itizikyuumeisyoti ni saisite, hannou no kakunin wo suru.

A natural reading is:

いちじ きゅうめい しょち に さいして、はんのう の かくにん を する。

Word by word:

• 一次救命処置 = いちじきゅうめいしょち
• に際して = にさいして
• 反応 = はんのう
• 確認 = かくにん

This is fairly formal, technical language, so it is common in manuals, training materials, and official instructions.

に際して is a formal expression meaning something like:

• on the occasion of
• when
• at the time of
• in carrying out

In this sentence, it means that the action 反応の確認をする is done when performing / when dealing with 一次救命処置.

Compared with simpler expressions:

• とき / ときに = general when
• に際して = more formal and often used in important, specific situations or procedures

So:

• 一次救命処置のとき、反応を確認する。
  = simpler, more conversational
• 一次救命処置に際して、反応の確認をする。
  = more formal, instruction-manual style

際して comes from 際する, and this expression is commonly used as:

• Noun + に際して
• Verb dictionary form + に際して

So に is just part of the standard pattern.

Examples:

• 試験に際して = at the time of the exam
• 出発に際して = upon departure
• 使用に際して = when using

Here:

• 一次救命処置に際して = when carrying out primary/life-saving emergency treatment

So this is not a special meaning of に by itself; it is the normal construction used with 際して.

Here, の links two nouns:

• 反応 = response / reaction
• 確認 = confirmation / checking

So 反応の確認 means:

• confirmation of response
• checking for a response

This is a very common Japanese pattern:

• A の B = B of A / B related to A

Examples:

• 名前の確認 = confirmation of name
• 安全の確認 = safety check
• 内容の確認 = checking the contents

So 反応の確認をする literally means to do the confirmation of response, which in more natural English is to check for responsiveness or to check the person’s response.

Both are possible.

• 確認する
• 確認をする

Both mean to confirm / to check.

The version with をする often sounds a little more noun-based and procedural, which fits formal instructions well. In technical or manual-style writing, Japanese often uses:

• Noun + の + Noun + をする
• Noun + を行う
• Noun + を実施する

So 反応の確認をする sounds like perform a response check, which is very natural in procedural writing.

That said, 反応を確認する would also be grammatically correct and more compact.

The difference is small, but there is a nuance.

反応を確認する

• directly means to check the response
• a little more straightforward and verbal

反応の確認をする

• literally to do a confirmation/check of the response
• sounds slightly more formal, procedural, or bureaucratic

In practical meaning, they are very close. In manuals and training documents, the noun-heavy style is common because it sounds systematic and step-by-step.

Japanese often omits the subject when it is obvious from context.

In a sentence from a manual, training guide, or instructions, the implied subject is usually:

• the person performing the procedure
• you
• medical personnel / responder

So the sentence does not need to explicitly say:

• 救助者は
• あなたは
• 医療従事者は

because the context already tells us who should do the action.

This kind of omission is extremely common in Japanese, especially in instructions.

The comma separates the setting/situation from the main action.

• 一次救命処置に際して、 = in the context of performing emergency life-saving treatment,
• 反応の確認をする。 = check for a response.

The comma makes the sentence easier to read, especially because に際して introduces a formal contextual phrase at the beginning.

In Japanese, commas are often used more flexibly than in English. This comma is helpful, natural, and very common in formal writing, though punctuation can vary depending on style.

No, it is not an everyday casual word. It is technical vocabulary.

一次救命処置 refers to a formal medical/emergency-care concept, often equivalent to basic life support or primary life-saving measures, depending on context.

Breaking it down:

• 一次 = primary / first-stage
• 救命 = life-saving
• 処置 = treatment / measure / procedure

So this is the kind of word you are more likely to see in:

• first-aid training
• CPR materials
• emergency response manuals
• medical or safety documentation

Yes, it is formal and instructional.

Features that make it formal:

• に際して is formal
• 確認をする has a procedural feel
• 一次救命処置 is technical vocabulary

In normal conversation, someone would probably say something simpler, such as:

• まず反応を確認します。
• 救命処置をするときは、反応を確認します。
• まず相手が反応するか確認します。

So the original sentence sounds like something from a textbook, guideline, checklist, or training manual rather than casual speech.

Yes, it can be used with both nouns and verbs.

Common patterns:

• Noun + に際して
• Verb dictionary form + に際して

Examples:

• 入学に際して、必要書類を提出してください。
  = Upon enrollment, please submit the necessary documents.
• 契約を結ぶに際して、条件を確認する。
  = When concluding a contract, check the terms.

So in your sentence, 一次救命処置に際して follows the noun pattern.

Yes. A few simpler versions are:

• 一次救命処置をするとき、反応を確認する。
• 救命処置の前に、反応を確認する。
• まず反応があるか確認する。

These all express a similar idea, but with different nuance:

• をするとき = simpler when doing
• の前に = explicitly before
• あるか確認する = conversationally clear: check whether there is a response

The original version is more formal and sounds like a procedural instruction.