Eleven patients had medical instruments left inside them after surgery, according to a new audit of New South Wales Health.

They were among more than 20 grave errors - the highest level in three years - which included deaths after the incorrect administration of drugs.

They're called Sentinel Events, when patients suffer serious harm or death, and they're happening too often.

"It's actually really good to see that we are picking up events, what's not good to see is that events have increased in number,” said Dr Kean-Seng Lim, the President of the NSW Australian Medical Association.

Sentinel Events are on the rise. Credit: 7NEWS

There were 22 Sentinel Events in 2018/19, the highest number in three years.

They included four suicides in inpatient units... 11 medical instruments or other material left inside patients - Four Medication errors leading to the death of patients and three maternal deaths.

"These are all signs of a system where people are having to work harder and probably having to do more than what the system is set up to do,” Dr Kean-Seng Lim said.

Attendance in Emergency Departments hit 2.9 million in 2018/19. There were more than 225,000 elective surgeries, 588,000 Ambulance arrivals and 38,500 discharges from acute mental health units.

There were also more than 225,000 elective surgeries during the period. Credit: 7NEWS

There are also calls for an inquiry into the Healthcare watchdog to investigate allegations of misconduct and malpractice. Almost half of all cases before the Health Care Complaints Commission have dragged on for more than a year, up 34% from the previous year.

"We've told the government not to cut $250million out of the current Health budget, a health budget that's already under enormous pressure,” said Ryan Park, Shadow Health Minister.

The Auditor General also looked at the finances of New South Wales Health – which recorded a surplus of $1.1billion last financial year.

Read the Auditor General’s report here.

NSW Health Statement to 7NEWS

Clinical incidents that result in serious patient harm, known as sentinel events, are very rare. Of the almost 2 million patients admitted to one of our 228 public hospitals in NSW in 2018-19, just 0.0009 per cent of those resulted in a sentinel event.

Dr Kean-Seng Lim, the President of the NSW Australian Medical Association. Credit: 7NEWS

While NSW Health deeply regrets any adverse outcome to its patients, we have a strong reporting culture that ensures that incidents are identified and mitigation strategies are put in place to avoid similar events from occurring in the future.

With an aging and increasing population, demands on our health system are great. We performed elective surgery on 83,000 more patients between 1 July and 31 October than for the same period the previous year.

In our Emergency Departments, the first four months of this financial year have seen around 1 million people, an increase of 6 per cent on the same time in 2018, equating to over 58,000 additional patients.

This includes an 8.4 per cent increase in patients arriving by ambulance to emergency departments.

The positive net result for NSW Health ($1.1 billion in 2018–19) does not mean that Health had unspent funds.