Asian Cardiovasc Thorac Ann 1999;7:353-358
© 1999 Asia Publishing EXchange Pte Ltd
Comparison of Nikkiso and Bio-Medicus Pumps in Thoracoabdominal Aortic Surgery
Joseph S Coselli, MD,
Dwayne F Ledesma, MD,
Scott A LeMaire, MD,
Eiki Tayama, MD, PhD,
Steve A Raskin, CCP,
Satoshi Ohtsubo, MD,
Stuart Harlin, MD,
Neil G Browning, MD,
Yukihiko Nosé, MD, PhD
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Department of Surgery Baylor College of Medicine The Methodist Hospital Houston, Texas, USA
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For reprint information contact: Joseph S Coselli, MD Tel: 1 713 790 4313 Fax: 1 713 790 0202 email: jcoselli{at}bcm.tmc.edu 6560 Fannin Street, Suite 1100, Houston, Texas 77030, USA.
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Abstract
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Left heart bypass reduces the risk of ischemic complications during the repair of extensive thoracoabdominal aortic aneurysms. This prospective study compared the performance of the recently developed Nikkiso centrifugal pump with the well-established Bio-Medicus pump during left heart bypass for thoracoabdominal aortic aneurysm surgery. Thirty-five consecutive patients undergoing graft repair of extensive thoracoabdominal aortic aneurysms were prospectively assigned to have left heart bypass using either the Bio-Medicus (in the first 19 patients) or Nikkiso pump (in the next 16 patients). There were no significant differences in pump flow rates or patient hemodynamics between the two groups and there was no evidence of pump malfunction. All patients survived and none developed postoperative coagulopathy, myocardial infarction, or left heart failure. Paraparesis developed in 2 patients in the Nikkiso group (12.5%); there were no neurologic complications in the Bio-Medicus group (p = 0.202). One patient in the Bio-Medicus group developed renal failure (5.3%; p = 1.000 vs. Nikkiso group). Overall, no significant differences were found in the incidence of postoperative complications. Although a small series, this comparison demonstrates that the Nikkiso centrifugal pump is as effective and safe in providing left heart bypass during thoracoabdominal aortic aneurysm repair as the widely-used Bio-Medicus model.
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Introduction
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Recent clinical data have supported the role of left heart bypass (from the left atrium to the femoral artery or distal aorta) in providing protection against spinal cord ischemia and subsequent neurologic deficits following graft replacement of extensive (Crawford extents I and II) thoracoabdominal aortic aneurysms (TAAAs).1–3 Previously, we and others have reported using the Bio-Medicus centrifugal pump (Bio-Medicus, Inc., Eden Prairie, MN, USA) for left heart bypass during TAAA repair.1,3–6 A more compact centrifugal pump developed at the Baylor College of Medicine (Nikkiso pump; Himex Production Co., Inc., Houston, TX, USA) was recently approved for clinical use (Figure 1
).7 Several investigators have reported excellent results using the Nikkiso pump for cardiopulmonary bypass.8–10 The recent report of our initial experience using the Nikkiso pump for left heart bypass during TAAA repair described excellent pump function that provided sufficient flow for both distal aortic and selective visceral perfusion and successfully prevented permanent spinal cord injury and organ failure in 10 patients.11 The purpose of this study was to prospectively compare the performance of the Nikkiso and Bio-Medicus pumps for left heart bypass during the repair of extensive TAAAs.
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Figure 1. The Bio-Medicus (left) and Nikkiso centrifugal pump heads. Reprinted with permission from the authors and Blackwell Science, Inc.10
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Patients and Methods
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Thirty-five consecutive patients undergoing repair of extensive TAAAs were studied. In the first 19 patients, a Bio-Medicus BP-80 pump was used for left heart bypass; this group served as a contemporary cohort for comparison with the subsequent 16 patients in whom the Nikkiso pump was used. There were 23 men and 12 women and the median age was 66 years (range, 25 to 82 years). Sixteen TAAAs were Crawford extent I (46%) and 19 were extent II (54%). Aneurysms were degenerative in 26 patients (74%) and due to dissection in 11 (31%; 8 chronic and 3 acute). No patient presented with rupture. Two patients (5.7%) had Marfan syndrome and 7 (20%) had previous operations on the thoracic aorta (Table 1). Concurrent medical problems included atherosclerotic heart disease in 11 patients (31%), cerebrovascular disease in 4 (11%), hypertension in 23 (66%), chronic lung disease in 14 (40%), and 21 (60%) were smokers.
The Nikkiso pump housing and impeller are made of polycarbonate. The pump housing is 66 mm in diameter and 58 mm in height. The pump head has an impeller diameter of 50 mm, a priming volume of 25 mL, and a weight of 145 g. The impeller has 6 straight vanes and is mounted on a magnetic shaft. Six small washout holes in the impeller reduce thrombus formation. A V-shaped fluoro-rubber ring behind the impeller separates the pump from the actuator chamber. The pump head is attached to the driver console using a flexible shaft, allowing placement of the head very close to the surgical field. The total priming volume of the Nikkiso circuit is 720 mL.
All left heart bypass circuits consisted of inflow and outflow cannulae, 3/8 inch polyvinyl chloride tubing, and a centrifugal pump. No blood reservoirs, heat exchangers, or oxygenators were incorporated into the circuits. For selective perfusion of the kidneys and other viscera, balloon catheters were connected to the return tubing using a three-way stopcock (Figure 2).
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Figure 2. (A) Left heart bypass during initial aortic clamping. (B) After the proximal anastomosis, selective perfusion via balloon catheters is used during reattachment of intercostal arteries. (C) During reattachment of visceral vessels, selective perfusion continues and intercostal arteries receive antegrade perfusion. As published previously.12
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The surgical technique, standardized by the author performing all operations (JSC), has been previously described in detail.12 All patients were intubated with a double-lumen endotracheal tube to permit deflation of the left lung. The patients were placed in an oblique lateral decubitus position with the pelvis rotated to the left to allow easy access to the left femoral artery. Exposure of the aorta was achieved via a left thoracoabdominal incision through the 6th intercostal space and a transperitoneal approach with medial visceral rotation. A drainage cannula was inserted into the left atrium and secured with a pursestring suture. The return cannula was inserted into either the mid descending thoracic aorta or the left common femoral artery. After mild systemic heparinization (1 mg•kg–1), left heart bypass was initiated at 500 mL•min–1 and the proximal aorta was clamped. Flow rates were adjusted to maintain the mean distal aortic pressure near 70 mm Hg. The descending aorta was then clamped above the critical intercostal arteries and the proximal portion of the aneurysm was opened (Figure 2A
). After completion of the anastomosis of the proximal aorta and a woven Dacron tube graft, left heart bypass was discontinued and the distal aortic clamp was removed. The remainder of the aneurysm was then opened to its distal extent. In the 19 patients who had aneurysms involving the entire thoracoabdominal aorta (extent II), balloon catheters were inserted into the origins of the celiac axis, superior mesenteric artery, and both renal arteries; selective perfusion was then initiated by occluding the return tubing and resuming pump flow (Figure 2B). Critical intercostal arteries were reattached as an island. The visceral and renal arteries were reattached either via a beveled distal anastomosis (extent I) or as an island (extent II, Figure 2C). After reattaching the visceral vessels in the extent-II repairs, the balloon catheters were removed, the graft was flushed, and the distal clamp was repositioned below the visceral arteries, thereby restoring their perfusion during completion of the distal anastomosis.
Preoperative variables evaluated included sex, age, dissection, aneurysm extent, and prevalence of major risk factors. Intraoperative variables included pump type, blood product transfusion requirements (red blood cells, cell saver, fresh frozen plasma, platelets, cryoprecipitate), aortic clamp time, visceral ischemic time, and spinal ischemic time. Additionally, intraoperative hemodynamic parameters (mean arterial pressure, mean pulmonary arterial pressure, central venous pressure, and heart rate) and rectal temperatures were serially recorded in all patients at four specific times: prior to aortic clamping, while clamped with left heart bypass, while clamped without left heart bypass, and after clamp removal. Postoperative variables included incidence of paraparesis and paraplegia (lower limb weakness and paralysis, respectively), stroke, reoperation for bleeding, renal failure (serum creatinine exceeding 30 mg•L–1 or need for hemodialysis), pulmonary complications (ventilator support exceeding 48 hours or pneumonia), cardiac complications (myocardial infarction, inotropic support exceeding 48 hours, or dysrhythmias), number of days in the intensive care unit, length of hospital stay, and early mortality rate (within 30 days or during the initial hospitalization). Predicted risks of paraplegia or para-paresis for both groups were calculated using the formula described by Acher and colleagues13 which has been shown to have extremely strong predictive power (correlation coefficient = 0.997).
The statistical analysis was performed using the SAS (release 6.10; SAS Institute, Inc., Cary, NC, USA) and SPSS (release 6.1.3; SPSS, Inc., Chicago, IL, USA) systems for Windows. All continuous data are presented as the mean ± one standard deviation. Categorical variables were compared by univariate analysis using Pearson's chi-squared test or the Fisher exact test (two-tailed) and ordinal data were compared using the Mann-Whitney U test. The intraoperative hemodynamic and temperature data were analyzed using two-way repeated measures analysis of variance. Associations were considered statistically significant when the value of p was less than 0.05.
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Results
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Comparisons of preoperative factors and intraoperative data are presented in Tables 2 and 3. The Nikkiso group had less extensive aneurysms and, therefore, shorter aortic and spinal ischemic times. Otherwise, the patients and operations in the two groups had similar characteristics. There were no significant differences in patient hemo-dynamics, body temperature trends, or pump flow rates between the two groups and there was no evidence of pump malfunction in either group.
All patients survived operative repair of their TAAA (Table 4). Paraparesis developed in 2 patients in the Nikkiso group (12.5%); there were no neurologic complications in the Bio-Medicus group (p = 0.202). There were no cases of paraplegia and both paraparetic patients were ambulant at the time of discharge. Renal failure did not occur in the Nikkiso group but developed in 1 patient in the Bio-Medicus group (5.3%; p = 1.000); consequently, the mean maximum postoperative serum creatinine and blood urea nitrogen were higher in the later group. No patient in either group developed postoperative coagulopathy, myocardial infarction, or left heart failure. One patient in the Bio-Medicus group required reoperation to control splenic bleeding. Both intensive care and total hospital stays were significantly longer in the Bio-Medicus group. One patient in the Bio-Medicus group had a prolonged hospitalization related to treatment of severe depression.
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Discussion
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Despite continuing improvements in operative morbidity and mortality following TAAA repair, neurologic complications related to spinal cord ischemia remain problematic and the optimal strategy for their prevention remains unclear.14,15 Our current approach to spinal cord protection includes selective left heart bypass, moderate heparinization, permissive mild hypothermia, and reattachment of critical intercostal and lumbar arteries. By maintaining distal aortic perfusion during proximal crossclamping, left heart bypass provides protection to the spinal cord and viscera. Left heart bypass has been shown to substantially reduce the intercostal arterial ischemic time and lower the risk of spinal cord injury during repair of extensive TAAAs.1,16 Although the left heart bypass circuit does not require heparin at flow rates above 1500 mL•min–1, we used moderate heparinization to prevent thrombosis of vessels supplying the spinal cord. The lack of a heat exchanger in the circuit allows permissive mild hypothermia, providing additional spinal cord protection.12,14,17
In 1976, the Bio-Medicus centrifugal pump, using an indirect-drive system with a magnetically coupled impeller-rotor, was introduced as an alternative to the roller pump for cardiopulmonary bypass. The reliability of the Bio-Medicus pump has been well-established in several settings, including cardiopulmonary bypass, postcardiotomy support, and left heart bypass during aortic surgery. Most groups reporting the use of left heart bypass during TAAA repair have used the Bio-Medicus pump.1,3–6
The Nikkiso pump was developed as an alternative with important potential advantages. It is the smallest and lightest (145 g versus 280 g for the Bio-Medicus) commercially available centrifugal pump.9,10,18 The pump's priming volume is very small (25 mL versus 80 mL for Bio-Medicus), enabling quick and easy setup, priming, and air evacuation, characteristics that make the Nikkiso system well suited for emergency procedures such as ruptured aneurysms. The flexible drive shaft of the Nikkiso pump separates the motor and pump head, which effectively reduces heat-induced hemolysis. Regarding hemolysis, both in vitro and in vivo studies have demonstrated that the Nikkiso pump compares favorably and may be superior to roller pumps and other commercially available centrifugal pumps, including the Bio-Medicus model.9,18–20
In this study, the Bio-Medicus group had a larger number of the more complex extent II aneurysms, which likely accounts for the longer ischemic times in this group and increases the risk of paraplegia or paraparesis. In contrast, all 3 patients with acute aortic dissection (a well-established risk factor for paraplegia) occurred in the Nikkiso group.16 Despite these imbalances between the groups, their calculated predicted paraplegia and paraparesis rates were similar, suggesting that the two groups were at comparable overall risk for developing neurologic complications.
In terms of performance, both pumps demonstrated excellent function without any adverse mechanical events. Despite its small design, the Nikkiso pump provided flows for distal aortic and selective organ perfusion that were comparable to the Bio-Medicus pump. The prevention of permanent spinal cord injury was successful in both groups. The more extensive aneurysms in the Bio-Medicus group translated into longer clamp and operative times. This factor, rather than the difference in the pump used, best explains the increased frequency of respiratory failure in the Bio-Medicus patients as well as their significantly longer recovery times (both intensive care and hospital stay). Only 1 patient developed renal failure, accounting for the higher maximum serum creatinine and blood urea nitrogen in the Bio-Medicus group. Overall, no significant differences were found in the incidence postoperative complications.
Although a small series, this comparison demonstrates that the Nikkiso centrifugal pump seems to be as effective and safe in providing left heart bypass during TAAA repair as the widely used well-established Bio-Medicus model. The compact direct-drive Nikkiso pump has several potential advantages over other available pumps. Additional studies, such as a larger randomized comparison, are required to further evaluate these potential benefits of the Nikkiso pump.
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References
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Abstract
Introduction
