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Ann Thorac Surg 1996;61:296-300
© 1996 The Society of Thoracic Surgeons

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Experience With Generally Available Devices

Use of Centrifugal Pumps for Postcardiotomy Ventricular Failure: Technique and Anticoagulation

Division of Cardiothoracic Surgery, University of Missouri School of Medicine, Columbia, Missouri

Abstract

Background. Centrifugal pumps have been employed most commonly for postcardiotomy mechanical support after intraaortic balloon pumping has failed. Despite their effectiveness in some patients, morbidity remains high.

Methods. Our clinical experiences with centrifugal pumps were reviewed with particular attention to common morbidity such as bleeding, coagulopathy, and thromboembolism. Evolution of cannulation techniques and anticoagulation strategies were defined. Morbidity during early and more recent experience was compared.

Results. Deranged coagulation and excessive mediastinal bleeding were commonly observed in patients undergoing centrifugal mechanical assist for postcardiotomy cardiogenic shock. Evolved strategies to reduce blood loss included meticulous cannulation techniques, early use of blood components, and an aggressive policy of mediastinal reexploration. Thromboembolism occurred with centrifugal mechanical assist, was underestimated by clinical events, and dictated pursuit of improved anticoagulation strategies and device refinement. A clinically significant trend of decreasing morbidity from early to recent experience was observed.

Conclusions. Increasing clinical experience with centrifugal mechanical assist appears to result in a clinically relevant decrease in morbidity.

Centrifugal pumps have been employed most commonly for postcardiotomy support after intraaortic balloon pumping has failed [1]. This is not surprising in that centrifugal pumps are generally available to all surgeons, are relatively simple to operate, and are much less expensive than many other cardiac assist devices. In the setting of postcardiotomy support in anticipation of myocardial recovery, patient survival is independent of the type of device employed [1]. Despite the effectiveness of these devices in salvaging some patients who otherwise face certain death, morbidity and mortality remain high [2–4].

At the University of Missouri-Columbia, we have had laboratory experience with in vitro [5] and in vivo testing of all three centrifugal pumps that are presently commercially available in the United States. Our clinical experience to date has been exclusively with Sarns centrifugal pump (3M Health Care, Ann Arbor, MI) [6]. Since 1986 we have used 138 Sarns centrifugal pumps in 97 patients for a variety of indications including operation on the thoracic aorta [7, 8], cardiac allograft rejection, extracorporeal membrane oxygenation, limb perfusion for cancer, and postcardiotomy cardiogenic shock [6, 9]. These laboratory and clinical experiences have yielded valuable lessons regarding the use of centrifugal pumps. The purpose of this report is to discuss techniques and anticoagulation when centrifugal pumps are employed for mechanical assist in the setting of postcardiotomy ventricular failure. Techniques and anticoagulation strategies are predicated on knowledge of anticipated morbidity.

Bleeding and Coagulopathy

The most common complications after centrifugal mechanical assist (CMA) for postcardiotomy support are coagulopathy and bleeding [1]. Adamson and colleagues [10] reported that 95% of their patients experienced significant bleeding, defined as the need for administration of greater than 20 units of blood products. Golding and associates [4] reported significant bleeding in 87.3% of their 79 patients undergoing postcardiotomy CMA. Transfusion of blood products averaged 53.2 units in their patients. A high incidence of bleeding and coagulopathy has been reported by others [2, 9]. Table 1 shows the coagulation profile obtained on consecutive patients at the University of Missouri Hospital and Clinics on arrival in the intensive care unit and at 24 hours after institution of CMA for postcardiotomy failure. Although these patients had received no anticoagulants postoperatively, prothrombin times and partial thromboplastin times were rarely within normal limits and platelet counts were generally reduced.

Renal failure occurs in a significant number of patients undergoing postcardiotomy CMA and has an adverse effect on hospital survival [1, 11]. The reasons for this are multifactorial but may include inadequate perioperative renal perfusion, administration of multiple blood products, prolonged cardiopulmonary bypass, thromboembolism, sepsis, high-dose -adrenergic inotropes, and other nephrotoxic pharmacology including antibiotics.

Thromboembolism

With the high incidence of coagulopathy and bleeding associated with centrifugal pumping, one would wonder if anticoagulation is indicated. As suggested in Figure 1, thromboembolism does occur with CMA for postcardiotomy ventricular failure, and the clinically recognized thromboembolism rate probably underestimates the true magnitude of this problem. We initially believed that the engineering designs of the Sarns centrifugal pump prevented thromboembolism. This was subsequently disproved by reviewing 43 consecutive patients who did not survive CMA for postcardiotomy shock at our institution [12]. Autopsy was obtained in 8 of these patients, and 5 of 8 (63%) had documented thromboembolism including 3 patients with pulmonary thromboembolism, 2 with cerebrovascular infarcts, 2 with liver infarcts, 2 with splenic infarcts, 2 with kidney infarcts, and 1 each with gastric, pancreatic, prostate, adrenal, cervical, and ileal infarcts. None of these findings were clinically apparent. In the 35 patients who died but no autopsy was obtained, one thromboembolic event was diagnosed clinically with the true incidence of thromboembolism in these patients remaining speculative. This experience suggests that thromboembolism is a major threat in these patients, indicating that some improvement in anticoagulation regimen must be formulated. It remains to be proved if the use of heparin-bonded tubing and devices will diminish the incidence of thromboembolism [2, 13].

View larger version (27K): [in this window] [in a new window]   Fig 1. . Autopsy studies have shown that thromboembolism associated with centrifugal mechanical assist is greatly underestimated by clinical events.

Cannulas commonly employed for univentricular or biventricular CMA at the University of Missouri are shown in Figure 2. Wire-reinforced cannulas are preferred. Potential sites for left and right heart cannulation are as follows:

View larger version (60K): [in this window] [in a new window]   Fig 2. . Cannulas frequently employed for centrifugal mechanical assist for postcardiotomy ventricular failure (from left to right): 36F wire-reinforced venoatrial (two-stage) cannula (Sarns 3M Health Care, Ann Arbor, MI) used for right atrial cannulation; DLP VAD 36F venous cannula (DLP, Inc, Grand Rapids, MI) used for cannulation of the left atrium at its junction with the right superior pulmonary vein; 32F or 36F wire-reinforced straight venous return cannula (Sarns) used for cannulation of the left atrium or the pulmonary artery; 8-mm aortic arch cannula (Sarns) used for aortic cannulation and less frequently for pulmonary artery cannulation; and William Harvey wire-reinforced aortic perfusion cannula (C R Bard, Inc, Tewsbury, MA) less commonly employed for aortic or pulmonary cannulation.

• Left heart egress
  • Junction of superior pulmonary vein with left atrium
    
  • Left atrial appendage
    
  • Left atrium between superior and inferior pul monary veins
    
  • Dome of left atrium
    
  • Left ventricular apex
    
  
  
• Left heart blood return
  • Ascending aorta
    
  • Aortic arch
    
  • Femoral artery
    
  
  
• Right heart egress
  • Right atrial appendage
    
  • Right atrial free wall
    
  
  
• Right heart blood return
  • Pulmonary artery
    
  • Pulmonary artery via right ventricular outflow tract
    
  
  

Cannulation of the aortic arch distal to the left common carotid artery has theoretical attractiveness as a technique to reduce cerebrovascular thromboembolism. However, in the setting of inability to wean the patient from cardiopulmonary bypass, we usually accomplish left heart CMA using the existing aortic cannula. Our technique for aortic cannulation and conversion to centrifugal assist is depicted in Figure 3. Concentric sutures are placed in the ascending aorta (Fig 3A). The untied sutures are ensnared through stiff, clear plastic tubing (economically created by cutting segments of oxygen tubing). Tension is maintained on the pursestring sutures with hemostats (Fig 3B). At the time of conversion to centrifugal mechanical assist, the hemostats are removed and the inner pursestring suture is tied snugly about the cannula. Tension is maintained on this suture as well as the untied outer suture using ``Christmas tree'' connectors as shown in Figure 3C. The excess suture is then wrapped around the Christmas tree connector and held in place with a small plug of bone wax, which allows easy retrieval at the time of cannula extraction.

View larger version (58K): [in this window] [in a new window]   Fig 3. . (A) Concentric pursestring sutures are employed at all cannulation sites. During routine cardiopulmonary bypass, tension is maintained on the ensnared pursestring sutures using surgical clamps. (C) At the time of conversion from routine cardiopulmonary bypass to centrifugal mechanical assist, surgical clamps are eliminated. The inner pursestring suture is tied snugly about the cannula to prevent bleeding. Tension is maintained on pursestring sutures using plastic ``Christmas tree'' connectors (female Luer-Lok polypropylene argyle connector; Sherwood Medical, St. Louis, MO). Excess suture is wrapped around the connector and the ends are held in place in the hollow of the connector using a small plug of bone wax. (D) Low-pressure cannulation sites are secured with soft narrow snares (Tournikwik DLP, Inc, Grand Rapids, MI).

Our preferred site for left atrial cannulation is at the junction of the right superior pulmonary vein with the left atrium. This site has frequently been used intraoperatively for left ventricular venting. No attempt is made to cross the mitral valve with the venous cannula. The right-angled 36F cannula (see Fig 2) is a little more difficult to insert and remove but accomplishes good drainage. A 32F or 36F straight-wire reinforced venous catheter will also function satisfactorily.

For right ventricular CMA, we use the existing 36F two-staged wire-reinforced venous return catheter (see Fig 2) employed during routine cardiopulmonary bypass using the ensnaring technique described. Our choice of blood return to the pulmonary circulation is by direct cannulation of the pulmonary artery just distal to the pulmonic valve. Although arterial cannulas can be used, we commonly employ a 32F wire-reinforced venous return catheter at this site (see Fig 2).

It is important to avoid movement at the cannulation sites postoperatively to prevent bleeding. Exiting cannulas through the intercostal spaces should be avoided if possible because chest wall excursion or use of a sternal retractor can cause motion of the cannulas. We generally exit the aortic cannula through the mediasternotomy incision superior to the sternum. The right and left atrial cannulas exit inferior to the right costal margin and the pulmonary artery cannulas inferior to the left costal margin.

No bleeding at the cannulation sites is acceptable. If bleeding is present after the above technique has been accomplished, the second (outermost) pursestring is tied. If bleeding still persists, additional pursestring suture(s) should be placed. Postoperative bleeding is common after CMA, and the most common source of bleeding is at the cannulation sites. Although coagulopathy is also common, bleeding at cannulation sites is never due to coagulopathy. Meticulous cannulation technique is the single most important factor for avoiding postoperative bleeding.

The sternum is left open in the majority of cases because the cannulas and expanding lungs crowd the heart and interfere with venous drainage. The unapposed sternal edges can be a major source of bleeding in the patient with coagulopathy. Sternal edge bleeding is controlled in this situation by liberal application of warmed bone wax to the sternal edge. Transparent silicone sheeting is then sutured to the skin edges using continuous suture. An iodophor adhesive drape is placed over the silicone sheeting in an effort to accomplish an airtight seal.

Mediastinal exploration for relief of tamponade or excessive bleeding is accomplished at bedside in the intensive care unit by incising the silicone sheet in the midline, evacuating the mediastinum, controlling hemorrhage, irrigating with warm saline solution, closing the silicone sheet, and applying an additional iodophor drape. Persistent or new mediastinal drainage of greater than 400 or 500 mL/h is rarely due to coagulopathy. The practice of waiting until the coagulation profile normalizes to reexplore the mediastinum in this situation may result in depletion of the blood bank and only delay the inevitable.

Because the coagulation profile is initially abnormal in all patients, fresh frozen plasma is administered as soon as the decision to apply CMA is made. Platelet counts are usually diminished and remaining platelets may be functionally impaired secondary to aspirin, prolonged cardiopulmonary bypass, intraaortic balloon pumping, and so on. Consequently, single-donor apheresed platelets are administered early to all patients. This gives the equivalent quantity of platelets that would be obtained by component separation from 8 donors of whole blood with the infectious disease transmission risk of a single donor. Suggested strategies for reduction of postoperative bleeding and coagulopathy can be summarized as follows:

• Concentric pursestring sutures at all cannulation sites; tie inner and snare both
  
• Accept no bleeding at cannulation site
  
• Affix cannulas to nonmoving body part
  
• Bone wax sternum
  
• Administer platelet apheresis and fresh frozen plasma early
  
• Delay anticoagulation until mediastinal bleeding is less than 150 mL/h or coagulation profile normalizes
  
• Aggressive mediastinal reexploration policy
  

We routinely interpose a disposable plastic connector with Luer-Lok between the cardiac cannulas and bypass tubing. This facilitates priming and air removal when elective or urgent device exchange is necessary secondary to device failure [14]. This also allows a ready access vascular port when hemodialysis or flow-limited ultrafiltration are required for renal failure [15] (Fig 4).

View larger version (33K): [in this window] [in a new window]   Fig 4. . A centrifugal pump is used for postcardiotomy ventricular assist (A). The outflow limb of the ventricular assist device provides the driving pressure for ultrafiltration (B). A hollow-fiber filter removes excess intravascular volume (C). An intravenous infusion pump (D) allows one to precisely control the volume of effluent (E) taken from the ultrafiltration device. The inflow limb of the ventricular assist circuit receives outflow (F) from the filter. (Reproduced from [15] with permission from Artificial Organs.)

Heparin is reversed with protamine in all cases. Our past practice has been to delay heparin administration until the coagulation profile normalizes. We have not used heparin during the first 24 hours in our patients and only rarely during the first 48 hours in the majority of our patients. With the recognition of a high incidence of subclinical thromboembolism with this practice, a more aggressive anticoagulation regimen may be warranted. We would presently recommend that the partial thromboplastin time be maintained between 60 and 80 seconds, with heparin administration being instituted as soon as mediastinal blood drainage is less than 150 mL/h, even if the remaining coagulation profile is abnormal.

A critical window of opportunity for device removal may present between myocardial recovery and device-induced complications that should not be missed. Device removal at the earliest feasible time is our goal. Our device weaning techniques and management of patients during CMA have been previously reported [6, 16].

Clinical Outcome

We recently reviewed 65 consecutive patients requiring CMA to wean from cardiopulmonary bypass in an effort to observe the impact of increasing experience with centrifugal pumps on clinical outcome [16]. The patients were arbitrarily divided into an early group (n = 33) and a recent group (n = 32). Patient demographics, surgical procedures performed, patient selection criteria, and other variables including the need for biventricular assist were similar in the two groups. In our early group, 11 of 33 patients (33%) were weaned from the device(s) and 5 patients (15%) survived hospitalization. In the recent group of 32 patients, 17 (53%) were weaned from the device(s) and 9 patients (28%) survived hospitalization. The median value for shed mediastinal blood during the first 24 hours of CMA in our early group was 3,024 mL compared with 1,535 mL in our more recent group. Renal failure, defined as the need for dialysis, has decreased from 39.4% in the early group to 18.8% in our recent group. Although these improvements in outcome are clinically relevant, they did not reach statistical significance possibly because of the small numbers involved.

Conclusions

Although life saving, centrifugal mechanical assist applied as univentricular or biventricular support for postcardiotomy ventricular failure is associated with considerable morbidity. Coagulopathy and excessive post operative bleeding are common. Though unproved, we suspect that postoperative blood loss may be diminished by meticulous cannulation techniques, early administration of component blood products, and an aggressive approach at mediastinal exploration. Thromboembolism does occur and probably at an incidence exceeding that which is suspected clinically, necessitating anticoagulation protocol revision. Increasing experience with these devices appears to result in improved clinical outcomes with regard to both patient survival and decreased morbidity.

Acknowledgments

The clerical assistance of Paula Threet is greatly appreciated. Special gratitude is expressed to the manufacturers of centrifugal pumps (Medtronic BioMedicus, Inc, Eden Prairie, MN; Sarns 3M Health Care, Ann Arbor, MI; and St. Jude Medical, Inc, Chelmsford, MA) for their support of our investigational and clinical efforts at the University of Missouri.

Footnotes

Presented at The Third International Conference on Circulatory Support Devices for Severe Cardiac Failure, Pittsburgh, PA, Oct 28-30, 1994.

Address reprint requests to Dr Curtis, MA312 Health Sciences Center, One Hospital Dr, Columbia, MO 65212.

References

1. Pae WE Jr, Miller CA, Matthews Y, Pierce WS. Ventricular assist devices for postcardiotomy cardiogenic shock. J Thorac Cardiovasc Surg 1992;104:541–53.[Abstract]
2. Magovern GJ Jr. Use of the BioMedicus pump in postoperative circulatory support. Cardiac Surg State Art Rev 1993;7(2):249–64.
3. Curtis JJ, Walls JT, Demmy TL, et al. Clinical experience with the Sarns centrifugal pump. Artif Organs 1993;17:630–3.[Medline]
4. Golding LAR, Crouch RD, Stewart RW, et al. Postcardiotomy centrifugal mechanical ventricular support. Ann Thorac Surg 1992;54:1059–64.[Abstract/Free Full Text]
5. Curtis JJ, Wagner-Mann CC, Turpin TA, et al. In vitro evaluation of five commercially available perfusion systems. Int J Angiol 1994;3:128–33.
6. Curtis JJ. Centrifugal mechanical assist for postcardiotomy ventricular failure. Semin Thorac Cardiovasc Surg 1994;6:140–6.[Medline]
7. Walls JT, Boley TM, Curtis JJ, Schmaltz RA. Experience with four surgical techniques to repair traumatic aortic pseudoaneurysm. J Thorac Cardiovasc Surg 1994;106:283–7.[Abstract]
8. Walls JT, Curtis JJ, Boley T. Sarns centrifugal pump for repair of thoracic aortic injury: case reports. J Trauma 1989;29:1283–5.[Medline]
9. Curtis JJ, Walls JT, Schmaltz R, Boley TM, Nawarawong W, Landreneau RJ. Experience with the Sarns centrifugal pump in postcardiotomy ventricular failure. J Thorac Cardiovasc Surg 1992;104:554–60.[Abstract]
10. Adamson RM, Dembitsky WP, Reichman RT, Moreno-Cabral RJ, Daily PO. Mechanical support: assist or nemesis? J Thorac Cardiovasc Surg 1989;98:915–21.[Abstract]
11. Pennington DG, Swartz MT. Temporary circulatory support in patients with postcardiotomy cardiogenic shock. Cardiac Surg State Art Rev 1991;5:373–92.
12. Curtis JJ, Walls JT, Boley TM, Schmaltz RA, Demmy TL. Autopsy findings in patients on postcardiotomy centrifugal ventricular assist. ASAIO J 1992;38:M688–90.[Medline]
13. Hsu L-C. Duraflo II heparin-immobilized cardiopulmonary bypass circuits. Cardiac Surg State Art Rev 1993;7(2):265–76.
14. Curtis JJ, Boley TM, Walls JT, Demmy TL, Schmaltz RA. Frequency of seal disruption with the Sarns centrifugal pump in postcardiotomy assist. Artif Organs 1994;18:235–7.[Medline]
15. Curtis JJ, Deese LR, Walls JT, Boley TM. The use of a rate limited ultrafiltration circuit with centrifugal ventricular assist. Artif Organs 1994;18:465–6.[Medline]
16. Curtis JJ, Walls JT, Schmaltz RA, et al. Improving clinical outcome with centrifugal mechanical assist for postcardiotomy ventricular failure. Artif Organs 1995;19:761–5.[Medline]

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Jack J. Curtis Joseph T. Walls Richard A. Schmaltz Todd L. Demmy Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Curtis, J. J. Articles by McKenney, C. A. Search for Related Content PubMed PubMed Citation Articles by Curtis, J. J. Articles by McKenney, C. A.