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Ann Thorac Surg 2001;71:735-736
© 2001 The Society of Thoracic Surgeons

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How to do it

Use of ECMO without the oxygenator to provide ventricular support after Norwood Stage I procedures

^a Divisions of Perfusion Services, Duke University Medical Center and Health Systems, Durham, North Carolina, USA
^b Thoracic Surgery, Duke University Medical Center and Health Systems, Durham, North Carolina, USA

Accepted for publication June 2, 2000.

Address reprint requests to Dr Ungerleider, Division of Cardiothoracic Surgery, L-353, Oregon Health Sciences University, 3181 SW Sam Jackson Park Rd, Portland, OR 97201-3098

	Abstract

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Extracorporeal membrane oxygenation (ECMO) has been found effective in supporting infants with severe cardiac dysfunction following open heart surgery. Centers using this mode of support can also, in instances of single ventricle morphology, consider the option of eliminating the oxygenator from the standard ECMO set-up and thereby provide roller pump ventricular assist. In these cases, the infant’s own lungs can provide excellent oxygenation simply by leaving the aortopulmonary shunt open. Since ventricular support ensures maintenance of normal cardiac output, manipulation of pulmonary versus systemic flows is not necessary. This configuration retains the safety features of the ECMO system and is easily staffed by the ECMO support personnel. There may be several benefits to employing this type of management.

	Introduction

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In infants, postcardiotomy mechanical support is most commonly achieved by using extracorporeal membrane oxygenation (ECMO) [1, 2]. This is likely due to the ready availability of ECMO systems and trained ECMO support staff in pediatric centers. In addition, the technical barriers to conventional forms of ventricular assist (ie, intraaortic balloon counterpulsation, centrifugal ventricular assist devices) imposed by small patient size has made ECMO the default form of post-cardiopulmonary bypass support in neonates.

In instances of post-cardiopulmonary bypass ventricular dysfunction with single ventricle morphology in neonates who require mechanical support, it may be beneficial to eliminate the oxygenator from the standard ECMO system. In this configuration, the circuit becomes a roller pump ventricular assist device. We have used the term NOMO-VAD for "No membrane oxygenator-ventricular assist device." This system, as opposed to centrifugal pump systems, retains the desirable aspects of the ECMO circuit including pump servo-regulation, pressure monitoring, access ports for fluid/drug administration, air bubble detection, in-line blood gas monitoring, and a heat exchanger. Oxygenation is provided by the infant’s own lungs, simply by leaving the aortopulmonary shunt open [3].

	Technique

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NOMO-VAD was initiated in the operating room for patients with hypoplastic left heart syndrome palliated with Norwood Stage I procedures when there was evidence of poor myocardial function. We defined poor myocardial function as increasing inotrope requirements, low systolic blood pressure (< 55 mm Hg) or systemic venous oxygen saturation less than 60% with a hematocrit greater than 35%.

The NOMO-VAD set-up is done in the same fashion as a standard ECMO system with one exception; a x inch tubing connector is substituted in place of the oxygenator. This circuit is primed per ECMO protocol although less blood products may be necessary due to the reduction of prime volume resulting from the elimination of the oxygenator. Cannulation utilizes the same cannulae used for the surgical reconstruction with venous return from the right atrium and arterial infusion into the neoaorta. Initiation of NOMO-VAD should be done slowly since the circuit prime is not oxygenated. Target flow rates of 200 ml/kg/min should be achieved in order to support the dual circulations (systemic and pulmonary) present in Stage I palliation patients [3]. Monitoring and volume management of the NOMO-VAD system and patient would follow standard ECMO protocol. Since there is no oxygenator in the circuit, and flow rates are generally high, anticoagulation may not be essential and is usually not desirable in the first several hours after surgery. This promotes hemostasis in these patients who can often exhibit substantial bleeding due to the extensive suture lines. After hemostasis is secure, anticoagulation can be provided by infusion of heparin to maintain the activated clotting time at 180 to 200 seconds. The chest incision is usually covered with an eshmark dressing while the cannulae are in place. Patients often benefit from support for 2 to 5 days and then can be easily weaned, decannulated, and have chest closure in the intensive care unit. Weaning from NOMO-VAD is simple since the patient’s aortopulmonary shunt is open and cessation of VAD flow restores the patients to standard Stage I physiology. Since the circuit has an arterio-venous loop, flow through the system can be maintained while it is ascertained whether the patient is ready to be separated from the circuit.

We have now utilized this system for 5 (nonconsecutive) infants who have undergone Norwood Stage I palliation procedures. Four of these infants were placed on VAD in the operating room because of signs of deteriorating myocardial function during or immediately following a period of modified ultrafiltration. Deterioration in myocardial function was manifested by falling blood pressures, a need for increasing inotropic support beyond dopamine (10 µg/kg/min), a decrease in arterial oxygenation below 70% or (in 2 cases) cardiac arrest requiring reinstitution of cardiopulmonary bypass. One patient had deterioration in the intensive care unit on the first postoperative day despite an initially smooth clinical course. After resuscitation with epinephrine, this patient was placed on NOMO-VAD in the intensive care unit. The NOMO-VAD course was 2 to 5 days. In 2 patients who could not be weaned at 2 days, echocardiogram performed at 5 days revealed large posterior pericardial effusions which, once drained, enabled easy weaning from the circuit. It was suspected that these probably interfered with the attempt at weaning after 2 days of support. One patient, who had had a cardiac arrest in the operating room, required 5 days of NOMO-VAD support before he could be weaned. From this experience, we would suggest performing an echocardiogram on any infant who cannot be weaned after 2 days of support to rule out the presence of a large posterior pericardial effusion. One patient died in the hospital due to problems not related to his cardiovascular system. The other 4 patients have been discharged from the hospital and have all undergone successful bidirectional Glenn procedures.

There have been no complications related to the NOMO-VAD circuitry. In all cases, we were able to maintain support at flow rates of 150 to 200 ml/min with normal arterial blood gases. Manipulation of the ventilator to control shunt balance in these patients was not necessary.

	Comment

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We introduced the concept of leaving the aortopulmonary shunt open during ECMO in 1997 when we recognized the increased risk of lung injury resulting from shunt occlusion [3, 4]. The lungs did not "flood" and in fact, it was possible to ventilate patients normally with respect to oxygen and carbon dioxide. By providing adequate cardiac output with the ECMO circuit, the patients "balanced" themselves and quickly recovered to a point where support was no longer necessary. ECMO, however, due to the presence of the membrane oxygenator which greatly increases the foreign surface area of the system, requires anticoagulation and can significantly complicate the immediate postoperative period. After observing that patients had adequate pulmonary blood flow with the shunt open, we theorized that the oxygenator was not necessary.

The use of ECMO circuitry, equipment, and personnel makes the NOMO-VAD technique a simple and versatile way to provide cardiac support to this "physiologically challenged" population of patients. The elimination of the oxygenator may have the positive benefits in reducing associated thromboemboli, preserving coagulation factors, minimizing hemolysis, and reducing the inflammatory response [5, 6]. Despite our somewhat limited clinical experience, we are encouraged by the simplicity of this technique and report it because of its potential for enormous value in helping improve survival rates for this challenging group of patients. Support of the increased cardiac output needs following Norwood Stage I palliation may not only lead to increased survival, but protects the infant from hemodynamic instability and diminished tissue oxygen delivery from low cardiac output in the immediate postoperative period. This may lead to improved long-term outcomes.

	References

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1. Del Nido P. Extracorporeal membrane oxygenation for cardiac support in children. Ann Thorac Surg 1996;61:336-339.[Abstract/Free Full Text]
2. Rogers A.J., Trento A., Siewers R.D., Griffith B.P., Hardesty R.L., Pahl E., Beerman L.B., Fricker F.J., Fischer D.R. Extracorporeal membrane oxygenation for post-cardiotomy cardiogenic shock in children. Ann Thorac Surg 1989;47:903-906.[Abstract]
3. Jaggers J.J., Forbess J., Shah A., Meliones J.N., Kirshbom P.M., Miller C.E., Ungerleider R.M. Extracorporeal membrane oxygenation (ECMO) for post-cardiotomy failure in children: significance of shunt management in the single ventricle. Ann Thorac Surg 2000;69:1476-1483.[Abstract/Free Full Text]
4. Chai P.J., Williamson A., Lodge A.J., Dagget C.W., Scarborough J.E., Meliones J.N., Cheifetz I.M., Jaggers J., Ungerleider R.M. Effects of ischemia on pulmonary dysfunction after cardiopulmonary bypass. Ann Thorac Surg 1999;67:731-735.[Abstract/Free Full Text]
5. Fink S.M., Bockman D.E., Howell C.G., Falls D.G., Kanto W.P., Jr Bypass circuits as the source of thromoboemboli during extracorporeal membrane oxygenation. J Pediatrics 1989;115:621-624.[Medline]
6. Steinhorn R.H., Isham-Schopf B., Smith C., Green T.P. Hemolysis during long-term extracorporeal membrane oxygenation. J Pediatrics 1989;115:625-630.[Medline]

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This Article Abstract Full Text (PDF) 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): James J. Jaggers Ross M. Ungerleider Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Darling, E. M. Articles by Ungerleider, R. M. Search for Related Content PubMed PubMed Citation Articles by Darling, E. M. Articles by Ungerleider, R. M. Related Collections Congenital - cyanotic Extracorporeal circulation