KCL is very hypertonic therefore irritating to the veins and tissues hence care must be taken to prevent perivascular infiltration and extravasation which could lead to tissue necrosis.
Of course that is not the only adverse effect of potassium administration. We do use it in lethal injection.
I'd have to respectfully offer a different suggestion. If you look at the osmolality of the bags of 10-30mEq K/L D5...the oslmolality ranges from 272-312 mOsm. Normal blood mOsm is 280-310.
However, the pH of these solutions is very low - 4.5 - where normal blood pH is 7.35-7.45.
We don't normally have an issued running up to 40mEQ/L in a vein, as long as the veing is large & the IV is running fairly rapidly - its not staying in contact with the venous walls too long.
Any greater content, or slower flow, we try to use a central line, which allows very rapid dilution therefore rapid pH equilibration.
Just my thoughts on the subject.