Waiting for external requests are occupying db connections

[JonasRueegsegger]

I am using flask-sqlalchemy for my web application. A request from a client has more or less these steps

1. Preparing data provided by the client (incoming request from client)
2. Store some information about the request to an database (here the db connection is retrieved from the connection pool)
3. Make external request and wait for an answer. These requests are taking around 15 secs in average.
4. Store some information about the answer into the database (here we need the db connection again)
5. Return response to client

Now my issue is, that when scaling up and using flask-sqlalchemy, the request bound sessions provided by flask-sqlalchemy are occupying the db connections from the pool also during the time waiting for the external provider. This is leading to lots of db connections occupied for several seconds. So I started to close the session before making the requests to the external providers.
This is working, but I have to pay lots of attention to not close the shared session (within the request) at the wrong time.
My question would be, is it also possible to have more than one session at the same time within one request with flask-sqlalchemy or would you recommend me to switch using the sqlalchemy package directly in this case?