Final answer:
The nurse should first check the baby's vital signs and address any issues causing dehydration or weight loss. The symptoms indicate a potential medical emergency, possibly pyloric stenosis, requiring urgent pediatric assessment.
Step-by-step explanation:
The mother's report that her infant is vomiting "all the time" and the physical assessment findings of poor skin turgor, significant weight loss, and the presence of a palpable abdominal mass suggest that the infant may be experiencing a medical emergency.
The first intervention a nurse should implement is to ensure the baby's vital signs are stable and to prevent further dehydration and weight loss. The clinical assessment findings indicate potential signs of a serious condition such as pyloric stenosis, or another disorder that requires urgent attention. Immediate referral to a pediatrician or emergency care is warranted for further evaluation and treatment. Maintaining the infant's homeostasis is crucial.