Priming Volume Research Articles

Continuous renal replacement therapy in neonates and small infants: development and first-in-human use of a miniaturised machine (CARPEDIEM)

Peritoneal dialysis is the renal replacement therapy of choice for acute kidney injury in neonates, but in some cases is not feasible or effective. Continuous renal replacement therapy (CRRT) machines are used off label in infants smaller than 15 kg and are not designed specifically for small infants. We aimed to design and create a CRRT machine specifically for neonates and small infants. We prospectively planned a 5-year project to conceive, design, and create a miniaturised Cardio-Renal Pediatric Dialysis Emergency Machine (CARPEDIEM), specifically for neonates and small infants. We created the new device and assessed it with in-vitro laboratory tests, completed its development to meet regulatory requirements, and obtained a licence for human use. Once approved, we used the machine to treat a critically ill neonate The main characteristics of CARPEDIEM are the low priming volume of the circuit (less than 30 mL), miniaturised roller pumps, and accurate ultrafiltration control via calibrated scales with a precision of 1 g. In-vitro tests confirmed that both hardware and software met the specifications. We treated a 2·9 kg neonate with haemorrhagic shock, multiple organ dysfunction, and severe fluid overload for more than 400 h with the CARPEDIEM, using continuous venovenous haemofiltration, single-pass albumin dialysis, blood exchange, and plasma exchange. The patient's 65% fluid overload, raised creatinine and bilirubin concentrations, and severe acidosis were all managed safely and effectively. Despite the severity of the illness, organ function was restored and the neonate survived and was discharged from hospital with only mild renal insufficiency that did not require renal replacement therapy. The CARPEDIEM CRRT machine can be used to provide various treatment modalities and support for multiple organ dysfunction in neonates and small infants. The CARPEDIEM could reduce the range of indications for peritoneal dialysis, widen the range of indications for CRRT, make the use of CRRT less traumatic, and expand its use as supportive therapy even when complete renal replacement therapy is not indicated. Associazione Amici del Rene di Vicenza.

A novel rat model of cardiopulmonary bypass for deep hypothermic circulatory arrest without blood priming

Background Large animal cardiopulmonary bypass (CPB) models are expensive, and prevent assessment of neurocognitive function, and difficulties with long-term recovery. The purpose of this study was to establish a novel rat model of cardiopulmonary bypass for deep hypothermic circulatory arrest without blood priming. Methods Twenty adult male Sprague-Dawley rats weighing 450–560 g were randomized to CPB with deep hypothermic circulatory arrest (DHCA) and control groups, with 10 rats each. The experimental protocols, including blood and crystalloid fluid administration, anesthesia, orotracheal intubation, ventilation, cannulation, and heparinization were identical in both groups. After inducing cardiac arrest, the circuit was turned off and rats were left in a DHCA state for 15 minutes. Rats were rewarmed to 34°C to 35°C over a period of 36 to 42 minutes using CPB-assisted rewarming, a heating blanket, and a heating lamp along with administration of 0.1 mEq of sodium bicarbonate and 0.14 mEq of calcium chloride. The remaining priming volume was reinfused and animals were weaned from CPB. Results All CPB with DHCA processes were successfully achieved. Blood gas analysis and hemodynamic parameters were in the normal range. The vital signs of all rats were stable. Conclusions Our CPB circuit has several novel features, including a small priming volume, active cooling/rewarming processes, vacuum-assisted venous drainage, peripheral cannulation without thoracotomy or sternotomy, and an accurate means of monitoring peripheral tissue oxygenation.

Blood conservation strategies in cardiac surgery: more is better

Recent data show that up to 50% of heart procedures require blood transfusion, which can have adverse long- and short-term outcomes for the patient. This led to the updated 2011 Society of Thoracic Surgery (STS)/Society of Cardiovascular Anesthesiologists (SCA) guidelines in an attempt to adopt more effective blood conservation techniques. We present our results after the implementation of a more aggressive strategy for intraoperative blood conservation in cardiac surgery. Our cardiac surgery database was reviewed retrospectively, comparing outcomes from two different time periods, after the implementation of a more effective two-way blood conservation strategy beginning in March 2012: more aggressive intraoperative autologous donation (IAD) based on a newly constructed nomogram, and the use of a shorter length circuit of the cardiopulmonary bypass (CPB) which allowed for lower fluid volume as a prime. The method of retrograde autologous priming (RAP) was the same for both time periods. A total of 1126 patients (Group 1) were studied in a 12-month period (March 2012-February 2013) after the implementation of the new strategy, and compared with 3758 patients (Group 2) of the previous 36-month period (March 2009-February 2012). There was a significant reduction in the percent change of the intraoperative haematocrit between Groups 1 and 2 (14 vs 28%, P = 0.01), with an increase in the mean IAD volume (655 vs 390 ml, P = 0.02) and a reduction in the CPB priming volume (1000 vs 1600 ml, P = 0.03). Group 1 required significantly less blood transfusions in the perioperative period (29 vs 49%, P = 0.02) and had significantly reduced postoperative rates of respiratory failure (3 vs 7%, P = 0.03), pneumonia (1 vs 3.1%, P = 0.01), chest tube output (350 vs 730 ml, P = 0.01), reoperation for bleeding (1.2 vs 2.5%, P = 0.04) and length of stay (6.1 vs 8.2 days, P = 0.05). Blood conservation is safe and effective in reducing transfusions in cardiac surgery, minimizing perioperative morbidity and mortality. Aggressive IAD and low CPB prime, along with effective RAP, is the three-way blood conservation strategy that leads to improved outcomes in cardiac surgery.

The promise of microfluidic artificial lungs.

Microfluidic or microchannel artificial lungs promise to enable a new class of truly portable, therapeutic artificial lungs through feature sizes and blood channel designs that closely mimic those found in their natural counterpart. These new artificial lungs could potentially: 1) have surface areas and priming volumes that are a fraction of current technologies thereby decreasing device size and reducing the foreign body response; 2) contain blood flow networks in which cells and platelets experience pressures, shear stresses, and branching angles that copy those in the human lung thereby improving biocompatibility; 3) operate efficiently with room air, eliminating the need for gas cylinders and complications associated with hyperoxemia; 4) exhibit biomimetic hydraulic resistances, enabling operation with natural pressures and eliminating the need for blood pumps; and, 5) provide increased gas exchange capacity enabling respiratory support for active patients. This manuscript reviews recent research efforts in microfluidic artificial lungs targeted at achieving the advantages above, investigates the ultimate performance and scaling limits of these devices using a proven mathematical model, and discusses the future challenges that must be overcome in order for microfluidic artificial lungs to be applied in the clinic. If all of these promising advantages are realized and the remaining challenges are met, microfluidic artificial lungs could revolutionize the field of pulmonary rehabilitation.

S0220105 携帯型軸流血液ポンプの流体力学特性に関する研究([S022-01]循環器系医療機器セッション(1),バイオエンジニアリング部門)

Though many kinds of implantable LVADs are available nowadays in the world, portable circulatory assist pumps for bridge-to-decision use are lacking. The purpose of the present study is to develop a portable axial-flow pump for bridge-to-decision use. We have developed an axial-flow pump whose priming volume is only 11 ml and pump volume is 50 ml. The blood contacting surfaces are all polymer. The pump performance was found experimentally to be sufficient for bridge-to-decision use.

Gas Exchange Efficiency of an Oxygenator with Integrated Pulsatile Displacement Blood Pump for Neonatal Patients

Oxygenators have been used in neonatal extracorporeal membrane oxygenation (ECMO) since the 1970s. The need to develop a more effective oxygenator for this patient cohort exists due to their size and blood volume limitations. This study sought to validate the next design iteration of a novel oxygenator for neonatal ECMO with an integrated pulsatile displacement pump, thereby superseding an additional blood pump. Pulsating blood flow within the oxygenator is generated by synchronized active air flow expansion and contraction of integrated silicone pump tubes and hose pinching valves located at the oxygenator inlet and outlet. The current redesign improved upon previous prototypes by optimizing silicone pump tube distribution within the oxygenator fiber bundle; introduction of an oval shaped inner fiber bundle core, and housing; and a higher fiber packing density, all of which in combination reduced the priming volume by about 50% (50 to 27 mL and 41 to 20 mL, respectively). Gas exchange efficiency was tested for two new oxygenators manufactured with different fiber materials: one with coating and one with smaller pore size, both capable of long-term use (OXYPLUS® and CELGARD®). Results demonstrated that the oxygen transfer for both oxygenators was 5.3-24.7 mlO2/min for blood flow ranges of 100-500 mlblood/min. Carbon dioxide transfer for both oxygenators was 3.7-26.3 mlCO2/min for the same blood flow range. These preliminary results validated the oxygenator redesign by demonstrating an increase in packing density and thus in gas transfer, an increase in pumping capacity and a reduction in priming volume.

Five‐Year Experience With Mini‐Volume Priming in Infants ≤5 kg: Safety of Significantly Smaller Transfusion Volumes

Reducing the cardiopulmonary bypass (CPB) priming volume in congenital cardiac surgery is important because it is associated with fewer transfusions. This retrospective study was designed to compare safety and transfusion volumes between the mini-volume priming (MP) and conventional priming (CP) methods. Between 2007 and 2012, congenital heart surgery using CPB was performed on 480 infants (≤5 kg): the MP method was used in 331 infants (MP group, 69.0%), and the CP method was used in 149 infants (CP group, 31.0%). In the MP group, narrow-caliber (3/16″) tubing was used, and the pump heads were vertically aligned to shorten the tubing lengths. The smallest possible oxygenators and hemofilters were used, and vacuum drainage was applied. Ultrafiltration was vigorously applied during CPB to avoid excessive hemodilution. The mean age and body weight of the patients were 48 ± 41 (0-306) days and 3.8 ± 0.8 (1.3-5.0) kg, respectively. The total priming and transfusion volumes during CPB were lower in the MP group than in the CP group (141 ± 24 mL vs. 292 ± 50 mL, P < 0.001, and 82 ± 40 mL vs. 162 ± 82 mL, P < 0.001, respectively). In the MP group, the smallest priming volume was 110 mL. However, there was no significant difference in the lowest hematocrit level during CPB between the two groups (22 ± 3% vs. 22 ± 3%, P = 0.724). The incidence of postoperative neurological complications was not significantly different between the MP and CP groups (1.8% vs. 2.7%, P = 0.509). After adjustment for the Risk Adjustment for Congenital Heart Surgery category, body surface area, and age, MP was not an independent risk factor of postoperative neurological complications or early mortality (P = 0.213 and P = 0.467, respectively). The MP method reduced the priming volume to approximately 140 mL without increasing the risk of morbidity or mortality in infants ≤5 kg. The total transfusion volume during CPB was reduced by 50% without compromising hematocrit levels. We recommend the use of mini-volume priming, which is a safe and effective method for reducing transfusion volumes.

Bloodless Surgery in a Pediatric Jehovah’s Witness

Pediatric cardiac surgery in Jehovah’s Witness patients who refuse the use of blood products remains a challenge because of the extreme hemodilution caused by priming the circuit and subsequent cardiopulmonary bypass. We report our successful strategy for reducing the prime volume for a 2-year-old Jehovah’s Witness patient who required open heart surgery. We modified our conventional bypass circuit requirements for this size child by incorporating a lower prime oxygenator and reducing the size of the venous line and circuit, which decreased the circuit prime volume. We managed to reduce our initial sanguineous prime volume from 315 to 210 mL. The prime was further reduced to 160 mL by minimizing circuit length at the field and with venous prime sequestration prebypass. The postbypass hematocrit was 31%. Bloodless pediatric cardiac surgery in Jehovah’s Witness patients can be performed safely. Incorporating a lower prime oxygenator into a revised circuit alleviated the need for blood transfusion and allowed us to achieve our calculated flow rate of 2.6 L/min/m2 while maintaining a hematocrit of 31%.

Reply to Bauer et al.

We appreciate the comments from Bauer et al. regarding our previously published article in this journal [1, 2] and would like to take the opportunity to clarify some important points of our study. The experimental set-up of our study included a sample closed perfusion system without a reservoir and without an air removal device on the venous side, as the main goal was to analyse pressure dynamics during cardiopulmonary bypass (CPB) and their effects on the formation of gaseous microemboli (GME) using a minimized closed perfusion circuit (MPC). We did not focus on the minimal extracorporeal circulation (MECC) system with a venous bubble trap (VBT) and with an oxygenator with an integrated arterial filter. To the best of our knowledge, this is the first study providing continuous recordings of venous line pressures every 250 ms during CPB. Independent of the further development of CPB techniques, in our opinion, it remains very important to document these pressure changes. The observed pressure differences reflected mostly volume requirements and underlined the need for an appropriate sensitive sensor to detect them. As Bauer et al. comment, this is the case in most current systems. However, venous pressure monitoring is not always sensitive enough to detect these differences [3]. In addition, the current automatic pump flow regulation involves a delay and under certain circumstances, is not fast enough to compensate negative pressure peaks sufficiently, leading to flow reduction. Even experienced perfusionists and anaesthesiologists, carefully handling the volume management, cannot provide 100% safety. To address this problem, our group developed a new device for automatic pressure and volume compensation during MPC, which was also evaluated in this experimental model, and these data are currently in submission. A large number of references within the comment of Bauer et al. state that MPC may be more vulnerable to accidental air introduction—the main trigger that develops de-airing devices [1]. In the in vitro study of Kutschka et al. [4], clinical aspects such as volume depletion were not considered. The better neurocognitive outcome after MPC when compared with CPB by Anastasiadis et al. [5] may be related to differences in cerebral perfusion that are influenced by various factors. However, the used MPC system had no VBT and the presence of GME was not investigated. All components of our experimental perfusion system are nowadays in routine clinical use. We used the same CPB equipment in order to make a realistic comparison between MPC and CPB. We agree with Bauer et al., that modern MECC systems with de-airing devices are safe and show a clinical benefit in daily routine use. Nevertheless, some aspects regarding these specific devices such as the use of more priming volume, more foreign surface contacts and additional costs should be studied further. Our newly developed compensation device may ameliorate or avoid these effects. Finally, we would like to mention that, following our experimental results, we plan to clinically compare MPC with clampless off-pump strategies, as the latter are well known for excellent postoperative neurological outcomes [6].

019 * BLOOD CONSERVATION STRATEGIES IN CARDIAC SURGERY: MORE IS BETTER

Objectives: Recent data show that up to 50% of heart procedures require blood transfusion, which can have adverse long- and short-term outcomes for the patient. This led to the updated 2011 STS/SCA guidelines in an attempt to adopt more effective blood conservation techniques. We present our results after the implementation of a more aggressive strategy for intraoperative blood conservation in cardiac surgery. Methods: Our cardiac surgery database was reviewed retrospectively, comparing outcomes from two different time periods, after the implementation of a more effective two-fold blood conservation strategy beginning in March 2012: more aggressive intraoperative autologous donation (IAD) based on a newly constructed nomogram, and the use of a shorter length circuit of the cardiopulmonary bypass (CPB) which allowed for lower fluid volume as a prime. The method of retrograde autologous priming (RAP) was the same for both time periods. Results: A total of 1126 patients (group 1) were studied in a 12-month period (March 2012-February 2013) after the implementation of the new strategy, and compared to 2758 patients (group 2) from the previous 36-month period (March 2009-February 2012). There was a significant reduction in the percentage change of the intraoperative haematocrit between groups 1 and 2 (14% vs 28%, P = 0.01), with an increase in the mean IAD volume (655 ml vs 390 ml, P = 0.02) and a reduction in the CPB prime volume (1000 ml vs 1600 ml, P = 0.03). Group 1 required significantly fewer blood transfusions in the perioperative period (29% vs 49%, P = 0.02) and had significantly reduced postoperative rates of respiratory failure (3% vs 7%, P = 0.03), pneumonia (1% vs 3.1%, P = 0.01), chest tube output (350 ml vs 730 ml, P = 0.01), reoperation for bleeding (1.2% vs 2.5%, P = 0.04), and length of stay (6.1 days vs 8.2 days, P = 0.05). Conclusions: Aggressive IAD and low CPB prime, along with effective RAP, is the three-fold blood conservation strategy that leads to improved outcomes in cardiac surgery.

Reply

Reply We thank Koga and colleagues for referring to our article (1) and reporting the successful use of endotoxin adsorption therapy for pediatric endotoxin shock, in their letter to the editor. We would like to make a few comments regarding this case report. Sepsis remains a major cause of morbidity and mortality among children despite the availability of various treatments using antibiotics, fluids, or vasopressive/inotropic approaches. Children with severe sepsis have hospital mortality rates of 10.3% in the United States (2) and 17% in the United Kingdom (3). Several factors, including age and immune status, influence the defense mechanisms against infection in children. Susceptibility to infection in some children is linked to immaturity of the immune system or the immunocompromising effects of chemotherapy. In these children, bacteria and virulence such as endotoxin in the blood stimulate the systemic inflammatory response. Even under intensive care, these processes can rapidly progress to multiple organ dysfunction syndrome and death. Endotoxin, an outer membrane component of gram-negative bacteria, plays an important role in the pathogenesis of severe sepsis and septic shock. Endotoxemia is common in children admitted to pediatric intensive care units and may be associated with increased severity of illness (4). The international guidelines for the management of severe sepsis and septic shock recommend fluid resuscitation, antibiotics, source control, inotropes/vasopressors, and corticosteroids, if needed, for the treatment for pediatric septic shock (5). When these treatments are ineffective and the plasma endotoxin concentration or endotoxin activity assay is increased, endotoxin adsorption therapy by polymyxin B–immobilized fiber column direct hemoperfusion (PMX-DHP) can be used as an optional treatment in Japan. In their letter to the editor, Koga and colleagues reported the effective use of PMX-DHP therapy for endotoxin shock in an immunocompromised child. Polymyxin B–immobilized fiber column direct hemoperfusion therapy has been widely used in adult patients with septic shock in Japan. We have shown in the meta-analysis that PMX therapy for adult patients with septic shock had beneficial effects on the hemodynamics, pulmonary oxygenation, and mortality (1). These beneficial effects may be attributable to the direct adsorption of endotoxin, monocytes, activated neutrophils, and anandamide, as well as indirect decrease in inflammatory cytokines and other mediators. Children with septic shock have also received PMX-DHP therapy, but the pediatric use of the therapy has only been reported in English once, in a letter to the editor in Digestive Diseases and Sciences (6). The Japan Society for Premature and Newborn Medicine issued a guideline for PMX-DHP therapy for infants/neonates in Japanese in 2010. Polymyxin B–immobilized fiber column direct hemoperfusion therapy is indicated for pediatric patients with septic shock when the patients manifest endotoxemia associated with the criteria for pediatric sepsis (7). The criterion for excluding PMX-DHP therapy for pediatric patients with septic shock is intracranial bleeding or a tendency to bleed in general. The following are important points for PMX-DHP performance in children: (1) an appropriately sized catheter should be inserted for vascular access; (2) an appropriately sized PMX column should be used; (3) the blood flow rate should be gradually increased to 2 to 5mL/kg per minute to prevent circulatory collapse; (4) nafamostat mesilate should be infused at a rate of 0.5 to 1.0 mg/kg per hour for anticoagulant and thereafter maintained at the rate necessary to sustain activated clotting time for 150 to 200 s. When the priming volume is greater than 10% of the patient’s body weight, a mixture of a red blood cell suspension and physiological saline is needed to prevent anemia. The PMX-05R column or PMX-01R column is usually used for children with endotoxin shock, because circulating blood volumes are low. The former, the PMX-05R column, has a low priming volume (40 mL) and is used for children with body weights of 10 kg or over. The PMX-01R column, which has a lower priming volume (8 mL), has been used for smaller children (body weights <10 kg) since its introduction in Japan in April 2012. When administering PMX-DHP for children, physicians should be mindful of their lower circulating blood volumes. Electrocardiogram and blood pressure must be monitored during this therapy. Severe arrhythmia such as ventricular tachycardia or ventricular fibrillation may occur as a consequence of low circulating volumes several minutes after the initiation of extracorporeal circulation. Hence, the safety and efficacy of PMX-DHP therapy for high-risk children with septic shock have not yet to be confirmed. Nevertheless, we believe that PMX-DHP is a useful therapy for severe pediatric endotoxin shock. Chieko Mitaka Department of Critical Care Medicine Tokyo Medical and Dental University Graduate School Tokyo, Japan Makoto Tomita Clinical Research Center Tokyo Medical and Dental University Hospital of Medicine Tokyo, Japan

Prescriptive Patient Extracorporeal Circuit and Oxygenator Sizing Reduces Hemodilution and Allogeneic Blood Product Transfusion during Adult Cardiac Surgery

The goal of this cardiopulmonary bypass (CPB) quality improvement initiative was to maximize hemoglobin nadir concentration by minimizing hemodilution and, in turn, eliminating allogeneic blood product transfusion. The effects of transitioning from “one-size-fits-all” to “right-sized” oxygenators, reservoirs, and arterial–venous tubing loops were evaluated through a 2-year retrospective review of 3852 patient perfusion records. Using a sizing algorithm, derived from manufacturers’ recommendations, we were able to create individualized “right-sized” extracorporeal circuits based on patient body surface area, cardiac index, and target blood flows. Use of this algorithm led to an increase in the percent of algorithm-recommended smaller oxygenators being used from 39% to 63% (p&lt; .01) and an increase in average hemoglobin nadir from 8.38 to 8.76 g/dL (p&lt; .01). Decreased priming volumes led to increased hemoglobin nadir and decreases in allogeneic blood transfusion (p= .048). Patients with similar body surface areas who previously were exposed to larger oxygenators, reservoirs, and arterial–venous loops were now supported with smaller circuits as a result of the use of the right-sized algorithm. Adjustments to the algorithm were made for unique patients and procedural situations including age, gender, and length and type of procedure. Larger heat exchanger surface area oxygenators were used for circulatory arrest procedures as a result of the need for increased heat exchange capability. Despite the generally higher costs of smaller circuits, reduced transfusion-related expenditures and decreased exposure risks justify the use of smaller circuit components. This quality improvement initiative demonstrated that as an integral part of a multidisciplinary, multimodal blood conservation effort, the use of the “right-sized” circuit algorithm can help to elevate hemoglobin nadir during CPB and eliminate allogeneic blood transfusions to patients undergoing CPB.

A Low-Cost, Small Volume Circuit for Autologous Blood Normothermic Perfusion of Rabbit Organs

We have designed a laboratory extracorporeal normothermic blood perfusion system for whole organs (e.g., kidney) that achieves pulsatile flow, low levels of hemolysis, and a blood priming volume of 60 mL or less. Using this uniquely designed extracorporeal circuit, we have achieved perfusion of two isolated ex vivo constructs. In the first experiment, we successfully perfused a rabbit epigastric flap based on the femoral vessels. In the second experiment, we were able to perfuse the isolated rabbit kidney for 48 h (range for all kidneys was 12-48 h) with excellent urine output, normal arterial blood gasses at 24 h, and normal ex vivo kidney histology at the conclusion of the experiments. These parameters have not been achieved before with any known or previously published laboratory extracorporeal circuits. The study has implications for prolonged organ perfusion prior to transplantation and for tissue engineering of vascularized tissues, such as by the perfusion of decellularized organs.

First serial in vivo results of mechanical circulatory support in children with a new diagonal pump

Mechanical circulatory support (MCS) is a rescue therapy for infants and children suffering from severe cardiorespiratory failure with specific system-related complications like bleeding, thromboembolism and device failure. Novel circuit components for temporary MCS with improved haemodynamic properties may improve patients' outcome and reduce system-related morbidities. The Deltastream DP3 (Medos Medizintechnik AG, Stolberg, Germany) is a newly designed rotational pump with a diagonally streamed impeller that can be used in children of all ages (priming volume 16 ml, flow 0-8 l/min). The aim of this study was to analyse the feasibility and safety of the DP3 pump system in children. We retrospectively investigated a consecutive series of 16 children [median age 0.9 months (0.1-55 months), median weight 3.2 kg (2.5-14 kg)]. The DP3 circuit was used 22 times in these children for different indications: (I) extracorporeal life support (ECLS) in post-cardiotomy heart failure (n = 11), (II) ECLS in cardiopulmonary resuscitation (CPR) (n = 7) and (III) extracorporeal membrane oxygenation (ECMO) in acute respiratory distress syndrome (ARDS) (n = 4). Median duration of MCS was 4 days (0-18 days), 12 patients (75%) were weaned successfully from MCS, 4 of these children (25%) died after weaning, with a median survival time of 15 days (6-28 days). Overall survival rate was 50% and all 8 survivors were discharged home without neurological injury. There was no case of severe bleeding, thromboembolic complications or device failure. Mean lactate dehydrogenase (LDH) before MCS was 700 (±384) U/l, and increased to a maximum of 2279 (±2635) U/l during MCS (P = 0.04). Baseline D-dimer values were 3.4 (±3.0) mg/l and rose significantly to 19.5 (±11.5) mg/l during MCS (P < 0.001). The mean of the highest plasma-free haemoglobin during MCS was 21.0 (±42.9) mg/dl. The increase in plasma-free haemoglobin correlated moderately with the duration of MCS (Pearson's r: 0.78). The use of the Deltastream DP3 seems to be safe and effective for MCS in children and may show a low degree of haemolysis. We observed no system-related complications and an overall good outcome in this demanding patient cohort.

A retrospective comparison of blood transfusion requirements during cardiopulmonary bypass with two different small adult oxygenators

A low haematocrit during cardiopulmonary bypass (CPB) is associated with adverse outcomes and often results in homologous blood transfusions. Oxygenators with improved venous reservoir designs aid in reducing the priming volume. Recently, we changed our small adult oxygenator model from the D905 EOS oxygenator (Dideco, Mirandola, Italy) to the Capiox FX1540 (Terumo Corporation, Tokyo, Japan). We conducted a retrospective study of 42 patents to evaluate the impact of the Capiox FX 1540 on blood transfusion requirements in small patients (body surface area (BSA) up to 1.8 m(2)). The D905 EOS group had a lower minimum intraoperative haematocrit than the FX1540 group (20 ± 3 v 22 ± 4, p = 0.029) with 73% of the patients receiving intraoperative blood transfusions compared with 30% in the FX 1540 group (p = 0.012). Patients in the D905 EOS group received one blood transfusion more during CPB than the FX 1540 patients (p = 0.002). The haematocrits at the end of CPB and in the early postoperative period were identical in both groups. The postoperative ventilation time, length of stay in the intensive care unit and postoperative chest drain bleeding were similar in both groups. In conclusion, the Capiox FX1540 was effective in reducing intraoperative packed red cell transfusions.

The effect of retrograde autologous priming on intraoperative blood product transfusion in coronary artery bypass grafting

Retrograde autologous priming (RAP) of the cardiopulmonary bypass (CPB) circuit could reduce the degree of haemodilution associated with priming with acellular solutions. However, there is no strong evidence to prove that the practice of RAP reduced intraoperative packed red cell (PRC) or blood product transfusion. To evaluate the effect of RAP on intraoperative PRC usage in coronary artery bypass grafting (CABG). This study is a prospective, observational study on patients who underwent first-time, isolated CABG using CPB between April 2012 and July 2012. Two groups of patients were identified: 1. Non-RAP group (n=128) and 2. RAP group (n=73). The primary outcome for the study was the amount of PRC and blood product usage between the induction of anaesthesia and the cessation of CPB. Use of PRC and blood products in the operating room was comparable in both groups. Univariate logistic regression showed that RAP was not an independent predictor of PRC or blood product transfusion (p=0.43). Multivariate logistic regression showed that CPB time, preoperative haemoglobin (Hb) levels and creatinine clearance were independent predictors of blood product transfusion. Practising RAP with mean volumes of 300 ml does not necessarily reduce PRC and other blood product transfusion requirements during CABG. In our practice, RAP was performed, aiming at displacing CPB circuit prime volume with which the perfusionist felt comfortable and dictated by haemodynamic parameters prior to commencing CPB. We presume this is the case in many units around the world. This practice, in our opinion, is not enough to achieve the benefits of RAP, if any, in the form of a reduction of packed red cell transfusion requirements. The true advantages of RAP in cardiac surgery need to be studied in a prospective, randomized, controlled trial.

Vacuum-Assisted Venous Drainage, Angel or Demon: PRO?

Vacuum-assisted venous drainage (VAVD) was proposed to optimize venous drainage during bypass through femoral venous cannulation. It is currently used in both adult and pediatric surgery when siphon gravity venous drainage is suboptimal. In pediatric surgery, the major advantages of VAVD are a significant decrease in cardiopulmonary bypass prime volume and an improved drainage with all collateral benefits. To limit gravity drainage, we use a two-level heart–lung machine dedicated to pediatric perfusion. The top level of the cardiotomy reservoir is positioned at the patient atrial level, making it possible to downsize the length and diameter of venous and arterial lines. Since 2008, a negative pressure of approximately −30 mmHg has been used for all patients. Initiation of bypass is performed in a classical way with a cardiotomy reservoir open; vacuum is added as soon as the maximal gravity drainage is reached. During bypass, when the blood level in the reservoir decreases to the safety limit level, a small increase in negative pressure is used to improve venous drainage. For weaning from bypass, the negative pressure is gradually decreased to zero, then the reservoir is opened and the venous line progressively closed. Prime volumes were significantly reduced to 100 mL for small neonates, 125 mL for infants, and 175 mL for older children with flow up to 1.5 L/min−1. A low prime volume is expected to improve blood conservation and decrease donor exposure, prevent drawbacks of transfusion (immunomodulation, infection), increase the incidence of blood-free surgery in smaller babies, and decrease whole body systemic inflammation by decreasing surface of foreign material in contact with blood and inflammation associated with blood transfusion. The main drawbacks described have been retrograde flow in the venous line with cerebral air embolus and an increased incidence of gaseous microemboli. These drawbacks are avoidable through appropriate training of perfusionists. When negative pressure is “reasonable,” complications are more theoretical than significant in clinical practice. A technique with a benefit/drawback ratio of 1:0 is utopian, but the advantages of VAVD far outweigh any potential drawbacks when applied properly.

Microbubble Transmission during Cardiotomy Infusion of a Hardshell Venous Reservoir with Integrated Cardiotomy versus a Softshell Venous Reservoir with Separated Cardiotomy: An In Vitro Comparison

An important mechanism for postoperative cognitive impairment after cardiac surgery using cardiopulmonary bypass (CPB) is microemboli. One component of the CPB circuit—the cardiotomy—is a major source of gaseous microemboli because it aspirates significant volumes of air with blood from the operative field and intracardiac chambers. Cardiotomies are either integrated within an open hardshell venous reservoir (IC-HSVR) or are a separate canister attached to a softshell collapsible venous reservoir bag (SC-SSVR). The purpose of this study was to compare the Medtronic IC-HSVR (Affinity NT CVR) with Medtronic’s SC-SSVR (CB 1351, CBMVR 1600) in terms of relative microbubble transmission during cardiotomy infusion. A recirculating in vitro circuit primed with blood was used to compare the two cardiotomy-reservoir systems with the venous reservoir in the SC-SSVR further assessed in a fully closed or partially open state (SC-SSVR-closed; SC-SSVR-open). Microbubbles were detected using a GAMPT BC100 Doppler system in the outflow line of the venous reservoir. Measurements were taken before (baseline) and after aerated prime was pumped into the cardiotomy while altering pump flow rates (3 L/min; 5 L/min) and reservoir prime volumes (400 mL; 900 mL). Infusing cardiotomy blood into the venous reservoir was associated with an increase in microbubbles and bubble volume transmitted by both cardiotomy-reservoir systems with the magnitude rising with reduced prime volumes. The effect was markedly greater with the IC-HSVR. The IC-HSVR also transmitted larger bubbles, particularly with reduced prime volumes. There was no significant difference in microbubble transmission seen between the SC-SSVR-closed and SC-SSVR-open. The SC-SSVR transmits fewer microbubbles than the IC-HSVR during cardiotomy infusion and should be considered as the preferential system. Because both cardiotomy-reservoir systems transmitted microbubbles during cardiotomy infusion, particularly at the lower venous reservoir volume, it is important to use strategies to minimize cardiotomy microbubble infusion.

EComment. The impact of blood conservation on outcomes in adult cardiac surgery

We read with great interest the study by Vandewiele and associates [1]. Many studies have shown the benefits of retrograde autologous priming (RAP) on preserving the patient's haematocrit to levels that do not require transfusion. Only a study by Murphy et al. failed to reproduce similar results in a large cohort of 545 patients [2]. Since our publication in 1998 on retrograde autologous priming [3], we have developed further strategies for blood conservation that have resulted in improved outcomes. Our strategy is three-fold: retrograde autologous priming, low prime volume in the cardiopulmonary bypass (CPB) circuit, and autologous blood donation immediately in the operating room immediately after incision is made. Our preliminary data in the first 300 patients showed a dramatic reduction in the post-operative blood transfusion requirement, with 70% of our patients requiring no blood transfusion at all. In the same time period, our 30-day mortality for all open heart procedures had decreased in an all-time low of 1.38%, and the respiratory complications had dropped from 7% in 2007, to 3% in the end of 2012. This proves that the above three techniques of blood conservation are safe and desirable, leading to reduced morbidity and hospital cost. Conflict of interest: none declared.

Residual anaesthesia drugs in intravenous lines – a silent threat?

Residual anaesthesia drugs in intravenous lines – a silent threat?