In major-haemorrhage and massive-transfusion physiology, three self-amplifying derangements define the lethal triad: a fall in core temperature, failure of clotting, and a drop in blood pH. Symbolically:
$\text{Lethal triad} = \{\,\text{hypothermia},\ \text{coagulopathy},\ \text{acidosis}\,\}$
Citrate in stored blood binds ionised calcium, producing hypocalcemia (the usual "fourth" metabolic partner), and old stored cells release potassium, producing hyperkalemia. Of the four listed, coagulopathy and hypothermia are core triad members and hypocalcemia is the closely linked metabolic associate, leaving potassium excess as the outsider.
\[\boxed{\text{Hyperkalemia is NOT a classic lethal-triad component}}\]