Invited Commentary

Abstract

Jha and associates [1Jha A.K. Gharde P. Devagourou V. Chauhan S. Kiran U. The effect of volume loading on systemic oxygenation after bidirectional superior cavopulmonary anastomosis.Ann Thorac Surg. 2014; 97: 932-937Google Scholar] present a thought-provoking study on the effects of administering intravascular volume early after a superior cavopulmonary connection (SCC). The study is prospectively conducted and controls many patient and procedural variables. Several of the study conditions are worth noting. The study was initiated 10 minutes after cardiopulmonary bypass, with the chest closed and the patients mechanically ventilated. The patients’ median age was 2 years. At the time of the study, each patient had two sources of pulmonary blood flow: a preserved native pulmonary outflow tract, and the SCC (“pulsatile SCC”). Volume administration resulted in increased common atrial pressure (measured in the inferior vena cava), SVC pressure, and blood pressure, with a decrease in heart rate. Systemic oxygen saturation and PO2 increased. Several indicators of cerebral blood flow improved: SVC saturation and cerebral near-infrared spectroscopy signal increased, while upper body arteriovenous saturation difference fell. From the presented data, we can also deduce that the transpulmonary gradient increased (from roughly 3 mm Hg to 10 mm Hg). How do we interpret these findings? Assuming relatively constant pulmonary vascular resistance, the increase in transpulmonary gradient indicates increased pulmonary blood flow. Increased systemic oxygenation is the result. Flow to the lungs likely increased through both sources of pulmonary flow. Increased common atrial pressure and systolic blood pressure will drive more flow through a patent outflow tract, so at least some of the investigators’ findings are due to increased antegrade pulmonary flow. The increased cerebral near-infrared spectroscopy signal and decreased upper body arteriovenous saturation difference also suggest an increase in cerebral blood flow, and therefore SCC flow. An increase in cerebral flow due to increased arterial blood pressure indicates some impairment of cerebral autoregulation. Although mildly hypothermic cardiopulmonary bypass is generally believed to preserve cerebral autoregulation, this issue has not been well studied in children early after SCC. The effects of intravascular volume administration depend on the baseline volume status of the patient. In the study patients, the low mean atrial pressure (inferior vena cava, 6 mm Hg) and SVC pressure (9 mm Hg) at T1, as well as the response of the blood pressure and heart rate to volume administration, suggest that the patients were hypovolemic at baseline. Optimization of volume status at the end of any operation is obviously good practice. Conversely, maintenance of an SVC pressure in the 16 to 20 mm Hg range in an infant is difficult to sustain, and can result in third-spacing with pleural effusions and ascites. Hypoxemia can be an important clinical problem early after SCC. Available approaches include minimization of positive pressure ventilation, judicious hypoventilation, early endotracheal extubation, optimization of cardiac output and hemoglobin level, and (occasionally) the addition of a systemic-pulmonary shunt. The current study specifically examines cardiac output optimization by the addition of intravascular volume. Whether the findings would apply in a more typical patient, such as a 6-month-old with a systemic-pulmonary shunt undergoing a nonpulsatile SCC, will require further study. Jha and colleagues [1Jha A.K. Gharde P. Devagourou V. Chauhan S. Kiran U. The effect of volume loading on systemic oxygenation after bidirectional superior cavopulmonary anastomosis.Ann Thorac Surg. 2014; 97: 932-937Google Scholar] are to be congratulated for carrying out this prospective, well-controlled, and interesting study. The Effect of Volume Loading on Systemic Oxygenation After Bidirectional Superior Cavopulmonary AnastomosisThe Annals of Thoracic SurgeryVol. 97Issue 3PreviewThe unique series arrangement of the cerebral and pulmonary circulation in bidirectional superior cavopulmonary anastomosis (BCPA) makes the pulmonary blood flow dependent upon the cerebral blood flow. Until now, several investigators have tried to correct post-BCPA hypoxemia with various methods such as induced hyperventilation, the addition of carbon dioxide, and inhaled nitric oxide with variable success rates. Full-Text PDF