Doctors at UCSF and California Pacific Medical Center were finishing the final of 18 surgeries Friday afternoon in a rare nine-way, two-day kidney transplant swap at the two San Francisco hospitals.

Transplant surgeons at both hospitals successfully completed 10 surgeries involving five donors and five recipients on Thursday and were on track Friday to finish the final eight surgeries for four donor-recipient pairs in what’s considered to be the longest kidney transplant chain performed in one city in such a short period of time.

Adding to the logistical hurdles of so many surgeries, kidneys had to be ferried back and forth between the two hospitals. On Friday, two kidneys were sent from California Pacific to UCSF via a special organ transport service and two kidneys were sent from UCSF to California Pacific for a total of four, 3-mile trips. Two trips were made Thursday.

“Everything went as planned and our team is just getting to transport the very last one,” said Noel Sanchez, spokesman for Donor Network West, late Friday afternoon. The Oakland company specializes in packaging and transporting organs.

While some may have friends or family members willing to donate, they may not be a match. So many have to wait an average of four to five years for a kidney from a deceased person.

But a computer software program, first developed by a former kidney transplant patient at California Pacific, has made domino-like kidney transplant chains possible by connecting willing donors with compatible recipients, even if their kidney does not match their intended recipient. The donor’s kidney will be paired with a matching recipient and, in exchange, the donor’s loved one will receive a kidney from a compatible donor in the same chain.

The software matches are based on basic factors like age and blood type, but also involve detailed information such as whether the donor’s blood contains certain proteins that might trigger a recipient to reject their organ.

The UCSF-California Pacific kidney swap was started by an altruistic donor, 56-year-old Reid Moran-Haywood, who had originally wanted to donate a kidney to a friend last fall. When the Napa man did not prove to be a match for his friend, he decided he wanted to help someone else. Moran-Haywood’s surgery was the first to be done Thursday morning.

UCSF officials said late Friday afternoon that surgeries were almost completed and that everything had gone smoothly. California Pacific officials also said the procedures were going well at their hospital.

California Pacific spokesman Dean Fryer said he spoke with several of the patients waiting to be operated on Friday morning and they were in high spirits. “They were all excited and anticipating and getting ready for surgery,” he said.