carbonyl)-L-leucine) could reduce pulmonary injury in a porcine model of CPB. NPC 15669 blocks adherence of activated neutrophils by inhibiting upregulation of the Mac-1 (CD11b/CD18) adhesion molecule. Sixteen piglets underwent 2 hours of hypothermic CPB followed by 2 hours of observation; 8 received NPC 15669 (10 mg/kg intravenous bolus followed by 6 mg.kg-1.h-1 intravenous infusion) and 8 received equal volumes of vehicle. After 90 minutes of CPB, expression of neutrophil adhesion molecule subunit CD18 increased 118% in control piglets but only 36% in piglets treated with NPC 15669 (p < 0.01). Although neutropenia developed in all animals during CPB, lung tissue myeloperoxidase content was significantly lower in treated than in control animals 2 hours after CPB (94.9 +/- 10.4 versus 46.9 +/- 5.5 mumol.10 mg-1.min-1; p < 0.002). Free radical-mediated lipid peroxidation (quantitated by spectrophotometric assay of plasma conjugated dienes) was significantly reduced by treatment with NPC 15669 during and after CPB. Pulmonary function was better in NPC 15669-treated animals: 2 hours after CPB, pulmonary vascular resistance increased 477% in control piglets but only 140% in piglets receiving NPC 15669 (p < 0.03); arterial oxygen tension was significantly greater in piglets receiving NPC 15669 (428 +/- 33 mm Hg) than in controls (141 +/- 46; p < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Granulocyte superoxide anion and elastase release during cardiopulmonary bypass

Cardiopulmonary bypass (CPB) is known to induce several pathogenic responses in cardiovascular surgery. To explore leukocyte activation during PCB, we investigated superoxide anion (O2-) production by granulocytes in 6 patients undergoing aortocoronary bypass surgery. O2- production was determined with chemiluminescence amplified by a cypridina luciferin analogue. Granulocytes collected from the blood in the arterial site of the CPB circuit were stimulated by phorbol myristate acetate, n-formyl-methionyl-leucyl-phenylalanine, and opsonized zymosan. All the stimulators failed to disclose a significant difference between the magnitude of chemiluminescence during and after CPB. However, significant complement activation was detected, and the plasma level of granulocyte elastase increased gradually during and after CPB. This discrepancy between the unchanged O2- production by stimulated granulocytes and the increase in inflammatory mediators including granulocyte elastase may be due to sequestration of activated granulocytes in extravascular tissues. Namely, it was highly likely that activated granulocytes responsible for the increased plasma elastase level were sequestered and remained outside the blood circulation.