Having to treat too many patients because of the shortage of physicians has been identified as a key factor driving medical specialists overseas.

The senior doctors' union has calculated New Zealand is short of 638 medical and surgical specialists, based on accepted benchmarks.

This situation has occurred at a time when the Government is trying to boost the number of specialists to help drive increases in elective surgery and further reduce cancer waiting times.

New Zealand would in fact need at least 1100 more specialists if it were to match the number per head of population in Australia, the union says in a discussion paper based on data from 2007 and 2008.

It lists the "onerous" hours spent on call for after-hours work and the "lack of real non-clinical time" as among factors, including pay, that encourage specialists to leave.

"I don't think patient care is being compromised [by the shortage]," the union's executive director, Ian Powell, said yesterday, "but the system is being held together by an overworked specialist workforce."

He said the effect was that specialists lacked the time needed for clinical audits, peer review and full involvement in clinical leadership.

These things are all aimed at improving the overall quality of health care for patients.

An anaesthetist at Counties Manukau District Health Board, Dr Rob Burrell, said he was given some non-clinical time but it was variable.

"Five years ago I had none. I have more than I did, so I'm happier than I used to be.

"It became apparent that because we weren't offering non-clinical time, we found ourselves short of anaesthetists and nobody wanted to come to us.

"Our department made a case for that and made it clear we were short because we didn't offer non-clinical time. We have since been able to offer some and have had less trouble recruiting people."

Dr Burrell said the feeling of collegiality that developed through non-clinical work was an important factor in retaining staff.

The head of the Government's Health Workforce NZ committee, Professor Des Gorman, said he accepted that the country had a shortage of specialists, and much was being done to address it, but there was little use in making a comparison with Australia because its health system was quite different.

He said that since October 2008, a net 1737 nurses, surgeons and anaesthetists had entered the New Zealand workforce, including 67 surgeons and 49 anaesthetists.

An extra 96 staff would be trained in 2010-11 to work in the eight new elective surgery theatres to be introduced in Auckland and Waitemata.

Short-staffed

To reach the number of specialists per capita that Australia has, New Zealand would need:

* 18 per cent more anaesthetists.

* 27 per cent more obstetrician/gynaecologists.

* 39 per cent more internal medicine specialists.

* 25 per cent more psychiatrists.

* 30 per cent more general surgeons.