Congratulations on the birth of Alexandra. Oxygen is the big one for a lot of nicu babies, however they can survive for months on an oscillating or jet vent if needed before they're ready to move to a traditional vent. Being on any form of ventilator does cause the lung tissue to harden, and it's a hard balance of when to move them to less support, as the vent is keeping them alive, but the longer they're on the vent the longer they will have to stay on it for their lungs to mature that bit more. Some babies even go home on a ventilator, it's rare but it can take years to wean off it - you're at a very early stage I'm by no means saying this will be your story, but if you're anything like I was you'll want to know that severe difficulty breathing is survivable and anything else you can deal with later. My daughter had to have half of her left lung removed because the ventilator kept making holes in it and it collapsed over and over again (pneumothorax), it was terrifying but two weeks later she was finally on cpap - sometimes a scary step is what is best for them. Nicu is a terrifying time, a lot of the time it feels like more steps backwards than forwards, but she's shown she wants to fight and the doctors will do everything they can to help her do that.