Investigation and quantification of the blood trauma caused by the combined dynamic forces experienced during cardiopulmonary bypass

Identification of Early Risk Factors for Mortality in Pediatric Veno-Arterial Extra Corporeal Membrane Oxygenation: The Patient Matters

Objective

Pediatric Veno-Arterial Extra Corporeal Membrane Oxygenation (VA ECMO) is a life saving technology associated with high mortality. A successful VA ECMO course requires attention to multiple aspects of patient care, including ECMO and patient parameters. Early, potentially modifiable, risk factors associated with patient mortality should be analyzed and adjusted for when assessing VA ECMO risk profiles.

Method

Retrospective single center experience of pediatric patients requiring VA ECMO from January 2021 to October 2023. Laboratory and ECMO flow parameters were extracted from the patients record and analyzed. Risk factors were analyzed using a Cox proportion hazard regression.

Main Results

There were 45 patients studied. Overall survival was 51%. Upon uncorrected analysis there were no significant differences between the patients who survived and those who died. Utilizing a Cox proportion hazard regression, platelet count, fibrinogen level and creatine level were significant risk factors within the first twenty-four hours of a patient's ECMO course.

Significance

Although we did not find a significant difference among ECMO flow parameters in this study, this work highlights that granular ECMO flow data can be incorporated to risk analysis profiles and potential modeling in pediatric VA ECMO. This study demonstrated, that when controlling for ECMO flow parameters, kidney dysfunction and clotting regulation remain key risk factors for pediatric VA ECMO mortality.

Mastering the Best Practices: A Comprehensive Look at the European Guidelines for Cardiopulmonary Bypass in Adult Cardiac Surgery

The successful outcome of a cardiac surgery procedure is significantly dependent on the management of cardiopulmonary bypass (CPB). Even if a cardiac operation is technically well-conducted, a patient may suffer CPB-related complications that could result in severe comorbidities, reduced quality of life, or even death. However, the role of clinical perfusionists in perioperative patient care, which is critical, is often overlooked. Therefore, the European Association for Cardio-Thoracic Surgery (EACTS), the European Association of Cardiothoracic Anaesthesiology (EACTA), and the European Board of Cardiovascular Perfusion (EBCP) have agreed to develop joint clinical practice guidelines (CPGs) for CPB due to its significant impact on patient care and significant variations in practice patterns between countries. The European guidelines, based on the EACTS standardized framework for the development of CPGs, cover the entire spectrum of CPB management in adult cardiac surgery. This includes training and education of clinical perfusionists, machine hardware, disposables, preparation for initiation of CPB, a complete set of procedures during CPB to help maintain end-organ function and anticoagulation, weaning from CPB, and the gaps in evidence and future research directions. This comprehensive coverage ensures that all aspects of CPB management are addressed, providing clinicians with a standardized approach to CPB management based on the latest evidence and best practices. To ensure better integration of these evidence-based recommendations into daily practice, this review aims to provide a general understanding of guideline development and an overview of essential treatment recommendations for CPB management.

Continuous renal replacement therapy in patients receiving extracorporeal membrane oxygenation therapy

Methods of continuous renal replacement therapy (CRRT) in extracorporeal membrane oxygenation (ECMO) patients include dedicated central venous cannula (CVC) (vCRRT), in-series with filter connected to ECMO circuit (eCRRT) or in-line with haemodiafilter incorporated within ECMO circuit. We assessed the efficacy and safety of eCRRT versus vCRRT in 20 ECMO-CRRT patients. Average filter lifespan was 42 vs 28 hours and filter runs completing 72hours were 40% vs 13.8% (eCRRT vs vCRRT, respectively). One incidence of ECMO circuit air embolus occurred (vCRRT). eCRRT achieved adequate filtration and increased filter lifespan, and has become our default for ECMO-CRRT if a pre-existing dialysis CVC is not present.

In Vivo Suction Pressures of Venous Cannulas During Veno-venous Extracorporeal Membrane Oxygenation

Extracorporeal lung support includes the risk of hemolysis due to suction pressures. Manufacturers measure the negative suction pressure across drainage cannulas for their products in vitro using water. Clinical experience suggests that hemolysis occurs in vivo already at much lower flow rates. The aim of this study was to analyze the in vivo suction pressure for veno-venous extracorporeal membrane oxygenation (VV-ECMO) cannulas. Prospective, observational study at a tertiary-care intensive care unit: 15 patients on VV-ECMO for severe ARDS were prospectively included. In vitro , the 25 Fr drainage cannula pressure drops below a critical level of around -100 mm Hg at a flow rate of 7.9 L/min, the 23 Fr drainage cannula at 6.6 L/min. In the clinical setting, critical suction pressures were reached at much lower flow rates (5.5 and 4.7 L/min; p < 0.0001, nonlinear regression). The in vitro data largely overestimate the safely achievable flow rates in daily clinical practice by 2.4 L/min (or 44%, 25 Fr) and 1.9 L/min (or 41%, 23 Fr). In vivo measurement of suction pressure of venous drainage cannulas differed significantly from in vitro derived measurements as the latter largely underestimate the resulting suction pressure.

Safety and Effectiveness of Veno-Venous Extracorporeal Membrane Oxygenation Combined with Continuous Renal Replacement Therapy

Patients receiving extracorporeal membrane oxygenation (ECMO) often suffer from acute kidney injury (AKI), requiring continuous renal replacement therapy (CRRT). In our clinical practice, we connected the inlet line of a CRRT machine to the postoxygenator Luer port and the outlet line to the inlet Luer port of the oxygenator. In this case series, we analyzed the interaction between the two machines. Between December 31, 2017, and December 31, 2019, we enrolled 15 patients from the ICU of the San Matteo Hospital, Pavia, Italy. All of them suffered from severe acute respiratory distress syndrome and AKI stage 3. We analyzed 570 hours of CRRT combined with venovenous ECMO and collected 261,751 CRRT data. No discontinuation of CRRT occurred before 48 hours. Most of the alarms occurred within 24 hours of the connection: 22/10,831 (0.2%) showed an outranged inlet pressure, 11/10831 (0.11%) showed an outranged transmembrane pressure, 14/10,831 (0.13%) showed an outranged inlet pressure, and 138/10,831 (1.27%) an outranged effluent pressure. The rate per minute set for the ECMO circuit was correlated with the inlet (β = 5.38; CI, 95% 1.42-9.35; p = 0.008), transmembrane (β = 4.6; CI, 95% 1.97-7.24; p = 0.001), effluent (β = 3.02; CI, 95% 1.15-4.90; p = 0.002), and outlet pressures (β = 597; CI, 95% 2.31-9.63; p = 0.001) of the CRRT circuit. We reported that our configuration could be safe and effective, however well-designed studies would be beneficial for determining the potential risks and benefits.

The Disconnect Between Extracorporeal Circulation and the Microcirculation: A Review

Extracorporeal circulation (ECC) procedures, such as cardiopulmonary bypass (CPB) and extracorporeal membrane oxygenation (ECMO), take over the function of one or more organs, providing clinicians time to treat underlying pathophysiological conditions. ECMO and CPB carry significant mortality rates for patients, despite prior decades of research focused on the resulting failure of critical organs. Since the focus of these procedures is to support blood flow and provide oxygen-rich blood to tissues, a shift in research toward the effects of ECMO and CPB on the microcirculation is warranted. Along with provoking systemic responses, both procedures disrupt the integrity of red blood cells, causing release of hemoglobin (Hb) from excessive foreign surface contact and mechanical stresses. The effects of hemolysis are especially pronounced in the microcirculation, where plasma Hb leads to nitric oxide scavenging, oxidization, formation of reactive oxygen species, and inflammatory responses. A limited number of studies have investigated the implications of ECMO in the microcirculation, but more work is needed to minimize ECMO-induced reduction of microcirculatory perfusion and consequently oxygenation. The following review presents existing information on the implications of ECMO and CPB on microvascular function and proposes future studies to understand and leverage key mechanisms to improve patient outcomes.

Risk factors for hemolysis with centrifugal pumps in pediatric extracorporeal membrane oxygenation: Is pump replacement an answer?

INTRODUCTION

Hemolysis during pediatric extracorporeal membrane oxygenation (ECMO) is associated with increased risk for renal failure and mortality.

OBJECTIVES

We aim to describe risk factors for hemolysis in pediatric ECMO supported by centrifugal pumps.

METHODS

We conducted an analysis of retrospective data collected at an academic children's hospital from January 2017 to December 2019.

MEASUREMENTS AND RESULTS

Plasma-free hemoglobin (PFH) levels were measured daily, and hemolysis was defined as PFH>50 mg/dL. Of 46 ECMO runs over 528 ECMO days, hemolysis occurred in 23 (58%) patients over a total of 40 (8%) ECMO days. In multivariable logistic regression models, VA-ECMO (aOR=4.69, 95% CI: 1.01-21.83) and higher hemoglobin (aOR = 1.38, 95% CI: 1.06-1.81) were independently associated with hemolysis. There were also non-significant trends toward increased risk for hemolysis with higher rotational pump speed (aOR=2.39, 95% CI: 0.75-7.65), higher packed red blood cell transfusions (aOR=1.15, 95% CI: 0.99-1.34), and higher cryoprecipitate transfusions (aOR=2.01, 95% CI: 0.83-4.86). Isolated pump exchanges that were performed in 12 patients with hemolysis led to significant decreases in PFH levels within 24 h (89 vs 11 mg/dL, p<0.01).

CONCLUSIONS

Hemolysis is common in pediatric ECMO using centrifugal pumps. Avoidance of high pump speeds and conservative administration of blood products may help to mitigate the risk for hemolysis. Furthermore, pump exchange may be an effective first-line treatment for hemolysis.

Effects of tubing degradation and pump position on extracorporeal circulation performance

Extracorporeal circulation (ECC) is an integral part of cardiac surgery. Yet, the contact with artificial surfaces, mechanical stress, shear, and suction forces within the ECC pose a pronounced risk for damaging the corpuscular components of the blood. These suction forces may be reduced by a repositioning of the roller pumps employed below the reservoir. Furthermore, the repeated compression of the involved silicone tubing is likely to cause degradation. We present our observations regarding changes in the ECC performance following this degradation process. In vitro experiments were performed in a standard as well as a simplified ECC setup and included measurements of pressure, effective flow, and tubing restoring force over a time frame of 12 hours with two different pump positions utilizing transit time flow measurement. Suction forces within the tubing could be significantly reduced by shifting the pump position below the reservoir. Regardless of the setup, the tubing showed significant loss of restoring force as well as effective flow over time. A shift of the pump position within the ECC setup can be recommended to prevent blood damaging negative pressures. Further research is necessary to evaluate the exact cause of the reduction of restoring force overtime as well as its risks for the patients. Finally, our results underline the importance of transit time flow measurements to collect reliable flow data.

Intravascular Hemolysis and Complications During Extracorporeal Membrane Oxygenation

Venovenous and venoarterial extracorporeal membrane oxygenation (ECMO) remains a crucial lifesaving therapy for critically ill neonates with severe cardiorespiratory failure. Both the roller pump as well as the centrifugal pump are safe and efficient systems, and some red blood cell breakdown and hemolysis occurs in all ECMO systems. The roller pump functions by gravity whereas the centrifugal pump promotes the flow of blood by a magnetically driven spinning rotor to generate negative pressure. Extracorporeal Life Support Organization data indicate a significant increase in intravascular hemolysis in neonatal and pediatric patients receiving ECMO when the centrifugal pump is used compared with its use in adults. Risk factors for developing hemolysis during ECMO are small cannula size, high negative inlet pressure in the pump head, and thrombosis in the pump head and oxygenator. Excessive red blood cell breakdown and release of plasma free hemoglobin (pfHb) saturate physiologic neutralizing mechanisms such as haptoglobin and hemopexin. The increase in pro-oxidant and proinflammatory pfHb levels causes endothelial dysfunction in a dose-dependent manner. Hemolysis also increases the risk of in-hospital morbidities such as renal injury, direct hyperbilirubinemia, and thrombosis without an increase in mortality in patients receiving ECMO. Hemolysis is an unavoidable side effect of current ECMO technology and there are no approved treatments or treatment guidelines for the neonatal population. Therefore, increased vigilance, recognition of the severity of the hemolytic process, and prompt management are essential to prevent severe endothelial injury leading to proinflammatory and prothrombotic events.

Vacuum-assisted venous drainage in adult cardiac surgery: a propensity-matched study

OBJECTIVES

Conventional cardiopulmonary bypass with gravity drainage leads inevitably to haemodilution. Vacuum-assisted venous drainage (VAVD) utilizes negative pressure in the venous reservoir, allowing active drainage with a shortened venous line to reduce the priming volume. The goal of this study was to analyse the efficacy and safety of VAVD.

METHODS

Data on 19 687 patients (18 681 with gravity drainage and 1006 with VAVD) who underwent cardiac operations between 1 January 2015 and 31 January 2018 were retrospectively collected from a single centre. Propensity matching identified 1002 matched patient pairs with VAVD and gravity drainage for comparison of blood product transfusion rate, major morbidities and in-hospital mortality rates.

RESULTS

The blood transfusion rate of the VAVD group was lower than that of the gravity drainage group (28.1% vs 35% for red blood cells, 13% vs 18% for fresh frozen plasma and 0.1% vs 1.8% for platelets; P = 0.0009, 0.0020 and <0.0001, respectively). The mean difference (95% confidence interval) between the groups for red blood cells, fresh frozen plasma and platelets was -6.9% (-11.0% to -2.8%), -5.0% (-8.1% to -1.8%) and -1.7% (-2.5% to -0.9%), respectively. No difference was observed regarding the major morbidities of cerebrovascular accidents, acute kidney injury, hepatic failure and perioperative myocardial infarction and the in-hospital deaths between the 2 groups.

CONCLUSIONS

VAVD was associated with a reduction in blood product transfusions, and an increase in the risk of major morbidities and in-hospital deaths of the VAVD group was not observed.

Technical implementation of percutaneous thrombus aspiration using the AngioVac system

OBJECTIVES

The AngioVac system (AngioDynamics, Latham, NY, USA) provides a method for the minimally invasive, percutaneous aspiration of thrombus formations originating from the central venous system as well as solid matter such as lead vegetations and right atrial thrombi.

METHODS

This retrospective, observational study describes the initial experience in 52 adult patients with the AngioVac system, focusing mainly on the development of the extracorporeal circuit to improve usability and safety.

RESULTS

The mean patient age was 62.9 years (range 23-86 years). 22 patients were female and 30 were male. Indications for percutaneous aspiration were lead vegetations (n = 36; 69.2%), right atrial thrombi (n = 9; 17.3%), central venous thrombi (n = 5; 9.6%) and pulmonary embolisms (n = 2; 3.8%). Successful aspiration was performed in 44 cases (84.6%) and partial success was achieved in five patients (9.6%), while failure to remove thrombi or vegetations occurred in three cases (5.8%). Our practical experience led to the installation of a shunt line for recirculation and the implementation of safety features concerning air handling, which are also employed in minimally invasive extracorporeal bypass circuits. Initial tests monitored the level of negative pressure according to differences in flow and access sites but these still have to be validated on a larger scale.

CONCLUSION

In this initial experience, the AngioVac system appeared to be safe regarding the extracorporeal circulation and the elimination of thrombi and lead vegetations.

The impact of roller pump-assisted cardiotomy suction unit on hemolysis

Hemolysis in cardiac surgery is often related to the contact of blood with air or artificial surfaces. Variations of negative pressure in the suction cannulas may represent an additional factor. Limited data exist on the contribution of a roller pump-assisted (RPA) cardiotomy suction unit to hemolysis. Elevation of free hemoglobin (fHb) following air suction (AS) or suction tip occlusion (STO) events of a pump-assisted cardiotomy suction unit was investigated in a mock circuit filled with blood from slaughtered domestic pigs. AS-associated hemolysis was measured over 240 minutes with 2 minutes of AS occurring every 10 minutes. STO-associated hemolysis was analyzed over 80-minute periods: configuration 1 (c1) comprised a cycle of 20 minutes (min) occlusion and 60 minutes RPA flow (20/60 minutes); c2 comprised 20 cycles of 1/3 minutes; c3 comprised 40 cycles of 0.5/1.5 minutes; and c4 comprised 80 cycles of 0.25/0.75 minutes. The AS setup did not lead to significant hemolysis after 2 (P = .97), 3 (P = .40) or 4 (P = .11) hours. The STO setup showed the greatest hemolysis (ΔfHb of 30 mg/dL) in c1 after 20 minutes. ΔfHb was different in c1 from all other configurations at 20 minutes (P < .0001) and 80 minutes (P < .05). Ex vivo generation of large negative pressures by STO events is the main cause of cardiotomy suction-associated hemolysis. The clinical relevance of this mechanism needs further investigations.

Peripheral cannulae selection for veno-arterial extracorporeal life support: a paradox

Explosive penetration of veno-arterial extracorporeal life support in everyday practice has drawn awareness to complications of peripheral cannulation, resulting in recommendations to use smaller size cannulae. However, using smaller cannulae may limit the effectiveness of extracorporeal support and thereby the specific needs of the patient. Selection of proper size cannulae may therefore pose a dilemma, especially since pressure-flow characteristics at different hematocrits are lacking. This study evaluates the precision of cannula pressure drop prediction with increase of fluid viscosity from water flow-pressure charts by M-number, dynamic similarity law, and via fitted parabolic equation. Thirteen commercially available peripheral cannulae were used in this in vitro study. Pressure drop and flow were recorded using water and a water-glycerol solution as a surrogate for blood, at ambient temperature. Subsequently, pressure-flow curves were modeled with increased fluid viscosity (0.0031 N s m^-2), and then compared by M-number, dynamic similarity law, and fitted parabolic equation. The agreement of predicted and measured values were significantly higher when the M-number (concordance correlation = 0.948), and the dynamic similarity law method (concordance correlation = 0.947) was used in comparison to the fitted parabolic equation (concordance correlation = 0.898, p < 0.01). The M-number and dynamic similarity based model allow for reliable prediction of peripheral cannula pressure drop with changes of fluid viscosity and could therefore aid in well-thought-out selection of cannulae for extracorporeal life support.

An Analysis of Risk Factors for Hemolysis in Children on Extracorporeal Membrane Oxygenation

OBJECTIVES

Hemolysis is a known complication of pediatric extracorporeal membrane oxygenation associated with renal failure and mortality. We sought to identify predictors of hemolysis in pediatric extracorporeal membrane oxygenation patients and determine its influence on outcomes.

DESIGN

Retrospective, single-center study.

SETTING

Urban, quaternary care center pediatric and neonatal ICU.

PATIENTS

Ninety-six patients requiring extracorporeal membrane oxygenation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Daily measurements of plasma-free hemoglobin were obtained while patients were on extracorporeal membrane oxygenation. Patients with a prior extracorporeal membrane oxygenation run, on extracorporeal membrane oxygenation for less than 24 hours, or without complete medical records were excluded from the study. Ninety-six patients met inclusion criteria, of which, 25 patients (26%) had plasma-free hemoglobin greater than 30 mg/dL. Of those patients, 15 of 25(60%) had plasma-free hemoglobin greater than 50 mg/dL, and 21 of 25(84%) occurred during the first 7 days on extracorporeal membrane oxygenation. Compared with patients without hemolysis, those with hemolysis were younger (0.2 mo [0.06-3.2 mo] vs 8.2 mo [0.6-86 mo]; p < 0.001), had a higher pericannulation international normalized ratio (3.9 [3.5-5.5] vs 2.6 [1.8-3.7]; p = 0.003), lower pericannulation platelet count (33 × 10/μL [22-42 × 10/μL] vs 61 × 10/μL [38-86 × 10/μL]; p < 0.001), and had a less negative inlet pressure (-3.5 mm Hg [-14 to 11.5 mm Hg] vs -19 mm Hg [-47 to 0 mm Hg]; p = 0.01). A greater proportion of patients with hemolysis had a heparin assay less than 0.2 mg/dL (50% vs 17%; p = 0.001) and had fluid removal via slow continuous ultrafiltration (32% vs 6%; p < 0.001). Patients with hemolysis had increased risk of in-hospital mortality (odds ratio 10.0; 95% CI 3.4-32; p < 0.001). On multivariable analysis, continuous ultrafiltration (odds ratio, 8.0; 95% CI, 1.9-42; p = 0.007) and pericannulation international normalized ratio greater than 3.5 (odds ratio, 7.2; 95% CI, 2.3-26; p = 0.001) were significantly associated with hemolysis.

CONCLUSIONS

Hemolysis is a common complication of pediatric extracorporeal membrane oxygenation. We found that patients with hemolysis (plasma-free hemoglobin > 30 mg/dL) had a 10-fold increase in in-hospital mortality. In our study cohort, hemolysis was associated with continuous ultrafiltration use, but not continuous renal replacement therapy. Additionally, our results suggest that the degree of coagulopathy (international normalized ratio > 3.5) at the time of cannulation influences hemolysis. Additional prospective studies are necessary to define further strategies to prevent hemolysis and improve outcomes in pediatric extracorporeal membrane oxygenation patients.

[Extracorporeal membrane oxygenation : System selection, (contra)indications, and management]

There are a large number of extracorporeal membrane oxygenation (ECMO) systems and configurations. Thorough planning and evaluation of specific therapeutic needs are necessary to tailor ECMO therapy to the individual patient situation. Indications tend towards lowering the threshold towards respiratory ECMO. Patients with severe acute respiratory distress syndrome (ARDS) not improving to optimization of ventilation and supportive therapeutic measures potentially qualify for ECMO. Contraindications are relative and have to be considered in the light of the individual risk-benefit ratio. The same is true for decisions to stop ECMO therapy in case of futility for which reliable evidence does not exist.

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.

American College of Critical Care Medicine Clinical Practice Parameters for Hemodynamic Support of Pediatric and Neonatal Septic Shock

OBJECTIVES

The American College of Critical Care Medicine provided 2002 and 2007 guidelines for hemodynamic support of newborn and pediatric septic shock. Provide the 2014 update of the 2007 American College of Critical Care Medicine "Clinical Guidelines for Hemodynamic Support of Neonates and Children with Septic Shock."

DESIGN

Society of Critical Care Medicine members were identified from general solicitation at Society of Critical Care Medicine Educational and Scientific Symposia (2006-2014). The PubMed/Medline/Embase literature (2006-14) was searched by the Society of Critical Care Medicine librarian using the keywords: sepsis, septicemia, septic shock, endotoxemia, persistent pulmonary hypertension, nitric oxide, extracorporeal membrane oxygenation, and American College of Critical Care Medicine guidelines in the newborn and pediatric age groups.

MEASUREMENTS AND MAIN RESULTS

The 2002 and 2007 guidelines were widely disseminated, translated into Spanish and Portuguese, and incorporated into Society of Critical Care Medicine and American Heart Association/Pediatric Advanced Life Support sanctioned recommendations. The review of new literature highlights two tertiary pediatric centers that implemented quality improvement initiatives to improve early septic shock recognition and first-hour compliance to these guidelines. Improved compliance reduced hospital mortality from 4% to 2%. Analysis of Global Sepsis Initiative data in resource rich developed and developing nations further showed improved hospital mortality with compliance to first-hour and stabilization guideline recommendations.

CONCLUSIONS

The major new recommendation in the 2014 update is consideration of institution-specific use of 1) a "recognition bundle" containing a trigger tool for rapid identification of patients with septic shock, 2) a "resuscitation and stabilization bundle" to help adherence to best practice principles, and 3) a "performance bundle" to identify and overcome perceived barriers to the pursuit of best practice principles.

The Great Britain and Ireland perspective: current perfusion safety issues, preparing for the future

The Great Britain and Ireland (GBI) recommendations for standards of monitoring and alarms during cardio-pulmonary bypass (CPB) came into force in January 2004. While perfusion departments in Great Britain and Ireland should now have a good baseline level of safety, it is important that department-specific safety is also considered. Patient safety is paramount, but safety within our speciality must also take into account the protection of the perfusionists’ health and the protection of their careers. These different aspects of safety are fundamentally interrelated.

This paper focuses on the importance of careful assessment, implementation and documentation when a new component or technique is being introduced to the CPB circuit, even when the aim is to increase safety.

Knowledge of the civil justice system and the trends in medical negligence claims are an integral part of perfusionist safety. Perfusion in Great Britain and Ireland is rightly striving for professional recognition from the Health Professions Council (HPC). As we raise the profile of perfusion, we educate more people about the importance of our role and level of responsibility within the cardiac operating team. This will increase the potential for medical negligence claims to be directed specifically at our speciality. All these issues are discussed in detail.

Miniature cardiopulmonary bypass — the Hammersmith experience

The decision to embark on a miniature cardiopulmonary bypass programme requires careful planning. The objective of this paper is to present our experience and initial findings for consideration by our multidisciplinary peers, who may wish to implement this technology at their own hospitals. The paper reviews the evolution of our programme over the first 150 clinical cases and our current position on the advantages and disadvantages of miniature cardiopulmonary bypass. Perfusion (2007) 22, 161—166.

Cerebral oxygen saturation during pulsatile and non-pulsatile cardiopulmonary bypass in patients with carotid stenosis

Pulsatile and non-pulsatile cardiopulmonary bypass (CPB) flows may have different impact on cerebral oxygen saturation in patients with restricted cerebral arterial blood supply. Twenty patients, ten diagnosed with carotid stenosis (CS, n = 10) and ten without known carotid disease (Controls, n = 10), were subjected to one period of pulsatile and one period of non-pulsatile flow (6-8 min each) during CPB at 32°C. Cerebral oxygen saturation was registered by near-infrared light spectroscopy (NIRS).The mean arterial pressure (MAP) was significantly lowered by pulsatile CPB flow. The NIRS tissue oxygenation index (TOI) tended to decrease in the CS group and increase in the Controls during pulsatile flow compared with non-pulsatile; however, the changes were not statistically significant.No significant correlations were seen between the changes in MAP and TOI across the observation periods.In conclusion, pulsatile CPB flow caused slightly decreased mean arterial pressure while the effect on cerebral oxygenation was unclear. Pulsatile flow was not found superior to non-pulsatile flow in patients with or without carotid stenosis.

Combination of extracorporeal membrane oxygenation and continuous renal replacement therapy in critically ill patients: a systematic review

Introduction

Extracorporeal membrane oxygenation (ECMO) is used in critically ill patients presenting acute cardiac and/or pulmonary dysfunctions, who are at high risk of developing acute kidney injury and fluid overload. Continuous renal replacement therapy (CRRT) is commonly used in intensive care units (ICU) to provide renal replacement and fluid management. We conducted a review to assess the feasibility, efficacy and safety of the combination of ECMO and CRRT and to illustrate the indications and methodology of providing renal replacement therapy during the ECMO procedure.

Method

We searched for all published reports of a randomized controlled trial (RCT), quasi-RCT, or other comparative study design, conducted in patients undergoing ECMO plus CRRT. Two reviewers independently selected potential studies and extracted data. We used the modified Jadad scale and the Newcastle-Ottawa for quality assessment of RCTs and non-RCTs, respectively. Statistical analyses were performed using RevMan 5.2.

Results

We identified 19 studies meeting the eligibility criteria (seven cohort, six case control, one historically controlled trial and five studies of technical aspects). There are three major methods for performing CRRT during ECMO: ‘independent CRRT access’, ‘introduction of a hemofiltration filter into the ECMO circuit (in-line hemofilter)’ and ‘introduction of a CRRT device into the ECMO circuit’. We conducted a review with limited data synthesis rather than a formal meta-analysis because there could be greater heterogeneity in a systematic review of non-randomized studies than that of randomized trials. For ECMO survivors receiving CRRT, overall fluid balance was less than that in non-CRRT survivors. There was a higher mortality and a longer ECMO duration when CRRT was added, which may reflect a relatively higher severity of illness in patients who received ECMO plus CRRT.

Conclusions

The combination of ECMO and CRRT in a variety of methods appears to be a safe and effective technique that improves fluid balance and electrolyte disturbances. Prospective studies would be beneficial in determining the potential of this technique to improve the outcome in critically ill patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0675-x) contains supplementary material, which is available to authorized users.

Advances in Perfusion Techniques: Minimally Invasive Procedures

There is a growing demand from patients and referring physicians for minimally invasive cardiac surgery. Minimally invasive cardiac procedures are technically unique from conventional cardiac procedures and require a thorough understanding of the surgical, anesthetic, and perfusion strategies. Strategies include routine use of augmented venous drainage, alternative arterial and venous cannulation sites, and special cannulas designed for minimally invasive procedures. The following review describes the strategies and safety systems that should be considered when performing minimally invasive cardiac surgery.

An in vitro model of a system of electrical potential compensation in extracorporeal circulation

OBJECTIVES

Extracorporeal circulation (ECC) in patients undergoing cardiac surgery induces systemic immune-inflammatory reaction that results in increased postoperative morbidity. Many factors are responsible for the adverse response after ECC. The present in vitro study aimed to investigate electric charges (ECs) generated during ECC, to set a device compensating the ECs, and checking its effect on red blood cells (RBC).

MATERIALS AND METHODS

The electrical signals of blood in ECC were collected by a custom developed low-noise electronic circuit, processed by a digital oscilloscope (DSO) and a dynamic signal analyzer (DSA). The compensation of ECs was performed using a compensation device, injecting a nulling charge into the blood circuit. The compensation effect of the ECs on RBCs was evaluated by scanning electron microscope (SEM).

RESULTS

The electrical analysis performed using both the DSO and the DSA confirmed the EC formation during ECC. The notable electric signals recorded in standard ECC circuits substantially nulled once the compensation device was used, thus confirming efficient EC compensation. After two hours of ECC, the SEM non-blended test on human RBC samples highlighted morphological changes in acanthocytes of the normal biconcave-shaped RBC.

CONCLUSIONS

The outcomes confirm the development of parasitic ECs during ECC and that a suppressor system may decrease the potential damage of ECs. Nevertheless, further studies are ongoing in order to investigate the complex mechanisms related to lymphocytes and platelet morphological and physiological chances during triboelectric charges in ECC.

Challenges of cardiopulmonary bypass-a review of the veterinary literature

Cardiopulmonary bypass (CPB) has been used in veterinary medicine in experimental surgery and to address congenital and acquired diseases. We review the veterinary literature and expose common challenges of CPB in dogs and cats. Specifically, we describe the most specific elements of this technique in veterinary patients. The variety in animal size has made it difficult to standardize cannulation techniques, oxygenators, and priming volumes and solutions. The fact that one of the most common cardiovascular disorders, mitral valve disease, occurs predominantly in small dogs has limited the use of bypass in these patients because of the need for small, low prime oxygenators and pumps that have been unavailable until recently. Coagulation, hemostasis, and blood product availability have also represented important factors in the way CPB has developed over the years. The cost and the challenges in operating the bypass machine have represented substantial limitations in its broader use.

A hemolysis study of an intravascular blood cooling system for localized organ tissue cooling

Therapeutic hypothermia can reduce both ischemic and reperfusion injury arising after strokes and heart attacks. New localized organ cooling systems offer a way to reduce tissue damage more effectively with fewer side effects. To assess initial blood safety of our new organ cooling system, the CoolGuide Cooling System (CCS), we investigated safe operating conditions and configurations from a hemolysis perspective. The CCS consists of a peristaltic pump, a custom-built external heat exchanger, a chiller, biocompatible polyvinyl cellulose (PVC) tubing, and a control console. The CCS cools and circulates autologous blood externally and re-delivers cooled blood to the patient through a conventional catheter inserted directly into the organ at risk. Catheter configurations used included: a 7F guide catheter only, a 7F guide with a 0.038” wire inserted through the center and advanced 2 cm distal to the catheter distal tip, a 6F guide catheter only and a 6F guide with a 0.014” guidewire similarly inserted through the center. Using porcine blood, an in vitro test rig was used to measure the degree of hemolysis generation, defined as the percentage change in free hemoglobin, adjusted for total hemoglobin and hematocrit, between exiting and entering blood. The highest degree of hemolysis generation was 0.11±0.04%, based on the average behavior with a 6F catheter and a 0.014” guidewire configuration at a blood flow rate of approximately 130 mL/min. In terms of average percentage free hemoglobin exiting the system, based on total hemoglobin, the highest value measured was 0.17%±0.03%, using this 6F and 0.014” guidewire configuration. This result is significantly below the most stringent European guideline of 0.8% used for blood storage and transfusion. This study provides initial evidence showing hemolysis generation arising from the CoolGuide Cooling System is likely to be clinically insignificant.

Effect of poly(2-methoxyethyl acrylate)-coated oxygenators on haemolysis

Blood contact with artificial device surfaces and mechanical trauma are two major factors for haemolysis. Poly(2-methoxyethyl acrylate) (PMEA) is an amphiphilic polymer with a polyethylene chain that is hydrophobic and a mildly hydrophilic tail. PMEA coating has showed positive effects on protein adsorption, platelet loss, platelet aggregation and post-operative bleeding in previous studies. In this study, effects of poly(2-metoxyethyl acrylate) (PMEA)-coated oxygenators on haemolysis was investigated. PMEA-coated (SX18-Capiox) oxygenators were used. Desorbed erythrocyte, free haemoglobin indirect bilirubin and total bilirubin quantities from fibre samples of oxygenators were studied. Erythrocyte, total bilirubin and direct bilirubin values were measured from blood aliquots taken in five different times during cardiopulmonary by-pass (CPB); baseline (T1), during CPB (T2), at the end of CPB (T3), after protamine injection (T4) and in intensive care (T5). In both coated and non-coated oxygenators haemolysis rate was in clinically acceptable safety range. Average desorbed free haemoglobin was 6663 mg/dl from coated and 29.405 mg/dl from non-coated fibres. Average desorbed total bilirubin was 0.0068 mg/dl from coated and 0.023 mg/dl from noncoated fibres. We observed less haemolysis, as reflected by lower desorbed free haemoglobin and indirect bilirubin from coated oxygenators and less decrease in blood erythrocyte number. Blood bilirubin concentration was low in the coated group when compared to the control group. This study describes the relationship between PMEA coating and haemolysis at the blood contacting surface. PMEA coating reduces red blood cell damage during extracorporeal circulation.

Venous drainage--gravity or assisted?

Since the early start of cardiopulmonary bypass, vascular access has been recognized as a main variable for obtaining optimal blood flow during cardiopulmonary bypass. In particular, venous drainage can limit the maximum flow as the wide, low-resistance, collapsible veins are connected with smaller stiff cannulas and tubing. Due to the introduction of long venous cannulas for minimally invasive cardiac surgery and the desire to limit hemodilution during cardiopulmonary bypass, more and more centers have started using assisted venous drainage techniques. This article gives an overview of these techniques, with their respective advantages and disadvantages.

Centrifugal pump inlet pressure site affects measurement

During extracorporeal life support (ECLS), blood is exposed to a myriad of unphysiological factors that can affect outcome. One aspect of this is the sub-atmospheric pressure generated by the ECLS pump and imparted to blood elements along the pump inlet line. This pressure can be measured on the inlet line close to the pump head by adding a connector, or at the venous cannula connection site. We compared the two measurement sites located at both points; between the venous cannula-inlet tubing and inlet tubing-pump, with a range of cannulae and flows. We also investigated the effects on inlet pressure from pump afterload and increasing inlet tubing length.

Intraoperative blood salvage and retransfusion from citrate treated wounds is safe and feasible

OBJECTIVES

Allogenic blood transfusions are associated with increased morbidity and mortality in surgical patients. The study objective was to investigate the feasibility and safety of intraoperative autotransfusion of unwashed shed whole blood using a novel method.

DESIGN

Twenty pigs were randomised to autotransfusion or crystalloid volume replacement. In two separate surgical wounds, the surfaces and 400 ml of shed blood were treated in situ with citrate, delivered with an equipment transforming suction to positive pressure. Central haemodynamics were monitored with a pulmonary artery catheter. Effects on oxygen-carrying capacity, formed blood elements, haemolysis, inflammation, metabolism, and coagulation were evaluated with biochemical analyses.

RESULTS

No clinically relevant adverse effects on haemodynamics were encountered, apart from a decrease in cardiac output and mixed venous saturation similar to that in control animals. Haemoglobin level was better preserved in the autotransfused group (97 vs. 86 g/L, p=0.0007). There were no major differences in biochemical variables and no macroscopic clot formation precluding autotransfusion.

CONCLUSIONS

The technique was safe and feasible for intraoperative blood salvage and autotransfusion. Haemodynamics and biochemical variables were similar to controls. The technique warrants further studies in humans, as it may contribute towards a reduction of allogenic blood transfusions.

The relationships between air exposure, negative pressure, and hemolysis

The purpose of this study was to describe the hemolytic effects of both negative pressure and an air-blood interface independently and in combination in an in vitro static blood model. Samples of fresh ovine or human blood (5 ml) were subjected to a bubbling air interface (0-100 ml/min) or negative pressure (0-600 mm Hg) separately, or in combination, for controlled periods of time and analyzed for hemolysis. Neither negative pressure nor an air interface alone increased hemolysis. However, when air and negative pressure were combined, hemolysis increased as a function of negative pressure, the air interface, and time. Moreover, when blood samples were exposed to air before initiating the test, hemolysis was four to five times greater than samples not preexposed to air. When these experiments were repeated using freshly drawn human blood, the same phenomena were observed, but the hemolysis was significantly higher than that observed in sheep blood. In this model, hemolysis is caused by combined air and negative pressure and is unrelated to either factor alone.

Effect of biopassive and bioactive surface-coatings on the hemocompatibility of membrane oxygenators

Postoperative complications associated with cardiopulmonary bypass (CPB) surgery and extracorporeal circulation (ECC) procedures are still a major clinical issue. Improving the hemocompatibility of blood contacting devices used for ECC procedures may ameliorate various postpump syndromes. In a simulated CPB model using human blood, we investigated the hemocompatibility, fibrinogen adsorption, and platelet receptor (GPIIb-IIIa) binding capacity of surface-modified membrane oxygenators (Jostra Quadrox). Three groups were compared: (i) biopassive protein coatings (SafeLine), (ii) bioactive heparin coatings (BioLine), and (iii) noncoated controls. During the 2 h recirculation period, plasma concentrations of activation markers for platelets (beta-thromboglobulin), inflammation (elastase), complement (C5a), and coagulation (prothrombin fragment 1+2, thrombin-antithrombin III) were lower in the groups with biopassive and bioactive coatings compared to the noncoated group (p < 0.01). These parameters did not significantly differ between the two surface-coated groups, except for complement activation: C5a levels were higher in the biopassive group compared to the bioactive group (p < 0.01). Moreover, surface-coated oxygenators showed less fibrinogen adsorption, GPIIb-IIIa binding, and platelet/leukocyte adhesion (p < 0.01). We assume that fewer fibrinogen and platelet receptor molecules bound to the surface-coated oxygenator surfaces results in fewer platelet adhesion and activation, which will significantly contribute to the improved hemocompatibility of the biopassive and bioactive oxygenators. Our results suggest that the application of bioactive oxygenators (BioLine) during CPB surgery may reduce postoperative complications for the patient more effectively than biopassive oxygenators (SafeLine).

Hemolytic characteristics of three commercially available centrifugal blood pumps

OBJECTIVE

As compared with traditional extracorporeal roller-occlusion blood pumps, nonocclusive centrifugal pumps offer the benefits of requiring a smaller circuit surface area and, thus, a smaller prime volume. However, centrifugal blood pumps have been reported to generate unacceptable levels of hemolysis. We hypothesize that the newer generation centrifugal pumps have an incidence of hemolysis similar to the traditional roller head pumps and, thus, could be used for extracorporeal membrane oxygenation circuits.

DESIGN

Randomized, prospective, bench study.

SETTING

University research laboratory.

INTERVENTIONS

Three centrifugal blood pumps (Cobe Revolution, Jostra Rotaflow, and Medtronic BioMedicus) were compared with a roller occlusion blood pump (Cobe Century). Hemolysis generation was examined during 6 hrs of continuous use. Two test runs per group were randomly performed on three consecutive days for a total of six test runs for each of the four pumps (n = 24).

MEASUREMENTS AND MAIN RESULTS

Plasma free hemoglobin values were determined using a Spectra MaxPlus spectrophotometer. A normalized index of hemolysis was calculated to compare the individual trials. The Cobe Revolution and the Jostra Rotaflow compared favorably with the Cobe Century roller occlusion blood pump in the amount of hemolysis produced.

CONCLUSIONS

These data are encouraging for the development of a low-prime, mobile neonatal extracorporeal membrane oxygenation circuit using centrifugal pump technology.

Immediate exercise hyperemia: contributions of the muscle pump vs. rapid vasodilation

A striking characteristic of the blood flow adaptation at exercise onset is the immediate and substantial increase in the first few (0–5 s) seconds of exercise. The purpose of this mini-review is to put into context the present evidence regarding mechanisms responsible for this phase of exercise hyperemia. One potential mechanism that has received much attention is the mechanical effect of muscle contraction (the muscle pump). The rapid vasodilatory mechanism(s) is another possible mechanism that has recently been shown to exist. This review will provide the reader with 1) an understanding of the basic physics of blood flow and the theories of muscle pump function, 2) a critical examination of evidence both for and against the contribution of the muscle pump or rapid vasodilatory mechanisms, and 3) an awareness of the limitations and impact of experimental models and exercise modes on the contribution of each of these mechanisms to the immediate exercise hyperemia. The inability to measure microvenular pressure continues to limit investigators to indirect assessments of the muscle pump vs. vasodilatory mechanism contributions to immediate exercise hyperemia in vivo. Future research directions should include examination of muscle-contraction-induced resistance vessel distortion as a trigger for rapid smooth muscle relaxation and further investigation into the exercise mode dependency of muscle pump vs. rapid vasodilatory contributions to immediate exercise hyperemia.

Physiological coagulation can be maintained in extracorporeal circulation by means of shed blood separation and coating

OBJECTIVE

Conventional extracorporeal circulation results in an activation of coagulation cascades. Coating of extracorporeal circulation tubes as well as avoidance of shed blood recirculation have been shown to reduce these phenomena. We evaluated a new shed blood separation system (AVANT D 970) utilizing a coated cardiopulmonary bypass tube system (PHISIO).

METHODS

Forty patients (62 +/- 10 years) underwent isolated coronary revascularization. Four groups (n = 10/group) were defined: no extracorporeal circulation, conventional uncoated extracorporeal circulation, uncoated extracorporeal circulation with shed blood separation, and coated extracorporeal circulation with shed blood separation. Thrombin-antithrombin complex and free Hb were analyzed and statistically compared.

RESULTS

Conventional extracorporeal circulation exhibited the highest intraoperative activation of coagulation (thrombin-antithrombin complex: extracorporeal circulation, 31.1 +/- 15.8 microg/L; uncoated extracorporeal circulation with shed blood separation, 15.3 +/- 7.8 microg/L; coated extracorporeal circulation with shed blood separation, 8.1 +/- 4.8 microg/L; no extracorporeal circulation, 2.4 +/- 0.6 microg/L; P <.05 extracorporeal circulation vs all others) and red blood cell damage (free Hb: extracorporeal circulation, 16.8 +/- 11.4 micromol/L; uncoated extracorporeal circulation with shed blood separation, 10.3 +/- 3.5 micromol/L; coated extracorporeal circulation with shed blood separation, 6.8 +/- 2.9 micromol/L; no extracorporeal circulation, 3.4 +/- 1.1 micromol/L; P <.05 extracorporeal circulation vs no extracorporeal circulation, coated extracorporeal circulation with shed blood separation). Coated extracorporeal circulation with shed blood separation showed only slight activation and cell trauma, which did not differ significantly from no extracorporeal circulation.

CONCLUSIONS

Combination of coating and avoidance of shed blood recirculation maintained physiological coagulation levels and markedly reduced red blood cell trauma in extracorporeal circulation procedures. These combined modalities may therefore offer an alternative for off-pump procedures in patients with contraindications for conventional extracorporeal circulation.