When apnea testing or CN testing difficult
Severe facial trauma preventing CN testing
High cervical cord injury making apnea testing impossible
Hemodynamically too unstable or significant lung injury making apnea testing impossible
Diagnostics must be done to evaluate for cerebral blood flow or activity
Cerebral angiography, nuclear imaging, CTA, or MRA
EEG monitoring
Severe facial trauma preventing CN testing
High cervical cord injury making apnea testing impossible
Hemodynamically too unstable or significant lung injury making apnea testing impossible
Cerebral angiography, nuclear imaging, CTA, or MRA
EEG monitoring
Brain death
Spinal shock
Hemorrhagic shock
Neurogenic shock
Heat exhaustion
Heat stroke
Stroke 
Tumor lysis syndrome