There's some footage[1] from One America News Network, which I gather is some kind of sub-Fox News outfit, of their reporter interviewing doctors at the same hospital Fisk writes about. They seem to tell pretty much the same story: on the day of the purported attack people were treated for dust inhalation, no-one died, a bunch of people suddenly appeared in the hospital shouting "chemical attack!" and spraying people with water, while filming themselves. Hospital staff joined in spraying water (as you would do) but no one exhibited symptoms of actual chemical weapons use.
I've read reports that doctors who spoke to the press had been intimidated and threatened if they verified the attack story[2]. The people in the video don't look intimidated to me, but I'm no expert.
I'm personally on the fence on this one, and haven't read in-depth either. But it's mighty strange to me seeing Fisk and a conservative cable news network on the same page on a mid-East controversy!
1: https://www.youtube.com/watch?v=N9w8j-avq_0
2: https://www.theguardian.com/world/2018/apr/17/syria-crisis-m...