Why was only one intern working in the emergency room? Why didn't the surgeon come? Why are these facts included?
To answer these questions, let's first focus on the relevant part of the story:
"Only Marin can’t explain why it mattered, the hours and hours, for somebody she didn’t even know. The hospital emergency room. Nobody but an intern working all alone. And maybe if the surgeon would’ve come, maybe if he hadn’t lost so much blood, if the surgeon had only come, they would know who to notify and where.
But what difference does it make? He wasn’t anything to her. He wasn’t her boyfriend or anything like that. Just another brazer who didn’t speak English. Just another wetback. You know the kind. The ones who always look ashamed."
So this is when Geraldo has been taken to the hospital after being the victim of a hit and run--meaning, someone had struck him with a car, then fled the scene of the crime.
Already Geraldo has been injured and abandoned, then, when in the hospital there are no extra staff members summoned when he arrives. And no one summons the surgeon, either. There's only one intern working in the emergency room because it's late at night, probably, but more care providers were likely on call. They just weren't notified to come help keep Geraldo alive. The intern probably should have called the surgeon and didn't, seeing as the patient was someone without any identification and was probably an illegal alien.
The narrator includes these facts in the story to illustrate how Geraldo's status as an illegal immigrant means that people treat him as if he doesn't matter, as if he's not fully human. Look at how the narrator, echoing the thoughts of the police, refers to Geraldo as "just another brazer" and a "wetback," derogatory terms for illegal immigrants. And notice how the narration, too, refers to Geraldo not as an individual but as a "kind," simply belonging to a category of people.
Put another way, these details about how people fail to take care of Geraldo when he needs medical attention reveal the callous indifference and neglect that our society shows to people like Geraldo.