mushmash

Before anyone jumps on my case, let me preface this story by saying I immediately questioned my preceptor and corrected my to-be questioned issue. Now: I had an alcoholic come into one of my MICU beds. Among other problems, he had fairly low K and Mag values. I went into lexicomp, looked at the IV compatibility, and saw that there was no apparent problem with running K and Mag concurrently through the same line. I piggybacked the K+ to run with the NS at 50 that was already on the Plum pump, and hooked the mag up distally to the pump in the port close to the patient. My understanding of both pumps and high school physics (which was a long time ago, granted) taught me that if the pump isn't running, nothing is coming out of the tip of the line. If the pump IS running (at say, 50?), then anything that's open and infusing into that port (if the bag is even with the line) is also running at 50 ml/hr, as the flow is restricted by what the pump is pushing into the patient (hence why the pump goes "DISTAL OCCLUSION! ALERT! ALERT!" when you try to push anything into that port while it's running...because you're increasing the pressure so much that it's restricting flow and sensed by the pump cartridge/pump/whatever it is that senses that). Since I knew the mag and K could both run at 50 an hour, I hooked it up to that distal port that's PAST the pump, and immediately went to question my preceptor if this was ok. After a quick "No!" and slight freak-out on both our parts, we returned to the room, and the mag was disconnected and reinfused through its primary pump that I went and found (within about 45 seconds. My preceptor said running the mag into that line was running it free-flow (which, considering it's mag, is incredibly dangerous). I explained my thought process, yet still received a scathing write-up on that week's orientee review. I thought that was a bit harsh, considering I immediately left the room and asked, but I was more concerned about whether my line of thinking was correct. When forming you're answer, please don't lecture me about the dangers of this. I know how dangerous this potentially was, which is why I asked so quickly when i left the room. Should I have asked her first about this? Yes, but I was in the room already, and I truly thought I was right. I've already been lectured about this, I promise. I'm just curious as to whether something in the free flow port, if it's hanging open, is running at the same rate as whatever the pump is infusing in. Thank you all for your answers in advance!