Ann Thorac Surg 1999;67:859-861
© 1999 The Society of Thoracic Surgeons
How To Do It
A simple technique to perform combined ultrafiltration
Francisco A. Portela, MDa,
Alberto Pensado, MDb,
Amelia Sánchez, MDc,
Rita Español, RNd,
Claudio Zavanella, MDa
a Section of Pediatric Cardiac Surgery, Complejo Hospitalario Juan Canalejo, La Coruña, Spain
b Section of Pediatric Anesthesia, Complejo Hospitalario Juan Canalejo, La Coruña, Spain
c Section of Pediatric Intensive Care, Complejo Hospitalario Juan Canalejo, La Coruña, Spain
d Section of Perfusion, Complejo Hospitalario Juan Canalejo, La Coruña, Spain
Accepted for publication July 21, 1998.
Address reprint requests to Dr Zavanella, Pediatric Cardiac Surgery Section, Complejo Hospitalario Juan Canalejo, Materno-Infantil, As Xubias, s/n, 15006 La Coruña, Spain
e-mail: zavanella{at}canalejo.cesga.es
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Abstract
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To combine the advantages of conventional and modified ultrafiltration while keeping cardiopulmonary bypass technique simple, we have developed a simplified circuit of combined ultrafiltration, which is presently used in our pediatric patients. In addition to the benefits of combined ultrafiltration, this circuit allows the rewarming and prevention of heat loss in small children and neonates.
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Introduction
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Conventional ultrafiltration (UF) has been used extensively during cardiopulmonary bypass (CPB) as a means to hemoconcentrate both the priming and the patient’s blood volume [1, 2]. It has also been shown that it may contribute to eliminating proinflammatory cytokines [3, 4]. More recently, Elliot [5] and Andreasson and coworkers [6] have introduced the concept of modified UF (MUF), by which the patient’s blood volume is hemoconcentrated after bypass. Their work has demonstrated the benefits of this technique, which results in improved postoperative hemodynamics, myocardial performance, and oxygenation.
In an effort to increase the benefits of this technology, we have been using a new circuit designed by one of us (F.P.), which allows combined (conventional and modified) UF (CUF) with a simplified technique, conventional UF to remove proinflammatory cytokines during CPB and MUF to increase hematocrit after bypass.
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Technique
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Circuit design
The UF circuit (IDEMSA, Segovia, Spain) (Figs 1, 2) consists of a piece of 
'' tubing (line C) that is inserted between the arterial line (distal to the oxygenator) and the venous reservoir. The position of the ultrafilter is kept constant. A 
'' tubing (line M) runs between the ultrafilter and the cardioplegia heat exchanger. A 3-way stopcock with luer-lock is attached at each end of the line. The ultrafilter consists of glycerin-free polysulfone membrane (Minifilter Plus/Diafilter-20 NR, Minntech Corp, Minneapolis, MN). The patient’s body weight determines the size (0.07 m2 < 7 kg, 0.26 m2 > 7 kg).
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Fig 1. Conventional ultrafiltration circuit, from the arterial cannula through line C ('') toward the venous reservoir. Ultrafiltration starts at the begining of the rewarming period until the end of bypass, while line M remains closed.
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Fig 2. Modified ultrafiltration circuit. At the end of bypass, the stopcock in line M is opened and line C is clamped. The bypass line of the arterial filter is unclamped and the filter excluded from the circuit. During modified ultrafiltration, blood circulates retrograde from the arterial cannula through line M, to the cardioplegia line, which goes to the right atrium. Contraction of the intravascular volume is compensated by slowly replacing blood from the venous reservoir.
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Cardiopulmonary bypass technique
Cardiopulmonary bypass is performed with a membrane oxygenator (COBE VPCML, COBE Cardiovascular, Inc, Arvada, CO) and a standard roller pump. A cardioplegia heat exchanger (CSC 14, Sorin Biomedica, Salugia, Italy) is used to cool down the cardioplegic solution. The extracorporeal circuit is primed with albumin, mannitol, sodium bicarbonate, and Ringer’s lactate solution for a total prime volume of 1,200 to 1,500 mL/m2. Fresh frozen plasma and packed red blood cells are added as needed to reach a final hematocrit of 25%. Heparin (2 IU/mL) is added to the priming solution. Aprotinin (Trasylol, Bayer Corp, Barcelona, Spain) is used in neonates, cyanotic patients, and reoperations. Cold crystalloid cardioplegia (St. Thomas or Roe’s solution) is used.
Combined ultrafiltration technique
Conventional ultrafiltration
Ultrafiltration is started at the begining of the rewarming period at a flow rate of 200 mL · min-1 · m-2, and total CPB flow is increased to compensate for the ultrafilter flow. Fluid level at the venous reservoir is kept constant with a replacement solution, similar to what is commonly used in intensive care units for hemofiltration.
Modified ultrafiltration
After completion of bypass, either central venous pressure or left atrial pressure is monitored and optimized for an adequate hemodynamic response. Line M is purged by opening the stopcock and placing a clamp on line C. This allows blood to flow to the cardioplegia heat exchanger, where it is warmed, and then on to the cardioplegia line, which is purged free of cardioplegic solution. A cannula is connected to the cardioplegia line and introduced into the right atrium. The bypass line of the arterial filter is unclamped and the filter excluded from the circuit. The venous line of the extracorporeal circuit is emptied into the oxygenator’s venous reservoir to be reinfused to the patient. Modified UF is then performed for 10 to 15 minutes to achieve an ultrafiltrate volume of approximately 750 mL/m2. During MUF blood circulates retrograde from the aortic cannula to the cardioplegia line and to a cannula introduced into the right atrium. Contraction of the intravascular volume is compensated by slowly replacing blood from the venous reservoir. Care must be taken not to run the arterial pump faster than the cardioplegia pump to preserve forward flow through the ultrafilter and to avoid forward flow to the aorta through the arterial cannula. When the oxygenator’s content has been returned to the patient, the arterial cannula may be removed, the arterial line of the extracorporeal circuit drained into the reservoir, and then the blood returned to the patient.
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Results
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We have performed this technique in 13 pediatric patients, ranging in weight from 4.8 to 34 kg, with a mean body surface area of 0.61 ± 0.26 m2. A mean volume of 627 ± 342 mL/m2 (range, 285 to 1,266 mL/m2) of ultrafiltrate fluid was obtained during CPB, and 820 ± 321 mL/m2 (range, 344 to 1,333 mL/m2) were obtained during MUF, for a mean combined (total) volume of 1,447 ± 562 mL/m2 (range, 700 to 2,600 mL/m2) of ultrafiltrate. As expected, hematocrit values rose from a mean of 25.4% ± 2.1% at the end of CPB to a mean of 33.6% ± 3.2% after MUF.
All patients showed hemodynamic improvement at the end of MUF. Systolic arterial blood pressure increased from a mean of 72.5 ± 12.9 mm Hg to a mean of 100.33 ± 19.10 mm Hg. Inversely, heart rate decreased from 130.9 ± 19.1 beats per minute to 124 ± 20.9 beats per minute. Central venous pressure remained constant (11.5 ± 3.6 mm Hg), although there was a trend of decreasing central venous pressures while systemic blood pressure rose.
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Comment
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Several reports have demonstrated the benefits of UF in pediatric cardiac surgery with either conventional or modified techniques [5, 7, 8]. Each one is capable, by itself, to produce a certain benefit (removal of proinflammatory cytokines or hemoconcentration), but there are scant reports of the combined use of both techniques [7]. We believe that one of the reasons for this scarcity of information is the use of cumbersome circuits designed for MUF, in which it is necessary to change tubing at one of the pumpheads at the end of bypass. With the idea of combining the benefits of both conventional UF and MUF and at the same time making them easy, we have developed this circuit that eliminates the necessary change of tubing mandatory with the Great Ormond Street Hospital design [5]. As a major heat loss was anticipated during MUF, particularly in neonates, the cardioplegia heat exchanger was incorporated into the circuit to provide the means of rewarming the returned blood and also to simplify the circuit [9].
One area for future developments is the flow rate through the ultrafilter. In the beginning of our study, ultrafilter flow rates were low during and after CPB, because we were concerned with the possibility of low blood levels in the oxygenator. As we gained confidence with this technique, ultrafilter flow rates were increased to our present 1,300 mL · min-1 · m-2 during MUF. As we believe that there is not enough evidence that higher ultrafilter flows can effectively eliminate harmful cytokines from the circulation [7], we plan to test this hypothesis to achieve a more effective and earlier reduction of inflammatory mediators.
In summary, this circuit offers the following advantages: (1) It allows CUF. (2) It is a simple design that is perfusionist-friendly. (3) No extra tubing is added to the CPB circuit. (4) There is no need to change tubing in the pump roller head. (5) Warming is achieved through the cardioplegia heat exchanger. (6) It can be used in adult patients.
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Acknowledgments
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The authors thank the following persons for their contribution and logistical support: Alberto Juffé, MD, PhD, José Quintans, RN, Alicia Figueira, MD, Angela López, MD, Ester Vila, RN, and Concepción Dopazo, RN.
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References
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Darup J., Bleese N., Kalmar G., et al. Hemofiltration during extracorporeal circulation. Thorac Cardiovasc Surg 1979;27:227-230.[Medline]
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Klineberg P.L., Kam C.A., Johnson D.C., et al. Hematocrit and blood volume control during cardiopulmonary bypass with the use of hemofiltration. Anesthesiology 1984;60:478-480.[Medline]
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Journois D., Pouard P., Greeley W., et al. Hemofiltration during cardiopulmonary bypass in pediatric cardiac surgery. Anesthesiology 1994;81:1181-1189.[Medline]
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Hoffmann J.N., Hartl W.H., Depisch R., et al. Effect of hemofiltration on hemodynamics and systemic concentrations of anaphylatoxins and cytokines in human sepsis. Intensive Care Med 1996;22:1360-1367.[Medline]
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Elliott M.J. Ultrafiltration and modified ultrafiltration in pediatric open heart operations. Ann Thorac Surg 1993;56:1518-1522.[Abstract]
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Andreasson S., Gothberg S., Berggren H., et al. Hemofiltration modifies complement activation after extracorporeal circulation in infants. Ann Thorac Surg 1993;56:1515-1517.[Abstract]
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Journois D., Israel-Biet D., Pouard P., et al. High-volume, zero-balanced hemofiltration to reduce delayed inflammatory response to cardiopulmary bypass in children. Anesthesiology 1996;85:965-976.[Medline]
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Draaisma A., Hazekamp M., Frank M., et al. Modified ultrafiltration after cardiopulmonary bypass in pediatric cardiac surgery. Ann Thorac Surg 1997;64:521-525.[Abstract/Free Full Text]
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Groom R., Akl B., Albus R., et al. Alternative method of ultrafiltration after cardiopulmonary bypass. Ann Thorac Surg 1994;58:573-574.[Abstract]
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Abstract
Introduction
