540573 research-article2014



Commentary on: Tetralogy of Fallot with pulmonary atresia and major aortopulmonary vessels

RA Jonas The article entitled “Tetralogy of Fallot with pulmonary atresia and major aortopulmonary collateral vessels” raises some important points regarding perfusion strategy in the presence of collateral vessels.1 In 1992, Wong et al. from Boston Children’s Hospital reported a virtual epidemic of choreoathetosis following cardiopulmonary bypass in children with aortopulmonary collaterals.2 The presumed mechanism was a steal from the cerebral circulation by aortopulmonary collaterals. Blood pumped into the aorta returns directly to the heart and is returned to the pump, either by a left heart vent or by venous cannulas in the presence of an atrial septal defect (ASD) and ventricular septal defect (VSD). Although Wong et al. were not able to demonstrate in their analysis that perfusion pH strategy was directly associated with the epidemic of choreoathetosis, the reality was that the pH strategy in Boston had been changed from the more acidotic pH-stat strategy to the alkalotic alpha-stat strategy shortly before the onset of the epidemic of choreoathetosis. There were no serious subsequent cases when the pH strategy was changed back to the pH-stat strategy. In 2004, Sakamoto et al. conducted a randomized trial of the influence of pH strategy on cerebral and collateral circulation.3 Forty cyanotic patients were randomized either to the pH-stat strategy or alpha-stat strategy. The authors confirmed that cerebral oxygenation was improved with the pH-stat strategy. They were also able to document reduced collateral blood flow with the pH-stat strategy. The findings of the trial by Sakamoto et al. were consistent with a previously published prospective randomized trial of pH strategy undertaken at Children’s Hospital, Boston, in infants with a range of congenital cardiac conditions. This trial documented that all perioperative complications were more likely with the alpha-stat strategy.4 In patients with transposition of the great arteries, there was a documented improvement in clinical outcomes, such as duration of intubation and duration of intensive care unit (ICU) stay.

Perfusion 1­–2 © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0267659114540573 prf.sagepub.com

In the present article, the authors, similar to Sakamoto et al., have documented reduced collateral run-off with the pH-stat strategy. By reducing sucker return to the oxygenator, they were also able to reduce the number of gaseous microemboli. The exact cellular mechanism by which collateral return was decreased remains unclear.5 Nevertheless, a simplistic explanation remains that the addition of carbon dioxide as the key feature of the pH-stat strategy to the sweep gas results in cerebral vasodilation and pulmonary vasoconstriction. Another important point to be noted from the current article is the rare association of Scimitar syndrome with tetralogy of Fallot. This patient demonstrated the principle features of Scimitar syndrome, namely a large aortopulmonary collateral vessel, an anomalous pulmonary vein draining to the right atrium and right lung hypoplasia. Although the classic Scimitar vein drains the entire right lung and usually connects to the inferior vena cava, nevertheless, variants of Scimitar syndrome in which one or two lobar pulmonary veins connect either to the IVC or right atrium have been noted. Often, the collateral vessel which supplies the right lower lobe arises from the abdominal aorta rather than the thoracic aorta and is duplicate in its distribution, i.e., the same bronchopulmonary segments supplied by the collateral are also supplied by branches of the true pulmonary artery. Under these circumstances, it is important to coil occlude the collateral vessel prior to cardiopulmonary bypass. This is the most effective method for preventing a dangerous steal from the systemic circulation during cardiopulmonary bypass. It will also accelerate postoperative recovery and often represents the definitive treatment of partial Scimitar syndrome where only part of the right lung drains anomalously. In conclusion, the pH-stat strategy is the preferable pH strategy in any patient in whom there is likely to be a steal from the systemic circulation by aortopulmonary collateral vessels. Preferably, large discrete collateral vessels that provide duplicate supply to bronchopulmonary segments should be coil occluded prior to placing a patient on cardiopulmonary bypass.

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References 1. Issitt RW, Robertson DA, Crook RM, Cross NT, Shaw M, Tsang VT. Tetralogy of Fallot with pulmonary atresia and major aortopulmonary collateral vessels. Perfusion 2014; DOI. 2. Wong PC, Barlow CF, Hickey PR, et al. Factors associated with choreoathetosis after cardiopulmonary bypass in children with congenital heart disease. Circulation 1992; 86: II-118–II-126. 3. Sakamoto T, Kurosawa H, Shin’oka T, Aoki M, Isomatsu Y. The influence of pH strategy on cerebral and collateral circulation during hypothermic cardiopulmonary bypass in cyanotic patients with heart disease: results of a randomized trial and real-time monitoring. J Thorac Cardiovasc Surg 2004; 127: 12–19. 4. du Plessis AJ, Jonas RA, Wypij D, et al. Perioperative effects of alpha-stat versus pH-stat strategies for deep

hypothermic cardiopulmonary bypass in infants. J Thorac Cardiovasc Surg 1997;114: 991–1000. 5. Chang AC, Zucker HA, Hickey PR, Wessel DL. Pulmonary vascular resistance in infants after cardiac surgery: role of carbon dioxide and hydrogen ion. Crit Care Med 1995; 23: 568–574.

Richard A. Jonas Chief, Cardiac Surgery Co-Director, Children’s National Heart Institute Children’s National Medical Center Professor of Surgery George Washington University Medical School Washington DC

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Tetralogy of Fallot with pulmonary atresia and major aortopulmonary vessels.

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