Ann Thorac Surg 2002;74:1700-1702
© 2002 The Society of Thoracic Surgeons
Case report
Nitric oxide: lifesaving measure for pulmonary vasospasm after modified Blalock-Taussig shunt
Rajeev Gulati, MDa,
William A. Lell, MDb,
Albert D. Pacifico, MDa*,
Walter H. Johnson, Jr, MDc,
Edward V. Colvin, MDc,
Ashwani Bhardwaj, MDa
a Divisions of Cardiovascular and Thoracic Surgery, The University of Alabama at Birmingham, Birmingham, Alabama, USA
b Anesthesia, The University of Alabama at Birmingham, Birmingham, Alabama, USA
c Pediatric Cardiology, The University of Alabama at Birmingham, Birmingham, Alabama, USA
Accepted for publication June 20, 2002.
* Address reprint requests to Dr Pacifico, Division of Cardiovascular and Thoracic Surgery, University of Alabama at Birmingham, Suite 760 THT, 1900 University Blvd, Birmingham, AL, 35226, USA.
e-mail: albert.pacifico{at}ccc.uab.edu
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Abstract
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Pulmonary vasospasm and hypertension may occur after repair or palliation of congenital cardiac defects, and can be fatal in spite of conventional treatment. Nitric oxide has been shown to improve pulmonary hypertension unresponsive to conventional measures after a variety of repairs, but use has infrequently been reported after palliative systemic to pulmonary artery shunts. We report a case of pulmonary hypertension and life threatening desaturation after a modified Blalock–Taussig shunt that responded rapidly to inhaled nitric oxide. Clinical use, further study, and prospective analysis of prophylactic use of nitric oxide appear warranted.
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Introduction
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Pulmonary vasospasm and hypertension can complicate repair or palliation of congenital cardiac defects. Conventional therapy consists of hyperventilation, alkalinization, and sedation, but fatal pulmonary hypertension may occur in spite of these measures. Inhaled nitric oxide (NO) has been shown to improve pulmonary hypertension unresponsive to conventional measures, after a variety of congenital repairs [1–3]. In repairs involving cardiopulmonary bypass, bypass itself is thought to disrupt the pulmonary vascular endothelium, changing the balance between endothelial production of nitric oxide, a natural vasodilator, and vasoconstricting substances such as endothelin-1 [4]. This may lead to pulmonary vasospasm and hypertension. Pulmonary vasospasm and hypertensive episodes after palliative systemic to pulmonary artery shunting have been infrequently reported, the mechanism is less clear, and the effect of inhaled NO is not as well documented. We report a case of near-fatal pulmonary vasospasm and desaturation after modified Blalock–Taussig shunting, which responded rapidly to NO administration.
The patient is a 13-month-old female infant with tetralogy of Fallot with anomalous origin of the left anterior descending coronary artery, from the right coronary artery. She was palliated at 6 weeks of age with a right 4-mm Gore-Tex (W.L. Gore & Assoc, Flagstaff, AZ) modified Blalock–Taussig (B–T) shunt and now presented with easy fatigability and worsening oxygenation. Room air blood oxygen saturation by pulse oximetry (SpO2) was in the mid 80s at rest, and would drop to the 70s with crying. Echocardiography showed a normally functioning right Gore-Tex shunt. Cardiac catheterization demonstrated tetralogy of Fallot with moderate infundibular and valvar pulmonary stenosis. Because of an anomalous left coronary artery crossing the right ventricular outflow tract, likely precluding transannular patching and necessitating conduit placement, it was elected to further palliate by adding a left modified B–T shunt, with definitive repair planned at 3 to 5 years of age. At operation, the left subclavian and left pulmonary arteries were found to be large, and the shunt was performed with a 5-mm Gore-Tex tube. Anesthetic technique consisted of heavy premedication with pentobarbital, morphine, and scopalamine, because of the history of desaturation with crying. General anesthesia was induced with ketamine and maintained with isofluorane. In anticipation of early extubation, no narcotics were used. Room air SpO2 after sedation was 82%, but rose to 100% on a fractional inspired concentration of oxygen (FIO2) of 1.0; it remained so until the operation was completed and the patient was turned supine, whereupon it decreased to 89%. Over the next 2 hours in the intensive care unit, SpO2, confirmed by arterial blood gas measurements (SaO2), dropped into the 70s. Auscultation revealed good bilateral breath sounds, and no wheezing. Chest radiograph confirmed proper endotracheal tube placement and no pneumothorax. Initially, a shunt murmur was audible bilaterally, but as oxygenation continued to deteriorate, the murmur became inaudible on the left and barely audible on the right. Shunt thrombosis was suspected although the large diameter of the shunt and the technical ease of the operation made this seem less likely. Immediate echocardiography demonstrated minimal flow in the right shunt with no flow in the left shunt or in the main pulmonary artery. There was no gradient between the pulmonary artery and right ventricle, suggesting near systemic pulmonary artery pressures. Despite aggressive hyperventilation, alkalinization, and sedation with fentanyl, and even though systemic pressure remained normal without inotropes, oxygenation continued to worsen. The SaO2 dropped to 58%, and SpO2 transiently was as low as 28%. Inhaled NO was instituted at 40 ppm. The response was dramatic: within 3 or 4 minutes, SpO2 rose to 96% and bilateral shunt murmurs returned. Nitric oxide was weaned off over 4 hours and SaO2 remained in the 85% to 93% range. The FIO2 was also weaned, and the patient was extubated on postoperative day 1. No significant methemoglobinemia was noted. Repeat echo showed good bilateral shunt flow. The patient was discharged on postoperative day 3.
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Comment
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When desaturation occurs after a systemic-pulmonary artery shunt, various causes should be considered. These include: ventilation problems; pulmonary overcirculation, with edema due to an oversized shunt; and pulmonary undercirculation due to shunt thrombosis, undersized shunt, technical error, or pulmonary vasospasm. True pulmonary hypertensive crisis, defined as acute pulmonary hypertension with arterial desaturation, and systemic hypotension may occur. While systemic hypotension would be expected when a pulmonary hypertensive crisis occurs after a corrective procedure, it may not occur after a palliative procedure in a patient with an open ventricular septal defect, because of increased right to left shunting. Absence of an audible shunt murmur may suggest shunt thrombosis, but as illustrated by this case, loss of a murmur may instead reflect severe pulmonary hypertension causing reduced shunt flow. Echocardiography may provide more definitive information by directly visualizing thrombus or obstruction, or providing an indication of severe pulmonary hypertension.
The exact etiology of pulmonary hypertension after modified B–T shunting is not clear. Pulmonary hypertensive episodes in patients undergoing complete repair appear to correlate with preoperative pulmonary hypertension and postrepair high pulmonary artery pressure [3], but patients undergoing shunting usually have low pulmonary artery pressure. It may be that a pulmonary vascular endothelial abnormality related to the underlying diagnosis predisposes to pulmonary vasospasm. This may be the case in tetralogy of Fallot. One may speculate that direct manipulation of the pulmonary artery with endothelial disruption, similar to that induced by cardiopulmonary bypass, plays a part. The sudden increase in pulmonary blood flow, created by the shunt itself, in a pulmonary vascular bed accustomed to low flow and pressure perhaps could also lead to reactive pulmonary vasospasm and hypertension.
In this case, oxygenation initially decreased when anesthetic agents were stopped, coincident with turning the patient supine after the case. Narcotics were omitted to facilitate "fast track" extubation, and the patient was awake and moving vigorously shortly after arrival in the intensive care unit, so it is possible that a catecholamine response to operation prompted the pulmonary vasospastic episode.
Numerous studies have demonstrated reduction of postoperative pulmonary hypertension by inhaled NO, in patients undergoing complete repair of congenital defects. However, use of NO has been infrequently documented after systemic to pulmonary artery shunting. Shah and colleagues reported successful use of NO in a patient presumed to have severe pulmonary vasospasm after a modified B–T shunt placed for transposition, ventricular septal defect, and severe pulmonary stenosis [5]. Beghetti and associates reported that of 15 patients treated postoperatively with NO for pulmonary hypertension, 10 did not respond, and all were found to have anatomic obstruction [6].
In retrospect, we believe it is common to observe moderate transient hypoxemia in the first few hours after shunting. This raises the question of whether NO should be used routinely. Randomized prospective studies of prophylactic NO use after congenital cardiac repairs have had mixed results. Russell and coworkers showed improvement in patients with elevated pulmonary pressures, but Day and colleagues showed no reduction of pulmonary hypertension, or incidence of pulmonary hypertensive crises [2, 3]. The situation after B–T shunting has not been well studied and may be different since preoperative pulmonary hypertension does not exist, but direct manipulation of the pulmonary artery and a sudden increase in pulmonary blood flow due to the shunt does occur. Further study may identify a subset of patients undergoing shunting who could benefit from prophylactic NO.
In our patient, the use of NO for acute pulmonary vasospasm after modified B–T shunting was rapid and clearly lifesaving. We suggest that NO be strongly considered when acute pulmonary hypertension due to vasospasm is suspected postoperatively, and conventional measures have failed. This can be therapeutic as well as diagnostic, quickly differentiating pulmonary vasospasm from shunt thrombosis. Use of prophylactic NO for a period of hours after B–T shunting may be warranted.
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References
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- Zobel G., Gamillscheg A., Schwinger W., et al. Inhaled nitric oxide in infants and children after open heart surgery. J Cardiovasc Surg 1998;39:79-86.[Medline]
- Russell I.A.M., Zwass M.S., Fineman J.R., et al. The effects of inhaled nitric oxide on postoperative pulmonary hypertension in infants and children undergoing surgical repair of congenital heart disease. Anesth Analg 1998;87:46-51.[Abstract/Free Full Text]
- Day R.W., Hawkins J.A., McGough E.C., Crezee K.L., Orsmond G.S. Randomized controlled study of inhaled nitric oxide after operation for congenital heart disease. Ann Thorac Surg 2000;69:1907-1913.[Abstract/Free Full Text]
- Bando K., Palaniswamy V., Turrentine M.W., et al. Dynamic changes of endothelin-1, nitric oxide, and cyclic GMP in patients with congenital heart disease. Circulation 1997;96(Suppl 2):346.
- Shah A.S., Smerling A.J., Quaegebeur J.M., Michler R.E. Nitric oxide treatment for pulmonary hypertension after neonatal cardiac operation. Ann Thorac Surg 1995;60:1791-1793.[Abstract/Free Full Text]
- Beghetti M., Morris K., Cox P., Bohn D., Adatia L. Inhaled nitric oxide differentiates pulmonary vasospasm from vascular obstruction after surgery for congenital heart disease. Intensive Care Med 1999;2:1126-1130.
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Abstract
Introduction
