A little background: I've been a nurse for over 20 years. My specialties have included Pediatrics and Mother/Baby. In February, I switched to NICU. I took an 8 week orientation course and had 12 weeks orientation on the unit, and I've been independently taking care of four Level 2 babies per shift for about 6 weeks (our unit routinely gives us 4 level 2 babies, which I know is unusual compared to most facilities). Two nights ago, I was supposed to have my four babies back from the night before but at the last moment (literally 10 minutes before my shift, after I had looked up all my orders), my assignment was changed. Instead of 4 grower-feeders, I was given one of my grower-feeders back, one baby on HFNC and one baby on continuous TPN via PIV.This was the first time I independently took care of a baby on a HFNC as well as the first time I had a baby with a continuous IV and TPN, so I was nervous but doing everything I could to be extra vigilant because the HFNC baby kept pulling out her OG tube and I was terrified she would aspirate on her gavage feeds, and the TPN baby was 4200 grams, a really hard stick, and on Q 3 hour accuchecks. She was PO feeding 10mls Q 3 hrs and her TPN was running at 16ml/hr, which I understand is quite a high rate. At 0415, I noticed the IV site in her thigh was starting to leak. I stopped the infusion, pulled the IV, and another 2 nurses helped me get a new IV into her AC. At 0515 we restarted her TPN and at 0530 and 0630, her IV site looked good and was infusing well. Change of shift 0720, me and the oncoming nurse opened the blanket and her already fat arm was noticeably swollen and firm. We stopped the infusion immediately and pulled the IV. To say I felt terrible is an understatement; I was unsuccessfully trying not to cry as I finished my charting. My ex-preceptor, bless her heart, saw that I was upset and pulled me aside. She was almost more upset for me than I was. She felt I wasn't given a safe assignment based on my clinical experience, so we went to the manager. The manager was very kind and understanding, even told me of her own experience with a bad infiltrate early in her NICU career... so I know it happens. But damn, I still feel incompetent and wonder if there is anything I could have done to prevent it. The baby is fine now; elevating the extremity was the only intervention needed. Lessons learned: Don't just look at/palpate the IV site, observe the area around the IV including the dorsal/dependent side, basically the entire extremity! Compare both extremities.Don't rely on the pump! It may not alarm even with the increasing pressure!Always manually prime the tubing, then use the pump prime feature before infusing. (I learned this after doing some internet sleuthing on syringe pumps.)Finally: check those PIVs more than once per hour if at all possible. It only takes a few minutes and could prevent a bad outcome.Looking back, I wonder if I should have questioned the TPN order (knowing she was a hard stick and we lost the site on her thigh that took 3 nurses an hour and a half to find) or asked the Neo if we could increase her feeds and decrease the TPN rate... If anyone else with more experience can offer additional advice, I would be so grateful!! Thank you!