Dunedin Hospital's emergency department has had a big increase in people leaving without being treated.

In a recent six-week period, almost 500 people opted to leave rather than wait to see a clinician, a report to yesterday's Southern District Health Board commissioners meeting said.

Specialist services executive director Patrick Ng had analysed emergency department data from the past three years, and focused particularly on July 1 to mid-August - usually a time when winter ailments lead to patient numbers rising markedly.

He said in both years, about 6100 cases were handled by the department.

"Over this six-week timeframe, 495 patients did not wait to be seen this year compared to 231 last year, which is a fairly significant increase," Mr Ng said.

"This is of concern, as patients may have elected not to wait but then subsequently deteriorated."

Those who stayed to obtain treatment spent, on average, an hour longer in the emergency department than last year, and they also appear to have been sicker - there were increased numbers of presentations in all triage categories other than the lowest priority.

"The number of patients arriving by ambulance has increased. This also seems to suggest a higher level of acuity is being treated in the ED than last year," Mr Ng said.

"The average length of time spent in ED has gone up from 3.4 hours last year to 4.3 hours; that appears to be significant and we need to drill a bit more into that to see what that means."

Admission numbers to hospital from emergency during the survey period were up 6.2% from the previous year.

While more work needed to be done to understand the raw numbers, they seemed to support anecdotal reports from Dunedin emergency department staff that the service was under extreme pressure, Mr Ng said.

"All the markers point to what our staff have been telling us - that it has been a very busy ED services over the recent period of time."

A similar analysis was being done at Southland Hospital, which had also reported it was struggling to cope with pressure at its emergency department.

SDHB chief executive Chris Fleming suggested there might be a good news story in the report; that primary care was seeing more lower needs patients and freeing up the emergency department for more serious cases.

"It may be that some cases that might historically have come to ED are now not coming, and that would be a good thing."

The volume of cases coming from emergency through to the general hospital wards had occasionally resulted in elective lists being cancelled so doctors could focus on acute caseloads - a regular occurrence in winter.

"We have also had a number of occasions during August where we had to cancel elective cases despite the acute volumes being low because of insufficient inpatient beds," Mr Ng said.

"This does not happen very often at the Dunedin hospital and appears to be symptomatic of the overall demands on the hospital."

The SDHB has long known it has issues in its emergency departments, and like many DHBs has difficulty achieving the national health target of 95% of patients being admitted, discharged, or transferred within six hours.

It has tried a range of initiatives to shorten waiting times, and will shortly be considering relocating an inpatient medical assessment unit to be nearer the emergency department.