The medical evidence that finally caught Lucy Letby

The case of nurse Lucy Letby – found guilty today kill seven trying to kill premature babies and seven others – depending on the medical evidence.

Time and time again, consultant pediatricians Dr Dewi Evans and Dr Sandie Bohin suggested that they had been injected with air – either into their blood or through feeding tubes into their stomachs.

Both medics told the jury that air embolism had virtually never been researched, because injecting an air bubble into the bloodstream of a patient, let alone a premature baby, was highly unethical.

They said it was virtually impossible to say how much air would be enough to block blood flow to vital organs and stop the heart.

However, they estimate that in such fragile preterm newborns, just 5 ml – or a teaspoon – of air would be enough to kill.

Consulting pediatricians Dr Dewi Evans and Dr Sandie Bohin provided crucial evidence in Letby’s case

They also pointed to a research paper on air embolism in infants, written by scientists at the University of Western Ontario, in Canada, in 1989, which described a “migratory” discoloration of the skin, usually manifesting as pale, with fluttering bright pink spots .

This strange rash became a ‘hallmark’ of the case and was observed by different doctors in five of the babies – baby A, baby B, baby D, baby M and baby O – prior to death or while they were being resuscitated.

The scientists explained that while the babies’ tissues and muscles were deprived of oxygen during their collapses, making them appear white, the pink spots could be explained because air injected into the bloodstream temporarily oxygenates red blood cells when it comes into contact with with them in the blood vessels themselves.

In two of the cases, baby A and baby E, X-rays taken shortly before they died revealed air bubbles in major arteries or veins.

In cases where air was injected into the infants’ feeding tubes in excessive amounts, it caused their little tummies to swell and “splinter” or push up the diaphragm, crushing their lungs and compromising their breathing, which also caused their collapse, the experts explained.

While some children recovered, as in the case of Baby G, who suffered severe brain damage as a result, for others, including that of Baby C, a tiny baby boy who was just five days old when he was attacked, and Baby P, the second triplets, was fatal to him.

Lucy Letby’s conviction for multiple murders depended on the medical evidence

In their cases, X-rays taken before their deaths showed excessive amounts of gas or air bubbles in their intestines.

Air couldn’t be accidentally injected, the experts said, because nurses were in danger of “pushing” air into lines and cannulas during their training.

Letby underwent training herself, allowing her to administer drugs through special cannulas highlighting the dangers of air embolism, just two weeks before killing her first victim in June 2015.

Midway through the trial, Letby’s defense team unsuccessfully tried to sideline Dr. Evans’ expert evidence.

They said he had been heavily criticized and discredited by a judge in a previous family court case for being “partisan,” and defense KC Ben Myers accused him of providing “biased and emotional” evidence.

Mr Myers said Dr Evans had been too close to the police investigation from the start, undermining his objectivity.

The prosecution also had to show that the conclusions of the original autopsy examinations in six of the murder victims were flawed and that their actual cause of death, as proven by expert pathologist Professor Andreas Marnerides, was foul play.

A cot in a nursery where Letby worked at the Countess of Chester hospital

Only in the case of Baby F and Baby L, the baby boys of two separate twins who became ill on the ward eight months apart, was the medical evidence beyond doubt.

Even Letby herself admitted that there was no doubt about the results of specialist tests on their blood, which showed that both had been poisoned by insulin.

The analysis, which compared the amount of insulin to the amount of C-Peptide, a substance produced by the pancreas at the same time and at the same rate as insulin, showed that the levels of insulin were off scale, so could not pass the babies produced themselves and had to have been administered exogenously as medicine.

Letby also told the court she did not believe one of her colleagues would have been so careless in making a mistake and accidentally giving the babies insulin.

She accepted that they were poisoned, but insisted she was not responsible. In the end, the jury refused to believe that another poisoner was at work on the ward and concluded that she had tried to kill them.

WATCH THE MAIL’S FULL LUCY LETBY DOCUMENTARY HERE