Private Clinton-John Botha, 21, died in the hospital on March 7 after an operation the previous day to relieve severe headaches.
He had been diagnosed with Chiari malformation -- a congenital defect at the back of the head that can cause headaches.
While the hospital has yet to release the findings of an internal investigation, Canterbury District Health Board (CDHB) inquiry leader George Downward has told the family there were "clearly a number of issues" surrounding the monitoring of Mr Botha, The Press reported.
In an email to Charlotte Botha, Dr Downward said her son died of "progressive respiratory failure based on the fact that his respiratory centre did not respond normally to a rising carbon dioxide level in his blood".
Issues had been identified in the hospital's routine monitoring of Mr Botha that resulted in staff not detecting the deterioration in his condition, he said.
"Although we have already made changes in these, I'm seeking to strengthen them even further without at the same time introducing new risks."
Ms Botha, of Christchurch, said the hospital had not told her son, or the family, of the seriousness of the surgery and the associated risks.
There had been "blocks and obstacles" every way they turned and the family had felt as if they were fighting a "losing battle against the mighty and powerful machine of the CDHB".
Ms Botha intended to lodge a complaint with the Health and Disability Commissioner.
The findings of the hospital's inquiry would be released to the family in four weeks, a hospital spokeswoman said.
Pte Botha was nominated for a bravery award during his time in East Timor and had been looking forward to a stint in Afghanistan.
He and three others were manning a patrol base when they broke up a riot involving 300 men.
