Final answer:
The first diagnosis identifies an actual problem, while the second predicts a potential problem.
Step-by-step explanation:
The major difference between the two nursing diagnoses is that the first diagnosis, 'inadequate nutritional intake related to vomiting as manifested by a 3lb weight loss,' identifies an actual problem that the patient is currently experiencing. This diagnosis focuses on the present issue of inadequate nutritional intake and weight loss due to vomiting. On the other hand, the second diagnosis, 'risk for impaired skin integrity related to inadequate nutrition,' predicts a potential problem that may occur if the patient continues to have inadequate nutrition. This diagnosis addresses the possibility of future skin integrity problems due to poor nutrition.