A public inquiry into the deaths of four children in Northern Ireland found that doctors had covered up their failings in properly treating a condition known as hyponatremia.

The condition, which is the result of abnormally low sodium levels in the blood, led to at least five children's deaths in Belfast, four of which were ruled as avoidable by the inquiry.

Sir John O'Hara QC led the inquiry and said some medics had behaved "evasively, dishonestly and ineptly", ITV News reported yesterday (31 January).

He examined whether fatal errors were made in the administration of intravenous fluids during the children's treatment.

A mother of one of the deceased, Marie Ferguson, whose daughter Raychel died in 2001, said: "No family should have to go through the mental and physical stress, hurt and undermining that we are still going through.

"I would like, in memory of Raychel, the introduction of a statutory duty of candour - Raychel's Law" she added.

"Surely there can be no greater pain for a parent than to lose their child and then to learn that errors occurred which were avoidable."

Medical chiefs at some of hospitals criticised have apologised.

Dr Cathy Jack, a medical director with the Belfast, Western and Southern Health and Social Care Trusts, said there had been "many failings" and apologised for the lack of transparency. She said that measures would be taken to stop such cases from happening again.

What is hyponatremia?

Sodium is an essential mineral for many bodily functions including fluid balance, blood pressure management and how our muscles and nerves work, according to Mayo Clinic.

When the blood contains low levels of sodium (below 135 milliequivalents per litre) this causes hyponatremia.

How is it caused?

It can be caused by drinking too much water during strenuous exercise. The sudden intake of water when vitamins have been lost dilutes blood levels in the body.

Dehydration is another cause as vital minerals are lost.

Other causes include a result of severe vomiting or diarrhoea and heart, kidney and liver problems.

What are the symptoms?

Symptoms of the illness vary from person to person, according to Healthline. Losing sodium rapidly is fatal and can result in seizures or a coma.

Common symptoms include weakness, fatigue or low energy, headache, nausea, vomiting, muscle cramps or spasms, confusion or irritability.

How can it be treated?

Depending on how severe the case is, treatment can include taking an intravenous (IV) sodium solution, medication for other symptoms or cutting back on fluid intake.