Supply range and quiescent current — the BOM decision
The 140 µA supply current per channel at 36 V is the figure that determines whether this part stays in a battery-powered loop or gets bumped to a lower-power family. At 4.5 V the current drops proportionally, but the headline 140 µA is the worst-case number to budget for the rail. The 5 pA input bias current means the OPA191IDGKT can interface directly with high-impedance sources like pH probes or photodiode transimpedance stages without an external buffer — the bias error stays negligible.