Kelly Denton died at Treliske Hospital in 1998
Witnesses said Kenneth Woodburn became aggressive while trying to fit a catheter in 16-year-old Kelly Dent's chest at Treliske Hospital, Truro.
On Thursday, Exeter Crown Court was told how Mr Woodburn expressed his sadness at the death at Treliske Hospital.
In a statement read to the court, he said he met Kelly's mother, Carol, five days after her daughter's death.
He told her Kelly had died because of a rare but recognised complication of the technique, said the statement.
Earlier in the trial the court heard of a statement by Mrs Dent, saying she would have objected to the operation if she had known the tube would be close to her daughter's heart.
Mr Woodburn, 39, of Mill Farm, Idless, near Truro, denies manslaughter.
Kelly, of Illogan, near Redruth, Cornwall, died during a "simple" operation on 2 September 1998.
The catheter tube punctured her heart and she died of massive internal bleeding.
Operation stopped
It was being inserted to assist her treatment for myeloid leukaemia.
Radiographer Jennifer Clark told the jury that Mr Woodburn was very angry during the operation and slightly rougher than would normally be expected.
But she said she did not feel he had lost his professional control.
Mrs Clark said that when Kelly's blood pressure dropped Mr Woodburn stopped.
She then said: "All hell broke loose and everybody started to rush around.
"I remember seeing a nurse coming out of the changing room crying."
The court heard Kenneth Woodburn was "very shaken" and emotional when efforts to revive Kelly failed.
The trial continues.