A diagram, prepared ahead of time by a bioengineer, shows where various medical personnel would stand for the high-risk delivery of a baby named Addison Mosley at Children's National Medical Center. Addison was born with a tumor on her neck and needed 32 people standing ready for her birth. (Courtesy of Children's National Medical Center)

Mary Donofrio is a fetal cardiologist, expert in the ways tiny hearts work and the ways they sometimes don’t. She’s also director of something called the complex fetal delivery team at Children’s National Medical Center, and when she learned about the baby Silver Spring couple Erin and Andrew Mosley were expecting, she knew the word “complex” applied.

An ultrasound at 20 weeks had detected a mass growing around the throat of the fetus, a little girl that today the world knows as Addison Grace Mosley. An MRI — its probing rays shot through Erin’s belly — provided more information. It appeared that Addison had a lymphangioma, a condition in which lymphatic fluid isn’t flushed properly through the body but pools, typically around the neck.

“What was noted on the fetal scans was a very large tumor that was in the neck region, extending onto the jaw, all the way down to the chest,” Dr. Donofrio said. “It was a mass that I think was larger than anyone on our team had ever seen. Certainly the fear was that when Addison was born, she wouldn’t be able to breathe.”

As long as Addison was inside her mother, she was fine, because Erin provided oxygen and nutrients for her. But as soon as a newborn’s umbilical cord is clamped, the lungs spring to life and the baby gasps for breath. If Addison’s airway was obstructed — blocked or kinked because of her tumor — she would be in grave danger.

“So because of that,” Dr. Donofrio explained, “the decision was made that the only way to safely bring Addison into the world would be to bring her into the world with a stable airway, to put a breathing tube in place, even before she was detached from her mother.”

Addison needed something called an EXIT procedure, short for ex utero intrapartum treatment. She would be delivered by caesarean section, but only partially. Before the cord was clamped, surgeons would work to establish an airway.

This is a complicated procedure. Dr. Donofrio counted up the number of specialists Addison would need: fetal surgeons, ENT surgeons, anesthesiologists, neonatologists, the concomitant nurses and assistants, not to mention the obstetricians for the other patient in the operating room, Erin Mosley.

She came up with 32.

The team started meeting months before Addison was due. The members compiled checklists and flow charts. May-Britt Sten, a nurse whose title is manager, process improvement, kept track of their notes and refinements.

Ozzie Rivera, a clinical engineer at Children’s, sat down at a computer. He had the list of personnel who would be required and of the necessary medical equipment. He knew which direction the arms of machines could swing. Like a football coach diagramming a play, he used software to position the virtual players in Addison’s EXIT procedure, producing a series of floor plans indicating where everyone would stand at certain points in the operation.

Once the floor plan and flowcharts were approved, the team assembled for a dry run. Very few babies are born at Children’s Hospital; Addison would be one of them. Washington Hospital Center obstetricians David Downing and Melissa Fries came to Children’s for the run-through. They had with them a life-size manikin with a baby inside. The baby had a tumor on its neck, designed to the precise specifications of the one on Addison.

The team performed an hour-long simulated EXIT procedure, getting a feel for the choreography that would be required.

They were ready. Everyone marked Oct. 13 on their calendars: the date Erin would be rolled into Operating Room 5. Then on Sept. 22, while at her job at a nonprofit near Dupont Circle, Erin’s water broke.

Addison was coming early.

Tomorrow: Delivering Addison.

Helping children

I’ve heard it again and again: Healing sick children is a team effort. Nowhere is that more true than with Addison Mosley. But you can be part of a team, too — the team that ensures no child is turned away from Children’s Hospital.

So far this year, 436 readers have donated a total of $48,161 to our annual fundraising campaign. Won’t you please join that team? You can make a tax-deductible contribution by sending a check or money order (payable to Children’s Hospital) to Washington Post Campaign, P.O. Box 17390, Baltimore, Md. 21297-1390. To donate online, go to washingtonpost.com/childrenshospital.