**4.4 Interstage problems**

In children who have one functioning ventricle requiring Fontan correction, the systemic and pulmonary circulations work in-parallel in place of the usual in-series circulation. A fragile equilibrium between the two circulations must be preserved so that adequate systemic and pulmonary perfusions are maintained. There is substantial interstage mortality ranging from 5 to 15% [66–68] which may be due to restrictive atrial communication, obstruction of the aortic arch, blockage of the shunt, distortion of the PAs, atrioventricular valve insufficiency, or a combination thereof [66]. Intercurrent illnesses such as dehydration, respiratory tract illness, or fever disturb this balance and make the patients to become critically ill and have been blamed for interstage mortality [66, 68]. The surgically created BT and Sano shunts may also get thrombosed producing severe hypoxemia [69]. Indeed, these abnormalities produce significant interstage mortality [67]; these appear to occur more frequently between Stages I and II than between Stages II and III. Consequently, extreme vigilance in managing these patients should be maintained by the caregiver [68, 70]; even trivial illnesses must be aggressively monitored and addressed as appropriate.

### **Figure 7.**

*Stage IIIB. (a) Selected frames from cineangiograms in anteroposterior projection illustrating Stage IIIA of the Fontan operation in which the inferior vena caval (IVC) flow is diverted into the pulmonary arteries by a non-valve conduit (Cond). The fenestration (fen) is shown by the arrow in (a). (b) Closure of the fenestration with an Amplatzer septal occluder device (D) is shown with an arrow in (b). HV, hepatic veins; LPA, left pulmonary artery; RPA, right pulmonary artery (Reproduced from [30]).*

### **Figure 8.**

*Stage IIIB. (a) Selected frames from cineangiograms in lateral view of the same patient illustrated in* **Figure 5** *showing Stage IIIA of the Fontan operation in which the inferior vena caval (IVC) flow is diverted into the pulmonary arteries by a non-valve conduit (Cond). The fenestration (fen) is shown by the arrow in (a). (b) Closure of the fenestration with an Amplatzer septal occluder device (D) is shown with an arrow in (b). (Stage IIIB). Reproduced from [30].*
