Every generation of medicine has its totems—high-tech gizmos that measure, promising mastery over the human form if we can just capture the numbers precisely, continuously, and in triplicate. For my teachers the Swan–Ganz, a fancy catheter snaked into the hearts of ICU patients, held this role.
It offered heart and capillary pressures, saturations, and cardiac outputs to two decimal places. More numbers than any mortal clinician could use. And yet, even with the full force of physiology, the Swan–Ganz somehow never helped people. When careful trials finally showed the catheters were risky, harmful, and didn’t improve outcomes, the lesson was uncomfortable but undeniable: Even in medicine, there is such a thing as too much information.
Last month a large, high quality randomized trial brought this lesson back to the bedside, by testing the humble arterial line catheter. In people suffering from shock the A-line has for decades been a default—a badge of ICU care, offering second-by-second blood pressures, instant sampling for endless labs, and a reassuring sense that even the deep interior is under the watchful eye of modern tech.
The ‘EVERDAC’ trial randomized over a thousand people with shock to either routine A-line insertion or no A-line, and found what decades of habit had hidden: People didn’t survive more, recover faster, or fare better in any way with an A-line. But harms—bleeding, infections, pain—were clearly, and statistically, higher. More precision delivered only more injury.
In other words, arterial lines represent a catastrophic failure of medicine’s first principle: Primum non nocere. First, do no harm.
This is more than just the story of another failed catheter. It’s the story of our failed relationship with information. The modern medical mind is taught to believe that more data moves us closer to truth, as though the human form were a transparent machine, and shock a solvable equation. But our physiology knowledge isn’t a sprawling continent; it’s a tiny lit island in a vast dark sea. We see a few trees and decide we understand the forest. That false confidence is how numbers become idols.
The Enlightenment gave us the scientific method, which gave us modern medicine, which saves lives every day. That, in turn, gave us a misplaced faith in measurement—the belief that if we can quantify something, we can control it. It is delusion to believe we understand the causal web of shock physiology well enough to convert better numbers into better outcomes.
The EVERDAC trial reveals the gap. What clinicians did with the A-line was order more labs, poke and flush more often, bleed more patients, infect more arteries, and cause more pain. The A-line didn’t improve outcomes; it merely gave clinicians more numbers to chase. All with no measurable benefit.
It isn’t moral failure; it’s human nature. Give clinicians a number and they’ll try to change it. Give them a stream of numbers and they’ll invent trends. When we think we understand the system, we feel compelled to manipulate it. With no proper studies to clarify its effects, the arterial line has been, til now, like bloodletting or frontal lobotomy or the Swan-Ganz catheter—a long-standing, harm-inducing practice distorted by the prism of cognitive bias. When people recovered, we believed it was because of the arterial line, when in fact it was in spite of it. That is textbook experiential delusion, described by Hippocrates more than two thousand years ago.
EVERDAC is therefore not just a trial, but a philosophical reminder: Medicine’s job is not acquiring good data, it is delivering good care. Which means admitting our limits.
So will we?
There was never a randomized trial showing the benefit of arterial lines. Much like Swan-Ganz catheters and countless other gizmos, arterial lines were introduced based on misplaced faith, that more information is always better. Now, the only randomized trial of arterial lines is complete, and the results published for all the world to see: No benefit, serious harms.
For doctors who claim evidence-based practice (read: all doctors) the path is obvious: Abandon arterial monitoring unless future trials reverse this finding.
We will always practice on that small island. To claim the banner of our first principle, do no harm, the trick will be to do what all good islanders must—respect the sea.
