When he was brought to the hospital, he was as good as dead.
Literal
Hospital [to-に] carried-in [when-たとき] he [topic-は] dead same-as was.
運び込まれたとき uses passive 運び込む ('to carry in'). 死んだも同然だった means 'was the same as dead' — 同然 is a na-adjective meaning 'equivalent to, practically.' A dramatic medical narrative sentence.