Low extracorporeal priming volumes for infants: a benefit?

Blood Conservation and Hemostasis Management in Pediatric Cardiac Surgery

Pediatric cardiac surgery is associated with significant perioperative blood loss needing blood product transfusion. Transfusion carries serious risks and implications on clinical outcomes in this vulnerable population. The need for transfusion is higher in children and is attributed to several factors including immaturity of the hemostatic system, hemodilution from the CPB circuit, excessive activation of the hemostatic system, and preoperative anticoagulant drugs. Other patient characteristics such as smaller relative size of the patient, higher metabolic and oxygen requirements make successful blood transfusion management extremely challenging in this population and require meticulous planning and multidisciplinary teamwork. In this narrative review we aim to summarize risks and complications associated with blood transfusion in pediatric cardiac surgery and also to summarize perioperative coagulation management and blood conservation strategies.

Patient Blood Management in Pediatric Cardiac Surgery: A Review

Efforts to reduce blood product transfusions and adopt blood conservation strategies for infants and children undergoing cardiac surgical procedures are ongoing. Children typically receive red blood cell and coagulant blood products perioperatively for many reasons, including developmental alterations of their hemostatic system, and hemodilution and hypothermia with cardiopulmonary bypass that incites inflammation and coagulopathy and requires systemic anticoagulation. The complexity of their surgical procedures, complex cardiopulmonary interactions, and risk for inadequate oxygen delivery and postoperative bleeding further contribute to blood product utilization in this vulnerable population. Despite these challenges, safe conservative blood management practices spanning the pre-, intra-, and postoperative periods are being developed and are associated with reduced blood product transfusions. This review summarizes the available evidence regarding anemia management and blood transfusion practices in the perioperative care of these critically ill children. The evidence suggests that adoption of a comprehensive blood management approach decreases blood transfusions, but the impact on clinical outcomes is less well studied and represents an area that deserves further investigation.

Functional Performance of Different Venous Limb Options in Simulated Neonatal/Pediatric Cardiopulmonary Bypass Circuits

OBJECTIVE

Hemodilution is a concern in cardiopulmonary bypass (CPB). Using a smaller dual tubing rather than a single larger inner diameter (ID) tubing in the venous limb to decrease prime volume has been a standard practice. The purpose of this study is to evaluate these tubing options.

METHODS

Four different CPB circuits primed with blood (hematocrit 30%) were investigated. Two setups were used with two circuits for each one. In Setup I, a neonatal oxygenator was connected to dual 3/16" ID venous limbs (Circuit A) or to a single 1/4" ID venous limb (Circuit B); and in Setup II, a pediatric oxygenator was connected to dual 1/4" ID venous limbs (Circuit C) or a single 3/8" ID venous limb (Circuit D). Trials were conducted at arterial flow rates of 500 ml/min up to 1500 ml/min (Setup I) and up to 3000 ml/min (Setup II), at 36°C and 28°C.

RESULTS

Circuit B exhibited a higher venous flow rate than Circuit A, and Circuit D exhibited a higher venous flow rate than Circuit C, at both temperatures. Flow resistance was significantly higher in Circuits A and C than in Circuits B (P<0.001) and D (P<0.001), respectively.

CONCLUSION

A single 1/4" venous limb is better than dual 3/16" venous limbs at all flow rates, up to 1500 ml/min. Moreover, a single 3/8" venous limb is better than dual 1/4" venous limbs, up to 3000 ml/min. Our findings strongly suggest a revision of perfusion practice to include single venous limb circuits for CPB.

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.

Evaluation of different paediatric venous cannulae using gravity drainage and VAVD: an in vitro study

Six different commercially available paediatric venous cannulae, together with a specially constructed cannula, were tested in vitro for their pressure-flow relationship. With the cannulae placed in an open reservoir, flow increased with larger diameters and higher pressures. At a pressure of 30 cm H2O, flows were 219± 20, 285± 13, 422± 11 and 728± 4 ml/min for the 12, 13.2, 14 and 16 French, respectively. No differences were found between angled and straight cannulae. When the cannulae were tested in a latex model simulating the right atrium and vena cavae, the highest flow obtained by gravity was 164 ml/min using an angled 14-French cannula. When vacuum was applied to augment venous return, a maximum flow of 179 ml/min was measured using an angled 14-French cannula. Collapse can occur when the pressure difference becomes too high in the test system. This is important, since most children are selectively cannulated in both major veins. Monitoring of the intravascular pressure might help to prevent collapse. A larger-diameter venous cannula does not always produce the highest flow when placed in a vein. This is most obvious when augmenting venous return. The design of the cannula tip, in combination with VAVD, can affect the venous return.

Using a Miniaturized Circuit and an Asanguineous Prime to Reduce Neutrophil-Mediated Organ Dysfunction Following Infant Cardiopulmonary Bypass

BACKGROUND

Contemporary infant cardiopulmonary bypass circuits require a blood prime. Blood, especially when stored, generates an inflammatory response, and may contribute to organ dysfunction following cardiopulmonary bypass. We determined whether using a miniaturized circuit and an asanguineous prime attenuated the post-bypass inflammatory response, and improved right ventricular and pulmonary function.

METHODS

Sixteen infant piglets were placed into 3 groups based on prime components: group I (fresh blood), group II (stored blood), and group III (miniaturized circuit and asanguineous prime). Piglets were placed on cardiopulmonary bypass (100 mL.kg(-1).min(-1)), cooled to 18 degrees C, and underwent continuous perfusion (50 mL.kg(-1).min(-1)) for 30 minutes. They were rewarmed and separated from bypass. Serum tumor necrosis factor-alpha, right ventricular function, and pulmonary function were measured before and 30 minutes after bypass. Neutrophil priming activity in fresh and stored donor blood was also assessed.

RESULTS

Animals in group III had significantly improved cardiopulmonary function than the groups receiving blood (right ventricular cardiac index [mL.kg(-1).min(-1)]: group I [18.8 +/- 4.8], group II [21.5 +/- 6.2], and group III [81.2 +/- 11.4], p < 0.001; and pulmonary vascular resistance index [dynes.mL(-1).kg(-1)]: group I [1169 +/- 409], group II [1610 +/- 486], and group III [214 +/- 63], p = 0.03). Tumor necrosis factor-alpha (pg.mL(-1)) was lower in group III (1465 +/- 39) than in the groups receiving blood (3940 +/- 777), p = 0.002. Neutrophil priming activity (nmol.min(-1)) was also higher in stored blood (3.7 +/- 6) than in fresh blood (1.9 +/- 0.2), p = 0.02.

CONCLUSIONS

We have devised a unique miniaturized circuit that allows an asanguineous prime without hemodilution in an infant swine model. The employment of this circuit attenuates the post-bypass inflammatory response and has salutary effects on cardiopulmonary function.

MAST system: a new condensed cardiopulmonary bypass circuit for adult cardiac surgery

There have been many refinements in cardiopulmonary bypass (CPB) techniques over the past few decades specific to design, materials and function. Despite these improvements, use of the standard length circuit tubing and pump oxygenator alter cellular, biochemical and rheological properties by inducing a systemic inflammatory response, persisting well into the early postoperative phase. We have designed a new condensed CPB circuit, the MAST system, where the oxygenator and the pumps are brought closer to the operating table (within 30 inches) with the help of a series of telescopic swivel steel poles to which they are attached. The control console is retained at the usual remote location of 2ft behind the MAST system. This configuration accomplishes a decrease in tubing length, priming volume and blood circulatory time within the extracorporeal circuit. Early experience of a hundred consecutive cases utilizing the MAST CPB system is presented along with a comparative analysis of prime volume, hemodilution and transfusion parameters of MAST system vs the low prime system, which is another newly developed CPB circuit utilizing a pediatric oxygenator to reduce prime volume and hemodilution.

Clinical application of vacuum-assisted cardiopulmonary bypass with a pressure relief valve

OBJECTIVES

Hemodilution induced by cardiopulmonary bypass (CPB) often prevents open heart operations without blood transfusion because of a large CPB-priming volume. A vacuum-assisted venous drainage system appears to overcome this problem and our previous experimental study demonstrated the beneficial effect of a vacuum-assisted CPB with a pressure relief valve. In this study, we clinically applied this novel system, and evaluated its efficacy by comparing it with the results of a conventional siphon-dependent drainage system.

METHODS

Sixty patients undergoing open heart operation were divided into Group V (vacuum-assisted system, n=30) and Group S (siphon-dependent system, n=30). The vacuum-assisted system contains a powerful vacuum generator and a pressure relief valve to keep the negative pressure in the reservoir constant when the blood suction is used.

RESULTS

The CPB-priming volume was significantly smaller in Group V (V vs. S: 1071+/-88 vs. 1405+/-137 ml; P<0.01), resulting in the lower hemodilution in Group V evidenced by the minimum hemoglobin level (V vs. S: 6.83+/-1.06 vs. 5.78+/-0.79 mg/dl; P<0.01) and blood transfusion rate (V vs. S: 9 vs. 20%; P<0.01). There were no significant differences in the plasma free hemoglobin level and the reduction ratio of plasma haptoglobin between the groups.

CONCLUSIONS

These data demonstrate that this vacuum-assisted CPB can provide simplification of the CPB circuit, resulting in a smaller CPB-priming volume and lower hemodilution. This vacuum-assisted CPB may attenuate the negative effect of CPB by minimizing hemodilution and appears to be a useful modification to accomplish no blood-requiring open heart operations.

Impact of modifying priming components and fluid administration using miniaturized circuitry in neonatal cardiopulmonary bypass

Following a succession of changes in circuitry and priming additives between 1993 and 1998, a comprehensive re-evaluation of neonatal cardiopulmonary bypass (CPB) practice was undertaken. Samples from 10 infants (Group 1) undergoing CPB were evaluated for osmolality, oncotic pressure, total protein, hematocrit, glucose, and electrolytes (Na+, K+, iCa2+). These samples were tested at six measurement points: (1) after priming, (2) patient pre-CPB, (3) CPB-start, (4) CPB-mid, (5) CPB-end, and (6) post-modified ultrafiltration (MUF). Prime volumes were also carefully measured as well as the type and amount of volume given during CPB. After evaluating the initial data, changes in protocol regarding mannitol, calcium correction, and oncotic strength on CPB were made. Following implementation of these protocol changes, a second set (Group 2) of 10 infants was identically evaluated. Group 1 prime osmolality was 379 +/- 44 mOsm/kg, while Group 2 prime osmolality was 324 +/- 14 mOsm/kg (p = 0.003). There were no differences in osmolality between groups during bypass and osmolality was unaffected by modified ultrafiltration. Ionized calcium levels were significantly different at the end of bypass between Group 1, 0.6 +/- 0.1 mmol/l; and Group 2, 1.17 +/- 0.24 mmol/l (p < 0.001). In Group 1, there was a 40% drop (p = 0.001) in colloid osmotic pressure (COP) levels from pre-CPB (13.3 +/- 3.4 mmHg) to CPB-end (8.8 +/- 1.2 mmHg). In Group 2, there were no differences in COP during CPB. COP levels of Group 1 and Group 2 at CPB-end were 8.8 +/- 1.2 mmHg and 14 +/- 1.9, respectively (p < 0.0001). Total volume addition during bypass for Group 1 was 363.5 +/- 148.7 ml and for Group 2 was 245.1 +/- 92.2 ml (p < 0.05). In conclusion, progressive changes in neonatal circuits and techniques can have potentially wide-ranging effects on electrolyte and osmotic/oncotic homeostasis. An audit of perfusion management through expanded laboratory tests is recommended, especially in periods of change.

Affinity pump system: a new peristaltic blood pump for cardiopulmonary bypass

An in vitro study has been carried out to assess the pump performance of a new peristaltic, extracorporeal displacement pump (Affinity) for cardiopulmonary bypass. The pump system consists of a pump rotor (0-110 rpm), a pump chamber, a venous reservoir with a 5/8" connecting tube and the Affinity console. The polyurethane chamber is connected to the venous reservoir by a 5/8" tube and fills passively due to the hydrostatic pressure exhibited by the fluid height in the venous reservoir. The implementation of an occlusive segment in the pump chamber, which collapses in low filling states, should prevent significant negative pressures. An in vitro circuit was filled with bovine blood (37 degrees C, hematocrit 35%) and the pump flow was measured by an ultrasonic transit time flow probe with respect to pre-load, diameter and length of attached tubing in the venous line, pump speed (rpm) and size of the connecting tube (3/8" and 5/8"). At 108 rpm and a preload equal to 10 mmHg, the flow was 8.6 +/- 0.42 l/min for an afterload of 80 mmHg. The reduction of the inlet connector to 3/8" diminished the pump flow significantly to 5.2 +/- 0.31 l/min (p < 0.0001). The pump flow decreased linearly with respect to the length of the attached tube in the venous line and for a 2 m long 5/8" silicon tube, the rpm-optimized flow was still 6.0 +/- 0.28 l/min at a preload of 10 mmHg. In case of low filling state or too high rpm, the occlusive segment collapsed and no cavitation bubbles could be detected. Our in vitro measurements yield a nomogram for rpm-optimized blood flow with respect to the pre-load in the venous reservoir. The delivered 5/8"connecting tube facilitates optimum filling of the pump chamber for high blood flow, but limits the use of venous reservoirs to Affinity products. The pump yields a high blood flow even when long tubing in the venous line is used. This makes the pump a candidate for a ventricular assist device. In hypovolemia or high rpm, the occlusive segment collapses and no negative pressure is generated at the inflow site of the pump chamber.

Impact of a remote pump head on neonatal priming volumes

Reduction of priming volumes of the cardiopulmonary bypass (CPB) circuit in neonatal cardiac surgery to decrease haemodilution and blood transfusion requirements can be achieved with the use of neonatal low prime oxygenators and smaller diameter tubing. We have further reduced our prime volume with the use of a custom-designed arm allowing for remote positioning of a double-headed roller pump. This arm enables the double pump to be placed alongside the main heart-lung machine close to the operating table, and to position the pump inlet and outlet tubing immediately at the reservoir outlet and oxygenator inlet, respectively, therefore reducing tubing lengths. Priming volumes of four cases using this configuration were compared to four cases using our standard neonatal bypass setup. Results showed a 29% decrease in priming volume and a 58% reduction in blood utilization during CPB. This reduction in priming volume is clinically significant as it lowers the ratio of priming volume to patient blood volume and reduces homologous blood requirements.

A minimal priming technique that allows for a higher circulating hemoglobin on cardiopulmonary bypass

Reduction in circuit prime during cardiopulmonary bypass has benefits for the patient with a low body surface area, anemia, patient refusal to receive blood products, and aids the practitioner's goal to minimize exposure to blood products. Described here is a simple, low-cost technique that has been shown to decrease priming volume in any bypass circuit and allow a significant increase in 'on bypass hemoglobin'.

Can an oxygenator design potentially contribute to air embolism in cardiopulmonary bypass? A novel method for the determination of the air removal capabilities of neonatal membrane oxygenators

At present, air handling of a membrane oxygenator is generally studied by using an ultrasonic sound bubble counter. However, this is not a quantitative method and it does not give any information on where air was entrapped in the oxygenator and if it eventually was removed through the membrane for gas exchange. The study presented here gives a novel technique for the determination of the air-handling characteristics of a membrane oxygenator. The study aimed at defining not only the amount of air released by the oxygenator, but also the amount of air trapped within the oxygenator and/or removed through the gas exchange membrane. Two neonatal membrane oxygenators without the use of an arterial filter were investigated: the Polystan Microsafe and the Dideco Lilliput. Although the air trap function of both oxygenators when challenged with a bolus of air was similar, the Microsafe obtained this effect mainly by capturing the air in the heat exchanger compartment while the Lilliput did remove a large amount of air through the membrane. In conclusion, the difference in trap function was most striking during continuous infusion of air. Immediate contact with a microporous membrane, avoidance of high velocities within the oxygenator, pressure drop, transit time and construction of the fibre mat all contribute to the air-handling characteristics of a membrane oxygenator.

A novel technique for cardiopulmonary bypass using vacuum system for venous drainage with pressure relief valve: an experimental study

To decrease the circuit priming volume, develop safety, and simplify the equipment, a cardiopulmonary bypass (CPB) circuit using a vacuum suction venous drainage system with a pressure relief valve was developed. The efficacy of this vacuum system was compared to that of a conventional siphon system. The system contains a powerful vacuum generator and a pressure relief valve to keep the negative pressure constant when blood suction is used. Using 8 mongrel dogs, the feasibility and the efficacy of this CPB system was tested. The changes in the negative pressure in the reservoir were within 5 mm Hg whether the suction lines were switched on or off. In all animals the amount of blood in the venous reservoir was stable throughout bypass. The decrease of priming volume was from 725 ml (siphon system) to 250 ml (vacuum system). At the end of CPB, the levels of hemoglobin in the vacuum system were significantly higher than those in the siphon system. These results demonstrated that this vacuum drainage system can provide simplification and a miniaturization of the cardiopulmonary bypass circuit resulting in low hemodilution during CPB.