La paciento ricevis anestezon antaŭ la kuracado.

Because anestezon is the direct object of the verb ricevis (received).

In Esperanto, the direct object usually takes the -n ending:

• La paciento ricevis anestezon. = The patient received anesthesia.

The patient is the one doing or experiencing the verb, so paciento does not get -n here. The thing received, anestezo, is the object, so it becomes anestezon.

Because la paciento is the subject of the sentence, not the direct object.

Compare:

• La paciento ricevis anestezon. = The patient received anesthesia.
• La kuracisto traktis la pacienton. = The doctor treated the patient.

In the second sentence, pacienton gets -n because the patient is the object of traktis.

Ricevis is the past tense form of ricevi, meaning to receive.

Esperanto verb endings are very regular:

• -as = present
• -is = past
• -os = future
• -us = conditional
• -u = imperative / jussive
• -i = infinitive

So:

• ricevas = receives / is receiving
• ricevis = received
• ricevos = will receive

That makes La paciento ricevis anestezon clearly a past-time statement.

Because after a preposition like antaŭ (before), you normally use the noun without -n.

So:

• antaŭ la kuracado = before the treatment

The -n ending is usually for direct objects, and kuracado is not the direct object here. It is part of a prepositional phrase introduced by antaŭ.

You may sometimes see -n after prepositions to show direction or movement toward something, but that is not what is happening here. This sentence is just talking about time: before the treatment.

This is a very useful word-building point.

• kuraci = to treat medically
• kuraco = a cure, remedy, or treatment in the sense of the result or means
• kuracado = treatment, the process of treating

The suffix -ad- often emphasizes an ongoing process, repeated action, or activity.

So la kuracado here suggests the treatment procedure/process, which fits naturally with before the treatment.

La is the Esperanto definite article, meaning the.

So:

• la paciento = the patient
• la kuracado = the treatment

Esperanto has only one article, la, and it does not change for gender, number, or case.

It is used much like English the, when the speaker means a specific patient and a specific treatment. If you removed it, the meaning would become less specific:

• Paciento ricevis anestezon antaŭ kuracado. = A patient received anesthesia before treatment.

That is grammatically possible, but it means something different.

Yes, Esperanto word order is fairly flexible, because endings show grammatical roles.

The neutral order is:

• La paciento ricevis anestezon antaŭ la kuracado.

But you could also say:

• Antaŭ la kuracado la paciento ricevis anestezon.

That puts more emphasis on the time phrase before the treatment.

Because anestezon has -n, it is still clearly the object even if you move it:

• Anestezon la paciento ricevis antaŭ la kuracado.

That said, the original order is the most natural and straightforward.

Yes, anestezon is singular because the base noun anestezo ends in -o, and there is no plural -j.

Forms:

• anestezo = anesthesia
• anestezon = anesthesia (direct object)
• anestezoj = anesthesias
• anestezojn = anesthesias (direct object plural)

In practice, anestezo is often used like a mass noun, much like English anesthesia, so the singular is very natural here.

If you wanted to say some anesthesia, Esperanto often simply uses the bare noun:

• La paciento ricevis anestezon.

If needed, you could add a word like iom da:

• La paciento ricevis iom da anestezo.

Here antaŭ means before in a time sense:

• antaŭ la kuracado = before the treatment

But antaŭ can also mean in front of in a physical/location sense:

• La paciento staris antaŭ la kuracisto. = The patient stood in front of the doctor.

So antaŭ can refer to either time or space. In this sentence, the context makes it clearly temporal.

In meaning, yes, that is very close.

Literally, ricevis means received, so the Esperanto sentence is more directly:

• The patient received anesthesia before the treatment.

But in natural English, was given anesthesia is often how we would express the same idea. So if the learner already knows the meaning, it is helpful to remember that Esperanto may choose a different but perfectly normal way to phrase it.

A simple pronunciation guide is:

• an = like ahn with an n
• taŭ = roughly like tow in one syllable, with aŭ sounding like a diphthong similar to ow

So antaŭ is approximately ahn-TAU.

A few pronunciation notes:

• Stress in Esperanto normally falls on the second-to-last syllable.
• In antaŭ, the stress is on an? Actually, since aŭ counts within the final syllable, the stress falls on AN-taŭ.

So say it roughly as AHN-tow.