CAIRO(Reuters) - A U.S. vascular surgeon who left Gaza after a stint as a volunteer said on Wednesday nothing had prepared him for the scale of injuries he had faced there.

Dozens of patients a day. Most of them young. Most facing complicated injuries caused by shrapnel. Most ending up with amputations.

"Vascular surgery is really a disease for older patients and I would say I had never operated on anybody less than 16, and that was the majority of patients that we did this time around," Shariq Sayeed, from Atlanta, Georgia, told Reuters in Cairo.

"Most were patients 13, 14, 15, 16 and 17 years of age. Mostly shrapnel wounds, and that was something I have never dealt with, that was something new."

In his stint at the European Hospital in Gaza, Sayeed said his team would deal with 40-60 patients a day. The vast majority were amputation cases.

"And unfortunately there is a very high incidence of infection as well so once you have an amputation that doesn't heal, you end of getting a higher amputation," he said.

Around 70 percent of the surgeries he performed were on injuries caused by shrapnel, the rest mostly from blast injuries and collapsing buildings.

Ismail Mehr, an anaesthesiologist from New York State, who led the Gaza mission, said the volunteer medics were "speechless at what we saw" when they arrived this month in southern Gaza.

Mehr is chairman of IMANA Medical Relief, a programme that focuses on disaster medical relief and healthcare support and has provided treatment to over 2.5 million patients in 34 countries and counting.

He has been to Gaza several times in the past, but could not imagine what he saw this time: "Truly everywhere I saw was destruction in Khan Younis, not a single building standing."

Out of 36 hospitals that used to serve more than 2 million residents, just 10 were somewhat functional by early April, according to the World Health Organization.

Health facilities lacked medical supplies, equipment, staff, and power supplies, Mehr said. His biggest fear now is an expected Israeli assault into the southern city of Rafah, where half of Gaza's 2.3 million people have sought shelter.

"I hope and I pray that Rafah is not attacked," he said. "The health system will not be able to take care of that. It will be a complete catastrophe."

(Reporting and writing by Nidal al-Mughrabi; Editing by Aidan Lewis and Peter Graff)

By Nidal al-Mughrabi