Learn Spanish (Latin America): Esperamos que el paciente se duerma antes de la operación. - We hope that the patient falls asleep before the operation.

This is a great example of a verb changing its meaning when used as a pronominal verb. Dormir means to sleep (the ongoing state), but dormirse means to fall asleep (the moment you transition into sleeping). Since we are waiting for the patient to fall asleep, we must use the pronominal form with se.

Why is the verb spelled duerma with an 'a' at the end, rather than duerme?

It is in the subjunctive mood. The phrase Esperamos que (We hope that) expresses a hope, desire, or expectation. In Spanish, when you express a wish for someone else to do something (in this case, el paciente), the second verb must be in the subjunctive.

Where does the 'ue' in duerma come from if the infinitive is dormirse?

Dormir is a stem-changing verb where the o changes to ue. In the present subjunctive, stem-changing verbs keep that vowel change for most forms, including the one for el paciente (the he/she/it form). So the stem becomes duerm- before adding the subjunctive ending -a.

Why do we need the word de in antes de la operación?