Despite mounting pressure, hospital administrators hardly ever admit to making mistakes that can result in death.

In this case, the hospital has issued five death certificates, all with different explanations on what happened to Valerie Prowd.

More people die in our hospitals every year as a result of medical mistakes, than on our roads.

• Australia's busiest hospital
• Emergency calls ignored
• Cocaine doctor investigation

Issued with five death certificates, all with different explanations on how his wife died, Ray Prowd is still no closer to finding out what caused her death.

Ray doesn't know how or why his wife of 27 years was taken away from him.

“You don't die of broken legs. That’s what everyone's telling me,” he said.

Today Tonight's latest health stories

In 2005, Valerie Prowd, a 63-year old grandmother, known as Suzie to her friends, was rushed to Nambour Hospital on Queensland's Sunshine Coast for surgery on a broken leg. Seventeen days later she died.

However it was not from a broken leg, but rather from Chronic Obstructive Airways Disease. Or at least that's what the first death certificate said.

Then on the second death certificate a fall was added, and on the next death certificate Atelectasis, or collapsed lung and immobility was added. On the fourth a draft Emphysema was added, and finally on the fifth the original cause of death from certificate one - Chronic Obstructive Airways Disease - was removed.

More stories from reporter Adam Marshall

Seven years on Ray says he still doesn't know what killed his wife. “It’s criminal. This should be looked at straight away by police or by the coroner.”

Lorraine Long from the Medical Error Action Group says it’s most likely not ‘what’ killed Ray's wife, BUT rather ‘who’, as this sounds like a classic case of medical negligence.

According to Long, this is now our leading cause of harm or death.

Yahoo!7 News: Thousands of Victoria's nurses to quit

“Medical procedures are not guaranteed. There is a risk to all of them,” she said.

She says while figures are outdated, in 1995 a report found 18,000 patients die every year due to medical negligence, and a further 330,000 are being harmed. Long believes these are conservative estimates.

Each week MEAG is inundated with calls about all kinds of medical errors, incorrect diagnoses, incorrect medicine dosages, equipment sterilisation failures, and even surgery on the wrong patients.

“Their idea is secrecy first. Safety comes later, if it comes at all,” Long said.

She says the Prowds’ case bears a striking similarity to her mother’s who, despite having breathing problems, was given the opiate drug Endone and died.

The Victorian Coroner found doctors gave June an incorrect dosage of Endone.

Ray believes the same mistake killed his wife, who suffered from emphysema, and was given Endone when she shouldn't have been.

“Endone is a drug that you do not give to patients with head injuries or respiratory problems. That is a fact you and I can find by Googling,” he said.

The death of sixteen-year-old girl Vanessa Anderson in New South Wales due to Endone in 2005 sparked an inquiry into the use of the drug and hospital procedures.

139 recommendations were made, but despite this more than six years on Vanessa's father Warren believes not enough has been learnt from his daughter's death and the mistakes made.

Ray says that's exactly how he feels. Nothing's clear even seven years on.

Long says this case has been handled poorly, and after their own investigation believes Ray's wife's medical file has been tampered with.

Rhey will now take up Ray's battle and urge the Queensland coroner to finally look into his wife's death.