The amount of alcohol in the system of a hotel guest who died of alcohol poisoning after downing a cocktail of spirits could have changed after death, a court heard.
Poisons expert Dr Joseph Tracey told a manslaughter trial that alcohol levels can rise as the body decomposes.
Bar manager Gary Wright and barman Aidan Dalton have pleaded not guilty to the manslaughter of Graham Parish in Hayes Hotel, Thurles, Co Tipperary, on June 30, 2008.
The British father of two, from Calder Terrace in Lomeshaye village near Nelson, east Lancashire, was celebrating his 26th birthday before he died.
Dr Tracey, former clinical director of the National Poisons Information Centre at Beaumont Hospital, Dublin, was recalled to give evidence on the fourth day of the trial.
He told Judge Thomas Teehan that a person's blood alcohol levels can both rise and fall after death because of putrefaction, the decomposition of the body.
"Blood alcohol level is not a definite diagnostic tool when it comes to port mortem," he said.
Nenagh Circuit Court previously heard that 375mg of alcohol was found in the victim's blood, above the average fatal dose taken from a study of 175 similar deaths.
But the medic also referred to a study of more than 100 patients who attended casualty departments with between 400mg and 600mg of alcohol in their system and lived.
"Maybe 80% were conscious and talking in casualty," he added.
Mr Parish had been drinking heavily with five British contractors in the hotel. He had downed two pints of Guinness with shots in them and drank a cocktail of at least eight spirits in one glass.
Within minutes he slumped off his bar stool and was carried to a conference room on the first floor of the hotel, where a night porter found him dead shortly after 6am the following morning.
His parents David and Julie and sister Jess have travelled to Ireland for the landmark case which is the first of its kind under liquor liability laws.
If convicted, Mr Wright, 34 and Mr Dalton, 28, who are both from Kilfithmone, Borrisoleigh in Co Tipperary, can be imprisoned for life.
Dr Tracey said side-affects of a rapid increase in blood alcohol levels can be respiratory and heart problems, convulsions and low blood sugar.
"Basically you would go in to severe coma," he said.
"If you have an anaesthetist you could be fine but not on your own."
The trial was adjourned until tomorrow.