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Ann Thorac Surg 1998;65:340-345
© 1998 The Society of Thoracic Surgeons
Department of Surgery, Columbia University College of Physicians and Surgeons, New York, New York, USA,
Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York, USA,
Department of Anesthesiology, Columbia University College of Physicians and Surgeons, New York, New York, USA
Dr Argenziano, Division of Cardiothoracic Surgery, Milstein Hospital, Rm 7-435, 177 Fort Washington Ave, New York, NY 10032 (e-mail: ma66@columbia.edu).
Presented at the Thirty-third Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Feb 35, 1997.
| Abstract |
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Methods. Eleven of 23 patients undergoing LVAD insertion met criteria for elevated pulmonary vascular resistance on weaning from cardiopulmonary bypass (mean pulmonary artery pressure >25 mm Hg and LVAD flow rate <2.5 L · min-1 · m-2) and were randomized to receive either inhaled NO at 20 ppm (n = 6) or nitrogen (n = 5). Patients not manifesting a clinical response after 15 minutes were given the alternative agent.
Results. Hemodynamics for the group at randomization were as follows: mean arterial pressure, 72 ± 6 mm Hg; mean pulmonary artery pressure, 32 ± 4 mm Hg; and LVAD flow, 2.0 ± 0.3 L · min-1 · m-2. Patients receiving inhaled NO exhibited significant reductions in mean pulmonary artery pressure and increases in LVAD flow, whereas none of the patients receiving nitrogen showed hemodynamic improvement. Further, when the nitrogen group was subsequently given inhaled NO, significant hemodynamic improvements ensued. There were no significant changes in mean arterial pressure in either group.
Conclusions. Inhaled NO induces significant reductions in mean pulmonary artery pressure and increases in LVAD flow in LVAD recipients with elevated pulmonary vascular resistance. We conclude that inhaled NO is a useful intraoperative adjunct in patients undergoing LVAD insertion in whom pulmonary hypertension limits device filling and output.
| Introduction |
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In patients receiving a left ventricular assist device (LVAD) for advanced heart failure, pulmonary hypertension often limits the adequacy of device filling, which leads to right ventricular failure in up to 40% of patients [4]. Because the effectiveness of inotropic and nonspecific vasodilator agents in the management of these patients is frequently limited by systemic hypotension and inhibition of alveolar oxygenation [5], the institution of right ventricular mechanical support is sometimes required [6]. Although right ventricular assist devices effectively improve cardiac output in these situations, their use is complicated by prolongation of operative time, the need of reestablishment of cardiopulmonary bypass, and an increased risk of hemorrhage [7]. Furthermore, biventricular assistance greatly inhibits patient mobility and necessitates additional operation for device removal.
Nitric oxide (NO), initially described as an endotheliumderived relaxation factor [8], has been implicated in a wide variety of physiologic and pathophysiologic processes. Inhaled NO has been shown to cause pulmonary vasodilation in primary pulmonary hypertension [9], in pulmonary hypertension secondary to congenital heart disease [10], and in the adult respiratory distress syndrome [11]. Recently, inhaled NO has been used to selectively lower PVR in patients undergoing cardiac surgical procedures [12]. Prompted by the successful use of inhaled NO in 2 LVAD recipients with right ventricular failure, we initiated the present randomized, placebo-controlled study to investigate the short-term effects of inhaled NO in patients with hemodynamically significant pulmonary hypertension after insertion of an LVAD for end-stage heart failure.
| Material and Methods |
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Hemodynamics were recorded for the 23 LVAD recipients on arrival in the operating room, throughout the device insertion procedure, and during the postoperative intensive care unit stay. On meeting the two selection criteria 5 minutes after weaning from cardiopulmonary bypass, LVAD patients were blindly randomized to receive inhaled NO at a delivered concentration of 20 ppm or nitrogen (N2) at an equivalent flow rate. A clinical response was defined as a decrease in mean PAP of 5 mm Hg or greater, an increase in LVAD output of more than 20%, or both in the absence of other pharmacologic or surgical interventions. In the absence of a clinical response to the assigned agent within 15 minutes, patients were given the alternative agent, again in a blinded manner. If a clinical response was observed, the assigned agent was continued postoperatively. On arrival in the intensive care unit, the patient was weaned from the administered gas mixture (NO or N2) to maintain mean PAP at less than 25 mm Hg and LVAD flow at higher than 2.5 L · min-1 · m-2.
Nitric Oxide Administration
Nitric oxide, an NO stock gas mixture (800 ppm) (Airco Special Gases, Riverton, NJ) diluted appropriately with oxygen, was administered intraoperatively through the operating room ventilator system. The breathing circuit was equipped with an in-line oxygen analyzer downstream as well as a chemiluminescence monitor attached as close to the patient as possible to monitor the delivered concentration of oxygen and NO. Delivered inhaled NO concentration was controlled by adjusting the ratio of NO flow to ventilator flow. All exhaled gases were scavenged appropriately. In the intensive care unit, NO, again an 800-ppm stock gas mixture, was administered through a modified ventilator circuit.
Analysis of Data
Hemodynamic and clinical data are reported as the mean ± the standard error of the mean. Paired variables were analyzed by the paired Students t test, and unpaired variables were compared using the Wilcoxon nonparametric test. A p value of less than 0.05 was considered significant.
| Results |
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There were two perioperative deaths. One occurred on postoperative day 1 and was due to intractable hemorrhage in a patient with multiple-system failure. The other occurred on postoperative day 3 and was due to brain death in a patient with an intraoperative cerebrovascular embolic event.
| Comment |
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Whatever the mechanism, secondary elevations in PVR are initially reactive in nature and are usually reversible if underlying pathologic processes (eg, congestive heart failure and hypoxia) are corrected early in their course [15]. Persistent elevations in PAP, however, are associated with an increased risk of right heart failure and death after cardiac transplantation [2] [3] and LVAD placement [4]. Accordingly, reversibility of pulmonary hypertension with vasodilators such as sodium nitroprusside and most recently by inhaled NO [16] is generally considered to be a requirement in the selection of candidates for cardiac transplantation (and therefore LVAD recipients) [17].
Right ventricular failure refractory to pharmacologic therapy occurs in 20% to 40% of patients supported with an LVAD [4] [18] [19]. Left ventricular assist device support induces a variety of hemodynamic changes with important effects on right ventricular physiology and function. Improvements in systemic perfusion result in augmented venous return to the right ventricle, which increases preload but may precipitate right ventricular failure because of volume overload [18]. In addition, although left ventricular unloading may passively reduce right ventricular afterload by decreasing postpulmonary capillary pressures [20], resultant acute increases in pulmonary blood flow may transiently increase PVR and afterload [18]. Finally, although LVAD support may improve right ventricular systolic function by increasing coronary perfusion, the disturbances to ventricular interaction caused by leftward displacement of the interventricular septum and reduction of left ventricular pressure generation result in a net decrease in right ventricular contractility [21].
Medical management of right ventricular failure in LVAD recipients includes the provision of adequate right ventricular preload and the maintenance of sinus rhythm [22]. Volume infusion is usually limited, however, by the risk of volume overload and right ventricular decompensation. Although pharmacologic management with inotropic and vasodilatory drugs is often successful [23], the effectiveness of these agents may be limited by an increased incidence of cardiac arrhythmias, profound systemic hypotension, and derangement of alveolar gas exchange by inhibition of hypoxic vasoconstriction [5].
Inhaled NO is an extremely effective, specific pulmonary vasodilator in animals, infants, and adults with pulmonary hypertension [9] [10] [11] [12]. After easily crossing the alveolus, NO is absorbed into the bloodstream, rapidly bound to hemoglobin, and converted into relatively inactive nitrate and nitrite by the enzyme methemoglobin reductase. At clinically useful concentrations, fewer than 80 ppm, there does not seem to be systemic vasodilatation because the inhaled gas affects only the vascular smooth muscle subjacent to ventilated bronchioles and alveoli. In addition, because the vasodilatory effect of inhaled NO gas is limited to ventilated areas of lung, it selectively dilates vessels in well-ventilated lung regions, thus improving ventilation-perfusion matching.
The present study identified 11 patients undergoing LVAD placement for end-stage heart failure who manifested hemodynamically significant elevations in PVR and signs of right ventricular failure despite maximal medical therapy on weaning from cardiopulmonary bypass. Patients randomized to receive inhaled NO at a concentration of 20 ppm demonstrated rapid, significant reductions in PVR that were manifested as decreases in PAP and increases in LVADassisted cardiac output. Patients receiving N2 placebo showed no response but demonstrated impressive hemodynamic improvement when crossed over to the inhaled NO group. The beneficial effects of inhaled NO were not associated with systemic hypotension, hypoxia, or other adverse consequences. Importantly, all patients were successfully weaned from inhaled NO in less than 1 week. The vasodilator acted as a hemodynamic bridge while reactive elevations in PVR and temporary right ventricular dysfunction gradually improved. The use of inhaled NO averted the need of right ventricular assist device insertion in all but 1 patient, and in this patient, hemodynamic collapse resulted from abrupt discontinuation of this agent. Prior to the availability of inhaled NO at our center, 4 of 19 LVAD recipients with right ventricular failure required right ventricular assist device support, with an associated mortality rate of 50% [6].
In conclusion, inhaled NO is a potent and specific pulmonary vasodilator. When administered to patients receiving LVADs, it results in significant improvements in PVR and right ventricular function without adverse sequelae. Because pulmonary hypertension is a risk factor for the development of right ventricular failure and death in patients undergoing orthotopic cardiac transplantation, mitral valve operations, and other cardiac operations, further study of this agent as an intraoperative adjunct in the management of cardiac surgical patients is warranted.
| Acknowledgments |
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| References |
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