Potassium Acetate and Potassium Chloride will do that to yah depending on drip rate and sedative dosage.
Sounds like they wanted him to have a warm send off.
Having experience a KCl drip that was too fast I can attest to it feeling like napalm coursing in my vein before I ripped the IV port out.
I suspect that whomever calculated the dose of KCL equivalent of K-acetate did it wrong. The total amount of free K ion is what kills you. Also he should have been asleep from a sedative prior to starting the potassium drip. I think two mistakes were made.