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Ann Thorac Surg 2001;71:1267-1271
© 2001 The Society of Thoracic Surgeons
a Division of Cardiovascular Surgery, Miami Children’s Hospital, Miami, Florida, USA
Accepted for publication September 14, 2000.
Address reprint requests to Dr Hannan, Division of Cardiovascular Surgery, Miami Children’s Hospital, 3200 SW 60 Ct, Ste 102, Miami, FL 33155-4069
e-mail: rhannan001{at}aol.com
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Abstract |
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 TopFootnotes Abstract IntroductionMaterial and methodsResultsCommentReferences |
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Methods. Four hundred consecutive patients undergoing open heart repair of congenital heart lesions by one surgeon were studied. The first 200 patients were supported by gravity drainage and the next 200 patients were supported by assisted venous drainage. No patient in the time period was excluded from the study.
Results. The two groups did not differ significantly in weight, bypass time, or cross-clamp time. Priming volumes were less in the assisted group than in the gravity group (576 ± 232 mL versus 693 ± 221 mL, p < 0.001). Venous cannula size was smaller in the assisted group when compared with the gravity group (33.2F ± 7.4F versus 38.5F ± 7.1F, p < 0.001). There was a trend to lower operative mortality in the assisted drainage group (5 of 200, 2.5% versus 11 of 200, 5.5%; p = 0.10). Hospital stay and pulmonary, infectious, and neurologic complications were comparable in both groups. Cardiac complications were less common in the assisted group than in gravity group (22 of 200, 11% versus 38 of 200, 19%; p = 0.017). Hematologic complications were less common in the assisted group than the gravity group (6 of 200, 3% versus 19 of 200, 9.5%; p < 0.01).
Conclusions. These findings suggest that assisted venous drainage is safe in congenital heart operations and facilitates the use of smaller venous cannulas.
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Introduction |
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TopFootnotesAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Material and methods |
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TopFootnotesAbstractIntroductionMaterial and methodsResultsCommentReferences |
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A relational database (CardioAccess, Miami, FL) was used to collect data at time and point of service or event in all patients. The following data were compared: surgery date, age, weight, bypass time, cross-clamp time, prime volume, cannula size, hospital mortality, hospital stay, and postoperative complications (Tables 1, 2). Hospital mortality was defined as death within 30 days of operation or at any time if the patient had not been discharged from the hospital. Postoperative complications were defined as outlined in the Appendix. In general, complications were identified on clinical grounds and documented by further investigations aggressively undertaken as clinically indicated. Complications were recorded concurrently and contemporaneously by nurse practitioners who used the same definitions (Appendix) throughout the study.
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-inch arterial and venous tubing for patients less than 30 kg in weight and 3/8-inch arterial and venous tubing in all larger patients, a BP-50 BioMedicus cone (Medtronic BioMedicus, Eden Prairie, MN) in those less than 30 kg and a BP-80 in all others, a Minimax plus oxygenator (Medtronic Cardiopulmonary) for all patients less than 30 kg and a Maxima plus oxygenator (Medtronic Cardiopulmonary) in all others, a cardiotomy reservoir (Medtronic Cardiopulmonary), a Terumo bubble trap, a CDI 400 blood gas monitor (CDI 3M Health Care, Tustin, CA), and a Biotrend hematocrit/oxygen saturation monitor (Medtronic Cardiopulmonary). The circuit is mounted on a flexible arm connected to the pump cart (Medtronic Cardiopulmonary), using a BioMedicus external drive unit (Medtronic BioMedicus), cardiotomy reservoir bracket, bubble trap bracket, and oxygenator bracket. The venous line contains a Biotrend saturation probe, a temperature probe, and a prebypass filter. The outlet of the cardiotomy reservoir is attached along with the venous line onto the inlet of the bubble trap. The outlet of the bubble trap is connected to the Bio-cone and then the oxygenator. The arterial line is connected to both the outlet and recirculation ports of the oxygenator with a CDI blood gas probe and a luer-fitted Y connector (Fig 1). One-way purge lines are attached to the top of the bubble trap, the oxygenator, and the luer-fitted arterial line connector. The circuit is flushed with CO2 and primed with crystalloid solution in the usual manner. During the procedure, the bubble trap is continuously purged into the cardiotomy reservoir using a separate roller head pump. Patient blood volume is adjusted during bypass by partially restricting the outlet of the cardiotomy reservoir with a tubing clamp. The outlet of the cardiotomy reservoir is never completely occluded during the procedure to prevent the build up of excessive negative pressure in the circuit. A transonic flow probe and bubble detector is used on the arterial line. Preoxygenator and venous line pressures are monitored throughout the procedure.
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-inch arterial and venous tubing, those between 15 and 30 kg, with -inch arterial and 
-inch venous, those between 30 and 50 kg, with -inch arterial and venous, and those larger than 50 kg, with -inch arterial and 
-inch venous. Patient blood flow requirements during CPB were determined using the same calculated weight-dependent formula in both study groups: patients less than 5 kg, 150 mL · kg-1 · min-1; 5 to 15 kg, 120 mL · kg-1 · min-1; 15 to 30 kg, 100 mL · kg-1 · min-1; 30 to 50 kg, 80 mL · kg-1 · min-1; and larger than 50 kg, a cardiac index of 2.2 to 2.4L · (m · m2)-1.
Venous cannula selection was determined by comparing the patient’s calculated blood flow with the maximum blood flow rates generated through the cannulas—negative 40 mm Hg for the conventional system and negative 60 mm Hg for the assisted system. Almost all patients were cannulated with bicaval venous cannulas. A single venous cannula was used only in procedures requiring aortic arch reconstruction (such as Norwood stage I procedures and repair of interrupted aortic arch) and for repair of total anomalous pulmonary venous connection in neonates.
Data analysis
The assisted group (group 1) and gravity group (group 2) were compared in this study using two main treatment effects: bypass time and cross-clamp time. A two-way analysis of variance was performed to identify statistical significance with respect to patient size between both groups. Case complexities in both groups are defined by Jenkins [18] and reproduced in Table 3. The Mann-Whitney U test used for mean complexity. The Student’s unpaired t test was used to determine statistical significance for differences in age, weight, bypass time, cross-clamp time, priming volume, postoperative hospital stay, and venous cannula diameter size between the two groups. Fisher’s exact probability test was used to compare case complexity, hospital mortality, and postoperative cardiac, neurologic, pulmonary, hematologic, and infectious complications between experimental groups with the use of a standard statistical software program (Microsoft Corp, Seattle, WA). Exact p values are reported, with a p value of less than 0.05 considered significant. Data are expressed as mean ± standard deviation.
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Results |
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TopFootnotesAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Comment |
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TopFootnotesAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Small venous cannulas and excellent venous drainage are advantageous in any open heart operation, and especially so when operating on small babies or through small incisions. The current trend in congenital heart operations to operate on smaller babies and use minimally invasive techniques makes smaller venous cannulas advantageous. Using small-diameter cannulas that take up less of the operative field facilitates these new approaches, which limit surgical exposure.
Using conventional bypass circuits, these smaller cannulas may result in compromised venous drainage. As a consequence, several bypass circuit modifications have recently been reported that safely increase venous drainage using smaller venous cannulas [14–17].
New CPB techniques use one of two methods to actively aspirate blood from the patient and augment venous return. One approach uses a centrifugal pump in the venous line of a conventional bypass circuit. Another technique uses standard wall vacuum. Both techniques, although effective, have limitations; including (1) the centrifugal pump can become air-locked and ineffective during the procedure if large amounts of venous air are present; (2) small amounts of venous air can be churned into microemboli and potentially delivered into the circulation; and (3) the added expense of using two pump heads (one pump is used to aspirate the venous blood from the patient and a second pump to return arterial blood back to the patient).
Vacuum-assisted circuits are dependent on a reliable suction source, a vacuum regulator, and an airtight hard-shell reservoir. In this configuration, the reservoir may become overpressurized if the inflow rates from the sucker return exceed the vacuum outflow rate, which requires close monitoring to avoid complications. When the arterial line is clamped distal to any shunt connected directly to the reservoir, exposing the oxygenator to negative pressure, the potential exists for air to be pulled across the oxygenator fibers.
To address these limitations, we modified our conventional bypass circuit by replacing the venous reservoir bag with a bubble-trap. Connecting the venous line and cardiotomy reservoir to the bubble trap inlet allows the perfusionist to filter and remove air from the blood before delivery to the centrifugal pump. The same Bio-cone is then used to pump the blood into the oxygenator, and finally back to the patient; eliminating the need for a second pump head or the use of wall vacuum.
The bubble trap is vented in the same manner as a conventional venous reservoir bag, with a one-way purge line connected to one of the pump suckers. During initiation of bypass, the cardiotomy outlet line is partially occluded to maximize venous drainage and carefully adjusted to the desired amount of negative pressure on the venous line. Blood is then slowly transferred into the cardiotomy reservoir until the heart is adequately decompressed and full flow is initiated.
Using this circuit, the potential also exists for pulling air across the fibers if the arterial and venous lines are clamped, and the bubble trap is vented excessively into the cardiotomy. For this reason, the cardiotomy outlet is never completely occluded.
With active venous drainage, the system can be mounted on an adjustable arm at the patient’s level, rather than significantly below the level of the patient, as is required with gravity drainage. This decreases the overall priming volume of the circuit by reducing tubing length and diameter. The adjustable arm also allows for safe repositioning of the circuit during the procedure to conform to frequent changes in patient height and location, which are common during minimal access procedures.
The safety and efficacy of perfusion management with this approach is enhanced by its similarity to common closed systems. The circuit consists of components used during conventional gravity venous drainage, and eliminates the added expense associated with other venous assisted techniques. Other advantages are a lower priming volume and decreased blood product requirements (Table 1). An intangible advantage of the system is the ability to improve venous drainage simply by transferring volume into the cardiotomy reservoir and out of circulation. Although difficult to measure, surgeons using the venous assisted circuit uniformly observe that venous drainage is markedly improved over gravity circuits.
This study demonstrates that the "venous pull" technique for assisted venous drainage is a safe and efficacious way to perform CPB. Although the consecutive nonrandomized design of this study makes it impossible to prove that the assisted venous technique is safer than conventional techniques, the results demonstrate that it is a safe and useful method. It reduces the necessary priming volume and allows the use of smaller venous cannulas without compromising surgical outcomes. This system of assisted venous drainage has now been used in more than 1,000 patients with congenital heart disease in our institution and remains our method of choice for CPB.
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Footnotes |
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TopFootnotesAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Appendix |
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Cardiac failure—Inability to wean from mechanical cardiac support.
Low cardiac output—Decreasing end-organ function with increasing pressor support and evidence of myocardial dysfunction on echocardiogram.
Pulmonary failure—Inability to wean from ventilator support with objective evidence (eg, chest roentgenogram) of pulmonary disease.
Arrhythmia—Determined with 12-lead electrocardiogram and 24-hour Holter monitoring and requiring medical intervention.
Pericardial effusion—Documented by echocardiogram.
Pulmonary hypertension—Evidence of hypoxemia in the absence of intracardiac shunting or chest roentgenogram changes, echocardiography evidence of increased right ventricular systolic pressure in the absence of right ventricular outflow tract obstruction, clinical evidence of pulmonary hypertension including elevated right-sided pressures, clinically responsive to standard treatment modalities, ie, hyperventilation, increased fraction of inspired oxygen, nitric oxide.
Adult respiratory distress syndrome—Documented by chest roentgenogram and requirement for ventilator support.
Atelectasis—Decreased breath sounds and chest roentgenogram.
Seizure—Clinical evidence of seizure documented with electroencephalogram.
Intraventricular hemorrhage—Documented with head ultrasound, computed tomography, or magnetic resonance imaging.
Anoxic—Clinical neurologic injury documented with head ultrasound, computed tomography, or magnetic resonance imaging.
Bleeding—Postoperative blood loss greater than 5 mL · kg-1 · h-1.
Thrombosis—Evidence of intravascular thrombus documented by echocardiogram.
Pneumonia—Clinical criteria including increased ventilator settings, increased white cell count, increased secretions, and increased temperature and chest roentgenogram.
Sepsis—Fever with positive blood cultures or bandemia.
UTI—Fever with positive urine cultures or bandemia.
Wound—Positive wound cultures, redness of site, or drainage.
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References |
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TopFootnotesAbstractIntroductionMaterial and methodsResultsCommentReferences |
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