ABG / acid-base interpreter

Deterministic math (Winters', AG, delta-delta, P/F, A-a) + qwen 14b synthesis grounded in MKSAP/StatPearls/UpToDate.

Normal 7.35-7.45.
Normal 35-45.
Normal 22-26.
Required for AG.
Required for AG.
Corrects AG if <4.0.
For P/F + A-a.
0.21 = room air; 1.0 = 100% O2.
>4 = sepsis red flag.
Narrows differential.