The consequences of healthcare going wrong is "a critical issue", consuming 30c for every $1 spent on health, according to a parliamentary select committee.
The health committee, in its report on this year's estimates for Vote Health,
called for steps to tackle the high incidence of "adverse events" and indicated exhausted doctors and nurses as one factor.
On an average, it cost $10,200, to treat a patient who suffered an unintended or negative event while in care. Such events cost the health system a total of $870 million a year.
Green MP, Sue Kedgley, the committee chairwoman said. "It's a shocking figure but what horrified me is there is no new money to do anything about it. This is a huge, preventable expense; we could do something about it."
Kedgley wanted hospitals to be open about their adverse-event rates as an incentive to reduce them. "It's not to blame and shame, but we need to put the spotlight on this area."
Adverse events include infections that develop as an aftermath of a hospital stay, allergic reactions to drugs, medication errors, heart attacks, pneumonia and blood clots after surgery.
Two-thirds of these adverse events were preventable and one-third was considered "highly preventable".
Health boards were adequately funded to address the issue and were doing so, according to Health Minister Pete Hodgson.