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Ann Thorac Surg 1998;66:821-828
© 1998 The Society of Thoracic Surgeons


Original articles: Cardiovascular

Effect of modified ultrafiltration in high-risk patients undergoing operations for congenital heart disease1

Ko Bando, MDa, Mark W. Turrentine, MDa, Palaniswamy Vijay, PhDa, Thomas G. Sharp, MDa, Yasuo Sekine, MDa, Brian J. Lalone, CCPa, Laszlo Szekely, MDa, John W. Brown, MDa

a Section of Cardiothoracic Surgery, James W. Riley Hospital for Children and Indiana University Medical Center, Indianapolis, Indiana, USA

Address reprint requests to Dr Bando, Section of Cardiothoracic Surgery, Indiana University Medical Center, 545 Barnhill Dr, EM 215, Indianapolis, IN 46202-5123

Presented at the Thirty-fourth Annual Meeting of The Society of Thoracic Surgeons, New Orleans, LA, Jan 26–28, 1998.


    Abstract
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 
Background. Modified ultrafiltration (MUF) after cardiopulmonary bypass (CPB) in children decreases body water, removes inflammatory mediators, improves hemodynamics, and decreases transfusion requirements. The optimal target population for MUF needs to be defined. This prospective, randomized study attempted to identify the best candidates for MUF during operations for congenital heart disease.

Methods. Informed consent was obtained from 100 consecutive patients with complex congenital heart disease undergoing operations with CPB. They were randomized into a control group (n = 50) of conventional ultrafiltration during bypass and an experimental group using dilutional ultrafiltration during bypass and venovenous modified ultrafiltration after bypass (MUF group, n = 50). Postoperative arterial oxygenation, duration of ventilatory support, transfusion requirements, hematocrit, chest tube output, and time to chest tube removal were compared between the groups stratified by age and weight, CPB technique, existence of preoperative pulmonary hypertension, and diagnosis.

Results. There were no MUF-related complications. In patients with preoperative pulmonary hypertension, MUF significantly improved postoperative oxygenation (445 ± 129 mm Hg versus control: 307 ± 113 mm Hg, p = 0.002), shortened ventilatory support (42.9 ± 29.5 hours versus control: 162.4 ± 131.2 hours, p = 0.0005), decreased blood transfusion (red blood cells: 16.2 ± 18.2 mL/kg versus control: 41.4 ± 27.8 mL/kg, p = 0.01; coagulation factors: 5.3. ± 6.9 mL/kg versus control: 32.3 ± 15.5 mL/kg, p = 0.01), and led to earlier chest tube removal. In neonates (<=30 days), MUF significantly reduced transfusion of coagulation factors (5.4 ± 5.0 mL/kg versus control: 39.9 ± 25.8 mL/kg, p = 0.007), and duration of ventilatory support (59.3 ± 36.2 hours versus 242.1 ± 143.1 hours, p = 0.0009). In patients with prolonged CPB (>120 minutes), MUF significantly reduced the duration of ventilatory support (44.7 ± 37.0 hours versus 128.7 ± 133.4 hours, p = 0.002). No significant differences were observed between MUF and control patients for any parameter in the presence of ventricular septal defect without pulmonary hypertension, tetralogy of Fallot, or aortic stenosis.

Conclusions. Modified ultrafiltration after CPB is safe and decreases the need for homologous blood transfusion, the duration of ventilatory support, and chest tube placement in selected patients with complex congenital heart disease. The optimal use of MUF includes patients with preoperative pulmonary hypertension, neonates, and patients who require prolonged CPB.


    Introduction
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 
A number of adverse effects are associated with the use of cardiopulmonary bypass (CPB) in children [1, 2]. There is an increase in capillary permeability that leads to an overall increase in total body water and edema formation [3]. Pulmonary compliance and gas transfer are decreased and myocardial edema may result in diastolic dysfunction.

Conventional efforts to reduce the detrimental effects of capillary leak syndrome after CPB include reducing circuit volumes, optimizing bypass techniques, various antiinflammatory therapies, postoperative diuresis, and peritoneal dialysis. In 1991, Naik and associates [4] from the Hospital for Sick Children at Great Ormond Street developed the technique of modified ultrafiltration (MUF) as an alternative method to reduce the adverse effects of CPB in pediatric patients.

Early studies with MUF demonstrated decreases in the accumulation of total body water after CPB, reduced perioperative blood loss, and decreased blood use [5]. Later studies demonstrated improvements in systolic myocardial function [6] and cerebral oxygenation after circulatory arrest [7]. Furthermore, our recent study indicated that MUF reduces endothelin-1 and the pulmonary/systemic pressure ratio after CPB and thus may become an important adjunct for prevention of postoperative pulmonary hypertension (PH) after operations for congenital heart disease [8].

Although these improvements have been shown to be related to the ability of MUF to remove excess water and low molecular weight inflammatory mediators from the patients, the optimal target population for MUF needs to be defined. This prospective, randomized study attempted to identify those patients who benefited most from MUF during operations for congenital heart disease.


    Patients and methods
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 
One hundred children with complex congenital heart disease who were undergoing operations with the use of CPB at Riley Hospital for Children between September 1996 and March 1997 were included in this study. The study protocol was approved by the Institutional Review Board of the Indiana University School of Medicine. Informed consent was obtained from the parents of each child.

Patient groups
Using a random number table, we assigned 100 patients to one of two groups as follows: control group (n = 50) undergoing conventional ultrafiltration during CPB and experimental group (n = 50) having dilutional ultrafiltration during CPB and modified ultrafiltration (MUF) after CPB (MUF group). The preoperative diagnoses and patient characteristics for each group are depicted in Tables 1 and 2. Except for weight, no significant differences were observed between the groups with respect to diagnoses and demographics.


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Table 1. Preoperative Diagnosis

 

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Table 2. Patient Demographics

 
Preoperative evaluation
Preoperative evaluation was performed by cardiac catheterization in all patients with ventricular septal defect (VSD), complete atrioventricular canal, patients with truncus arteriosus, and 1 patient with transposition of the great arteries (TGA) and ventricular septal defect, and by echocardiography in all patients with total anomalous pulmonary venous connection, patients with TGA and intact ventricular septum, 1 patient with TGA + VSD, and 3 patients with hypoplastic left heart syndrome. Preoperative PH was defined as a systolic pulmonary/systemic arterial pressure ratio >60% by catheterization. The 9 patients not catheterized had systemic or supersystemic pulmonary arterial pressure as estimated by echocardiography.

Operative management
Operative management was standardized during the time frame of this study. Cannulation was accomplished by use of the ascending aorta for inflow and separate caval cannulas were inserted through the right atrial appendage, superior vena cava, or both. After 300 U/kg of heparin was infused, CPB was instituted at a flow rate of 2.4 L · min-1 · m-2, and the perfusate was cooled to 25° to 28°C in 75% of patients (moderate hypothermia group). In patients with TGA with or without VSD, total anomalous pulmonary venous connection, the perfusate was cooled to 20°C and repair was performed with low flow (0.5 to 0.8 L · min-1 · m-2) (see Table 2; deep hypothermia group). For patients with total anomalous pulmonary venous connection (1 patient) and hypoplastic left heart syndrome (3 patients) requiring circulatory arrest, a single venous cannula was used and the repair was performed after the perfusate was cooled to 15°C and maintained for 15 minutes. The left side of the heart was vented with a catheter inserted through the apex of the left ventricle or the left atrial appendage. The pump prime consisted of an electrolyte solution (PlasmaLyte-A, Baxter Healthcare Corp, Chicago, IL) 400 to 900 mL, sodium bicarbonate 20 to 30 mEq, albumin 25% (12.5 g/250 mL of prime, to a final concentration of 5%) and washed packed red blood cells sufficient to maintain a hematocrit value of 14% to 18%. Ascorbic acid, 1 g/10 kg, and methylprednisolone sodium 30 mg/kg were added to the prime at the initiation of bypass. Arterial partial pressure of carbon dioxide was managed by the {alpha} stat method and NaHCO3 was added when the base excess was >=3. Cold crystalloid cardioplegic solution was injected at a total volume of 15 mL/kg. Topical hypothermia was added. The infusion of cardioplegic solution was repeated at 20- to 25-minute intervals or sooner if electrical activity was noted.

Technique of conventional ultrafiltration
In the conventional ultrafiltration group, patients were treated with ultrafiltration during CPB, which removed excess fluid when it was present (n = 21) and hemoconcentrated the patient’s blood. Patients received ultrafiltration during CPB when it was estimated that hemoconcentration would increase the hematocrit by at least two units and still maintain a safe minimum operating volume in the venous reservoir. In such patients, a hemoconcentrator (model HPH400, Minntech, Minneapolis, MN) was inserted into the arterial line–venous reservoir recirculation line and blood was intermittently ultrafiltered to hemoconcentrate the CPB circuit contents to the minimum safe operating volume. The total amount of fluid filtered by conventional ultrafiltration was 25.6 ± 28.6 mL/kg. After CPB processing of blood from the extracorporeal circuit by a centrifugal red cell salvage process was also used in these patients.

Technique of dilutional ultrafiltration
The MUF patients received an augmented form of ultrafiltration during CPB. In this dilutional ultrafiltration, the patient CPB circuit is actively exchanged by (1) setting the circuit parameters to allow ultrafiltrate formation at a rate equivalent to the crystalloid cardioplegia volume plus 40 to 70 mL/kg per hour and (2) adding small aliquots of diluent (PlasmaLyte-A <20 mL/kg) as necessary to maintain a safe blood level in the venous reservoir of the CPB circuit. The dilutional ultrafiltration was carried out continually throughout the CPB run but was interrupted during weaning from CPB while inotropic or vasoactive drugs were being administered. The total amount of fluid removed by dilutional ultrafiltration was 42.2 ± 10.6 mL/kg.

Technique of modified ultrafiltration
A venovenous modified ultrafiltration method was used on all patients in the MUF group. The technique was previously reported in detail [8]. Briefly the patient’s inferior vena caval blood was drawn into the modified ultrafiltration circuit. The inferior vena caval blood within the modified ultrafiltration circuit was both ultrafiltered with a hemoconcentrator (model HPH400; Minntech) and oxygen supplemented with aliquots of oxygenated, warmed CPB circuit blood that had previously been translocated to a supplemental reservoir bag. After being oxygen supplemented and ultrafiltered, the modified ultrafiltration circuit blood was returned to the patient’s right atrium through the proximal side holes of the dual lumen catheter. Modified ultrafiltration was terminated when the supplement reservoir bag was empty. The total amount of fluid filtered by modified ultrafiltration was 113.6 ± 65.3 mL/kg.

After modified ultrafiltration, the dual lumen cannula was removed, protamine was administered, and the patients were transfused as required with the residual modified ultrafiltration circuit blood. Protamine reversal was completed after the modified ultrafiltration circuit blood transfusions.

Intraoperative evaluation and monitoring after repair
As patients were being warmed and weaned from bypass, a right atrial oxymetric catheter was inserted for intraoperative and postoperative hemodynamic monitoring in all patients. Pulmonary arterial and left atrial catheters were used as needed. For the patients with preoperative PH, intraoperative nitroglycerin at a dose of 0.5 to 10 mg/kg per minute was given in the early postoperative period. This agent was administered through a right atrial or pulmonary arterial line and titrated to keep pulmonary to systemic arterial pressure <40%. If dopamine or dobutamine was required at a dose of >5 mg/kg per minute, it was delivered through the left atrial line in an attempt to reduce the potential for inducing pulmonary vasoconstriction.

Prevention strategy for postoperative pulmonary hypertension
Patients with preoperative PH were paralyzed and mechanically ventilated for at least 6 hours. Moderate hyperventilation was used when the postoperative systolic pulmonary/systemic arterial pressure ratio exceeded 40%. These patients also received prophylactic {alpha}-blockers (chlorpromazine or prazosin, or both) after CPB on the basis of a routine clinical protocol [9].

Strategy for extubation
The protocol for initial respiratory management consisted of mechanical ventilator support to maintain the arterial oxygen tension at >120 mm Hg, the arterial carbon dioxide tension at 30 to 35 mm Hg, and the pH at 7.45 to 7.50 to achieve minimal physiologic response to stimulation. Once the child exhibited hemodynamic stability, mechanical ventilatory support and sedation were weaned. When the child demonstrated the ability to sustain adequate spontaneous respiratory effort and required minimal supplemental oxygen as reflected by normal arterial blood gases, the child was extubated. Patients who underwent a Fontan procedure were extubated in the operating room or early after operation, whereas neonatal patients or high-risk patients for postoperative PH required longer ventilatory support.

Prevention strategy for perioperative mediastinal bleeding
Coagulation factors (prothrombin time, partial thromboplastin time, international normalized ratio, platelet counts, and fibrinogen) as well as complete blood cell counts and hematocrit were determined on arrival at the intensive care unit (ICU). No patient in this study received aprotinin perioperatively. For patients with chest tube output <2 mL · kg-1 · h-1 and elevated prothrombin time or partial thromboplastin time, fresh frozen plasma (5 to 20 mL/kg), cryoprecipitate (5 to 20 mL/kg), or platelets (5 to 20 mL/kg) were transfused as required. Washed packed cells were transfused to maintain hematocrit at 40% for neonatal patients or patients with cyanotic congenital heart disease. A hematocrit greater than 32% was accepted for patients with VSD or aortic stenosis.

Postoperative evaluation
A complete set of postoperative physiologic data was collected for all 100 patients, including arterial blood gas (oxygen tension, carbon dioxide tension, and pH), requirement for inotropic support, cardiac rhythm, right atrial pressure, and systemic pressure. Postoperative arterial oxygenation was determined by alveolar–arterial oxygen tension gradient (in mm Hg). Pulmonary and left atrial pressure were obtained as necessary. Postoperative hematocrit levels and requirements for red blood cells, platelets, fresh frozen plasma, and cryoprecipitate were also collected in all patients. The duration of ventilatory support and chest tube drainage were also monitored. These data were compared between the groups stratified by age, CPB technique, existence of preoperative PH, and diagnosis.

Statistical analysis
Data were analyzed with the SAS (Statistical Analysis System, Inc, Cary, NC) software package. The difference of postoperative arterial oxygenation, duration of ventilatory support, transfusion requirements, chest tube output, and time to chest tube removal were compared between the groups using a Mann-Whitney U test. Hematocrit, systemic and pulmonary arterial pressures between the group were determined by analysis of variance for repeated measures. The incidence of blood transfusion were compared between the groups by Fisher’s exact test. All values were expressed as mean ± standard deviation of the mean.


    Results
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 
Operative outcome
There was one postoperative death for the 101 operations for an overall operative mortality of 1%. The death was a patient from the MUF group who died due to low cardiac output after his arterial switch repair and VSD closure for transposition of great arteries with VSD complicated by side by side coronary anatomy. This patient died after 5 days of extracorporeal membrane oxygenation support, and was excluded from analysis in this study thus leaving 100 patients to be analyzed in this study. No late death occurred in this series. There were no MUF-related complications.

No patients required mediastinal reexploration for bleeding. However, 1 patient from the control group underwent mediastinal reexploration to control chylothorax.

Immediate postoperative changes in hemodynamics
In the MUF group, systemic pressure improved from a mean of 69.5 ± 14.2 mm Hg to 85.1 ± 15.8 mm Hg immediately after modified ultrafiltration (p < 0.05). However, no significant differences were observed in systemic pressure at 3, 6, and 12 hours after admission to the ICU between the control and MUF groups. In patients with preoperative PH, postoperative systolic pulmonary arterial pressure was significantly lower in the MUF group compared to controls for up to 12 hours after operation (Fig 1).



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Fig 1. Changes of systolic pulmonary arterial pressure at different times during the perioperative period in patients with preoperative pulmonary hypertension. Patients with hypoplastic left heart syndrome were not included. (MUF = modified ultrafiltration; *p < 0.01 versus control.)

 
Immediate postoperative changes in hematocrit and arterial oxygenation
In the MUF group, hematocrit was improved from 20.3% ± 4.1% to 31.9% ± 5.2% immediately after modified ultrafiltration. However, changes in hematocrit after operation were similar between the groups (Fig 2). Excluding patients with hypoplastic left heart syndrome and total cavopulmonary connection, alveolar–arterial oxygen tension gradient was significantly better in the MUF group compared with controls in patients with preoperative PH (445 ± 129 mm Hg versus 307 ± 113 mm Hg, p = 0.002) and neonates (371 ± 176 mm Hg versus 285 ± 105 mm Hg, p = 0.05). There were no significant differences between the groups in arterial oxygenation overall or in other subgroups of patients.



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Fig 2. Changes of hematocrit at different times during the perioperative period (there are no significant differences between groups). (MUF = modified ultrafiltration.)

 
Duration of ventilatory support
Duration of ventilatory support was significantly longer in controls compared with MUF patients overall, and in the groups of patients with preoperative PH, neonates, those with prolonged CPB (Table 3), and both moderate (MUF: 28.0 ± 31.0 hours versus control: 65.5 ± 77.2 hours, p = 0.007) and deep hypothermia groups (MUF: 50.3 ± 34.3 hours versus control: 246.1 ±150.7 hours, p = 0.005). No significant differences were observed between the groups in patients with VSD without PH, tetralogy of Fallot, or aortic stenosis (34.4 ± 41.2 hours versus control: 52.7 ± 87.5 hours, p = 0.41).


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Table 3. Duration of Ventilatory Support (hours)

 
Blood transfused
Requirements for red blood cell and coagulation factors (fresh frozen plasma, platelets, and cryoprecipitates) were significantly lower in the MUF patients compared with controls in our overall experience and in neonates, as well as those groups of patients with preoperative PH or prolonged CPB (Table 4 ). In both moderate and deep hypothermia patients, MUF significantly reduced the requirement for blood transfusion (Table 5).


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Table 4. Requirements of Red Blood Cells and Coagulation Factors (Fresh Frozen Plasma, Platelets, and Cryoprecipitate)

 

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Table 5. Requirements of Red Blood Cells and Coagulation Factors (Fresh Frozen Plasma, Platelets, and Cryoprecipitate), Stratified by Bypass Techniques

 
Only 14% of control patients (7 of 50) did not require red blood cell transfusion, whereas 36% of patients (18 of 50) in the MUF group were free from postoperative red blood cell transfusion (p = 0.018 by Fisher’s exact test). Moreover, 70% (35 of 50) of MUF patients did not require coagulation factor transfusion, whereas only 24% (12 of 50) of controls were free from transfusion of coagulation factors (p = 0.001 by Fisher’s exact test).

Blood loss
Blood loss was determined by the chest tube output during the first 24 hours. Although no significant differences were observed between the groups in our overall experience (MUF: 21.2 ± 16.8 mL/kg per 24 hours versus control: 26.0 ± 23.7 mL/kg per 24 hours, p = 0.25), MUF significantly reduced the chest tube output in patients with preoperative PH (MUF: 16.4 ± 11.2 mL/kg per 24 hours versus control: 32.1 ± 28.9 mL/kg per 24 hours, p = 0.03) and in patients who underwent CPB using moderate hypothermia (MUF: 15.9 ± 8.8 mL/kg per 24 hours versus control: 27.2 ± 25.9 mL/kg per 24 hours, p = 0.01). In the deep hypothermia patients, the difference between groups did not reach statistical significance (MUF: 20.7 ± 9.4 mL/kg per 24 hours versus control: 32.7 ± 24.0 mL/kg per 24 hours, p = 0.09).

Other clinical observations
Time to chest tube removal was significantly longer in patients with preoperative PH (MUF: 3.2 ± 1.6 days versus control: 6.3 ± 2.4 days, p = 0.03). Otherwise, there were no significant differences between the groups.

The length of ICU stay was significantly longer in controls compared to the MUF group (MUF: 3.8 ± 3.2 days versus control: 6.9 ± 5.7 days, p = 0.001) in the overall experience. This was also the case in patients with preoperative PH (5.1 ± 4 days versus control: 9.1 ± 5.9 days, p = 0.01), neonates (6.7 ± 4.5 days versus control: 12.4 ± 7 days, p = 0.05), and patients who required prolonged CPB (4.8 ± 3.9 days versus 7.9 ± 5.9 days, p = 0.03).


    Comment
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 
Cardiopulmonary bypass in children is associated with the accumulation of water as a consequence of an inflammatory capillary leak [10]. That increase in total body water is associated with tissue edema and subsequent organ dysfunction, particularly in the heart, lungs, and brain. Previous studies have shown that MUF after CPB in children decreases body water, removes inflammatory mediators, improves hemodynamics, and decreases transfusion requirements [1, 2]. This study attempted to determine the optimal target population for MUF.

In this prospective, randomized study, the most striking benefits of MUF were found in patients with preoperative PH. Modified ultrafiltration significantly improved immediate postoperative arterial oxygenation in patients without intracardiac mixing and an extracardiac conduit. Modified ultrafiltration also resulted in lower pulmonary arterial pressure. Moreover MUF patients required less homologous blood transfusion and had shorter ventilatory support. Removal of free water and use of fewer transfusions may contribute to improved pulmonary mechanics after CPB [11] and result in earlier extubation in the MUF patients. Removal of small molecule inflammatory agents including endothelin-1 (a potent pulmonary vasoconstrictor) [8], and other cytokines may also play a significant role in lowering postoperative pulmonary arterial pressure and reducing lung injury after reperfusion [12].

Young age and long duration of bypass have been shown to be incremental risk factors for the accumulation of water [3]. Moreover, a recent study from Children’s Hospital in Boston indicated that coagulation system of a neonate undergoing CPB is profoundly affected by hemodilution [13]. In neonates, MUF resulted in better arterial oxygenation and significantly reduced duration of ventilatory support, and amount of blood transfusion. In patients who required prolonged CPB, MUF reduced ventilatory support time, blood transfusion, and the length of ICU stay. This randomized study clearly demonstrates that the effect of MUF is particularly prominent in these high-risk patient groups. However, there is a valid concern that some overlap in the high-risk groups (Table 6 ), for example, patients with PH, neonates, and patients who required prolonged CPB, may exist that limits the ability to distinguish them as truly independent risk factors. Moreover, although this study was performed strictly in prospective fashion based on diagnosis, there were significant differences in weight and borderline differences in age between the control and MUF groups (see Table 2). In a smaller study, Naik and colleagues [4] found benefits of MUF only in the neonatal population, suggesting that perhaps the major effect seen in our study was attributable to that group of patients. However, in older patients (>30 days) with preoperative PH, MUF significantly reduced ICU stay (control: 9.1 ± 5.9 days, MUF: 5.1 ± 4.0 days, p = 0.01). Moreover, nonneonatal patients with prolonged CPB times (>120 minutes), MUF required shorter ventilatory support (control: 91.5 ± 140.4 hours versus MUF: 39.3 ± 36.5 hours, p = 0.037) and had less blood loss (control: 221 ± 48 mL/kg versus MUF: 117 ± 28 mL/kg, p = 0.008) after operation.


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Table 6. Number of High-Risk Patients Stratified by Age

 
Temperature and flow of CPB are important factors in determining the production of cytokines and accumulation of water after CPB [3, 4, 7] In this study, MUF reduced the duration of ventilatory support, the amount of blood transfusion, and the length of ICU stay in both moderate and deep hypothermia patients. Without MUF, patients who underwent CPB with deep hypothermia required much longer ventilatory support (246 ± 151 hours versus moderate hypothermia: 66 ± 77 hours) and ICU stay (12.8 ± 7.3 days versus moderate hypothermia: 5.6 ± 4.3 days). By using the ultrafiltration technique, these were significantly reduced.

In the presence of VSD without preoperative PH, tetralogy of Fallot, or aortic stenosis, no significant differences were observed between MUF and control patients for any parameter. This was not surprising because these patients are relatively older. However, the size of this group of patients is small in this study and statistical power is not adequate to make firm conclusions on these individual lesions.

No MUF-related complication was observed in this study, and we believe there were several advantages of our venovenous approach. First, there were no limitations attributable to aortic size or anatomy in performing the venovenous approach. In fact, the smallest patient in this series was a 2.1-kg baby with hypoplastic left heart syndrome. Second, circuit blood contents can be translocated to the reservoir enabling a hemoconcentrated blood product for later transfusion, thus avoiding the use of centrifugal cell processing with its attendant loss of platelets, clotting factors, and other plasma proteins. Third, by semicontinuous titration of the warm supplement reservoir blood to the venovenous MUF circuit, the patient’s filling pressures and blood temperature can be easily maintained.

The relative importance of dilutional ultrafiltration versus modified ultrafiltration remains unclear after this study. Because the amount of fluid filtered by dilutional ultrafiltration is significantly smaller than that filtered by MUF, dilutional ultrafiltration may not be important to reduce postoperative morbidity. However, comparison of groups treated with dilutional ultrafiltration alone versus MUF are necessary to draw definite conclusions.

Although low mortality and good long-term outcome for surgical correction of congenital heart defects is now common for most lesions, perioperative care can be very expensive for the more complex repairs [14]. Therefore, the cost/benefit ratio of MUF is important to discuss. The additional cost of MUF includes double lumen catheter ($42) and hemoconcentrator ($85), a total of $127. Because other investigators [15, 16] have shown that post-pump hemoconcentration of CPB circuit contents using an ultrafilter can be an effective and safe method of blood conservation, we designed our MUF circuit with an integral bag reservoir that enables the additional use of the MUF circuit for post-pump processing of the CPB circuit blood, thus avoiding the cost of the cell-saving system. Because we eliminated the cell-saving system ($120) in the MUF group, the additional cost for the MUF circuit is only $7. Most groups that perform arterial–venous MUF use existing bypass cannulas and do not incur any additional MUF cannula cost. It is noteworthy that in the pilot animal studies, we used a dual-cannulation technique for venovenous MUF, but currently we have no clinical experience with this method. If two cannulas (for example, a vent catheter and a small venous cannula) already opened on the operative field could be used for venovenous MUF, the $42 cost of the dual-lumen cannula could be avoided. Although it takes a mean of 12 minutes to complete MUF, we usually perform transesophageal echocardiography to evaluate the repair during this period, and actual time in the operating room did not increase. Benefits of MUF includes reduction of ventilatory support, requirement of blood transfusion, and the length of ICU stay. Thus, MUF potentially has a significant impact on reducing the cost of congenital heart operations. Further study to elucidate the impact of MUF on the cost of treatment of complex congenital heart disease is now ongoing in our institution.

In conclusion, this study demonstrates that venovenous MUF is safe and decreases the need for homologous blood transfusion, duration of ventilatory support, and length of ICU stay in selected patients with complex congenital heart disease. The optimal use of MUF includes patients with preoperative PH, neonates, and patients who require prolonged CPB. Although no beneficial effect was observed in either subgroups with VSD without PH, tetralogy of Fallot, or aortic stenosis, this may simply be attributable to a small sample size of each diagnostic group in this study. Because the additional cost of MUF is only $7 and there were no MUF-related complications in this study, we continue to use MUF for every patient who requires CPB.


    Footnotes
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 
1 This article has been selected for the open discussion forum on the STS Web site: http://www.sts.org/annals Back


    References
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 

  1. Butler J., Pillai R., Rocker G.M., Westaby S., Parker D., Shale D.J. Effect of cardiopulmonary bypass on systemic release of neutrophil elastase and tumor necrosis factor. J Thorac Cardiovasc Surg 1993;105:25-30.[Abstract]
  2. Finn A., Naik S., Klein N., Levinsky R.J., Strobel S., Elliott M. Interleukin-8 release and neutrophil degranulation after pediatric cardiopulmonary bypass. J Thorac Cardiovasc Surg 1993;105:234-241.[Abstract]
  3. Maehara T., Novak I., Wyse R.K.H., Elliott M.J. Perioperative monitoring of total body water by bioelectrical impedance in children undergoing open heart surgery. Eur J Cardiothorac Surg 1991;5:258-265.[Abstract]
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  5. Elliott M.J. Ultrafiltration and modified ultrafiltration in pediatric open heart operations. Ann Thorac Surg 1993;556:1518-1522.
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  8. Bando K., Vijay P., Turrentine M.W., et al. Dilutional and modified ultrafiltration reduces pulmonary hypertension after operations for congenital heart disease: a prospective randomized study. J Thorac Cardiovasc Surg 1998;115:361-369.
  9. Bando K., Turrentine M.W., Sharp T.G., et al. Pulmonary hypertension after operations for congenital heart disease: analysis of risk factors and management. J Thorac Cardiovasc Surg 1996;112:1600-1609.[Abstract/Free Full Text]
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  11. Meliones J.N., Gaynor J.W., Wilson B.G., et al. Modified ultrafiltration reduces airway pressures and improves lung compliance after congenital heart surgery. J Am Coll Cardiol 1995;27:1A.
  12. Journois D., Pouard P., Greeley W.J., Mauriat P., Vouhe P., Safran D. Hemofiltration during cardiopulmonary bypass in pediatric cardiac surgery; effects on hemostasis, cytokines, and complement components. Anesthesiology 1994;81:1181-1189.[Medline]
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