Dan Buckley had tried to block Brockwell when the armed robber slashed a knife across his stomach, garda sources said.
A senior figure in the Prison Officers’ Association, Gabriel Keaveny, said his colleague’s stomach “was cut open” and that he was “blessed he didn’t die”.
Mr Buckley underwent emergency surgery in Tallaght Hospital, the scene of the stabbing and escape, and remains in intensive care.
Fellow prison officer Graham Flynn was also stabbed by Brockwell, receiving wounds to his hands and back. He was due for release as early as last night.
Brockwell, 53, attacked the officers in a toilets in Tallaght Hospital where he had gone to give a urine sample.
It is thought the Glaswegian went into one of two cubicles. He came out brandishing a knife and attacked the men. It is not clear where he got the weapon from, but gardaí suspect he might have got it from inside the cubicle.
After the stabbing, he ran from the hospital where a man was waiting for him on a motorbike. The bike was seen going to the Tallaght bypass.
Before Brockwell’s capture in Belfast last night, gardaí had put an “all ports” alert for him and informed both the PSNI and Interpol, which told all the British police.
Garda sources called to associates of Brockwell as well as anyone who might have visited him, but didn’t get any leads.
They examined records from phone lines in Portlaoise as well as any illegal mobile phones there.
They will also try and determine if Brockwell had any assistance from an inmate there.
It is thought three people were moved from the main block to the segregation unit of the prison, although it is not clear if they were linked to the escape.
Brockwell came here in 2012 after going on the run in the UK, where he was serving 22 concurrent life sentences for armed robberies in Britain.
He conducted a spree of robberies in Dublin and was subsequently charged in relation to four incidents, between August and October 2012.
After holding up a bookies shop in Kilmainham on August 31, he robbed a man at knife point in the toilets of the Gresham Hotel on O’Connell St on September 22.
The victim, Conor Palmer, told gardaí he was standing at the urinal when a man pressed himself close to him and pushed a sharp implement into his neck and said: “Give me whatever is in your fucking pockets.”
He gave him his wallet, which contained €120 in cash.
Three days later he entered the Bon Espresso newsagent on Merrion Row, Ballsbridge. He grabbed a shop assistant and marched her down to the post office in the rear.
The assistant, Caroline Doyle, said the man pushed a gun into her arm and told other staff to give him the money. He got away with €3,525 in cash.
The following month, he robbed €6,436 from the Bank of Ireland on Main Street in Blackrock.
Remy Farrell, defending, said Brockwell told gardaí he kept the knife in a newspaper in his back pocket and would only use it as a last resort.
“If some have-a-go hero had grabbed me I would have pulled that on him,” he said.
The court heard Brockwell had 64 previous convictions from the UK dating between 1984 and 2000, and was described by the British authorities as a “Category A” prisoner.