A senior nurse had “sleepless nights” over incidents at a hospital neo-natal unit where her colleague Lucy Letby is accused of murdering seven babies and attempting to kill 10 others.

Kathryn Percival-Calderbank recalled a night shift in which Letby, 32 is said to have administered a fatal amount of air into the bloodstream of a baby girl.

The infant, referred to as Child D, suffered three collapses at the Countess of Chester Hospital in the early hours of June 22 2015.

On the first occasion, Mrs Percival-Calderbank told Manchester Crown Court she noticed an “unusual, mosaic-type” rash on the youngster’s torso and arms which was “reddy-brown” in colour.

Child D is alleged to be the third infant murdered by the defendant in a two-week period in June 2015, with another suffering a life-threatening collapse during the same time.

The baby's monitor was showing she was desaturating and her heart rate had dropped.

Giving evidence on Wednesday behind a screen, Mrs Percival-Calderbank said she had worked at the unit for newborn infants since 1993.

She recalled checking in on Child D while the infant’s designated nurse, Caroline Oakley, was on a break.

“I remember looking in,” she said. “She was nice and stable, the baby seemed quite settled.

“I popped in another time about 10 minutes later. She was OK.”

Some time later, the witness said she returned to the intensive care room when alarms sounded.

Mrs Percival-Calderbank added: “The baby’s monitor was showing she was desaturating and her heart rate had dropped.

“I don’t know whether there was anyone else around at the time but I think there may have been.”

She said she checked Child D’s head position, gave “gentle stimulations” with her hand and then used a facemask to provide oxygen.

She went on: “I was assisted by someone. I can’t clearly remember who it was. I have a feeling it might have been Lucy, but I can’t categorically say.”

Asked by prosecutor Philip Astbury if she noticed anything while assisting Child D, Mrs Percival-Calderbank said: “There was a rash on her trunk and arms. It was on her body from the chest downwards.

“It was not like a normal rash that you would know if a baby was becoming septic. The blood vessels tend to more bluey.

“This seemed to be a largely mosaic-type rash and it was a reddy brown colouring.

“It was not like a spotty rash. It was oval-type markings on the skin. The vessels of the blood seemed to be meeting up with each other.

“She was quite a pale-skinned baby, so they seemed to be pronounced browny/red.”

The witness said the discolouring “seemed to disappear and dissipate after a while” and that Child D settled back into a normal pattern of breathing after doctors assisted in the intervention.

I was very surprised to hear a crash call because although I was concerned after the first episode she didn’t appear to be a baby in extremis. Yes I admit these things can happen but that was not what I was expecting to happen that night

Ben Myers, KC, defending, asked if the “extra detail” she had provided about the rash, compared to her police statement, was something she may have picked up in conversation at work.

Mrs Percival-Calderbank replied: “I might have done, but it’s also my recollections which have come back. It was an odd rash. It wasn’t like a normal septic rash, it was a different type of rash.”

Mr Myers said: “Can you help us with how you got the extra details?”

The witness said: “Because I started thinking about the events. As I was getting sleepless nights I was thinking about the events that happened.”

On-call consultant paediatrician Dr Elizabeth Newby told the court she was asked to attend the first collapse of Child D but was “very surprised” when later asked to return.

Child D had recovered by the time she arrived at the unit, she said, but she stayed for “about an hour or so” to check if she remained stable and await blood test results.

Dr Newby said: “So I left and then not long after I was called back urgently as (Child D) had a further episode of collapse. When I arrived there was a full resuscitation in process.

“I was very surprised to hear a crash call because although I was concerned after the first episode she didn’t appear to be a baby in extremis.

“Yes I admit these things can happen but that was not what I was expecting to happen that night.”

She improved far more rapidly than I expected. She was essentially out of danger. The pneumonia was not responsible in any way for her death

Expert witness Dewi Evans told the court he concluded Child D – who was born 60 hours after her mother’s waters broke – had early on-set pneumonia but that was not the cause of her death.

He added he thought the condition had developed pre-birth when the membranes ruptured.

Lead prosecutor Nick Johnson KC asked: “If (Child D’s) pneumonia had been sufficient to cause her death what would you have expected the pattern of her decline to have been?

Consultant paediatrician Dr Evans replied: “If a baby is born with severe pneumonia what you would find is that increasing amount of clinical support does not lead to improvement

“In (Child D’s) case she got better, she improved far more rapidly than I expected. She was essentially out of danger.

“The pneumonia was not responsible in any way for her death.”

Dr Evans said the only explanation he had for Child D’s death was from an injection of air through a vein into her circulation.

Asked by Mr Myers to explain his finding, Dr Evans said the five factors were her “rapid” collapse, the skin discolouration, that resuscitation was unsuccessful, air was present in the vessels of the heart and none of the other issues affecting Child D were relevant.

He said: “In my opinion we had a full house of clinical characteristics of her having a sustained an air embolus, ie air injected into her circulation.”

Mr Myers said: “The fact is (Child D) was not anywhere near a complete recovery, was she?”

Dr Evans said: “She was recovering.”

Mr Myers said: “She still had the potential to be unwell, didn’t she?”

Dr Evans said: “She was in a neo-natal unit, the best place on the planet. She had nurses around her, she had doctors around the corner, as it were.

Mr Myers said: “What you are doing is deliberately seeking to exclude factors which goes to show she was actually unwell?”

Dr Evans replied: “She was stable.”

The witness denied his findings were “influenced by the allegations rather than the underlying facts”.

Letby, originally from Hereford, denies the offences, said to have been committed between June 2015 and June 2016.

The trial continues on Thursday.