Itachi, in the grips of exhaustion and chakra depletion, didn't hear any of the conversation.

His pulse had slowed since he laid back down, and he was breathing all right (considering his condition). But his face was still pale, and he was sweating. Fevers weren't an uncommon occurrence for Itachi. Widespread systemic inflammation is bound to raise body temperature. But under Kabuto's harsh treatment, it was just as possible that he had picked up a secondary infection of some kind.

But that's what medics like Kabuto were there for.