mcg/kg/min: build the chain instead of chasing the formula.

The math did not change. Everything around it did.

Shortly after takeoff on a calm nighttime interfacility flight, our patient's heart rate began to fall. Chest discomfort and shortness of breath followed, and the clinical picture was moving in the wrong direction. Atropine had not produced the response we needed. Under the protocol in use at the time, dopamine was selected while we kept transcutaneous pacing in mind.

There was one practical problem: our transport pump already had three infusions running and no free channel. We needed a gravity infusion at 10 mcg/kg/min. We estimated the patient at about 200 lb — roughly 90 kg — and had 60 gtt/mL tubing.

That should have been familiar math. I have a mathematics degree, and the shortcut formulas had once seemed obvious in training. But now the cabin was loud, the patient was deteriorating, my partner was clearing those pesky little bubbles from the line, and my working memory felt very different from the classroom.

I could not reliably retrieve the shortcut formula. What I could retrieve was an instructor's gravelly reminder: “There is no drug calculation you cannot handle with dimensional analysis.”

That gave me a plan.

First: what exactly do I need to know? Drops per minute — gtt/min.

Then: build one relationship at a time. The 60 gtt/1 mL drop factor was one piece. The prepared medication concentration was another. Keep arranging the fractions so every unwanted unit cancels and the only unit left is gtt/min.

I remember the performance problem and the process clearly; I do not want to reconstruct the exact historical bag concentration from memory, so I am intentionally not publishing a final drops-per-minute number from that flight. The point is what happened when the shortcut disappeared.

Once the setup was organized, the arithmetic was not difficult — but even straightforward arithmetic took more effort than usual. The harder I tried to hold the entire problem in my head at once, the farther away the answer seemed.

So I reset. One target. One correct move. Check it. Then the next move. That experience became part of what I later called RAGE the Freeze: Reset the noise, Anchor the target, Generate one correct move, Execute + evaluate.

We established the infusion, counted the drops, and the patient's condition stabilized. The rest of the flight was beautifully uneventful.

This is a retrospective educational account, not a current medication protocol. Medication concentrations, treatment algorithms, equipment, and local protocols change. Follow the current guidance that applies to your setting.