I worked 911 very briefly for my county.
The first questions were
"What is the address of your emergency?"
We would then verify the phone number and address with the caller.
Then we would ask what was the nature of the problem.
If they said drug overdose - we would ask if you knew what kind, how much, if they were alert and responsive and breathing, combative. Depending on what you answered - the questions with would determine if they stayed on the line.
If they were giving you CPR or other instructions, they would stay on the line. If not, then they would tell you to call back if anything changed.