When to call for IO access

Hi all, I have a question based on a scenario that occurred on my unit yesterday. We had a patient (who btw was the former director of nurse education for our hospital!) who came in for GI bleed, had multiple transfusions and was ready to be discharged. MD ordered 1 dose of IV iron before discharge and said she could go home after the infusion. She was fine during infusion and we took out her IVs which had been done by ultrasound as she is a hard stick.

While getting dressed she had anaphylactic reaction from the iron. Her primary nurse grabbed epi pen and MD wanted bolus as her BP went to 60s/70s systolic. I was called in to put in new IV as I am usually good at IVs. Both arms were swollen and covered in hives and I saw absolutely no veins. No time to look for US machine and set it up. I finally found tiny hand vein and put in 24G that I was able to run the bolus into and grabbed US in case we needed larger bore access but it was pretty scary. My question: how long in a semi-emergent situation do you spend looking for IV access before calling for IO? She was still alert but vitals were quickly becoming unstable. I spent about 3-5 mins looking. Patient and MDs were super cool about it... although having all of them staring at me made me more nervous! Left the room with shaking hands, LOL. Thanks for any input!