Plasma raak al hoe skaarser terwyl bloedvoorraad laag bly.

Here raak means become or get.

So Plasma raak al hoe skaarser literally means something like Plasma is becoming scarcer or Plasma is getting more and more scarce.

This is a very common Afrikaans use of raak:

• moeg raak = become tired
• kwaad raak = get angry
• beter raak = get better

Al hoe + comparative is a common Afrikaans pattern meaning more and more + adjective.

So:

• al hoe skaarser = more and more scarce
• al hoe moeiliker = more and more difficult
• al hoe groter = bigger and bigger / larger and larger

You can think of al hoe as a fixed expression. It does not mean all or how in the normal English sense here.

Because the sentence needs the comparative form of the adjective.

• skaars = scarce
• skaarser = scarcer

Since al hoe usually goes with a comparative idea, skaarser is the natural form.

Compare:

• Die water is skaars. = The water is scarce.
• Die water raak skaarser. = The water is becoming scarcer.

Terwyl means while.

It links two things happening at the same time or two related situations:

• Plasma raak al hoe skaarser = one situation
• terwyl bloedvoorraad laag bly = another situation happening at the same time

So terwyl introduces a subordinate clause, much like English while.

Because terwyl introduces a subordinate clause, and in Afrikaans subordinate clauses often send the verb to the end.

Main clause:

• Plasma raak al hoe skaarser

Subordinate clause:

• terwyl bloedvoorraad laag bly

That final position of bly is normal Afrikaans word order after words like:

• omdat = because
• terwyl = while
• dat = that
• as = if/when

So terwyl bloedvoorraad laag bly is structurally very typical.

Here bly means remain or stay.

So:

• laag bly = remain low / stay low

This is another very common Afrikaans verb:

• Hy bly kalm. = He remains calm.
• Die pryse bly hoog. = The prices stay high.

It does not mean live here, even though bly can also mean live/stay in other contexts.

Because laag is being used predicatively, not directly before a noun.

In Afrikaans:

• die lae voorraad = the low supply
  Here the adjective comes before the noun, so it often takes an -e ending.
• die voorraad is laag = the supply is low
  Here the adjective comes after the verb, so it usually stays in its basic form.

In your sentence:

• bloedvoorraad ... laag bly
  So laag is correct.

Afrikaans very often forms compound nouns as one word.

So:

• bloed = blood
• voorraad = supply/stock
• bloedvoorraad = blood supply

This is much more common in Afrikaans and Dutch than in English. English often writes these as two words, but Afrikaans prefers a single compound noun.

Other examples:

• waterbottel = water bottle
• huiswerk = homework
• sonbril = sunglasses

It is in the present tense, but it describes an ongoing current situation.

• raak = present tense
• bly = present tense

Afrikaans often uses the present tense where English also uses the present progressive:

• raak skaarser = is becoming scarcer
• bly laag = is remaining low / stays low

So even though the verbs are present tense, the meaning can be dynamic and current.

Yes. Plasma is functioning as an ordinary noun in the sentence, specifically as the subject of the main clause.

• Plasma = subject
• raak = verb
• al hoe skaarser = complement describing what it is becoming

Like English, Afrikaans can use medical or scientific nouns directly without an article when speaking generally:

• Water is belangrik.
• Plasma raak skaarser.

So there is nothing unusual grammatically about Plasma here.

Yes, Afrikaans allows some movement, especially if you want to emphasize the while clause.

For example:

• Terwyl bloedvoorraad laag bly, raak plasma al hoe skaarser.

That still means the same thing. The main difference is emphasis and rhythm.

Notice that if the subordinate clause comes first, the main clause then shows normal Afrikaans inversion:

• Terwyl bloedvoorraad laag bly, raak plasma ... not
• Terwyl bloedvoorraad laag bly, plasma raak ...

So word order changes, but according to regular rules.