Andrew D. Meyer

Hemolytic and thrombocytopathic characteristics of extracorporeal membrane oxygenation systems at simulated flow rate for neonates.

Objective: A state-of-the-art centrifugal pump combined with hollow-fiber oxygenator for extracorporeal membrane oxygenation has potential advantages such as smaller priming volumes and decreased potential to cause tubing rupture as compared with the traditional roller head/silicone membrane systems. Adoption of these state-of-the-art systems has been slow in neonates as a result of past evidence of severe hemolysis that may lead to renal failure and increased mortality. Extracorporeal systems have also been linked to platelet dysfunction, a contributing factor toward intracranial hemorrhage, a leading cause of infant morbidity. Little data exist comparing the centrifugal systems with the roller systems in terms of hemolysis and platelet aggregation at low flow rates commonly used in neonatal extracorporeal membrane oxygenation. Design: Prospective, comparative laboratory study. Setting: University research laboratory. Subjects: Centrifugal pump, roller pump, hollow-fiber oxygenator, and silicone membrane oxygenator. Interventions: Comparative study using two pumps, the centrifugal Jostra Rotaflow (Maquet, Wayne, NJ) and the roller-head (Jostra, Maquet, Wayne, NJ), and two oxygenators, polymethlypentene Quadrox-D (Maquet) and silicone membrane (Medtronic, Minneapolis, MN). Five test runs of four circuit combinations were examined for hemolysis and platelet aggregation during 6 hrs of continuous use in a simulated in vitro extracorporeal membrane oxygenation circuit circulating whole swine blood at 300 mL/min. Measurements and Main Results: Hemolysis was assessed by spectrophometric measurement of plasma-free hemoglobin. Platelet aggregation was evaluated using monoclonal CD61 antibody fluorescent flow cytometry profiles. All of the extracorporeal membrane oxygenation systems created plasma-free hemoglobin at a similar rate compared with static blood control. There was no difference in the mean normalized index of hemolysis of the centrifugal/hollow-fiber oxygenator system as compared with the roller-head/silicone membrane systems (0.0032 g/100 L vs. 0.0058 g/100 L, p ≥ .7). None of the extracorporeal membrane oxygenation systems had a significant increase in platelet aggregation above baseline. Conclusions: In a low-flow neonatal environment, a state-of-the-art centrifugal pump combined with new fiber-type oxygenators appear to be safe in regard to hemolysis and platelet aggregation.

The Persistence of Electrostatically Seeded Endothelial Cells Lining a Small Diameter Expanded Polytetrafluoroethylene Vascular Graft

Purpose: The purpose of this study was to evaluate the persistence of electrostatically seeded endothelial cells (ECs) lining an expanded polytetrafluorethylene (e-PTFE) graft after one week exposure to in vivo circulation in a canine femoral artery bypass model. This was accomplished by visualizing the PKH 26 (red fluorescent) label placed in the EC membranes prior to the seeding procedure. Furthermore, this study was performed to confirm that thesourceof the ECs lining thegraft werethosefrom theinitial inoculum. Methods: This evaluation consisted of harvesting autologous, canine jugular vein ECs, PKH 26 labeling of the ECs, electrostatic EC seeding the e-PTFE grafts (4 mm GORE-TEX®, Length = 6 cm), implanting thegrafts (femoral artery model) for one week, and explanting the grafts for light, fluorescent and scanning electron microscopy evaluations of the luminal surface. Results: The unseeded grafts (controls) had a mean fluorescence surface coverage of 6.82 ± 7.19%, while the EC seeded grafts had a mean of 90.3 ± 14.3% which is significantly (p<0.001) different from the controls. Overall, the seeding timeincluding the EC harvesting and PKH 26 labeling protocol was approximately 75 min. Conclusions: The electrostatically seeded ECs persisted after implantation of the graft as demonstrated by the PKH 26 labeling data. The fluorescent data also demonstrated that the neointima formed (EC luminal surface coverage) one week after implantation was in fact derived from the ECs initially seeded as determined by the abundance of the labeled ECs.

Endothelial cell seeding of a 4-mm I.D. Polyurethane vascular graft

We evaluated the extent (luminal coverage) of the endothelial cell (EC) lining/neointimal development and the thromboresistance of electrostatically EC seeded small diameter Chrono Flex-polyurethane vascular grafts. The evaluation consisted of harvesting autologous, canine jugular vein ECs, electrostatically seeding the polyurethane grafts (4-mm I.D., length = 6 cm) with the harvested ECs, implanting the grafts in a canine femoral artery model for four to six weeks, and excising the grafts for histological and scanning electron microscopy evaluations. Results of the histological evaluation (mid-graft region only) indicated that electrostatic EC seeding led to neointimal development and to minimal to no thrombus formation within the EC seeded grafts. The unseeded control grafts resulted in no neointimal development and substantial thrombus formation on the graft luminal surfaces. Scanning electron microscopy examination demonstrated a mature, confluent endothelium with a ‘‘cobblestone’’ appearance on the EC seeded graft luminal surface after six weeks. We conclude that electrostatic EC seeding enhanced the development of a neointima and reduced the incidence of thrombosis in polyurethane grafts implanted in a canine femoral artery model.

Evaluation of electrostatically endothelial cell seeded expanded polytetrafluoroethylene grafts in a canine femoral artery model.

(1) Purpose: The purpose of this study was to evaluate the extent (luminal coverage) of the endothelial cell (EC) lining/neointimal development and the thromboresistance of electrostatically EC seeded small diameter e-PTFE vascular grafts. (2) Methods: This evaluation consisted of harvesting autologous, canine jugular vein ECs, electrostatically EC seeding the e-PTFE grafts (4 mm GORE-TEX,® Length = 6 cm), implanting the grafts in a canine femoral artery model for six weeks, and excising the graft for histological and scanning electron microscopy evaluations. (3) Results: The results of the histological evaluation (mid-graft region only) indicated that the electrostatic EC seeding significantly affected neointimal development (p<0.01) and the degree of thrombus formation (p<0.001) within the EC seeded grafts versus the untreated control grafts. Scanning electron microscopy examination demonstrated a mature, confluent endothelium with a “cobblestone” appearance on the EC seeded graft luminal surface. The control grafts demonstrated an equal distribution of SMCs through the graft wall while the electrostatically EC seeded graft sections exhibited an uneven SMC cellular distribution which was skewed toward the graft luminal surface. (4) Conclusions: The presence of electrostatic EC seeding significantly (p<0.01) enhanced the development of a neointima and reduced the incidence of thrombosis in e-PTFE grafts implanted in a canine femoral artery model. Results of the mid-graft SMC migration measurements indicate that the electrostatic EC seeding had a significant (p<0.001) impact on the acute healing of the standard wall e-PTFE vascular graft specimens.

ROTEM significantly optimizes transfusion practices for damage control resuscitation in combat casualties

BACKGROUND Up to 40% of combat casualties with a truncal injury die of massive hemorrhage before reaching a surgeon. This hemorrhage can be prevented with damage control resuscitation (DCR) methods, which are focused on replacing shed whole blood by empirically transfusing blood components in a 1:1:1:1 ratio of platelets:fresh frozen plasma:erythrocytes:cryoprecipitate (PLT:FFP:RBC:CRYO). Measurement of hemostatic function with rotational thromboelastometry (ROTEM) may allow optimization of the type and quantity of blood products transfused. Our hypothesis was that incorporating ROTEM measurements into DCR methods at the US Role 3 hospital at Bagram Airfield, Afghanistan would change the standard transfusion ratios of 1:1:1:1 to a product mix tailored specifically for the combat causality. METHODS This retrospective study collected data from the Department of Defense Trauma Registry to compare transfusion practices and outcomes before and after ROTEM deployment to Bagram Airfield. Over the course of six months, 134 trauma patients received a transfusion (pre-ROTEM) and 85 received a transfusion and underwent ROTEM testing (post-ROTEM). Trauma teams received instruction on ROTEM use and interpretation, with no provision of a specific transfusion protocol, to supplement their clinical judgment and practice. RESULTS The pre and post groups were not significantly different in terms of mortality, massive transfusion protocol activation, mean injury severity score, or coagulation measurements. Despite the difference in size, each group received an equal total number of transfusions. However, the post-ROTEM group received a significant increase in PLT and CRYO transfusions ratios, 4× and 2×, respectively. CONCLUSION The introduction of ROTEM significantly improved adherence to DCR practices. The transfusion differences suggest that aggressive DCR without thromboelastometry data may result in reduced hemostatic support and underestimate the need for PLT and CRYO. Thus, future controlled trials should include ROTEM-guided coagulation management in trauma resuscitation. LEVEL OF EVIDENCE Therapeutic, level IV.BACKGROUND Up to 40% of combat casualties with a truncal injury die of massive hemorrhage before reaching a surgeon. This hemorrhage can be prevented with damage control resuscitation (DCR) methods, which are focused on replacing shed whole blood (WB) by empirically transfusing blood components in a 1:1:1:1 ratio of platelets:plasma:erythrocytes:cryoprecipitate (PLT:FFP:RBC:CRYO). Measurement of hemostatic function with thromboelastometry (ROTEM) may allow optimization of the type and quantity of blood products transfused. Our hypothesis was that incorporating ROTEM measurements into DCR methods at the US Role 3 hospital at Bagram Airfield, Afghanistan (BAF) would change the standard transfusion ratios of 1:1:1:1 to a product mix tailored specifically for the combat causality. METHODS This retrospective study collected data from the Department of Defense (DOD) Trauma Registry to compare transfusion practices and outcomes before and after ROTEM deployment to BAF. Over the course of six months, 134 trauma patients received a transfusion (pre-ROTEM) and 85 received a transfusion and underwent ROTEM testing (post-ROTEM). Trauma teams received instruction on ROTEM use and interpretation, with no provision of a specific transfusion protocol, to supplement their clinical judgment and practice. RESULTS The pre and post groups were not significantly different in terms of mortality, massive transfusion protocol activation, mean injury severity score, or coagulation measurements. Despite the difference in size, each group received an equal total number of transfusions. However, the post-ROTEM group received a significant increase in platelets and cryoprecipitate transfusions ratios, 4x and 2x, respectively. CONCLUSIONS The introduction of ROTEM significantly improved adherence to DCR practices. The transfusion differences suggest that aggressive DCR without thromboelastometry data may result in reduced hemostatic support and underestimate the need for platelets and cryoprecipitate. Thus, future controlled trials should include ROTEM-guided coagulation management in trauma resuscitation. LEVEL OF EVIDENCE Diagnostic Test Level 3.

Low-dose heparin anticoagulation during extracorporeal life support for acute respiratory distress syndrome in conscious sheep

Background: Over 32% of burned battlefield causalities develop trauma-induced hypoxic respiratory failure, also known as acute respiratory distress syndrome (ARDS). Recently, 9 out of 10 US combat soldiers’ survived life-threatening trauma-induced ARDS supported with extracorporeal membrane oxygenation (ECMO), a portable form of cardiopulmonary bypass. Unfortunately, the size, incidence of coagulation complications, and the need for systematic anticoagulation for traditional ECMO devices have prevented widespread use of this lifesaving technology. Therefore, a compact, mobile, ECMO system using minimal anticoagulation may be the solution to reduce ARDS in critically ill military and civilian patients. Methods: We conducted a prospective cohort laboratory investigation to evaluate the coagulation function in an ovine model of oleic acid induced ARDS supported with veno-venous ECMO. The experimental design approximated the time needed to transport from a battlefield setting to an advanced facility and compared bolus versus standard heparin anticoagulation therapy. Results: Comprehensive coagulation and hemostasis assays did not show any difference because of ECMO support over 10 h between the two groups but did show changes because of injury. Platelet count and function did decrease with support on ECMO, but there was no significant bleeding or clot formation during the entire experiment. Conclusions: A bolus heparin injection is sufficient to maintain ECMO support for up to 10 h in an ovine model of ARDS. With a reduced need for systematic anticoagulation, ECMO use for battlefield trauma could reduce significant morbidity and mortality from ventilator-induced lung injury and ARDS. Future studies will investigate the mechanisms and therapies to support patients for longer periods on ECMO without coagulation complications. Level of Evidence: V—therapeutic animal experiment.

Platelet-derived microparticles generated by neonatal extracorporeal membrane oxygenation systems

Current anticoagulation strategies do not eliminate thromboembolic stroke or limb loss during neonatal extracorporeal membrane oxygenation (ECMO), a form of cardiopulmonary bypass (CPB). In adults, CPB surgery generates prothrombotic platelet-derived microparticles (PMPs), submicron membrane vesicles released from activated platelets. However, information on PMP generation in neonatal ECMO systems is lacking. The objective of this study was to compare PMP generation in five different neonatal ECMO systems, using a simulated circuit with swine blood at 300 ml/min for 4 hours. Systems were composed of both newer components (centrifugal pump and hollow-fiber oxygenator) and traditional components (roller-head pump and silicone membrane oxygenator). Free plasma hemoglobin levels were measured as an indicator of hemolysis and flow cytometry-measured PMP. Hemolysis generated in all ECMO systems was similar to that observed in noncirculated static blood (p = 0.48). There was no difference in net PMP levels between different oxygenators with a given pump. In contrast, net PMP generation in ECMO systems with a centrifugal pump was at least 2.5 times greater than in roller-head pump systems. This was significant when using either a hollow-fiber (p < 0.005) or a silicone membrane (p < 0.05) oxygenator. Future studies are needed to define the relationship between pump-generated PMP and thrombosis.

Electron microscopy as a tool for assessment of anticoagulation strategies during extracorporeal life support: the proof is on the membrane

Extracorporeal life support (ECLS) is fast becoming more common place for use in adult patients failing mechanical ventilation. Management of coagulation and thrombosis has long been a major complication in the use of ECLS therapies. Scanning electron microscopy (SEM) of membrane oxygenators (MOs) after use in ECLS circuits can offer novel insight into any thrombotic material deposition on the MO. In this pilot study, we analyzed five explanted MOs immediately after use in a sheep model of different acute respiratory distress syndrome (ARDS). We describe our methods of MO dissection, sample preparation, image capture, and results. Of the five MOs analyzed, those that received continuous heparin infusion showed very little thrombosis formation or other clot material, whereas those that were used with only initial heparin bolus showed readily apparent thrombotic material.

Extracorporeal membrane oxygenation support in individuals with thoracic insufficiency

Introduction: Respiratory failure is the leading cause of mortality in individuals with congenital spine and rib deformities. We present a case report of a child with Jeune syndrome surviving respiratory failure using extracorporeal membrane oxygenation (ECMO). We also summarize thoracic insufficiency syndrome cases reported in the Extracorporeal Life Support Organization (ELSO) registry. Case Report: A two-year-old male with a chest circumference less than a third percentile for age was admitted with influenza pneumonia developing a peak oxygenation index of 103.5. The child survived to baseline pulmonary function after nine days of venous-arterial ECMO support. Discussion: The ELSO registry contained 27 individuals with a surrogate diagnosis of thoracic insufficiency (0.05%). There was no significant difference in survival to discharge for thoracic insufficiency patients (52%) compared to a previously healthy population supported with ECMO. Conclusion: ECMO is safe and may be effective in supporting individuals with thoracic insufficiency.