Antes da injeção, a enfermeira explicou que a anestesia ia funcionar depressa.

Because in Portuguese, de + a normally contracts to da.

So:

• de = of / from / before depending on context
• a = the (feminine singular)
• da = de + a

In this sentence:

• Antes da injeção = Before the injection

This kind of contraction is very common in Portuguese:

• de + o = do
• de + a = da
• em + a = na
• a + o = ao

So antes da injeção is the normal, correct form.

Portuguese uses definite articles very frequently, often more often than English.

Here:

• a enfermeira = the nurse
• a anestesia = the anaesthetic / the anesthesia

That is completely natural in Portuguese. In many contexts, Portuguese prefers a definite article where English might omit one or where article use feels less rigid.

In this sentence, both nouns refer to specific things in the situation:

• the specific nurse
• the specific anaesthetic being discussed

So the articles sound fully natural and expected.

Injeção means injection.

It is a feminine noun:

• a injeção = the injection
• uma injeção = an injection

This sentence is talking about a medical context, so antes da injeção means before the injection / before getting the injection.

A useful point for English speakers: the ending -ção is very common in Portuguese and often corresponds to English -tion:

• injeção = injection
• informação = information
• situação = situation

Explicou is the pretérito perfeito simples of explicar.

• eu expliquei = I explained
• ele/ela explicou = he/she explained

This tense is used for a completed action in the past. In the sentence, the nurse’s explanation happened at a specific moment before the injection, so explicou fits perfectly:

• a enfermeira explicou = the nurse explained

It presents the explanation as a finished event.

Here que means that and introduces a subordinate clause.

• A enfermeira explicou que... = The nurse explained that...

This is very common in Portuguese after verbs like:

• dizer que = to say that
• explicar que = to explain that
• achar que = to think that
• saber que = to know that

Just like in English, that can sometimes be omitted in English, but in Portuguese que is usually kept.

Ia funcionar literally means was going to work / was going to take effect.

It is made of:

• ia = imperfect of ir (to go)
• funcionar = to function / to work

So:

• a anestesia ia funcionar depressa = the anaesthetic was going to work quickly

In medical English, you might naturally translate it as:

• the anaesthetic would work quickly
• the anaesthetic would take effect quickly

So although the literal structure is was going to function/work, the natural meaning is about the anaesthetic taking effect.

Because the whole sentence is in the past.

The nurse explained something before the injection, so we are looking back at what she said from a past point of view. That is why Portuguese uses ia funcionar rather than vai funcionar.

Compare:

• A anestesia vai funcionar depressa. = The anaesthetic is going to work quickly.
  (present viewpoint)

• A enfermeira explicou que a anestesia ia funcionar depressa. = The nurse explained that the anaesthetic was going to work quickly / would work quickly.
  (past viewpoint)

This is a very common tense shift after a past reporting verb like explicou.

Yes, sometimes funcionaria could be possible, but ia funcionar is very natural and very common in everyday Portuguese.

Compare the two:

• ia funcionar = was going to work / would work
• funcionaria = would work

In many real-life situations, Portuguese prefers ir + infinitive, especially in speech, because it sounds more direct and conversational.

So in this sentence:

• a anestesia ia funcionar depressa sounds very natural
• a anestesia funcionaria depressa is grammatically possible, but it sounds a bit more formal or less immediate in tone

It can be used for machines, systems, plans, methods, medicines, and treatments too.

So funcionar can mean:

• a machine works
• a system works
• a plan works
• a medicine works

In this sentence, a anestesia funcionar means that the anaesthetic would work properly or take effect.

Examples:

• O carro não funciona. = The car doesn’t work.
• Este método funciona bem. = This method works well.
• A anestesia funcionou. = The anaesthetic worked.

Both can mean quickly, but depressa is generally more everyday and conversational.

• depressa = quickly / fast
• rapidamente = quickly, often a bit more formal or neutral

So:

• A anestesia ia funcionar depressa. = very natural spoken Portuguese
• A anestesia ia funcionar rapidamente. = also correct, slightly more formal or technical-sounding

You may also hear rápido in some contexts, but depressa is especially common as an adverb in European Portuguese.

Yes. Anestesia is the Portuguese word corresponding to English anaesthesia or anesthesia.

Depending on context, it can refer to:

• the process of anaesthesia
• the anaesthetic effect
• the anaesthetic being used

In this sentence, a anestesia ia funcionar depressa most naturally means:

• the anaesthetic would take effect quickly

So the focus is not on the abstract medical field, but on the medicine/procedure working in the patient.

Yes, adverbs can sometimes move around, but this order is very natural.

Standard order here is:

• explicou que
  • clause
• a anestesia = subject
• ia funcionar = verb phrase
• depressa = adverb

So:

• a anestesia ia funcionar depressa

This is the most neutral and natural way to say it.

You might also hear:

• a anestesia depressa ia funcionar — not natural here
• depressa, a anestesia ia funcionar — possible only with strong emphasis, but unusual in this context

So the original sentence has the normal word order.

A very natural English rendering would be:

• Before the injection, the nurse explained that the anaesthetic would work quickly.

Depending on context, even more natural might be:

• Before the injection, the nurse explained that the anaesthetic would take effect quickly.

That is because in English, with medicine, we often say take effect rather than simply work, even though Portuguese uses funcionar very naturally here.