Ann Thorac Surg 1998;66:1835-1836
© 1998 The Society of Thoracic Surgeons
How to Do It
Speed-controlled venovenous modified ultrafiltration for pediatric open heart operations
Ryo Aeba, MDa,
Toru Matayoshi, CPa,
Toshiyuki Katogi, MDa,
Shiaki Kawada, MDa
a Division of Cardiovascular Surgery, Keio University, Tokyo, Japan
Accepted for publication June 13, 1998.
Address reprint requests to Dr Aeba, Division of Cardiovascular Surgery, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160, Japan
e-mail: (aeba{at}mc.med.keio.ac.jp)
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Abstract
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Although modified ultrafiltration after pediatric open heart operations is used by several clinical centers, the risk of complications is a matter of concern. This report describes a simple, reliable, and reproducible technique of speed-controlled venovenous modified ultrafiltration.
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Introduction
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Modified ultrafiltration (MUF) performed just after the discontinuation of cardiopulmonary bypass (CPB) during pediatric open heart operations has become increasingly popular since it was first described by the team in the Hospital for Sick Children in London in 1991 [1, 2]. Modified ultrafiltration has been reported to reduce the amount of body water accumulation, concentrate the circulating blood, and eliminate a variety of low-molecular-weight bioactive mediators such as cytokines and leukocyte elastase [3]. It also has the advantage of delivering oxygenated blood in the pulmonary circulation, thus having the potential to reduce pulmonary vascular resistance. Hemodynamic improvements and reductions in the amount of donor blood required have both been reported previously with the use of MUF [1, 4–6]. In those reports, the entire CPB circuit was left in place during the MUF, and the ultrafilter inlet and outlet were positioned close to the arterial perfusion and the venous drainage cannulas, respectively. The plasma water was then ultrafiltered at a preset negative pressure. At present, the necessity of an additional complicated circuit and the need for careful monitoring of the patient’s intravascular volume and MUF circuit by both the surgeons and perfusionists may be an obstacle to increased use of the procedure. This report describes a simple, reliable, and reproducible technique for MUF, which might overcome several potential complications.
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Technique
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A Minntech Hemocor HPH hemoconcentrator (Minntech Corporation, Minneapolis, MN) with a molecular weight or cut-off point of 68,000 daltons was used for ultrafiltration (Fig 1). The ultrafilter was primed with the prime solution for the CPB circuit. During the rewarming period of the CPB, conventional ultrafiltration was employed, which was positioned in the bypass circuit with the inlet distal to the oxygenator and the outlet positioned in the venous reservoir. A roller pump was used for the ultrafiltration. Ultrafiltration speed was controlled by a second roller pump positioned along the aliquot drainage tube, instead of connecting the ultrafiltration circuit to the vacuum suction or partially clamping the outlet of the ultrafilter.
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Fig 1. The circuit for cardiopulmonary bypass with ultrafiltration. (A) Flow map during cardiopulmonary bypass with conventional ultrafiltration. (B) Flow map during modified ultrafiltration after cardiopulmonary bypass. (CPB = cardiopulmonary bypass; IVC = inferior vena cava; RA = right atrium; SVC = superior vena cava; UF = ultrafiltration.)
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Conventional ultrafiltration was switched to MUF immediately after the discontinuation of CPB, if the patient was judged to be hemodynamically stable. The venous cannula for CPB, which was usually placed through a pursestring suture in the right atrial appendage, was removed, and a double-lumen 11F catheter (Flexxicon; Vas-cath Inc, Mississauga, Ont, Canada) with a trimmed tip was placed so that the tip of the catheter was positioned in the center of the right atrium. Two tubes were primed with the rest of the CPB reservoir fluid and connected to the catheter for blood retrieval and blood return, creating a venovenous MUF circuit. The target volume for the ultrafiltered plasma was determined based on body surface area, using the formula 
where x = the target volume of ultrafiltered plasma (mL), BSA = body surface area (m2), and V = priming volume of CPB (mL). The pump speed was preset to achieve the above volume during the MUF run over a period of 10 to 15 minutes. During the MUF, the remainder of the priming volume of blood in the CPB circuit and reservoir was returned to the patient after being subjected to ultrafiltration. During the MUF, the arterial perfusion cannula was removed.
The blood in both the arterial and venous tubing of the CPB was returned in the same fashion. Modified ultrafiltration was completed either when the CPB reservoir emptied or when the ultrafiltrate volume reached the preset goal. The patient’s volume status was controlled by changing the rate of both the roller pumps for the MUF circuit and the aliquot drainage tube. After the completion of MUF, the MUF catheter in the right atrium was removed and protamine was administered.
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Comment
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We used the technique described here between May 1997 and January 1998, in 46 children with congenital heart disease undergoing open heart operations. Values reported are means ± standard deviation. Statistical analysis of data was performed by paired t test. A p value less than 0.05 was considered significant. The patient population and the operative procedures were heterogeneous, including arterial switch operations, Fontan-type procedures, bidirectional cavopulmonary shunt, and total anomalous pulmonary venous connection repair. No complications during or after the MUF arose, such as suboptimal volume status leading to hypotension or cardiac distention, catheter-induced arrhythmia, or obstruction of the MUF circuit. A marked rise in both the systolic and diastolic arterial blood pressures was observed during the MUF. Specifically, the percent rise in systolic and diastolic blood pressures was 28.8% ± 26.0% (range, -3.0% to 86.7%; p < 0.0001) and 46.2% ± 36.0% (range, 2.1% to 123.3%; p < 0.0001), respectively. The mean right atrial pressure was significantly decreased from 9.6 ± 4.6 mm Hg to 8.4 ± 4.2 mm Hg (p = 0.0015). Modified ultrafiltration achieved a significant degree of hemoconcentration, as demonstrated by an increase in the hematocrit from 25.3% ± 4.1% to 34.3% ± 5.1% (p < 0.0001). These observation are in keeping with previous studies using arteriovenous speed-uncontrolled MUF [1–6]. Control of the rate of MUF with a roller pump offers predictable and reproducible volume management during MUF, in which rapid volume shifts can occur.
Arteriovenous MUF has several potential complications. First, kinking of the arterial cannula may lead to air entrapment, causing air embolism formation in systemic organs. Second, the arterial and venous cannulas must be left in place during the MUF. As a result, the arterial cannula may cause obstruction of the ascending aorta, especially in a small ascending aorta, and the venous cannula may compress the atrial wall, inducing atrial or atrioventricular nodal arrhythmias. Third, the arteriovenous shunt fraction may have a significant impact on hemodynamic status, because the MUF is always initiated immediately after the termination of CPB, when the patient is often in one of the most critical hemodynamic states. Venovenous MUF using a small catheter avoids these potential complications, which may justify the cost of the required catheter and the difficulty and time consumption in restarting CPB in case of hemodynamic instability.
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References
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- Naik S.K., Knight A., Elliott M. A prospective randomized study of a modified technique of ultrafiltration during pediatric open-heart surgery. Circulation 1991;84(Suppl 3):422-431.
- 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]
- Wang M.J., Chiu I.S., Hsu C.M., et al. Efficacy of ultrafiltration in removing inflammatory mediators during pediatric cardiac operations. Ann Thorac Surg 1996;61:651-656.[Abstract/Free Full Text]
- Elliott M.J. Ultrafiltration and modified ultrafiltration in pediatric open heart operations. Ann Thorac Surg 1993;56:1518-1522.[Abstract]
- Draaisma A.M., Hazecamp M.G., Frank M., Anes N., Schoof P.H., Huymans H.A. Modified ultrafiltration after cardiopulmonary bypass in pediatric cardiac surgery. Ann Thorac Surg 1997;64:521-525.[Abstract/Free Full Text]
- Koutlas T.C., Gaynor J.W., Nicolson S.C., Steven J.M., Wernovsky G., Spray T.L. Modified ultrafiltration reduces postoperative morbidity after cavopulmonary connection. Ann Thorac Surg 1997;64:37-43.[Abstract/Free Full Text]
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Abstract
Introduction
