Answer: C - Inadequate weight gain happens because when the infant tires very easily, sufficient calories cannot be ingested to meet the nutritional needs. Other options do occur, but they are indirectly related to weight gain.
An infant diagnosed with Tetralogy of Fallot (TOF), a complex heart condition, may experience various challenges, including difficulty in gaining weight. The most directly related to underweight issues is "deficient caloric intake due to activity intolerance." In TOF, the heart's inefficiency in oxygenating blood can lead to fatigue and decreased stamina, making the infant less active and less likely to feed effectively. This reduced activity and feeding intolerance can directly contribute to an inadequate caloric intake, hindering weight gain.
While the other factors you mentioned, such as recurrent respiratory infections due to pulmonary hypertension and polycythemia caused by decreased arterial PO2, are serious concerns in TOF, they are less directly related to the issue of being underweight. These conditions are secondary complications that arise from the primary heart defect. Respiratory infections might indirectly affect nutritional status if they lead to decreased feeding or increased metabolic demands, but they are not the primary cause of being underweight. Similarly, polycythemia, a response to chronic low oxygen levels, increases red blood cell count but doesn't directly lead to weight issues.
