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A3442 - Mechanical Ventilation in Congenital Heart Disease: A Case of Complex Cardiopulmonary Interactions
Author Block: B. Gerke1, G. A. Cortes Puentes1, C. R. Bonnichsen2, R. A. Oeckler2; 1Mayo Clinic, Rochester, MN, United States, 2Mayo Clinic, Zumbro Falls, MN, United States.
Introduction: Positive-pressure mechanical ventilation (PPMV) in the setting of complex congenital heart diseases may negatively impact the unique cardiopulmonary interactions resulting from shunt physiology and surgical alterations in anatomy that often render pulmonary blood flow a passive process. We present a case of severe hemoptysis and refractory hypoxemia in the setting of a failing Fontan circulation in which the discontinuation of PPMV, despite high oxygen requirements, resulted in near-resolution of hypoxemic respiratory failure. Case Presentation: A 36 year-old-man with single ventricle physiology status post Fontan palliation with an extracardiac conduit presented to the emergency department with hemoptysis. Urgent bronchoscopy was performed, isolating the right lower lobe bleed by placement of a bronchial blocker to the Bronchus Intermedius. He then underwent interventional radiology (IR) embolization of the right intercostal bronchial trunk. Unfortunately, hemoptysis recurred in the right upper lobe requiring further IR embolization of a major aortopulmonary collateral artery. Overnight, the patient remained on PPMV with PEEP of 5 cmH2O and increasing FiO2 (to 1.0) and vasopressor requirements. Suspecting that cardiopulmonary failure was secondary to PPMV in this setting, the patient was extubated to high-flow nasal cannula which resulted in resolution of hypotension and improvement in hypoxemia to the point of transition to simple nasal cannula within 20 minutes. Discussion: The total cavopulmonary connection (TCPC) and intra-thoracic great veins are subjected to pleural pressure, which varies throughout the respiratory cycle. Systemic venous drainage then, depends on the pressure gradient between the extra-thoracic great veins (EGV) and TCPC; a difference greatest during spontaneous inspiration as pleural (and TCPC) pressure falls, and the intra-abdominal (and therefore EGV) pressure rises. Additionally, at lung volumes below functional residual capacity (FRC) extra-alveolar vessels become more tortuous leading to a net increase in PVR. At volumes above FRC, over-distended alveoli compress the microvasculature, similarly causing PVR to increase, decreasing preload to the single ventricle. Chronically elevated central venous pressures in the Fontan circulation lead to development of venovenous collaterals, resulting in hypoxemia. The loss of negative intra-thoracic pressure combined with the absence of a right ventricle to mitigate the effects of PVR on venous return, made our patient particularly vulnerable to worsening hypoxemia and hemodynamic instability with PPMV. Conclusion: Positive-pressure mechanical ventilation (PPMV) in the setting of complex congenital heart diseases demands a comprehensive understanding of their cardio-pulmonary interactions and a tailored strategy for extubation.