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Ann Thorac Surg 1999;68:650-654
© 1999 The Society of Thoracic Surgeons

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Patient Management and Device Selection for Acute/Temporary Support

Acute and temporary ventricular support with bioMedicus centrifugal pump

^a Department of Surgery, Baylor College of Medicine, The Methodist Hospital, Houston, Texas, USA

Address reprint requests to Dr Noon, Texas Surgical Associates, 6560 Fannin, Suite 1860, Houston, TX 77030

Presented at the Fourth International Conference on Circulatory Support Devices for Severe Cardiac Failure, Houston, TX, Oct 3–5, 1997.

Abstract

Background. Short-term ventricular and pulmonary support can be provided by the Medtronic BioMedicus (Eden Prairie, MN) centrifugal pump, which is available in most cardiovascular surgery centers. This versatile pump can provide support during cardiopulmonary resuscitation, cardiopulmonary bypass, extracorporeal membrane oxygenation, and ventricular assistance. A common use of the pump is to provide ventricular assistance for patients after cardiotomy or cardiogenic shock.

Methods. From January 1986 to September 1995, 141 patients at The Methodist Hospital in Houston, Texas were placed on the BioMedicus centrifugal pump after postcardiotomy cardiac failure. Patient treatment and postimplant complications are discussed.

Results. Fifty-four percent of the patients were weaned; however, only 22% survived to discharge. There was a very high mortality rate in the early stage after support was discontinued, after weaning, and after device removal.

Conclusions. A high incidence of complications and death is likely related to the period of attempted weaning from cardiopulmonary bypass before the initiation of ventricular support. When weaning a patient from the pump during cardiopulmonary bypass or during ventricular assistance, it is important to optimize preload, afterload, ventricular function, and cardiac rhythm. In patients who have had postcardiotomy support, avoiding fluid overload, low colloid oncotic pressure, hypoperfusion, and use of excessive inotropic and vasoactive medications improve results.

Short-term ventricular or pulmonary support can be provided with the Medtronic BioMedicus (Eden Prairie, MN) centrifugal pump, which is available in most cardiovascular surgery centers. It can be used for femoral-femoral bypass, cardiopulmonary bypass, ventricular assistance, and extracorporeal membrane oxygenation (ECMO). The pump has been on the market for over 12 years and has been used clinically more than 1.5 million times. The system is relatively inexpensive compared with other short-term ventricular assist devices. Because of the multiple applications and frequent use of the BioMedicus centrifugal pump, perfusionists and nursing personnel are familiar with its operation. We present our clinical application of the BioMedicus centrifugal pump as a short-term means of ventricular or pulmonary support.

In situations where acute support is required for resuscitation or ECMO, femoral-femoral bypass is commonly used. Cannulation of the femoral vessels can be done by percutaneous puncture or by a cut down on the femoral artery and vein as shown in Figure 1.

View larger version (132K): [in this window] [in a new window]   Fig 1. Femoral vein and artery cannulation used for resuscitation, cardiopulmonary bypass, or extracorporeal membrane oxygenation.

Temporary cardiopulmonary support with the BioMedicus pump is most commonly used for elective and emergency cardiac procedures requiring cardiopulmonary bypass. Cannulation is usually central using a single, dual-stage atrial cannula or bicaval cannulas for venous return. The distal ascending aorta is cannulated for pump arterial outflow. Femoral vein and artery cannulation is less commonly used. Most procedures are completed within 1 to 3 hours and the patient is weaned off cardiopulmonary bypass.

When a patient cannot be weaned, the BioMedicus pump is used to provide ventricular assistance. This application is continued until ventricular recovery occurs. When recovery is insufficient, it can be continued as a bridge to another device, or as a bridge to transplant. In this situation it is uncommon to support patients with the BioMedicus pump for more than 2 to 3 weeks. In patients requiring unilateral or bilateral ventricular support ECMO can be used; however, it does not provide good left ventricular decompression. Central or peripheral venous and arterial cannulation is required for cardiac support with ECMO. Veno-venous cannulation is often used for pulmonary support when cardiac function is normal.

The most common use of the BioMedicus ventricular assistance is for patients who have had postcardiotomy or cardiogenic shock. Postcardiotomy cardiac failure occurs in 2% to 6% of patients who have cardiac procedures. One percent will require mechanical support in addition to the intraaortic balloon pump for counterpulsation [1–5]. The BioMedicus pump can be used to provide left, right, or biventricular assistance. Cannulation for left ventricular assistance is most commonly performed through the right superior pulmonary vein into the left atrium with return into the ascending aorta. Right ventricular assistance is provided by cannulation of the right atrium and pulmonary artery. The pulmonary artery catheter is either placed through the right ventricle and threaded through the pulmonary valve or inserted directly into the pulmonary artery. Cannulas are secured in place with two pursestring pledgeted sutures and tourniquets as shown in Figure 2. At the time of decannulation, the catheters are removed and the pursestring sutures are tied down.

View larger version (127K): [in this window] [in a new window]   Fig 2. Patient with a BioMedicus centrifugal biventricular assist assist device and intraaortic balloon pump.

From January 1986 to September 1995, 141 patients at The Methodist Hospital in Houston, Texas were placed on the BioMedicus centrifugal pump after postcardiotomy cardiac failure. There were 112 men and 29 women (mean age, 61.6 years; range, 15 to 86 years). Left ventricular assistance was provided in 110 patients, right ventricular assistance in 8 patients, and biventricular assistance in 23 patients. In 114 patients weaning had been attempted in the operating room before insertion of the device, and 27 patients were returned from the intensive care unit for device implantation. These patients who required a ventricular-assist device had a variety of surgical procedures, which are summarized in Table 1. In 68.8% of the patients the intra-aortic balloon was inserted in addition to the pharmacologic weaning measures [7]. When weaning the patients from cardiopulmonary bypass or from the ventricular-assist device, it is important to optimize preload, afterload, cardiac rhythm, and ventricular function. If weaning from cardiopulmonary bypass is not successful, the ventricular assist device should be instituted. The patient is then weaned from cardiopulmonary bypass and maintained by the BioMedicus ventricular-assist device. We strive to maintain a cardiac index of at least 2.0 L/m² per minute. To minimize third space fluid accumulation, we normalize colloid oncotic pressure, avoid excessive crystalloid administration, and utilize hemofiltration. Medtronic Carmeda BioActive Surface (Anaheim, CA) circuits are used so that continued heparinization after implant is not required. The Medtronic Carmeda BioActive Surface circuits consist of a BioMedicus centrifugal pump head, tubing, cannulas, and connectors. Atrial cannulas used were 32-F x 60 cm or 40-F x 60 cm venous return catheters with a right-angle lighthouse tip. The aorta was cannulated with a 21-F angled aortic perfusion cannula. A 28-F single-stage venous return cannula with a straight tip was used to cannulate the pulmonary artery through the right ventricle. The inflow and outflow cannulas exit at the distal end of the sternotomy incision or through separate stab wounds in the infraxiphoid area. Coagulopathies are common and require prolonged periods of treatment with blood products, surgical hemostasis, and pharmacologic agents. We closed the chest in 71% of the patients. In 29%, the chest was left open because of continued bleeding, edema, and third space fluid accumulation. Patients were confined to bed and often were sedated and restrained to prevent dislodgment of the cannulas.

Patients with BioMedicus ventricular assist commonly have an intraaortic balloon pump in place to provide pulsatility; however, because of unsatisfactory vascular access, some patients cannot be supported with the intraaortic balloon pump. These patients have nonpulsatile blood flow, and a few have been supported for more than 1 week with evidence of adequate organ perfusion. During that time they were alert, oriented, and extubated.

Postcardiotomy or cardiogenic shock patients start out with single organ cardiac failure, but multiorgan dysfunction or failure is often the end result. The complications in the perioperative period are numerous and significant (Table 2). Eight intraoperative deaths occurred during the primary operation. Significant bleeding and coagulopathy occurred in 52% of the patients. Many of these complications were related to prolonged periods of attempted weaning with excessive use of inotropic and vasoactive drugs along with prolonged periods of low or impaired organ perfusion. Complications in patients with extended cardiopulmonary bypass who were easily weaned were less severe than in patients who had prolonged attempted weaning periods before initiation of ventricular assistance. That difference suggests that the high incidence of complications in the postcardiotomy patients is related to the weaning period rather than to the prolonged duration of cardiopulmonary bypass [7].

The BioMedicus pump was operated initially by the perfusionists in the operating room and intensive care unit. Once the patient is stabilized, the intensive care unit nurses monitor the pump function. A perfusionist is available in house throughout the implant period for occasional monitoring visits and emergencies.

When weaning the patient from the pump is considered, it is important to optimize preload, afterload, ventricular function, and cardiac rhythm. A weaning trial is performed first by evaluating hemodynamics during reduction of pump flow. If patients can maintain satisfactory hemodynamics, an echocardiogram or radioisotope imaging is considered to evaluate ventricular ejection fraction as pump flow is decreased. If patients can maintain satisfactory hemodynamics with reduction of pump flow, they can be considered for weaning [8]. If hemodynamics are unsatisfactory, the patients will require continued support and subsequent weaning trials. Figure 3 represents a patient with reduced pump flows and satisfactory hemodynamics. Over time flow is reduced gradually until it reaches 500 mL/min. This can occur over several hours or days, depending upon the patient’s response and stability. If patients remain hemodynamically stable with minimal ventricular assistance, they are taken to the operating room for further observation and explant [6, 9]. The chest is exposed and the pericardium and mediastinum are thoroughly cleansed and irrigated. The cannulas are removed and the pursestring sutures with pledgets are tied down. The sternum is then closed if adequate hemodynamic parameters can be maintained. If present, the intraaortic balloon is left in place for continued support. Most patients who were weaned had the device removed within the first 3 to 4 days of support. Patients who required support for more than 1 week were rarely weaned. The mean duration and range of support with the BioMedicus ventricular assist before death or device removal are listed in Table 3. The range is from less than 1 to 22 days.

View larger version (26K): [in this window] [in a new window]   Fig 3. Improving ventricular function with decreasing flow through the left ventricular-assist device. Aortic valve still opens at 3.5 L/min of flow.

Of the 141 patients supported with the Biomedicus ventricular assist, 54% were weaned, 46% could not be weaned, and 22% were discharged from the hospital alive. Results by type of support are listed in Table 4. There was a very high mortality rate early after support as shown in Figure 4. After weaning and device removal there was also a significant mortality rate, as shown in Figure 5. Ventricular failure was the major cause of death in patients who were weaned and not weaned. A summary of the causes of death in patients weaned and not weaned is given in Tables 5 and 6 [7].

View larger version (20K): [in this window] [in a new window]   Fig 4. Significant early mortality rate after BioMedicus ventricular assist device (VAD) support is initiated.

View larger version (18K): [in this window] [in a new window]   Fig 5. Significant mortality rate after weaning and device removal.

The BioMedicus centrifugal pump can provide short-term ventricular or pulmonary support. The pump is relatively inexpensive compared with other short- and long-term assist devices. Perfusionists and nursing personnel are also familiar with its operation.

The BioMedicus centrifugal pump can be used to provide temporary ventricular support in postcardiotomy patients. The high incidence of postimplant complications is related directly to prolonged periods of attempted weaning from cardiopulmonary bypass. Medtronic Carmeda BioActive Surface circuits were used so that continued heparinization after implant was not required. When weaning a patient from cardiopulmonary bypass or from ventricular assist is considered, it is important to optimize preload, afterload, ventricular function, and cardiac rhythm. To improve results in patients requiring postcardiotomy support, it is important to avoid fluid overload, low colloid oncotic pressure, hypoperfusion, and the use of excessive inotropic and vasoactive medications.

References

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