A BABY’S heart rate soared and his blood sugar level dropped dangerously low after he received fluids contaminated with insulin, the murder trial of Lucy Letby heard.

A medical expert told Manchester Crown Court on Friday, November 25 that poisoning was the only reasonable explanation for the premature-born twin boy’s sudden deterioration.

The 32-year-old nurse is accused of attempting to murder the infant by adding insulin to his intravenous feed on a night shift at the Countess of Chester Hospital’s neo-natal unit in the early hours of August 5, 2015.

Following the infusion of nutrients, that began after midnight, the heart rate of the youngster, referred to as Child F, surged to 200-210 beats per minute and his blood sugar fell to an “extremely low” reading.

His glucose levels remained low throughout the day shift of August 5, even after the intravenous line, and the connected bag containing the nutrients, had to be replaced.

Child F’s blood glucose only rose to safe levels after a decision was made to stop the nutrients from a second stock bag at 6.55pm and extra sugar was given independently, the court was told.

Giving evidence on Friday, Peter Hindmarsh, professor of paediatric endocrinology at University College London, said it was notable that low blood sugar was “persistent” for those 17 hours.

During that period Child F also received twice the amount of glucose normally given to correct hypoglycaemia in a baby, he said.

Prof Hindmarsh told jurors the brain was reliant on a “constant supply” of glucose to function and the dangers of low blood sugar included seizures, coma and, on occasion, death.

He said Child F’s initial rise in heart rate was “consistent with the release of adrenaline, your first line of defence against a low blood glucose”.

Prof Hindmarsh concluded that a commonly used synthetic human insulin known as Actrapid – a colourless solution – was administered via the infusion.

His calculations, he said, showed the synthetic insulin remained in a “steady state” in Child F’s system up until 6.55pm and disappeared more than 30 minutes later.

He also calculated from a subsequent blood sample, which showed an “extremely” high level of insulin, that the rate it was delivered was 17 times greater than a small “appropriately therapeutic” dose given to Child F in the days that followed his birth.

Prof Hindmarsh agreed with prosecutor Nick Johnson that the blood glucose measurements relating to the second stock bag suggested that it too had been contaminated “more or less to the same degree”.

Mr Johnson asked the witness: “Did you conclude the explanation for (Child F’s) clinical presentation from just after midnight on August 5, to the early evening of the same day was explicable and only reasonably explicable by the fact that the fluid he was receiving was contaminated by insulin?”

Prof Hindmarsh replied: “Yes I did.”

The witness agreed with Ben Myers KC, defending, that the blood sample reading of high insulin came from the second stock bag so could not show what level was in the first bag attached in the early hours of August 5.

But Prof Hindmarsh said that similar blood glucose readings around the same period from a single person would likely mean they had a similar amount of insulin in their system earlier.

Child F went on to make a full recovery and was later discharged, the court heard.

Letby is accused of trying to kill Child F less than 24 hours after she allegedly murdered his twin brother, Child E, by injecting air into his bloodstream.

The defendant, originally from Hereford, denies murdering seven babies and the attempted murders of 10 others between June 2015 and June 2016.

The trial continues on Monday, November 28.