Have you ever used an 18 Gauge IV cannula for an LP? I can now say yes. See the green tip object in the upper left on the tray? That's it. It's actually recommended in the essential drug list of Zimbabwe if no spinal needles are available - and routinely done throughout subsaharan Africa.
I actually failed the tap with the cannula, but I think it was because the patient was very dry and cachetic since I know I was in the right space. There is something about being volume down leading to unsuccessful taps short of crypto and having very high ICPs. Next time, a resident helped me sweet talk the nurses from the theatre (OR) to share their 19G spinal needles. She had to ring this old school bell to call them.
Despite getting a spinal needle, I have yet to see a manometer. Instead of giving up, we got creative and used IV tubing to literally measure the opening pressure.