Final answer:
The nurse's priority action is to assess the patient's lungs and oxygen saturation.
Step-by-step explanation:
The correct action for the nurse to take in this situation is to assess the patient's lungs and oxygen saturation (option b). Vomiting milky green fluid could indicate aspiration, where the feeding tube contents have entered the patient's lungs. Aspiration can lead to respiratory distress and compromised oxygenation, so assessing the patient's lungs and oxygen saturation is a priority.
While notifying the provider (option a) is important, it is not the immediate priority in this situation. Stopping the tube feeding (option c) is also necessary, but first, the nurse needs to assess the patient's respiratory status. Slowing the rate of the infusion (option d) may be done after the immediate assessment is completed.