Ann Thorac Surg 2000;70:990-992
© 2000 The Society of Thoracic Surgeons
How to do it
A circuit to perform a combined ultrafiltration procedure in pediatric open heart surgery
Gianluca Brancaccio, MDa,
Fabio Miraldi, MDa,
Luigi Tritapepe, MDa,
Massimo Goraccib,
Edvin Prifti, MDa
a Institute of Cardiovascular Surgery, University "La Sapienza", Rome, Italy
b Perfusion Service of Cardiac Surgery, University "La Sapienza", Rome, Italy
Address reprint requests to Dr Brancaccio, II Cattedra di Cardiochirurgia, Istituto di Chirurgia del Cuore e dei Grossi Vasi, Università degli Studi di Roma, "La Sapienza", Policlinico Umberto I, Viale del Policlinico, 155, 00161 Rome, Italy
e-mail: gbrancaccio70{at}hotmail.com
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Abstract
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Cardiopulmonary bypass (CPB) induces an increased capillary permeability and tissues water content due to hemodilution and the inflammatory response, resulting in organ dysfunction. The reduction of the water accumulation and inflammatory response can be achieved by employing ultrafiltration during CPB. Recently we developed a simple CPB circuit for ultrafiltration using the aortic venting tube as an inlet line. Such a technique offers the advantages of performing a combined ultrafiltration procedure and eliminating the danger of air embolism. We employed this circuit in 12 consecutive pediatric patients undergoing open heart surgery.
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Introduction
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Cardiopulmonary bypass (CPB) results in an increased capillary permeability and tissue water content. Hemodilution induced during CPB (priming volume) reduces colloid osmotic pressure. Furthermore, the main consequence of the blood exposure to the oxygenator surface is a significant inflammatory response. These factors may induce a capillary leak syndrome that can lead to tissue edema and multiple organ dysfunction. Reduction of the post-CPB water accumulation can be achieved by employing conventional and modified ultrafiltration [1, 2]. Conventional ultrafiltration is used during the rewarming phase of CPB, and it has been demonstrated that it may contribute to the elimination of proinflammatory cytokines. Modified ultrafiltration [1, 3] (MUF) is employed immediately after the cessation of CPB, significantly reducing water accumulation and improving fluid balance [4].
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Technique
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The CPB circuit consisted in a roller pump (Sarns 7400; Sarns lnc, 3M Health Care, Ann Arbor, MI) and a microporous polypropylene membrane oxygenator (COBE VPCML, COBE Cardiovascular, lnc, Arvada, CO), and it was primed with Normosol pH 7.4, mannitol, sodium bicarbonate, gluconate calcium, packed red blood cells to reach a final hematocrit of 25% to 28% and heparin (2 IU/mL). Myocardial protection during aortic crossclamping was achieved by using crystalloid cardioplegia solution (initially 15 mL/kg, and 7.5 mL/kg after the first administration every 20 minutes) infused into the aortic root. Moderate hypothermia (25°C to 28°C) was employed. Pump flows of 150 mL · kg-1 · min-1 and 120 mL · kg-1 · min-1 were employed for children weighing less than 10 kg and more than 10 kg, respectively. Alpha-stat blood gas management was used, and sodium bicarbonate was administered when necessary. Protamine was administered to neutralize heparin with a ratio of 1:1.
Our circuit design allows the employment of both conventional and modified ultrafiltration simultaneously. A hemofilter (Terumo CXHCO5S; Terumo Corp, Ashitaka, Tokyo, Japan) with a prime volume of 35 mL was employed. The molecular weight cut off was 65.000 daltons. The hemofilter was primed with crystalloid solution and kept isolated during CPB. The circuit consisted in: (1) the inlet (line X) interconnecting the aortic venting tube (Abbocath 14 to 16 gauge) with the hemofilter; (2) the outlet (line Y) interconnecting the venous line with the hemofilter, and 3) two separate lines (A and B) interconnecting the hemofilter with the arterial line and cardiotomy reservoir, respectively (Fig 1). Conventional ultrafiltration was started during the rewarming period, maintaining a minimal level in the venous reservoir. When the line X and Y are clamped, the blood arrives at the hemofilter (line A) because of the pressure gradient between the arterial line and hemofilter, and later is returned at the cardiotomy reservoir (line B) supported by the same pressure gradient. Modified ultrafiltration was initiated immediately after the discontinuation of CPB and was applied for 10 to 20 minutes if the patient was hemodynamically stable. After clamping lines A and B and declamping lines X and Y, ultrafiltration was initiated by venting blood from the line X to the hemofilter, which was later returned to the patient by line Y (Fig 2). The roller pump of the aortic vent was used to accelerate the blood flow through the hemofilter at a rate of 100 to 150 mL/min. A negative pressure of -40 mm Hg was applied at the hemofilter entrance for increasing the transmembrane pressure gradient and modifying the ultrafiltration flow; meanwhile, the pump was maintained at a constant flow rate. When low filling pressures are present, additional volume is added to the venous reservoir through the arterial line. When high filling pressure is present, the arterial pump may be slowed or stopped completely. If complications are present, the extracorporeal circulation can be reinitiated because the CPB circuit always remains fully primed.
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Fig 1. Conventional ultrafiltration. Boldface lines indicate lines A and B, interconnecting the hemofilter with the arterial line and cardiotomy reservoir. The inlet and outlet lines of the hemofilter are clamped, and the flow is direct from the arterial line to the cardiotomy reservoir.
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Fig 2. Modified ultrafiltration. Boldface lines indicate the inlet and outlet lines (X and Y) of the hemofilter. The aortic vent is opened, and aortic pump promotes filtrate reinfusion in the caval cannula (flow inverted). The arterial line is stopped but is unclamped for volume reinfusion.
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Results
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This circuit was employed in 12 consecutive pediatric patients undergoing open heart surgery. Their mean age was 2.33 ± 1.27 years (range, 0.6 to 4 years), mean weight 12.4 ± 4.7 kg (range, 6 to 17.5 kg), and mean body surface area 0.60 ± 0.26 m2. The preoperative diagnoses were ventricular septal defect (6 patients), atrioventricular septal defect (3 patients), and tetralogy of Fallot (3 patients).
Mean CPB time was 119.2 ± 46.4 minutes (range, 45 to 157 minutes) and mean crossclamping time was 97.7 ± 20.3 minutes (range, 70 to 121 minutes). A mean volume of 330 ± 164.8 mL (range, 80 to 500 mL) of ultrafiltration fluid was obtained from the conventional ultrafiltration, and 533.7 ± 278.2 mL (range, 145 to 800 mL) was obtained during modified ultrafiltration. Mean total ultrafiltration volume was 863.7 ± 221.5 mL. At the end of ultrafiltration, the mean hematocrit value increased from 25.5% ± 0.87% to 36.7% ± 3.4%.
All patients showed hemodynamic improvement at the end of the combined ultrafiltration. Mean systolic blood pressure increased from 55.7 ± 14.1 mm Hg (range, 44 to 78 mm Hg) to 105.2 ± 24.7 mm Hg, whereas mean heart rate decreased from 159.7 ± 34.1 beats/min (range, 121 to 205 beats/min) to 129.5 ± 27.2 beats/min (range, 98 to 160 beats/min).
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Comment
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Hemodilution and systemic inflammatory response are the major causes of post-CPB organ dysfunction. Both conventional and modified ultrafiltration have proved to be successful techniques in addition to CPB for improving the postoperative outcome, either by removing proinflammatory cytokines or by hemoconcentration [4]. The simultaneous employment of both techniques has been associated with a combination of the above mentioned advantages [5]. Another important advantage of our circuit is the elimination of air embolism risk during modified ultrafiltration [6], instead of the higher risk of air embolism when the CPB arterial line is used as an inlet line for such a procedure. When the arterial line is used as inlet, the blood is vented retrogradely from the arterial cannula to the hemofilter, but simultaneously the blood is pumped anterogradely in the same line for reinfusing the pump volume to the patient as needed. Thus, once retrograde flow through the arterial line has begun, any antegrade flow into the aorta represents a risk of air embolism. This risk is higher when there is a propensity to produce a negative pressure in the arterial cannula, especially in neonates, because of the possibility that the aortic wall is sucked down towards the aortic cannula, causing obstruction [6]. This results in air cavitation and a risk of air embolism. The present circuit reduces significantly such complications because of the employment of the aortic venting tube as the inlet line, which does not allow blood flow mismatch (antegrade–retrograde) in the aortic cannula and does not produce cavitation for smaller diameters.
In conclusion, the present circuit offers the following advantages: (1) it allows a combined ultrafiltration procedure; (2) it is a simple design; (3) it reduces significantly the risk of air embolism and air cavitation; (4) the extracorporeal circulation can be reinitiated because the CPB circuit always remains fully primed; and (5) it can be used in both pediatric and adult patients
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References
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Naik S.K., Knight A., Elliott M.J. A successful modification of ultrafiltration for cardiopulmonary bypass in children. Perfusion 1991;6:41-50.[Abstract/Free Full Text]
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Journois D., Pouard P., Geeley W.J., Mauriat P., Vouhé P., Safran D. Hemofiltration during cardiopulmonary bypass in pediatric cardiac surgery. Anesthesiology 1994;81:1181-1189.[Medline]
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Naik S.K., Knight A., Elliott M.J. A prospective randomized study of a modified technique of ultrafiltration during pediatric open heart surgery. Circulation 1991;84:422-431.
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Pouard P., Journois D., Greeley W.J. Hemofiltration and pediatric cardiac surgery. In: Greeley W.J., ed. Perioperative management of the patient with congenital heart disease. Baltimore: Williams & Wilkims, 1996:121-131.
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Portela A.F., Pensado A., Sanchez A., Espanol R., Zavanella C. A simple technique to perform combined ultrafiltration. Ann Thorac Surg 1999;67:859-861.[Abstract/Free Full Text]
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Darling E., Nanry K., Shearer I., Kaemmer D., Lawson S. Technique of pediatric modified ultrafiltration. Perfusion 1998;13:93-103.[Abstract/Free Full Text]
Accepted for publication April 4, 2000.
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Abstract
Introduction
