I worked handling Travel Insurance claims back in the 90s. I ended up being given all the US Medical claims and make direct transfers digitally (it was a long time ago, electronic payments were a very new thing).
The pre approved individual signing limit for all staff handling medical claims was no more than £2000. A senior manager had to apply for permission from underwriters to pay for helicopter airlifts from ski resorts on an individual basis.
Except me. My signing limit was a blanket £5 million for any single medical invoice. As was pointed out to me by the company accountant, he only had a limit of £250,000, but because I handled medical claims from the US, all the different underwriters we worked for gave me that level of authority - because they knew I was going to need it.
The most expensive things were;
Premature babies
RTAs
Strokes/Brain haemorrhages, especially where the patient had to be airlifted off cruise ships and then didn't die quickly or, worse, whilst pregnant.
Elderly travellers where a minor ED visit for something unconnected revealed that they had cancer/a benign tumour.
There were cases where they were effectively prisoners because the hospital would say they weren't fit to fly. At times, we paid for high dependency air ambulances just because it was a) inhumane to leave them trapped out there with random relatives being phoned up at 3am and chased for payment/credit card details - despite our guaranteeing the costs already/contact us and b) it was ultimately cheaper to fly them home to be cared for by the NHS than have the hospitals charging tens of thousands a day for somebody who was terminally ill and wanted to come home.
There were also many occasions where patients were being subjected to medically unnecessary and invasive treatment and tests - for example, somebody who had just given birth to a premature baby did not need a pregnancy test every week 'in case she'd got pregnant again'. They stopped happening when they were asked if they were saying there was a substantial chance that she was being regularly raped by a member of staff whilst in Intensive Care.
The US medical system is abominable for all but the rich and not operated particularly in the best interests of anybody with good coverage, either - never mind the poor.
My monthly medication is delivered to me free with a sharps bin, disposal of old injectors, free advice on phonecalls, free regular blood tests and admittedly, an occasional phone call from the consultant (which works better for me than a day off work to go up there at the moment - although I've also been given immediate appointments in person when I've called up with a particular issue).
My medication alone costs around the equivalent of $13,000 a year to the NHS and absolutely zero to me. The same medication costs up to & around $65,000 in the US even if it's part covered by Medicare (only about 2/3 of Medicare schemes cover it at all).
And they screech about the NHS having fucking 'Death Panels'.