The relationships between air exposure, negative pressure, and hemolysis

Intraoperative Hemolysis Monitoring by Real-time Point-of-care in Patients Undergoing Cardiopulmonary Bypass in Cardiac Surgery: A Single-centre Prospective Observational Study

OBJECTIVE

Hemolysis is a complication in surgical procedures requiring cardiopulmonary bypass (CPB). The primary aim of this study was to evaluate the effectiveness of the point-of-care device Hemcheck Helge V-Test, quantifying hemolysis during cardiac surgery with CPB.

DESIGN

Prospective-observational study.

SETTING

Single-center study.

PARTICIPANTS

Patients undergoing elective cardiac surgery with CPB.

INTERVENTIONS

Blood samples of 78 patients were simultaneously collected during surgery at T0: pre-CPB; T1: at aorta clamping; T2: at 20 minutes after the CPB start; T3: at the end of CPB; and T4: at the end of surgery. Samples were analyzed by the Hemcheck Helge V-Test device, which offers a real-time assessment of hemolysis through the value of plasma-free hemoglobin (PfHb) expressed in mg/dL.

MEASUREMENTS AND MAIN RESULTS

No case of hemolysis (PfHb ≥50 mg/dL) was recorded at T0. The results recorded median PfHb values at T0 = 0.5 (0-7.1) mg/dL, T1 = 3.75 (0-14.4) mg/dL; T2 = 8.25 (0.4-19.1) mg/dL, T3 = 27.5 (9.9-50) mg/dL, and T4 = 18.5 (2.4-41) mg/dL; for all T times, p-values were < 0.001. A statistically significant correlation was recorded between hemolysis values >50 mg/dL at T3 and CPB time >100 minutes (p < 0.05).

CONCLUSIONS

The use of Hemcheck Helge V-Test allows effective identification of hemolysis directly in the operating room, reducing wasted time for laboratory analyses. This could help the anesthesiologist, perfusionist, or cardiac surgeon address intraoperative hemolysis and its effects on organ function earlier and improve the postoperative course of patients undergoing cardiac surgery with CPB.

Enhancing the precision of in vitro hemolysis testing for blood pumps: A review

In vitro hemolysis, assessed through the normalized hemolysis index (NIH) and the modified hemolysis index (MIH), serves as a critical indicator of the hemocompatibility of rotary blood pump designs. Despite the widespread application of the American Society for Testing and Materials (ASTM) standards in conducting in vitro hemolysis testing, the NIH and MIH values for a specific pump can vary considerably across different research centers or even between individual tests. To reduce this variability and facilitate global comparisons of hemolysis levels, this article reviews the underlying theory, existing literature, and empirical knowledge, alongside the practices implemented at the authors' facility. The reviewed factors influencing the variability of the hemolysis index encompass the selection of blood donor species, the source and method of blood withdrawal, blood handling and regulation, the choice of anticoagulants, the configuration of the circulation loop, local flow conditions within the loop, and the measurement of plasma-free hemoglobin. Detailed justifications and recommendations for each factor within a standardized testing framework are provided. The three primary factors that may yield more reliable and universally comparable results include enhancing clinical relevance, minimizing additional blood damage, and preventing blood clot formation. By regulating the associated parameters, it is possible to minimize measurement variance even in the absence of a predictive device.

Cardiopulmonary bypass associated acute kidney injury: better understanding and better prevention

Cardiopulmonary bypass (CPB) is a common technique in cardiac surgery but is associated with acute kidney injury (AKI), which carries considerable morbidity and mortality. In this review, we explore the range and definition of CPB-associated AKI and discuss the possible impact of different disease recognition methods on research outcomes. Furthermore, we introduce the specialized equipment and procedural intricacies associated with CPB surgeries. Based on recent research, we discuss the potential pathogenesis of AKI that may result from CPB, including compromised perfusion and oxygenation, inflammatory activation, oxidative stress, coagulopathy, hemolysis, and endothelial damage. Finally, we explore current interventions aimed at preventing and attenuating renal impairment related to CPB, and presenting these measures from three perspectives: (1) avoiding CPB to eliminate the fundamental impact on renal function; (2) optimizing CPB by adjusting equipment parameters, optimizing surgical procedures, or using improved materials to mitigate kidney damage; (3) employing pharmacological or interventional measures targeting pathogenic factors.

Hemolysis during open heart surgery in patients with hereditary spherocytosis - systematic review of the literature and case study

BACKGROUND

Due to the distinctive nature of cardiac surgery, patients suffering from hereditary spherocytosis (HS) are potentially at a high risk of perioperative complications resulting from hemolysis. Despite being the most prevalent cause of hereditary chronic hemolysis, the standards of surgical management are based solely on expert opinion.

OBJECTIVE

We analyze the risk of hemolysis in HS patients after cardiac surgery based on a systematic review of the literature. We also describe a case of a patient with hereditary spherocytosis who underwent aortic valve repair.

METHODS

This systematic review was registered in the PROSPERO international prospective register of systematic reviews (CRD42023417666) and included records from Embase, MEDLINE, Web of Science, and Google Scholar databases. The case study investigates a 38-year-old patient who underwent surgery for an aortic valve defect in mid-2022.

RESULTS

Of the 787 search results, 21 studies describing 23 cases of HS undergoing cardiac surgery were included in the final analysis. Hemolysis was diagnosed in five patients (one coronary artery bypass graft surgery, two aortic valve bioprosthesis, one ventricular septal defect closure, and one mitral valve plasty). None of the patients died in the perioperative period. Also, no significant clinical hemolysis was observed in our patient during the perioperative period.

CONCLUSIONS

The literature data show that hemolysis is not common in patients with HS undergoing various cardiac surgery techniques. The typical management of a patient with mild/moderate HS does not appear to increase the risk of significant clinical hemolysis. Commonly accepted beliefs about factors inducing hemolysis during cardiac surgery may not be fully justified and require further investigation.

Turbulence in surgical suction heads as detected by MRI

BACKGROUND

Blood loss is common during surgical procedures, especially in open cardiac surgery. Allogenic blood transfusion is associated with increased morbidity and mortality. Blood conservation programs in cardiac surgery recommend re-transfusion of shed blood directly or after processing, as this decreases transfusion rates of allogenic blood. But aspiration of blood from the wound area is often associated with increased hemolysis, due to flow induced forces, mainly through development of turbulence.

METHODS

We evaluated magnetic resonance imaging (MRI) as a qualitative tool for detection of turbulence. MRI is sensitive to flow; this study uses velocity-compensated T1-weighted 3D MRI for turbulence detection in four geometrically different cardiotomy suction heads under comparable flow conditions (0-1250 mL/min).

RESULTS

Our standard control suction head Model A showed pronounced signs of turbulence at all flow rates measured, while turbulence was only detectable in our modified Models 1-3 at higher flow rates (Models 1 and 3) or not at all (Model 2).

CONCLUSIONS

The comparison of flow performance of surgical suction heads with different geometries via acceleration-sensitized 3D MRI revealed significant differences in turbulence development between our standard control Model A and the modified alternatives (Models 1-3). As flow conditions during measurement have been comparable, the specific geometry of the respective suction heads must have been the main factor responsible. The underlying mechanisms and causative factors can only be speculated about, but as other investigations have shown, hemolytic activity is positively associated with degree of turbulence. The turbulence data measured in this study correlate with data from other investigations about hemolysis induced by surgical suction heads. The experimental MRI technique used showed added value for further elucidating the underlying physical phenomena causing blood damage due to non-physiological flow.

Transport-Associated Vibrational Stress Triggers Drug-Reversible Apoptosis and Cardiac Allograft Failure in Mice

Increasingly complex and long-range donor organ allocation routes coupled with implementation of unmanned aerial vehicles (UAVs) have prompted investigations of the conditions affecting organs once packaged for shipment. Our group has previously demonstrated that different modes of organ transport exert unique environmental stressors, in particular vibration. Using a mouse heart transplant model, we demonstrated that vibrational forces exert tangible, cellular effects in the form of cardiomyocyte apoptosis and cytoskeletal derangement. Functionally, these changes translated into accelerated allograft loss. Notably, administration of an apoptosis inhibitor, Z-VAD-FMK, helped to ameliorate the detrimental cellular and functional effects of mechanical vibration in a dose-dependent manner. These findings constitute one of the first reports of the negative impact of transit environment on transplant outcomes, a contributing mechanism underpinning this effect, and a potential agent to prophylax against this process. Given current limitations in measuring donor organ transit environments in situ, further study is required to better characterize the impact of transport environment and to potentially improve the care of donor organs during shipment. Clinical and Translational Impact Statement: We show that apoptosis inhibitor, Z-VAD-FMK, ameliorated transport-related vibrational stress in murine heart transplants, which presents a potential therapeutic or preservation solution additive for future use in transporting donor organs.

Single-Center Experience With a Self-Expandable Venous Cannula During Minimally Invasive Cardiac Surgery

OBJECTIVE

Venous drainage is often problematic in minimally invasive cardiac surgery (MICS). Here, we describe our experience with a self-expandable stent cannula designed to optimize venous drainage.

METHODS

The smart canula^® was used in 58 consecutive patients undergoing MICS for mitral valve disease (n = 40), left atrial myxoma (n = 3), left ventricular outflow tract obstruction (n = 1), and aortic valve replacement via a right anterior minithoracotomy (n = 14) procedures. The venous cannula was placed under transesophageal echocardiography guidance to reach the superior vena cava. Vacuum-assisted venous drainage (between -20 and -35 mm Hg) was used to reach a target flow index of 2.2 L/min/m² at a core temperature of 34 °C using a goal-directed perfusion strategy aimed at a minimum DO₂ of 272 mL/min/m². Cardiopulmonary bypass (CPB) parameters were recorded, and hemolysis-related parameters were analyzed on postoperative days 1 to 7.

RESULTS

Mean body surface area and median body mass index were 1.9 ± 0.2 m² and 25.2 (23.4, 30.2) kg/m². Mean CPB and median cross-clamping times were 107.7 ± 24.4 min and 64.5 (53, 75.8) min, and median CPB flow during cardioplegic arrest was 4 (3.6, 4.2) L/min (median cardiac index 2.1 [2, 2.2] L/min/m²). Venous drainage was considered sufficient by the surgeon in all cases, and insertion and removal were uncomplicated. Mean SvO₂ during CPB was 80.2% ± 5.5%, and median peak lactate was 10 (8, 14) mg/dL, indicating sufficient perfusion. Mean venous negative drainage pressure during cross-clamping was 27.2 ± 12.3 mm Hg. Platelets dropped by 73.6 ± 37.5 K/µL, lactate dehydrogenase rose by 81.5 (44.3, 140.8) U/L, and leukocytes rose by 3.4 (2.2, 7.2) K/µL on postoperative day 1.

CONCLUSIONS

The venous smart canula^® allows for optimal venous drainage at low negative drainage pressures, facilitating sufficient perfusion in MICS.

The Hemodynamics of Small Arterial Return Cannulae for Venoarterial Extracorporeal Membrane Oxygenation

BACKGROUND

Venoarterial extracorporeal membrane oxygenation (ECMO) provides mechanical support for critically ill patients with cardiogenic shock. Typically, the size of the arterial return cannula is chosen to maximize flow. However, smaller arterial cannulae may reduce cannula-related complications and be easier to insert. This in vitro study quantified the hemodynamic effect of different arterial return cannula sizes in a simulated acute heart failure patient.

METHODS

Baseline support levels were simulated with a 17 Fr arterial cannula in an ECMO circuit attached to a cardiovascular simulator with targeted partial (2.0 L/min ECMO flow, 60-65 mmHg mean aortic pressure - MAP) and targeted full ECMO support (3.5 L/min ECMO flow and 70-75 mmHg MAP). Return cannula size was varied (13-21 Fr), and hemodynamics were recorded while keeping ECMO pump speed constant and adjusting pump speed to restore desired support levels.

RESULTS

Minimal differences in hemodynamics were found between cannula sizes in partial support mode. A maximum pump speed change of +600 rpm was required to reach the support target and arterial cannula inlet pressure varied from 79 (21 Fr) to 224 mmHg (13 Fr). The 15 Fr arterial cannula could provide the target full ECMO support at the targeted hemodynamics; however, the 13 Fr cannula could not due to the high resistance associated with the small diameter.

CONCLUSIONS

A 15 Fr arterial return cannula provided targeted partial and full ECMO support to a simulated acute heart failure patient. Balancing reduced cannula size and ECMO support level may improve patient outcomes by reducing cannula-related adverse events.

Extracorporeal Hyperoxygenation Therapy (EHT) for Carbon Monoxide Poisoning: In-Vitro Proof of Principle

Carbon monoxide (CO) poisoning is the leading cause of poisoning-related deaths globally. The currently available therapy options are normobaric oxygen (NBO) and hyperbaric oxygen (HBO). While NBO lacks in efficacy, HBO is not available in all areas and countries. We present a novel method, extracorporeal hyperoxygenation therapy (EHT), for the treatment of CO poisoning that eliminates the CO by treating blood extracorporeally at elevated oxygen partial pressure. In this study, we proof the principle of the method in vitro using procine blood: Firstly, we investigated the difference in the CO elimination of a hollow fibre membrane oxygenator and a specifically designed batch oxygenator based on the bubble oxygenator principle at elevated pressures (1, 3 bar). Secondly, the batch oxygenator was redesigned and tested for a broader range of pressures (1, 3, 5, 7 bar) and temperatures (23, 30, 37 °C). So far, the shortest measured carboxyhemoglobin half-life in the blood was 21.32 min. In conclusion, EHT has the potential to provide an easily available and effective method for the treatment of CO poisoning.

Video-based valve motion combined with computational fluid dynamics gives stable and accurate simulations of blood flow in the Realheart total artificial heart

BACKGROUND

Patients with end-stage, biventricular heart failure, and for whom heart transplantation is not an option, may be given a Total Artificial Heart (TAH). The Realheart® is a novel TAH which pumps blood by mimicking the native heart with translation of an atrioventricular plane. The aim of this work was to create a strategy for using Computational Fluid Dynamics (CFD) to simulate haemodynamics in the Realheart®, including motion of the atrioventricular plane and valves.

METHODS

The accuracies of four different computational methods for simulating fluid-structure interaction of the prosthetic valves were assessed by comparison of chamber pressures and flow rates with experimental measurements. The four strategies were: prescribed motion of valves opening and closing at the atrioventricular plane extrema; simulation of fluid-structure interaction of both valves; prescribed motion of the mitral valve with simulation of fluid-structure interaction of the aortic valve; motion of both valves prescribed from video analysis of experiments.

RESULTS

The most accurate strategy (error in ventricular pressure of 6%, error in flow rate of 5%) used video-prescribed motion. With the Realheart operating at 80 bpm, the power consumption was 1.03 W, maximum shear stress was 15 Pa, and washout of the ventricle chamber after 4 cycles was 87%.

CONCLUSIONS

This study, the first CFD analysis of this novel TAH, demonstrates that good agreement between computational and experimental data can be achieved. This method will therefore enable future optimisation of the geometry and motion of the Realheart®.

Investigating the cause of hemolysis in patients supported by a pulsatile ventricular assist device

A survey conducted by Abiomed, Inc. revealed that 10 of 60 patients who received ventricular assistance via the AB5000 ventricular assist device (VAD) experienced hemolysis. The present study was conducted to investigate which factors influence hemolysis under pulsatile-flow VADs such as the AB5000. We compared the specificity of the AB5000 and its driving console with those of the NIPRO-VAD and VCT50χ under severe heart failure conditions using a mock circulatory system with a glycerol water solution. We used the mock circuit with bovine blood to confirm which pump conditions were most likely to cause hemolysis. In addition, we measured the shear velocity using particle image velocimetry by analyzing the seeding particle motion for both the AB5000 and NIPRO-VAD under the same conditions as those indicated in the initial experiment. Finally, we analyzed the correlation between negative pressure, exposure time, and hemolysis by continuously exposing fixed vacuum pressures for fixed times in a sealed device injected with bovine blood. Applying higher vacuum pressure to the AB5000 pump yielded a larger minimum inlet pressure and a longer exposure time when the negative pressure was under - 10 mmHg. The plasma-free hemoglobin increased as more negative pressure was driven into the AB5000 pump. Moreover, the negative pressure interacted with the exposure time, inducing hemolysis. This study revealed that negative pressure and exposure time were both associated with hemolysis.

Comparison of effectiveness of the piston-pump method versus the pressure-infusor method for rapid infusion of crystalloids: A bench study

Background and Aims

The piston-pump method is a simple method for rapid administration of fluids but some problems are unsolved. We compared the effectiveness of using the piston-pump method with that of the pressure-infusor method.

Methods

Twelve anaesthetists were classified randomly into the piston-pump and pressure-infusor groups. They were asked to infuse 500 ml of saline three times successively through a 16-G intravenous cannula as rapidly as possible using a pump with a 50-ml syringe or a pressure-infusor at 300 mmHg. The time taken for infusion and the maximum or minimum pressure in the infusion circuit and substitute vessel were measured. Bacterial culture of the saline infused sterilely was performed to estimate bacterial contamination.

Results

The pressure-infusor group led to faster infusion of 500 ml of saline (233 ± 19 s) than the piston-pump group (301 ± 48 s) (P < 0.01). The infusion time at the third attempt (316 ± 43 s) was significantly longer than that at the first attempt (285 ± 53 s) only in the piston-pump group (P < 0.05). The maximum pressure (mmHg) in the circuit was 131 ± 9 and > 200 (P < 0.01) and in the substitute vessel was 5 ± 1 and 17 ± 7 (P < 0.01) in the pressure-infusor and piston-pump groups, respectively. A pressure of <-200 mmHg occurred at all infusion attempts in the piston-pump group. Bacterial contamination was not observed in either group.

Conclusion

If fluids must be administered rapidly, the pressure-infusor method is more efficient than the piston-pump method because the latter is less effective in infusing fluids rapidly and associated with excessive positive and negative pressure in the infusion circuit.

Nitric Oxide Attenuates the Inflammatory Effects of Air During Extracorporeal Circulation

Cardiopulmonary bypass causes a systemic inflammatory response reaction that may contribute to postoperative complications. One cause relates to the air/blood interface from the extracorporeal circuit. The modulatory effects of blending nitric oxide (NO) gas into the ventilation/sweep gas of the membrane lung was studied in a porcine model of air-induced inflammation in which NO gas was added and compared with controls with or without an air/blood interface. Healthy swine were supported on partial bypass under four different test conditions. Group 1: no air exposure, group 2: air alone, group 3: air plus 50 ppm NO, and group 4: air plus 500 ppm NO. The NO gas was blended into the ventilation/sweep site of the membrane lung. The platelets and leucocytes were activated by air alone. Addition of NO to the sweep gas attenuated the inflammatory response created by the air/blood interface in this model.

Hemolysis and Plasma Free Hemoglobin During Extracorporeal Membrane Oxygenation Support: From Clinical Implications to Laboratory Details

Venovenous and venoarterial extracorporeal membrane oxygenation (ECMO) are lifesaving supports that are more and more frequently used in critically ill patients. Despite of major technological improvements observed during the last 20 years, ECMO-associated hemolysis is still a complication that may arise during such therapy. Hemolysis severity, directly appreciated by plasma free hemoglobin concentration, may be present with various intensity, from a nonalarming and tolerable hemolysis to a highly toxic one. Here, we propose a review dedicated to extracorporeal membrane oxygenation (ECMO)-associated hemolysis, with a particular emphasis on pathophysiology, prevalence, and clinical consequences of such complication. We also focus on laboratory assessment of hemolysis and on the limits that have to be known by clinicians to prevent and manage hemolytic events.

The effect of vacuum-assisted venous drainage on hemolysis during cardiopulmonary bypass

BACKGROUND

In cardiac surgery, systemic venous drainage is provided by gravity. During the procedure, the amount of venous drainage can be increased by using a vacuum-assisted venous drainage (VAVD) technique. The purpose of this study is to compare the effects of VAVD and gravitational drainage (GD) techniques on hemolysis.

METHODS

Totally, 60 patients were included in the study. The patients were separated into three groups, and each group designed with 20 patients: Groups are defined as Group 1 (-40 mmHg VAVD), Group 2 (-60 mmHg VAVD), and Group 3 (GD). Preoperative and postoperative values of lactate dehydrogenase (LDH), haptoglobin (Hpt), mean platelet volume (MVP), and platelet count (Plt) were evaluated.

RESULTS

The duration of cardiopulmonary bypass, cross-clamp, and vacuum assistance times were similar in all groups (P > 0.05), whereas Group GD required more additional volume to maintain adequate perfusion (P = 0.034). Preoperative and postoperative measurements showed no significant difference in terms of LDH, MVP, Plt, and Hpt among the groups (P > 0.05).

CONCLUSION

There was no significant increase in hemolysis among the groups, which demonstrates that the VAVD technique, even if lower negative pressure is preferred, can be applied safely and effectively to improve venous drainage and consequently, cardiac decompression, even if smaller venous cannulas are used, and also avoid from superfluous fluid addition to sustain adequate extracorporeal perfusion.

Infrared Nanospectroscopy of Air-Sensitive Biological Substrates Protected by Thin Hydrogel Films

The air sensitivity of many substrates, and specifically biosurfaces, presents an experimental challenge for their analysis by vibrational spectroscopy and, in particular, infrared microscopy on a nanometer scale. The recent development of atomic-force-microscopy-based infrared spectroscopy (AFM-IR), which circumvents the Abbe diffraction limit, allows nanoscale chemical characterization of surfaces. Additionally, this technique has been shown to work for thin films under aqueous environments but is limited to substrates up to 10 nm thick, thus ruling out application to many biological surfaces. To circumvent this restriction, we have utilized hydrogels to cover such surfaces and maintain a more physiologically representative environment for biological substrates. We show that it is feasible to use AFM-IR to chemically characterize this type of substrate buried under a thin hydrogel film. Specifically, this work describes the AFM-IR spectra of red blood cells under polyvinyl alcohol hydrogels.

Inflammatory Effects of Blood-Air Interface in a Porcine Cardiopulmonary Bypass Model

Cardiopulmonary bypass (CPB) causes a systemic inflammatory response syndrome (SIRS) associated with multiorgan injury. A model was developed to test whether a blood-air interface (BAI) in the CPB circuit causes blood element activation and inflammation. Ten healthy swine were placed on partial CPB for 2 hours via the cervical vessels and monitored for 96 hours postoperatively. Five pigs (control group) had minimal air exposure in the circuit, while five were exposed to a BAI simulating cardiotomy suction. There were no significant differences in bypass flow or hemodynamics between the groups. In the BAI group, there was an increase in hemolysis after bypass (plasma-free hemoglobin 5.27 ± 1.2 vs. 0.94 ± 0.8 mg/dl; p = 0.01), more aggressive platelet consumption (28% vs. 83% of baseline; p = 0.009), leukocyte consumption (71% vs. 107% of baseline; p = 0.02), and increased granulocyte CD11b expression (409% vs. 106% of baseline; p = 0.009). These data suggest the inflammatory pattern responsible for the CPB-SIRS phenomenon may be driven by blood-air interaction. Future efforts should focus on BAI-associated mechanisms for minimizing blood trauma and inflammation during CPB.

In vivo comparison of the optiflow and EZ glide aortic dispersion cannulas

OBJECTIVES

Morbidity associated with coronary artery bypass grafts and embolization during aortic cannulation is strongly related to patient characteristics/comorbidities, arterial cannulation site used and the shape of arterial cannulae tips. The desired features of an arterial cannula should be to mitigate the morbid effects of these cannulas and to focus on achieving higher blood flows with lower cannula pressures (CPs).

MATERIALS AND METHODS

To evaluate the in vivo performance of two aortic dispersion flow cannulas: the Optiflow (Sorin Group, Italy) and EZ Glide (Edwards Lifesciences). They were evaluated for CPs, pump-flow rates (FRs), and plasma-free hemoglobin (Hb) over a 12-month period. Data were collected in a prospective, randomized (1:1), nonblinded, monocentric study with a cohort of 30 patients (optiflow group N = 15; EZ Glide group N = 15).

RESULTS

The optiflow cannula was found to have decreasing CPs as the pump FRs were increased (112.3 ± 10.9 vs 131.1 ± 11.4 mm Hg; P < .001). Results indicated no significant differences between groups for increases in plasma free Hb (P = .41) and total microembolic signals counts during the period of cardiac surgery (P = .63).

CONCLUSIONS

Both optiflow and EZ Glide dispersion flow arterial cannulas performed well, but the optiflow cannula demonstrated an ability to increase pump FRs with lower arterial line and CPs than the EZ Glide cannula. This implies an ability to improve peripheral perfusion while reducing cannula shear stress and the risk of endothelial damage, thereby having the potential to reduce the risk of atherosclerotic plaque dislodgement.

In Vitro Thrombogenicity Testing of Biomaterials

The short- and long-term thrombogenicity of implant materials is still unpredictable, which is a significant challenge for the treatment of cardiovascular diseases. A knowledge-based approach for implementing biofunctions in materials requires a detailed understanding of the medical device in the biological system. In particular, the interplay between material and blood components/cells as well as standardized and commonly acknowledged in vitro test methods allowing a reproducible categorization of the material thrombogenicity requires further attention. Here, the status of in vitro thrombogenicity testing methods for biomaterials is reviewed, particularly taking in view the preparation of test materials and references, the selection and characterization of donors and blood samples, the prerequisites for reproducible approaches and applied test systems. Recent joint approaches in finding common standards for a reproducible testing are summarized and perspectives for a more disease oriented in vitro thrombogenicity testing are discussed.

Can venous cannula design influence venous return and negative pressure with a minimally invasive extracorporeal circulation?

INTRODUCTION

Recent advances to make cardiopulmonary bypass more physiological include the use of kinetic-assisted venous drainage but without a venous reservoir. Despite manipulation of intravascular volume and patient positioning, arterial flow is frequently reduced. Negative venous line pressures can be generated, which may elicit gaseous microemboli. We investigated the influence of venous cannula design on venous return and negative venous line pressures.

METHODS

In a single-centre, single-surgeon, prospective, randomized, double-blind trial, 48 patients undergoing isolated coronary artery, aortic valve or combined coronary artery and aortic valve surgery, with a minimally invasive circuit, were randomized to a conventional two-stage (2S) or three-stage venous cannula (3S), or to a three-stage venous cannula with additional 'fenestrated' ridges (F3S). Blood flow, venous line pressures and gaseous microemboli number and size were measured.

RESULTS

The pump flow achieved was the same between groups, but in each case fell below the target range of 2.2-2.4 L min^-1 m^-2. The three-stage cannula recorded significantly lower negative pressure than the other cannulae. The total count and volume of gaseous emboli detected with the F3S cannulae was very high in some cases, with wide heterogeneity.

DISCUSSION

The low negative pressures recorded with three-stage cannula, despite having a larger drainage orifice area, suggest that negative pressure may be more influenced by lumen diameter and vena cava collapse rather than drainage hole size. The additional fenestrations resulted in flow characteristics and negative pressures similar to the larger two-stage cannula but are associated with generation of gaseous microemboli.

Hemolytic characteristics of three suctioning systems for use with a newly developed cardiopulmonary bypass system

INTRODUCTION

We have been developing a closed-circuit cardiopulmonary bypass (CPB) system ("Dihead CPB") for application during coronary artery bypass grafting (CABG) and valve surgery. To strive for minimal hemolysis during Dihead CPB, we compared the hemolysis caused by three different suction systems and performed a clinical study with the newly applied suction system.

MATERIALS & METHODS

We evaluated the hemolysis caused by roller-pump suction, the SmartSuction^® Harmony^® and wall suction systems with respect to suction speed and compared the systems by means of in vitro studies. A clinical study was also performed on 15 volunteers to assess hemolysis and the adequacy of the newly applied suction system with Dihead CPB.

RESULTS

Pressure inside the suction cannula was -22.5 ± 0.1 mmHg at a maximum flow of 1.5 L/min for roller-pump suction and -43.4 ± 0.1 mmHg at -150 mmHg of the set vacuum pressure of wall suction. With the SmartSuction, the pressure inside the cannula varied from -76.3 ± 1.0 to -130.3 ± 1.5 mmHg, depending on suctioning conditions. Suction speed (to suction 50 ml of blood) was fastest with the SmartSuction (69.7 ± 3.58 s) whereas, with roller suction, it was 117.3 ± 8.47 s and with wall suction 96.9 ± 7.10 s. The SmartSuction had the highest hemolysis rate (2.00 ± 0.33%) vs. 0.61 ± 0.10% for roller suction and 0.41 ± 0.11% for wall suction (p<0.001). The clinical study with wall suction showed no significant increase in plasma free hemoglobin during or after CPB compared with before surgery.

CONCLUSIONS

Wall suction had less hemolysis than roller suction or the SmartSuction in the in vitro study and the clinical study with wall suction showed efficient suction speed and acceptable hemolysis, suggesting that Dihead CPB with wall suction is feasible for CABG.

Improving hemolysis levels associated with cardiotomy suction

BACKGROUND

The major source of hemolysis during cardiopulmonary bypass (CPB) remains the cardiotomy suction.¹ Previous research has shown that the combination of negative pressures and the massive air-blood interface exponentially increases hemolysis in suctioned blood.

OBJECTIVE

This research aims to decrease hemolysis by eliminating the air-to-blood interface by implementing the Venturi effect to create powerful suction. This research effort hypothesizes that the Venturi suction will result in less hemolysis, indicated by lower plasma free hemoglobin levels (PFH) compared to current vacuum suction.

METHOD

The research hypothesizes that a paradigm approach to cardiotomy suction that utilizes the Venturi effect with shorter tubing lengths and weighted sucker tips will further reduce hemolysis.

RESULTS

The vacuum-suctioned blood showed PFH levels significantly increased from baseline levels (p=0.0039). Neither the Venturi nor paradigm groups showed PFH levels significantly increased from baseline levels (p=0.0625 and p=0.125, respectively). There was a significant difference in PFH levels among the three conditions (p<0.0001). The vacuum condition showed significantly higher levels of PFH compared to both the Venturi and the paradigm conditions (p<0.001 for both). There was no significant difference in the PFH levels between the Venturi and the paradigm groups (p=1.00).

CONCLUSION

This study concludes that vacuum suction causes excessive hemolysis. A Venturi-powered suction system does not cause hemolysis and can be employed to reduce the damaging effects of vacuum suction on blood.

The effect of air exposure on leucocyte and cytokine activation in an in-vitro model of cardiotomy suction

Introduction:

Cardiopulmonary bypass (CPB) is known to cause a systemic inflammatory and immune response.

Objective:

An in-vitro model of cardiotomy suction was designed to quantify the effects of incrementally increased air-blood exposure on leucocyte marker CD11b and cytokine activation in two common anticoagulants, heparin and citrate.

Methods:

Fresh human blood was exposed to increasing amounts of air flow for ten minutes. Leucocyte and cytokine levels were measured prior to and after ten minutes of air flow. Cytokine levels were also measured after air exposure when incubated for 24 hours at 37oC.

Results:

Leucocyte activation, measured by CD11b, was elevated between baseline and air flow rates up to 50 mL/min. After 10 minutes of air exposure, no measured cytokine levels were elevated. After 24 hours of incubation, cytokine levels of TNFα, IL-10, IL-6, and IL-8 were elevated. However, only IL-8 was significantly elevated in citrated blood, but not in heparinized blood, when compared to baseline samples that were also incubated for 24 hours.

Conclusion:

This study investigates CD11b levels in response to an air stimulus in blood that was anticoagulated with citrate or heparin. Exposure to an air stimulus activates leucocytes. Activation of CD11b was less when using heparin as an anticoagulant compared to citrate. Cytokine activation occurs with air stimulation, but levels do not immediately rise, indicating that time is required to generate free cytokines.

Hemolysis and Inflammatory Response to Extracorporeal Circulation during On-Pump CABG: Comparison between Roller and Centrifugal Pump Systems

Objective

To compare the perioperative incidence rates of hemolysis and inflammatory response in patients undergoing coronary artery bypass grafting with the two main types of cardiopulmonary bypass, centrifugal and roller pumps, and establish correlations among hemolytic and inflammatory changes.

Methods

This was a prospective, randomized trial of 60 patients assigned to either roller pump (G1, n=30) or centrifugal pump (G2, n=30) bypass. Markers of hemolysis (serum haptoglobin, lactate dehydrogenase [LDH]) and inflammation (interleukin [IL]1ß, IL-6, and TNF-α) were measured and analyzed.

Results

There was no significant between-group difference in the variables of interest. In G1, there was a positive association with IL-6 and TNF-α (P<0.01 and P<0.05, respectively). In G2, there was a positive association with LDH in the postoperative period (P<0.5). At 24h post-cardiopulmonary bypass, there were positive associations between LDH and IL-1ß (P<0.05), LDH and TNF-α (P<0.01), haptoglobin and TNF-α (P<0.05), and LDH and TNF-α (P<0.01) in G1, and between LDH and IL-6 (P<0.01), LDH and TNF-α (P<0.01), and LDH and IL-6 (P<0.01) in G2.

Conclusion

There were no significant between-group differences in markers of hemolysis or inflammation. IL-6 and TNF-α were positively associated with duration of cardiopulmonary bypass in G1, while LDH was positively associated with duration of cardiopulmonary bypass in G2. The rate of significant associations between markers of hemolysis and inflammation was higher in the roller pump group (G1).

Registration number

ReBEC (RBR-92b9dg).

Development of a prolonged warm ex vivo perfusion model for kidneys donated after cardiac death

PURPOSE

Ex vivo perfusion of marginal kidney grafts offers the chance to expand the donor pool, but there is no current clinical standard for the prolonged warm perfusion of renal grafts. This exploratory pilot study seeks to identify a stable ex vivo kidney perfusion model that can support low intravascular resistance and preserve histologic architecture in a porcine donation after cardiac death (DCD) model.

METHODS

15 kidneys were preserved in 1 of 3 settings: normothermic whole blood (NT-WB), normothermic Steen Solution™ (XVIVO Perfusion) with whole blood (NT-Steen/WB), or subnormothermic Steen Solution™ at 21°C (SNT-Steen). Kidneys were primarily assessed using hemodynamic parameters and histologic analysis.

RESULTS

NT-WB perfusion resulted in high vascular resistance and glomerular necrosis. NT-Steen/WB and SNT-Steen resistance ranged between 0.18-0.45 mmHg/mL per minute and 0.25-0.53 mmHg/mL per minute, respectively, enabling stable perfusion for up to 24 hours. NT-Steen/WB demonstrated tubular and glomerular necrosis, while the histologic architecture of SNT-Steen was preserved with the exception of numerous proteinaceous casts.

CONCLUSIONS

Our results suggest that ex vivo kidney perfusion with Steen Solution™ at 21°C supports low and stable vascular resistance and provides adequate histologic preservation during 24-hour perfusion.

Effect of air exposure and suction on blood cell activation and hemolysis in an in vitro cardiotomy suction model

Cardiopulmonary bypass (CPB) elicits a systemic inflammatory response. The cause may include surface-induced leukocyte activation and hemolysis. A study was designed to describe the effects of both suction and an air-blood interface independently and in combination on leukocyte and platelet activation, and hemolysis in an in vitro model. Fresh human blood was drawn and tested in four different conditions including control (A), 10 minutes of -600 mm Hg suction (B), 10 minutes of blood exposure to room air at 100 ml/min (C), and 10 minutes of simultaneous suction and air flow (D). Samples were analyzed by flow cytometry (platelets and leukocytes) and plasma-free hemoglobin (PFHb). Leukocyte CD11b expression and platelet P-selectin (CD62P) were analyzed by flow cytometry. In comparison with baseline, granulocytes were significantly activated by air (group C, p = 0.0029) and combination (group D, p = 0.0123) but not by suction alone (group B). Monocytes and platelets were not significantly activated in any group. The PFHb increased significantly in group C (p < 0.001) and group D (p < 0.001). This study suggests that the inflammatory response and associated hemolysis during CPB may be related to air exposure, which could be reduced by minimizing the air exposure of air to blood during cardiotomy suction.

Effect of flow rate and temperature on transmembrane blood pressure drop in an extracorporeal artificial lung

Introduction:

Transmembrane pressure drop reflects the resistance of an artificial lung system to blood transit. Decreased resistance (low transmembrane pressure drop) enhances blood flow through the oxygenator, thereby, enhancing gas exchange efficiency. This study is part of a previous one where we observed the behaviour and the modulation of blood pressure drop during the passage of blood through artificial lung membranes.

Methods:

Before and after the induction of multi-organ dysfunction, the animals were instrumented and analysed for venous-venous extracorporeal membrane oxygenation, using a pre-defined sequence of blood flows.

Results:

Blood flow and revolutions per minute (RPM) of the centrifugal pump varied in a linear fashion. At a blood flow of 5.5 L/min, pre- and post-pump blood pressures reached -120 and 450 mmHg, respectively. Transmembrane pressures showed a significant spread, particularly at blood flows above 2 L/min; over the entire range of blood flow rates, there was a positive association of pressure drop with blood flow (0.005 mmHg/mL/minute of blood flow ) and a negative association of pressure drop with temperature (-4.828 mmHg/oCelsius). These associations were similar when blood flows of below and above 2000 mL/minute were examined.

Conclusions:

During its passage through the extracorporeal system, blood is exposed to pressure variations from -120 to 450 mmHg. At high blood flows (above 2 L/min), the drop in transmembrane pressure becomes unpredictable and highly variable. Over the entire range of blood flows investigated (0 – 5500 mL/min), the drop in transmembrane pressure was positively associated with blood flow and negatively associated with body temperature.

Renal replacement therapy in critically ill patients receiving extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is a lifesaving procedure used in neonates, children, and adults with severe, reversible, cardiopulmonary failure. On the basis of single-center studies, the incidence of AKI occurs in 70%-85% of ECMO patients. Those with AKI and those who require renal replacement therapy (RRT) are at high risk for mortality, independent of potentially confounding variables. Fluid overload is common in ECMO patients, and is one of the main indications for RRT. RRT to maintain fluid balance and metabolic control is common in some but not all centers. RRT on ECMO can be performed via an in-line hemofilter or by incorporating a standard continuous renal replacement machine into the ECMO circuit. Both of these methods require specific technical considerations to provide safe and effective RRT. This review summarizes available epidemiologic data and how they apply to our understanding of AKI pathophysiology during ECMO, identifies indications for RRT while on ECMO, reviews technical elements for RRT application in the setting of ECMO, and finally identifies specific research-focused questions that need to be addressed to improve outcomes in this at-risk population.