Discussion

The mechanism of re-expansion pulmonary edema development is still unclear. Capillary endothelial injury from lung re-expansion, lung parenchymal injury from systemic inflammatory responses associated with cardiopulmonary bypass, and pulmonary ischaemia-reperfusion injury may all act synergistically and cause re-expansion pulmonary edema after minimally invasive cardiac surgery. ^{Reference Hirose, Miwa and Sakaguchi1,Reference Irisawa, Hiraoka and Totsugawa2,Reference Inoue, Hiraoka and Chikazawa4} The incidence of re-expansion pulmonary edema after minimally invasive cardiac surgery in adults is approximately 2.1%. ^{Reference Irisawa, Hiraoka and Totsugawa2} However, only a few paediatric re-expansion pulmonary edema cases have been previously reported, ^{Reference Choi, Romeo, Gutman and Smith5} and no cases have been reported after a paediatric cardiac surgery. To the best of our knowledge, this is the first case reported.

We have performed minimally invasive cardiac surgery with a small right axillary incision in many children and no re-expansion pulmonary edema happened other than these two cases. We also never experienced re-expansion pulmonary edema after cardiac surgery through a median sternotomy or partial sternotomy. When we retrospectively consider the cause for re-expansion pulmonary edema, the only possibility that arise is the Fogarty catheter that was used as a bronchial blocker. In these two patients, we used the Fogarty catheter for the first time that could collapse right lung completely. Complete lung collapse with cardiopulmonary bypass may have influenced re-expansion pulmonary edema development. Therefore, it was decided not to adopt the Fogarty catheter and single lung ventilation for subsequent patients. The lungs are ventilated with low ventilation and low positive end-expiratory pressure until cardiopulmonary bypass initiates and once the pericardium is fixed, the lungs do not interfere with the surgical field. No re-expansion pulmonary edema have occurred since then.

Inoue et al. reported that intermittent right lung ventilation, restoration of bilateral ventilation, mannitol administration, and institution of mild hypothermia are effective in re-expansion pulmonary edema prevention. ^{Reference Inoue, Hiraoka and Chikazawa4} Our results support that various damage due to complete lung collapse is the most important risk factor for re-expansion pulmonary edema development after minimally invasive cardiac surgery. We strongly believe that the lungs should be kept inflated with some degree of positive end-expiratory pressure to prevent re-expansion pulmonary edema. In our cases, fortunately, the lung condition improved rapidly with only ventilator management, possibly due to the shorter lung collapse and aortic cross-clamp times, and less severe lung injury.

In the second case, not only right lung but also left lung, that was intact during the surgery, was damaged on the chest radiography (Fig 2). The frothy sputum was prominent from the right bronchus, but not from the left bronchus by bronchoscopy. From this point of view, we thought that the inflammatory reaction that developed in the right lung developed into a systemic inflammatory reaction that spread to the left lung.