Briefly, this is a survey I did more than a decade ago, but I’m not sure it’s changed that much. It talks about the availability of ultrasound. So you can get an ultrasound by ordering it in the emergency and during the day, you can get this most of the time within 90 minutes, however-
At night what happens is that there is a technologist or technician who's at home, it’s much more difficult. So often even a quarter of emergency departments don’t have access to ultrasound in the middle of the night.