Sjokkelektrodene er på, det vil si at hjertestarteren er klar.

Because -ene is the usual ending for a definite plural noun in Norwegian.

• elektroder = electrodes (plural, indefinite)
• elektrodene = the electrodes (plural, definite)

Here the word is part of the compound sjokkelektrodene:

• sjokk = shock
• elektroder = electrodes

So sjokkelektrodene means the shock electrodes.

Norwegian often attaches the definite article to the end of the noun instead of using a separate word like the.

Er på is a very common expression in Norwegian, and it can mean different things depending on context, such as:

• is on / switched on
• is on the body / attached / in place

In this sentence, Sjokkelektrodene er på means the electrodes have been placed or attached properly. In an AED/defibrillator context, it is not mainly about electrical power; it is about the pads being on the patient.

So although på often means on, here it is better understood as in place / attached.

Det vil si at is a very common linking expression meaning:

• that is
• that means that
• in other words

It introduces an explanation or clarification of what came before.

In this sentence:

• Sjokkelektrodene er på
• det vil si at hjertestarteren er klar

The second part explains the consequence or practical meaning of the first part.

Literally, det vil si is something like that wants to say, but you should learn it as a fixed expression meaning that is / that means.

Because at introduces a subordinate clause, similar to that in English.

• det vil si at hjertestarteren er klar

This is like saying:

• that means that the defibrillator is ready

In everyday Norwegian, det vil si can sometimes appear without at, especially before a short explanation, but in a full clause like this, at is very natural.

Hjertestarteren is the definite singular form: the defibrillator.

• en hjertestarter = a defibrillator
• hjertestarteren = the defibrillator

The sentence refers to a specific device already present in the situation, so Norwegian uses the definite form.

Also, hjertestarter is a compound:

• hjerte = heart
• starter = starter

So literally it is something like heart-starter, which is the common Norwegian word for defibrillator / AED.

Because after at, Norwegian uses subordinate clause word order.

Main clause:

• Hjertestarteren er klar.

After at:

• ... at hjertestarteren er klar

The subject comes before the verb in the normal way.

A learner might expect inversion because Norwegian often puts the verb in second position in main clauses, but that rule applies to main clauses, not subordinate clauses introduced by words like at.

Yes. Here klar means ready.

• Hjertestarteren er klar = The defibrillator is ready

That is the natural word in this context. It means the device is prepared for the next step.

It does not mean finished. For finished, Norwegian often uses ferdig instead.

So:

• klar = ready
• ferdig = finished/done

The comma marks that the second part is an explanation of the first part.

• Sjokkelektrodene er på, det vil si at hjertestarteren er klar.

This is similar to English punctuation in explanatory structures like:

• The electrodes are on, which means the defibrillator is ready.

In Norwegian, det vil si often functions as an explanatory insert, and a comma is natural before it.

Yes. Norwegian very often forms long compound nouns by joining words together.

Here:

• sjokk
  • elektrodene → sjokkelektrodene

This is completely normal in Norwegian. English often writes similar ideas as separate words, but Norwegian frequently writes them as one word.

Other examples of this pattern are:

• hjertestarter
• sykehuslege
• barnesete

So if a word looks long, it is often just a compound made of smaller familiar parts.

Sometimes, yes. In many contexts, det vil si works like:

• that is
• i.e.
• in other words

But in this sentence, that means that or which means that sounds more natural in English, because the second clause gives the practical consequence of the first.

So while i.e. is close in function, the best natural English equivalent here is probably which means that.