Ten people - including a newborn - have died following serious medical events, some preventable, while under the care of Capital and Coast District Health Board in the past year.
Nine others were also involved in serious and sentinel events.
''Every one of these events is one too many, and I am sorry that they have occurred,'' chief executive Mary Bonner said.
''We always seek to learn from these incidents and improve safety.''
A serious adverse event is one that leads to significant additional treatment but is not life-threatening, and has not resulted in a major loss of function.
A sentinel adverse event is life-threatening or has led to an unexpected death or major loss of function.
The Health Quality and Safety Commission's serious and sentinel report for 2011/12 shows a person died when a blood clot in their lung was not diagnosed on a CT scan at Wellington Hospital.
Another person died following the delay in diagnosis and treatment of sepsis.
Staff in the emergency department failed to detect a bleed in a person's brain who sought help for a migraine. This person did not die.
Six cancer patients, one of which died, experienced a delay in diagnoses and treatment.
Of concern were the three patients who killed themselves and the six patients whose diagnoses and treatment was delayed, Ms Bonner said.
The suicides were the first since 2004 and had sparked an independent review of inpatient suicide incidents.
Two of the deaths were inpatients and one was a mental health patient who was on approved leave from the inpatient unit.
Each of family was given a formal apology.
While adverse events were rare, to have even one event was not good enough, Ms Bonner said.
''To put these numbers in context each year in our district we undertake more than 425,000 patient appointments, procedures and operations - including more than 115,000 radiology procedures - almost all without adverse incident.''
Fractures from falls made up the majority of Hutt Valley DHB's 10 serious and sentinel events during the past year.
Patients suffered fractures to their elbow, hip, nose and pelvis, two while getting in or out of bed, one on a bathroom, and one after fainting when standing up for a chest X-ray.
In November 2011 a patient who went to the emergency department with a fracture was sent home after the fracture was not identified by hospital staff.
The fracture was discovered 10 days later and had to be reset in an operation.
The clinician responsible had to undertake communication and ''listening skills training'', the report says.
In another event in October 2011 a hospital swab was left inside a patient for two weeks, and had to be later removed by a GP.
In that incident the DHB's correct swab procedure was not followed, and an action plan later developed to stop re-occurrence.
Two patients suffered pressure ulcers during hospital stays, leading to a review of the patient ''audit process''.
Two Wairarapa patients died from medication errors and a CT scan was performed on the wrong patient, the serious and sentinel events report shows.
The Wairarapa DHB reported four events in the last financial year.
Two occurred in the community and two in hospital.
In one incident incorrect thrombolytic medication was prescribed and administered to a patient who subsequently died.
Such medication is used to dissolve blood clots.
In another medication error, over-the-counter medication was left with a patient contrary to their care plan. The patient took an unintentional overdose and died.
A third patient died during an operation as a result of a clot in their lung.
A CT scan was also performed on the wrong patient, the report shows.
DHB quality, safety and risk director, Cate Tyrer, said all events had been fully investigated.
"An unexpected death is very sad and affects everyone involved.
''When there is an unexpected adverse outcome, we need to do everything we can to understand how and why, to prevent it happening again if possible.
''In Wairarapa DHB we have a robust reporting system where staff can report incidents in an atmosphere of trust, openness, shared responsibility and accountability.''
Chief executive Tracey Adamson said that even with the best people, processes and systems, errors could occur.
''When they do, we need to find out what went wrong, whether it could have been prevented, and what improvements or changes should be made.
''Any preventable error is unacceptable and the DHB seeks to learn from it."
Hawke's Bay District Health Board reported 11 serious and sentinel events in the Making our Hospitals Safer report released today by the Health Quality and Safety Commission.
These included the death of a patient who developed septicaemia after inadequate recognition of the patient's condition, failure to seek senior medical input, inadequate follow up of management plan and inadequate handover between shifts.
Other incidents included the death of a patient with pancreatitis, where there was a failure to recognise deterioration, inadequate pain management, failure communicate with next of kin, failure to document enduring power of attorney and delayed completion of death certificate and transfer to mortuary.
Other incidents included the suicide of a medical patient, and two patients who suffered injuries in falls and later died.
Lakes DHB had seven serious adverse, but non-life threatening, events during 2011-2012.
These included four falls, of which three of the falls occurred following operations for joint replacements.
The common factor was the use of a local anaesthetic to reduce pain, Lakes DHB said.
Other serious adverse events included one joint infection following surgery where the patient was "treated aggressively to reduce the infection was identified but had an extended hospital stay and a delay in recovery".
A fifth serious adverse event occurred when there was an "incorrect surgery site" as result of a documentation error before the operation.
The final serous adverse event occurred when a youth due to be admitted as an inpatient suddenly left the facility suddenly and allegedly assaulted a family member.
Tairawhiti District Health Board had five sentinel and serious events.
These included a baby who died due to aspiration pneumonia caused by meconium, the death of a patient due to post-operative complications and the unexpected death of a young adult admitted to ICU.
The death of the young adult is still under investigation.
Others included an adverse event for a patient soon after they had been discharged from the inpatient mental health unit and delays to treatment due to equipment failure.
Related story: DHB reports serious event increase
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