I was on night shift, asked to see a young thirty-something-year-old woman on the orthopaedic ward. She got chucked off her horse earlier that day and cracked her pelvis. Within 12 hours of admission, her blood pressure plummeted and she felt lightheaded, so a nurse asked me to review her.
Now, pelvic fractures have bleeding risks because of the complex and large blood vessels that run in close contact with it and, in healthy young people, you need relatively high impact trauma to actually crack it (think car accidents, chucked by horse, fall from a height). And you can bleed to death just from blood going into the pelvis. So there's this otherwise fit and well young woman, dropping her BP to her boots, so the nurses naturally get very concerned, as did I. As in "Shit, shit, shit, she needs surgery like right now." Young people compensate being unwell or bleeding very well, so their blood pressure does not drop until it gets to a near life-threatening stage.
I called the on-call A+E registrar (also acting orthopaedic registrar overnight) after seeing the patient and sticking two giant venflons in and squeezing lots of fluid. Blood pressure picks up, blood tests show a drop in haemaglobin -- but then I literally had just squeezed 2 litres of saline into her at the same time, so it could be dilutional. The reg comes in, prods her, then calls the on-call orthopaedic surgeon and general surgeon. She could be bleeding into her pelvis from her pelvic fracture. She could have plucked off her spleen and is haemorrhaging into her abdomen. This is potentially life-threatening.
He then calls the on-call radiologist and ask them to come in from home to do an urgent CT scan of her abdomen and pelvis. They even kindly reconstructed her blood vessel system in her pelvis in case anything needs reconstructing. (It was awesome to see it in 3D, by the way.)
After all this excitement, there was nothing abnormal beyond the known cracked pelvis we could find.
It turns out she was super sensitive to opiates, having never had it before, and had some liquid morphine for her pain prior to the initial blood pressure drop. One of the side effects of morphine is vasodilation (the blood vessels expand, systemic resistance decreases, so the blood pressure falls), which is why it's EXCELLENT for heart attacks aside from for pain relief: it opens up the otherwise clogged artery. She had vasodilated so much her BP plummeted.
So we dropped her morphine dose and carried on with work. She was fine, discharged two days later. It was a less exciting ending, but at least she remained well.