sinpaisosei no rensyuu ni saisite, kokyuu no kakunin wo suru.

A natural reading is:

しんぱいそせい の れんしゅう に さいして、こきゅう の かくにん を する。

Word by word:

• 心肺蘇生（しんぱいそせい）= CPR / cardiopulmonary resuscitation
• 練習（れんしゅう）= practice, training
• に際して（にさいして）= on the occasion of / when / in doing
• 呼吸（こきゅう）= breathing / respiration
• 確認（かくにん）= confirmation, checking
• をする = do, perform

に際して is a formal expression meaning something like:

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

So 練習に際して means when doing the practice or in the course of the practice.

In this sentence, it gives a formal, instructional tone. It sounds more official than a simple 〜とき.

Compare:

• 心肺蘇生の練習をするとき、呼吸の確認をする。
  = When practicing CPR, check breathing.
  → more plain and conversational
• 心肺蘇生の練習に際して、呼吸の確認をする。
  = When conducting CPR practice, perform a breathing check.
  → more formal, like a manual or instruction

Here, 心肺蘇生 modifies 練習 with の.

So:

• 心肺蘇生の練習 = CPR practice / practice of CPR

The particle の links the two nouns, showing that the practice is related to CPR.

This is very common in Japanese:

• 日本語の勉強 = study of Japanese
• 車の運転 = driving a car
• 避難の訓練 = evacuation drill

If you used を, the structure would be different:

• 心肺蘇生を練習する = to practice CPR

Both are possible in Japanese, but this sentence is built around the noun phrase 心肺蘇生の練習.

呼吸の確認 means checking breathing or more literally confirmation of breathing.

The の connects:

• 呼吸 = breathing
• 確認 = confirmation/check

So it is a noun phrase: the check of breathing.

This pattern is extremely common:

• 安全の確認 = checking safety
• 名前の確認 = checking the name
• 内容の確認 = checking the contents/details

In English, we often use check + noun, but Japanese often uses noun + の + 確認.

Both are correct.

• 確認する
• 確認をする

Both mean to check / to confirm.

The version with をする can sound slightly more explicit because 確認 is a noun and する turns it into an action. In formal or instructional writing, 〜をする often appears naturally.

So:

• 呼吸の確認をする
• 呼吸を確認する

Both are possible, and both would be understood as check breathing.

That said, the exact nuance is a little different:

• 呼吸を確認する focuses more directly on breathing as the thing being checked.
• 呼吸の確認をする focuses more on the act of checking.

Yes, definitely.

A very natural alternative is:

心肺蘇生の練習に際して、呼吸を確認する。

This is slightly more direct and may sound a bit simpler.

Compare:

• 呼吸の確認をする = perform a breathing check
• 呼吸を確認する = check breathing

The original sentence has a slightly more technical or procedural feel, which fits CPR instructions well.

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

This sentence sounds like an instruction or procedural statement, so the implied subject could be:

• you (in an instructional sense)
• one
• the person practicing
• the trainee

English usually needs a subject, but Japanese frequently leaves it out if it is obvious.

So this could be understood as:

• When practicing CPR, you should check breathing.
• During CPR practice, breathing is checked.
• One checks breathing when conducting CPR practice.

Which English version is best depends on context, but the Japanese does not need to state the subject.

In N に際して, the に attaches the noun to the expression 際して.

The pattern is:

• noun + に際して
• noun + に際し (a slightly shorter version)

Examples:

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

So 練習に際して means at the time of practice / when carrying out practice.

You do not need to think of this に as having a simple one-word English equivalent. It is part of the grammatical pattern.

Not very much in casual conversation. It is more common in:

• formal instructions
• announcements
• manuals
• official writing
• speeches
• warnings

In everyday speech, people would more often say:

• 〜とき
• 〜際は in notices/signs
• 〜するとき

For example, in conversation:

• 心肺蘇生の練習をするとき、呼吸を確認する。

In a manual or training document:

• 心肺蘇生の練習に際して、呼吸の確認をする。

So this sentence sounds formal and instructional.

The comma marks a pause after the introductory phrase:

• 心肺蘇生の練習に際して、 = when doing CPR practice,
• 呼吸の確認をする。 = check breathing.

This kind of comma is very common after a time or condition phrase at the beginning of a sentence.

It helps readability, especially in formal writing. It is not absolutely required in every case, but it is very natural here.

By itself, it sounds like a general instruction or procedure, not one single event.

Japanese non-past forms like する can mean:

• do
• will do
• do habitually
• should do in instructions

Here, because of the formal style, it most naturally means something like:

• check breathing when practicing CPR
• breathing should be checked during CPR practice

So this is the kind of sentence you might see in:

• a training manual
• a safety guide
• class instructions

The structure is:

[A の B] に際して、[C の D] をする。

Specifically:

• 心肺蘇生の練習 = CPR practice
• に際して = when conducting / on the occasion of
• 呼吸の確認 = checking breathing
• をする = do / perform

So the sentence is built from two noun phrases:

1. 心肺蘇生の練習
2. 呼吸の確認

Then it says that, at the time of the first, you do the second.

A very literal breakdown would be:

• At the time of CPR practice, do a check of breathing.

That is a bit stiff in English, but it shows how the Japanese is put together.