Sanaullah is on a "ventilator, remains unconsicious and is on dopamine and noradrenaline infusions to maintain his blood pressure", sources at the Post Graduate Institue of Medical Education and Research (PGIMER) said.
Sanaullah was brought to PGIMER last evening from Jammu after being airlifted from there.
The 52-year-old prisoner had been first rushed to Jammu's Government Medical College and Hospital.
Upon his arrival here, the PGIMER said Sanaullah was checked by neurosurgeons at the Jammu hospital, "who detected head injuries with a large fracture. CT scan showed multiple contusions with severe brain edema (brain capillaries damaged due to head injury)."
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According to PGIMER, Sanaullah's urine output appears to be adequate and further treatment "including neurosurgical intervention will depend on his stabilisation and neurological status".
Earlier today, a team of Pakistani High Commission officials visited Sanaullah at PGIMER after India granted consular access to them last night.
The sources said that the officials again visited PGIMER and were in touch with the doctors there to seek regular update on the prisoner's condition.
Two prison officials including jail superintendent Rajni Sehgal have been suspended by the Jammu and Kashmir government in connection with the assault.