Flash pulmonary edema in a post arterial switch operation - High flow oxygen as a treatment modality.

We report a case of a 3-year-old boy who underwent an arterial switch operation with relief of left ventricular outflow tract obstruction and later presented with recurrent episodes of flash pulmonary edema. High-flow humidified oxygen with positive pressure support (Vapotherm) was used as a treatment modality, thereby avoiding intubation and mechanical ventilation.

INTRODUCTION

Flash pulmonary edema is a condition characterized by sudden and recurrent episodes of dyspnea at rest resulting from acute pulmonary congestion in the presence of normal or well-preserved left ventricular (LV) systolic function. Flash pulmonary edema is often precipitated by acute myocardial infarction, acute mitral and, aortic regurgitation, accelerated hypertension or almost by any cause of elevated LV filling pressures. Flash pulmonary edema differs from the usual cases of LV failure with pulmonary edema in that it is usually not associated with severe LV dysfunction. This is mostly nocturnal and occurs suddenly. Management consists of adequate diuretics, pre and afterload reduction and a times patient may need the support of a mechanical ventilator.[1]

CASE REPORT

A 3-year-old boy presented with a history of cyanosis since 8 months of age, effort intolerance since infancy, and breathlessness on exertion with saturation of 64% on room air. Echocardiographically, he was diagnosed with d-transposition of great arteries, intact interventricular septum, moderate sized secundum atrial septal defect, moderate subvalvar pulmonary stenosis, Grade II tricuspid regurgitation, and normal right ventricular (RV) function with a semi prepared LV. A chest X-ray showed increased vascularity in the lung fields and a prominent right pulmonary artery. Echocardiographically, the left ventricle looked semi-prepared with a posterior wall thickness of 4 mm although cardiac catheterization revealed LV pressure of 69/12 mmHg and RV pressure of 100/14 mmHg.

The patient underwent an arterial switch operation with relief of LV outflow tract obstruction. He was stable for 24 hours after surgery. However, subsequently he became hemodynamicaly unstable with a chest X-ray suggestive of acute pulmonary edema. Left atrial (LA) pressures were high in spite of diuretics and adequate afterload reduction. An echo showed no residual LV outflow tract obstruction, tricuspid regurgitation gradient of 20 mmHg, mild mitral regurgitation with a LV ejection fraction of 50%. The patient required prolonged ventilation with diuretics and inotropic support and then showed gradual improvement with chest X-rays showing clear lung fields. The patient was finally extubated on the 12th day after the operation and he was discharged from the intensive care unit (ICU) on the 15th postoperative day

However, he was readmitted to the ICU four more times because of respiratory distress requiring mechanical ventilation. A series of chest X-rays taken during this period were suggestive of recurrent episodes of pulmonary edema. An echo done during these re-admissions showed fair LV without any LV outflow tract obstruction.

The hypothesis was that although the LV was partially prepared prior to the arterial switch operation, it did not tolerate having to pump at systemic pressures. In view of repeated intubations, the patient was put on a trial of high-flow humidified oxygen with positive pressure support (Vapotherm). Eventually this non- invasive method avoided further intubations and allowed the patient to be discharged from the ICU.

DISCUSSION

Flash pulmonary edema was first reported by Pickering, et al. in 1988 and subsequently there have been a number of papers confirming this as a distinct clinical entity but it is unclear as to how often it is recognized.[2] There are several studies that report the occurrence of flash pulmonary edema in adults due to bilateral renal artery stenosis.[12] Flash pulmonary edema is also a proven entity after coronary artery revascularizations due to myocordial ischemia leading to diastolic dysfunctions.[2]

Our case illustrates the occurrence of recurrent pulmonary edema in a 3-year-old male who underwent arterial switch operation with LV outflow tract obstruction release requiring repeated admissions in the ICU due to flash pulmonary edema. Finally the patient was weaned off the ventilator using high-flow humidified oxygen as a form of positive pressure non invasive ventilation (Vapotherm), which reduces the complications associated with endotrachael intubation and mechanical ventilation.[3]

We termed this as flash pulmonary edema due to its acute presentation and repeated occurrences. The acute onset of pulmonary edema may be due to underprepardness of the LV for surgery. Though the LV looked prepared, the increase in LV end diastolic pressure suggested LV diastolic dysfunction.

The reason for missing the diagnosis in the early stage might be due to the fact that echocardiographic findings showing good LV function, which gave us a sense of false security, as was reported in a previous study.[2]

CONCLUSION

Flash pulmonary edema, although uncommon in children is a well described entity. In our case, the repeated episodes of flash pulmonary edema occurred most probably due to the high LV end diastolic pressure. It is important to keep this diagnosis in mind in cases where postoperative patients present with repeated episodes of pulmonary edema. Such cases can be managed conservatively with adequate diuresis and high-flow oxygen therapy, which in our case was extremely useful until the high LV end diastolic pressure resolved.