THE risk of dying in hospital increases when nurses are replaced with nursing assistants, according to a new study.

Researchers warned that a shortage of nurses on a ward was clearly linked to a rise in mortality but that this was not alleviated by deploying more nursing support staff to plug the gap.

The study, based on an analysis of nearly 140,000 patients admitted to a hospital in the south of England between 2012 and 2015, comes as the NHS gears up for the busy winter period.

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The latest figures from ISD Scotland show that the vacancy rate for registered nurses and midwives in Scotland has increased by 0.5% over the past year, to 5.3%. In eight health boards, the number of registered nurses and midwives has also declined.

In common with trends elsewhere in the UK, NHS Scotland has seen the proportion of nursing support staff within the workforce increasing more than twice as fast as for registered nurses - by 7% compared to 3% since 2013.

Professor Peter Griffiths, an expert in health research at Southampton University and lead author of the study, published in the BMJ, said: "At a time when the NHS is facing increasing difficulties in recruiting and retaining staff, this research reveals the potential consequences of shortages of registered nurses in terms of the negative impact on patient safety.

"Assistant staff are an important part of the team but adding more of them is not the solution."

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The study found that the risk of a patient dying increased by 3% for every day that registered nurse staffing fell below the ward's average, and this increased to 5% if the number of admissions per registered nurse exceeded 125% of the ward's average. This is of particular significance during winter, when bed occupancy levels and overcrowding on wards tends to increase.

Oddly, researchers detected a pattern of increased mortality among patients both when nursing assistant levels dropped below average, but also when thy increased.

The authors state that while there findings "lend no support to a policy of compensating for deficits in the RN workforce by employing more nursing assistants", there appeared to be an "optimal level of assistant staffing".

They added: "When assistant staffing was close to this level, the hazard of death was reduced.

"The mechanism by which adding further assistants above this level can lead to worse outcomes requires further exploration...It may be that the presence of additional direct care staff creates a division of labour that means RNs spend less time with patients, reducing opportunities for ongoing monitoring, assessment and evaluation outside scheduled observations."

Consultant physician and co-investigator Dr Paul Schmidt said: "This study shows us how important it is to have properly qualified nurses working on wards and registered nurses and care assistants should not be treated as equivalent.

"We need to improve the supply of registered nurses because RN shortages can cause great harm to patients, and we can't fix it by increasing the numbers of lesser trained nursing staff in the workforce."

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It comes as MSPs prepare to debate Scotland's NHS 'Safe Staffing' Bill in the Scottish Parliament today.

Theresa Fyffe, Director, Royal College of Nursing, Scotland said: “This research shows that patients are paying the price for the failure to future proof the workforce.

“Over 3,300 nursing and midwifery posts are vacant across Scotland and these shortages are having an impact on patient safety right now. This publication is the latest in a long line that shows having the right number of nursing staff, with the right skills and experience to meet demand is fundamental for the safety of patients and the wellbeing of our members."

The Scottish Government has increased funding to boost the numbers of people studying to be registered nurses, which requires a four-year university degree.

During 2017/18, there were a total of 10,645 undergraduate nurses and midwives in Scotland, the highest since recording began in 2000.