This entity is what some paramedics have mentioned and fellow ED collegues of mine as well.
I haven't seen it but don't treat this entity as the Loch Ness Monster or Bigfoot. It's happened during the careers of attendings I trust and are still alive. Not Hippocrates or Napolean's Sergeant General. Its happened in the last 20 years and not stories from centuries ago.
Instead of acute flaccidity of the body including the jaw, the opposite can occur. Perhaps some perverse message from the brain as its suffering from profound hypoxia, hypoperfusion from arrhythmia or shock of any type. I bet in my career I will see 99 +% of acute laxity and flaccidity of the jaws during cardiac arrest.
But since I heard this boogie man story of airways. I have to think about it. Dr. Jeff Jarvis of Georgetown, Texas thinks it increased master muscle tone or from "airway" awareness pf the patient. The patient is out but not really out and needs induction sedation? I will need clarification of this. This was mentioned on 12/19/2016 twitter comments.
Advice from Dr. James Ducanto, an Anesthesiologist 8 years senior to my years of work, and who had to take the advice of his Anesthesiology attending of 20 plus years when he was an anesthesiology resident.
Sometimes learning is believing even if its not written in my EM textbooks.
Only solution, cpr to provide some circulation, and then give the paralytic ivp, and hope the jaws open.
Or just cut the neck.
Hope the patient is not in rigor mortis. This Cardiac Arrest Trismus on this post is in the period soon after losing a pulse.
If in rigor mortis, then your problems is when to declare the time of death and signing the death certificate.