Heather Hanna had signed up for a 150ft abseil at St Mary's Hospital in Paddington in aid of the More Smiles Appeal on 27 April - her 50th birthday.
But the mother-of-two, who works at the hospital in Paddington as a senior paediatric research nurse, fractured two vertebrae in her back in a horse riding accident last month and has been advised by her doctor not to take part in the event.
"Even though I’m not taking part in the event this year, I am still keen to support the charity for my birthday and I am hoping people will donate to the appeal instead of giving me presents. Raising money is a great way to celebrate being alive for 50 years and give something back at the same time," said the mother-of-two.
The More Smiles Appeal aims to raise at least £2million to expand and renovate the children's intensive care unit at St Mary's Hospital.
Every year, around 400 patients are cared for in the unit but it also turns away hundreds more critically ill children because it does not have enough beds. This means children may have to be transferred hundreds of miles for treatment.
Last year, the unit had to turn away 233 children, more than half the number actually admitted.
The new unit will have 15 beds, almost doubling the current number, allowing more than 200 extra children to be cared for each year. There will also be new equipment, a dedicated parents' room and a private room allowing space for doctors and nurses to provide emotional support and care to families whose children are very seriously ill.
Heather, who has raised more than £500 so far, is hoping to take part in the abseil next year.
She said she has been inspired to raise money for the appeal by the children she has met during her 32 years in nursing.
"I want to thank everyone who has donated. I'm spurred on thinking about the children I have met in the children's intensive care unit over the years that have shown extreme bravery when they haven't had a choice," she said.
Heather said one of these children was Jonathan Allen who came into the unit in December 2013 at the age of 12.
His family took part in research that Heather was carrying out in the unit, which is how she met them.
"The fact they were willing to take part in research at one of the hardest times in their lives was very brave and touching. It wasn't likely that he was going to survive but the team in the children's intensive care unit saved his life," she said.
Jonathan, of Brentwood in Essex, has now made a full recovery and will celebrate turning 15 the day after Heather turns 50.
His mum, Dawn, said: "It's every parent's worst nightmare. Just two hours after he arrived, the doctor told me to get my husband, Jeffrey, and our daughter, Rachel, to come to the hospital and prepare ourselves for the worst.
"I couldn't believe it. My son was walking around 24 hours earlier and then the doctor was telling me my son could die."
While Jonathan was in a coma, a St Mary's doctor worked out that Jonathan was suffering from a rare disorder of the adrenal glands known as Addison's disease.
"They told us that even if he did recover he would probably be brain damaged. It was a horrendous time," said Dawn.
"But when he went for his brain scan a few days later, they said they had never known anything like it. The doctor told us if he didn't know Jonathan's case he would have thought he was looking at the brain scan of a completely healthy person. My husband and I had tears rolling down our faces."
Jonathan woke from his coma just five days after arriving at St Mary's.
Dawn, who works as a music teacher, said: "He took one look at me and said 'mum, why are you crying?'. I will never forget that moment.
"It's just through the quick-thinking of one of the doctors that he was diagnosed with Addison's disease and given the medication he needed. They saved his life. As a family we are just so grateful to St Mary's for Jonathan's life."
Jonathan with his family after making a full recovery