Final answer:
The highest priority nursing intervention for a child with congenital heart disease and polycythemia is maintaining adequate hydration to prevent blood clots, with oxygen therapy and maintaining digoxin levels also being important aspects of care.
Step-by-step explanation:
When caring for a child with congenital heart disease and polycythemia, the nursing intervention with the highest priority is maintaining adequate hydration. The rationale behind this is to reduce the risk of blood clots that can occur due to the increased number of red blood cells in polycythemia. This can be particularly dangerous in patients with congenital heart disease, where circulation issues are already present. While administering oxygen therapy continuously is important, it may not be prioritized over hydration unless the child is showing signs of hypoxia. However, oxygen therapy can help with tissue oxygenation. It is also important to maintain digoxin levels within therapeutic range if the child is prescribed this medication to help manage heart function. Digoxin is a cardiac glycoside that can improve heart efficiency and control rate. Restricting fluids may be counterproductive since it can increase hematocrit and viscosity, thereby worsening polycythemia. Therefore, maintaining adequate hydration is critical.