The treatment plan above addresses all three concurrent clinical problems comprehensively. A few key points to emphasize:

Most time-critical action: HepB vaccine + HBIG must both be given within 12 hours of birth — this cannot be delayed regardless of the infant's prematurity or instability, as the window of HBIG effectiveness closes rapidly. The birth dose at this weight (<2000 g) does NOT count toward the 3-dose series, so a total of 4 doses will be given.

Most dangerous unknown: The echocardiogram result. With a 50% rate of CHD in Down syndrome — including potentially severe defects like complete AVSD — there may be a cardiac emergency requiring urgent cardiology input that supersedes other management priorities.

Most nuanced VLBW issue: This infant is at the lower end of VLBW (1.4 kg) and will require sustained NICU care; feeding, growth, and neurodevelopmental follow-up will be a long-term commitment, particularly given the co-existing Down syndrome.