Perfusion for paediatric open-heart surgery

The Capiox RX05 oxygenator: pediatric clinical observations

Terumo Cardiovascular Systems has released the X-Coated™ Capiox® RX05 or Baby RX™ oxygenator. This oxygenator is designed for neonate and infant patient populations. The device was integrated into our current perfusion practice and our clinical observations are described here. The Baby RX™ has a prime volume of 43 mL with a maximum flow of 1.5 L/min. The integrated hardshell venous reservoir has independent venous and cardiotomy filters, as well as a very low minimal operating level of 15 mL. A variety of options provide exceptional versatility for the device. The Baby RX proves to be a low-prime, high-flow oxygenator, enabling us to use it on a wide range of pediatric patients. It will be a useful tool for reducing our neonate and infant circuit priming volumes.

Glucose, sodium and plasma protein levels during deep hypothermic circulatory arrest using a low volume, minimal glucose priming solution based on washed packed red cells

The effect of a low volume, minimal glucose priming solution based on washed packed red cells on glucose, sodium and plasma protein levels during deep hypothermic circulatory arrest (DHCA) was studied in six patients of less than six months of age undergoing repair of congenital heart disease. Glucose levels during DHCA were not significantly different from prebypass values (6.2mmol/l±2.7 vs 7.1 mmol/l±2.8; p = 0.518), whereas plasma protein levels were significantly decreased (51.0g/l±0.7 vs 20.0g/l± 0.3; P = 0.0001) and sodium levels slightly but significantly increased (142mmol/l±3.8 vs 150mmol±3.8; p = 0.0026). In summary, the priming solution used in this study achieved good control of glucose levels during DHCA, although it needs some modification in regard to sodium and plasma protein content. A discussion of the choice of priming solution and a hypothesis for potential calcium-mediated reperfusion injury are also presented.

Clinical experience with Affinity Pixie oxygenation system in paediatric and infant patients

INTRODUCTION

Great Ormond Street Children's Hospital undertakes over 500 open heart cardiothoracic procedures requiring cardiopulmonary bypass per year. Data from our centre show that many of our neonatal/paediatric patients require higher cardiac indexes than previously thought. We evaluated the new Pixie oxygenation system, rated from 0.1 L/min to 2 L/min, to determine if it could be used for these patients.

METHODS

Between 2010 and 2012, 250 Pixie oxygenators were used on consecutive patients requiring correction of congenital cardiac defects. Data were collected on FiO2 requirements, oxygenator pressure drop and gaseous microemboli handling. Retrospective analysis was also undertaken on the procedures and demographics of all patients during 2011-2012 to determine the percentage of patients on whom the Pixie could be used.

RESULTS

Analysis of the procedures undertaken at Great Ormond Street Hospital (GOSH) showed that 89% were in patients under 20 kg, requiring a flow rate of <2 L/min (at a base cardiac index of 2.8 L/min/m2). The maximum FiO2 required at 2.5 L/min was 85%. Gaseous microemboli were reduced by 82.5±9.9% and bubble volume was decreased by 94.3±8.4% from the 'venous' pre-oxygenator to the 'arterial' post-oxygenator.

DISCUSSION

The Pixie oxygenator proved effective at flows up to 2.5 L/min, with air-handling capabilities comparable with other oxygenators. This represents a single oxygenator that could potentially be used to cover 89% of our surgical procedures. However, we believe that, for the smallest patients (i.e., < 2 kg), a smaller priming oxygenator should be used in order to limit unnecessary haemodilution in this vulnerable group.

A successful modification of ultrafiltration for cardiopulmonary bypass in children

Total body water (TBW) is increased after cardiopulmonary bypass (CPB) resulting in tissue oedema and organ dysfunction. Ultrafiltration has been used to reduce this accumulation of water, although conventional ultrafiltration seemed ineffective in reducing the rise in TBW after CPB in our clinical experience. We describe a modified technique in which ultrafiltration is performed in the first 10 minutes after the patient is weaned from bypass, returning nearly all the blood in the circuit to the patient and elevating the haematocrit (Hct) to any predetermined level. We carried out a pilot study on 21 children aged 4-144 months undergoing open-heart surgery and CPB for congenital heart defects. They were divided into three comparable groups: (1) controls (n = 6); (2) conventional ultrafiltration (n = 7); and (3) modified ultrafiltration (n = 8). TBW (bio-impedance), Hct, osmolality, mean corpuscular volume and mean corpuscular haemoglobin concentration were recorded at frequent intervals. Control patients showed elevation of TBW by 18.2% median (range 14.5-20.3), conventional ultrafiltration by 12.4% (7.9-15.0), modified ultrafiltration by 5.7% (4.5-7.1) (p less than 0.0001 compared to controls, p. less than 0.005 compared to conventional ultrafiltration, Mann-Whitney U test). Hct could be elevated to preoperative levels only by the modified method. Mean corpuscular volume, and mean corpuscular haemoglobin concentration osmolality were unaltered. Ultrafiltration by the modified method was more effective than conventional ultrafiltration in reducing the rise in TBW and elevating Hct after CPB.

Effects of pronounced haemodilution on the plasma protein binding of lidocaine

The effects of pronounced haemodilution on the protein binding of lidocaine was investigated in vitro in plasma from five healthy adult volunteers. The plasma was diluted with a phosphate buffer to reach a plasma protein concentration normally seen during paediatric cardiopulmonary bypass (CPB) and protein binding was determined at a low (1.5 micrograms/ml) and a moderate (4 micrograms/ml) total plasma concentration of lidocaine. The effects of different haematocrits on plasma protein binding was also determined over the haematocrit range 20-60%. The binding of lidocaine was found to be inversely related to the degree of dilution, i.e. the free fraction increased significantly with increasing dilution (p < 0.0001). Furthermore, the binding was dependent on the total plasma concentration of lidocaine, since a significantly higher percentage of free drug was found at the higher total lidocaine level (4 micrograms/ml) compared with the lower level (1.5 micrograms/ml) (p < 0.05). No significant difference in the free fraction of lidocaine could be found over the studied haematocrit range. The results of the present study indicate that plasma protein levels commonly associated with CPB in neonates and infants are associated with a significant increase in the free, unbound and pharmacologically active fraction of lidocaine compared with normal conditions. The use of commonly recommended dosages of lidocaine might result in toxic-free concentration in this setting.

Decreased postoperative drainage with addition of epsilon-aminocaproic acid before cardiopulmonary bypass

Desmopressin (DDAVP, 0.3 microgram/kg) has been used routinely after cardiopulmonary bypass, particularly in patients having antiplatelet therapy. Recently epsilon-aminocaproic acid (single dose of 5 g) given before cardiopulmonary bypass has been added to the protocol. One hundred consecutive patients taking desmopressin and epsilon-aminocaproic acid (group A) and another 100 taking desmopressin alone (group B) were analyzed. There was no difference among these two groups in patient age, sex, preoperative history of bleeding and drug consumption, or number of patients for elective, urgent, emergent, redo, and reoperation for bleeding. Results of routine preoperative coagulation studies were within normal limits in both groups. Preoperative hemoglobin level was 13.5 g/dL in group A and 13.8 g/dL in group B (p = 0.12). Estimated blood loss in the operating room was 513 mL for group A and 587 mL for group B (p = 0.07). The total chest drainage at the end of 24 hours was 492 mL in group A and 746 mL in group B (p = 0.0001). Amicar given before cardiopulmonary bypass does not lessen operating room blood loss, but significantly decreases postoperative chest drainage. Group B patients received more fresh frozen plasma (60 U versus 4 U), more platelets (130 U versus 16 U), and more cryoprecipitate (118 U versus 10 U) than group A patients. Adding epsilon-aminocaproic acid could save $206.18 in blood product use per patient, compared with the expense of $24.12 per patient for E-aminocaproic acid administration.

Conventional cardiopulmonary bypass in neonates. A physiological approach--10 years of experience at Marie-Lannelongue Hospital

There is still controversy about the optimal method of venoarterial cardiopulmonary bypass (CPB) for correction of congenital heart disease in neonates and young infants. High rates of CPB-related morbidity and mortality are still reported. Since 1980, conventional CPB with double caval cannulation with right-angled cannulae has been used in the high majority of neonates at Marie-Lannelongue Hospital. The extracorporeal circuit was miniaturized to be primed with a volume as small as possible. Priming (500 ml) was done with packed red cells and fresh frozen plasma. CPB was conducted at 30% haematocrit and normal ranges of flow rate, arterial pressure, systemic vascular resistances and oxygen delivery. These normal physiological parameters were also maintained during hypothermia. During the last two years, 151 neonates below 15 days old who underwent open-heart surgery were reviewed. The overall hospital mortality was 7.24%. None of the survivors had postoperative complications related to CPB. All physiological and biological values remained within normal ranges during the postoperative course.

Perioperative approaches to coagulation defects

Cardiac surgical procedures are known to be associated with coagulation defects and disordered hemostasis. Excessive perioperative and postoperative bleeding and the need for considerable volumes of blood and blood product transfusions are well recognized. The risks of blood transfusion with high donor-exposure levels have focused attention on blood conservation as a priority in reducing the complications of cardiac operations. Hemostatic defects may be related to patient-inherent coagulopathies, preexisting associated pathology, and preoperative drug therapy. In addition, hemostatic defects are induced during the operation itself. Two principal therapeutic approaches to this complex problem have evolved. Although different, these approaches are not mutually exclusive and may be used complementarily. The first is autotransfusion and the second is hemostatic drug therapy. Although many drugs have been tried, including antifibrinolytic agents (epsilon-aminocaproic acid, tranexamic acid), platelet-preserving agents (prostacyclin, dipyridamole), and desmopressin, the only drug that has shown significant and consistent efficacy in reducing bleeding in cardiac surgery patients is the serine protease inhibitor aprotinin. Aprotinin has been shown to be highly effective in reducing blood loss and blood and blood product transfusion requirements in high-risk patients. Clinical experience with aprotinin therapy in cardiac patients and specific issues such as dosage regimens and the target automated clotting time levels in patients on high-dose aprotinin therapy are outlined. Indications for the use of aprotinin and the balance between risk and benefit are discussed.

Aprotinin therapy in cardiac operations: a report on use in 41 cardiac centers in the United Kingdom

Aprotinin, a serine protease inhibitor, has recently been shown to reduce blood loss in cardiac surgical patients. Data on the safety and efficacy of aprotinin therapy administered to 671 cardiac surgical patients in 41 United Kingdom cardiac surgical units have been submitted to interim analysis. The patients studied were in high-risk categories for excessive bleeding, including 457 redo operations and 79 patients with active infective endocarditis. Overall mortality was 12% in redo cases and 5.1% in first-time operations. Adverse events were reported in only 20 patients (3%). Median blood loss at 24 hours after operation was 400 mL, and median transfusion volume throughout the operative and postoperative period was 2 units. These data confirm that the use of aprotinin therapy in high-risk cardiac surgical patients is associated with a low incidence of adverse events.