The nurse put down the bottle without labelling it and about 25 minutes later another nurse went to attend the patient and injected the morphine as saline solution.

What is the difference between 'attend' and 'attend to'?

Can I change 'attend' to 'attend to'?

Thanks in advance
(l) I will attend a concert; Mona attends a private school. (2) I have a lot of business to attend to; A nurse will attend to you as soon as possible. In your sentence, you might consider "another nurse treated the patient and...."
So 'attend' and 'attend to' are both bad word choices?
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If you want to, you may say: "...another nurse went to attend to the patient." But the use of "to" two times may be considered inelegant by some people.
Thanks a bunch!