Pippa Mae White died shortly before her third birthday at Orange Base Hospital after experiencing two cardiac arrests on June 13, 2022.
Admitted into hospital a day earlier after becoming unwell with a fever, vomiting and diarrhoea, tests revealed the toddler had pneumonia with a complete white-out of her left lung.
As an inquest into the toddler's death continued on Tuesday, Dr Christopher Morris was questioned about the steps taken to treat Pippa on June 12 and in the early hours of June 13.
The junior doctor said he should have escalated the toddler's care earlier than he did when her heart-rate increased to what was referred to medically as the "red zone".
Pippa was also grunting and showed "crackles" when she breathed, showing signs of abdominal pain.
Lidcombe Coroners Court was shown videos of the two-year-old grunting as she breathed.
In one, she had her head on her mother Annah's shoulder.
Dr Morris said he ordered blood tests instead of escalating the case because he wanted to be diligent and have more information on hand when discussing the case with his superiors.
"It was an oversight to not call a rapid response," he told the court.
He said this was an error of judgment but not a deliberate decision.
Dr Morris said he spoke with pediatrician Dr Adam Buckmaster about Pippa when she was showing signs of sepsis and formed a plan to treat her with antibiotics and fluids, and take blood tests to track her progress.
Sepsis is when the body's response to an infection starts damaging its internal tissues and organs.
While Dr Morris said he saw the toddler's left lung and signs of infection on the radiographer's screen as an X-ray was taken, he did not immediately notify Dr Buckmaster.
Pippa White's family and supporters gathered in the courtroom wearing her favourite colour yellow. (HANDOUT/)
Fearful of making an error by basing his diagnosis on a low-resolution image, Dr Morris said he waited to get the actual X-ray after the machine was turned off and wheeled out of the ward.
Dr Buckmaster attended the hospital hours later when he took over the toddler's treatment.
Struggling to talk as emotions took over, Dr Morris said he didn't feel that his diagnosis of Pippa could have been anchored to an earlier assessment of her that she was experiencing a viral infection.
"I didnt feel like I'd closed my mind to this only being one thing," he said.
"I didnt feel anchored but clearly I made an error of judgment.
"If I'd have my time over, sure, I'd do anything to make some different decisions."
As the doctor gave evidence, Pippa's mother, father, siblings, extended family and other supporters gathered in the courtroom wearing her favourite colour yellow.
A large portrait of the toddler wearing a yellow dress, running amongst a field of yellow flowers surrounded by butterflies sat on the opposite side of the courtroom to her family.
Under questioning by Richard O'Keefe SC, representing Pippa's parents Annah and Brock, Â Dr Morris also accepted that he could have been fatigued at the time after working a full shift and then being on call at the time he was examining Pippa.
Rostering at Orange Hospital changed after the toddler's death which Dr Morris inferred was in response to the tragedy.
During the inquest, Deputy State Coroner Joan Baptie will consider whether the treatment and care offered to Pippa at Cowra and Orange Hospitals was adequate and appropriate.
She will be asked to consider whether any recommendations can be made to prevent similar deaths in the future.
The hearing continues on Wednesday.
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