The Independent Double Check and the Risk of Human Error
A nurse on a telemetry floor had two orders to carry out. Forty milligrams of Lasix, to be given via IV. Two units of insulin lispro, given subcutaneously. At that hospital, every dose of insulin required a second nurse to co-sign, even subcutaneous doses.
She scanned the patient. She scanned both vials. She drew up both medications. Then she tapped a colleague on the shoulder.
The second nurse checked the patient. She checked the label on the insulin vial. She checked the order. She looked at the blood sugar. She confirmed that the order said two units. She signed.
The Lasix went in IV and the insulin went in subcutaneously, and then the first nurse walked out of the room to discard the vials and saw that the Lasix vial was still full.
The two vials were the same size. She had drawn each drug into the syringe intended for the other. A whole vial of insulin had gone in IV.
She called a rapid response and reported herself immediately. The patient went to the ICU on a dextrose drip and came out fine. She was, by her own account, horrified. She was also commended by her colleagues and her leaders, which is what should happen and often doesn't.
This is the third post I've written from a thread on the r/nursing subreddit where someone asked about the worst medication errors people had seen. I can't verify any of it. Anonymous accounts, no investigations attached, some of it secondhand. I'm reading it as a record of what nurses have figured out, and where they say it.
Here is the part that matters.
The second nurse did the check correctly. She followed the policy, every step of it. She was not distracted, not rushed, not cutting a corner.
Now look at what the policy asked her to check. The patient. The label on the insulin vial. The order. The blood sugar. The dose. Every one of those was correct. Every one of them had also been correct before the first nurse picked up a syringe, and stayed correct afterward.
The co-sign asked whether the right drug had been ordered, in the right dose, for the right patient. It never asked what was in the syringe.
Those are two different questions. Call the first one the decision and the second one the execution. The insulin co-sign is a check on the decision. The error was in the execution.
By the time she arrived, the insulin was in the Lasix syringe, intended for the IV. Lasix doesn't require a co-sign. The one drug on that unit the hospital had decided needed a second pair of eyes had ended up in the one syringe nobody was required to look at.
Which is true of every high-alert medication policy, and has to be. A policy that decides which medications get double-checked cannot defend against errors of medication identity. It can only inspect the thing labeled insulin. When the label and the contents have come apart, the check is aimed at the wrong syringe by definition. Not by anyone's carelessness. By design. You cannot write a policy that says double-check the drug you don't know you're holding.
Notice that she scanned both vials. The scanner did its job. It read two physical objects at the moment she was holding them, and both were correct. Then she drew the drugs, and the swap happened after the last step in that process that had looked at anything physical. Everything downstream of that point, the co-sign included, was reading a label rather than a drug.
The Arithmetic of an Independent Double Check
The promise of a second check is a probability argument, even when nobody says so out loud. If one nurse misses one time in twenty, then two nurses miss one time in four hundred. Add a third and you're at one in eight thousand. It's arithmetic, it's reassuring, and it holds only if the two checks are independent of each other.
They almost never are.
The second nurse in that room was primed by the first. She was pulled into the middle of somebody else's task and asked to confirm it. She stood on the same unit, on the same shift, with the same workload, looking at the same vial. Whatever conditions made the first nurse's hand reach for the wrong vial were all still present when the second nurse arrived. Correlated failures don't multiply.
There is direct evidence for this. Westbrook and colleagues observed 298 nurses giving 5,140 doses in a paediatric hospital and recorded whether each double check was independent, primed, incomplete, or absent. Compliance with mandated double-checking was very high, and the checks were rarely independent. Where double-checking was mandated, they found no significant association with fewer administration errors or with lower potential severity. Each check took an average of 6.4 minutes, which works out to 107 hours per 1,000 administrations.
But that isn't even what went wrong here. Run the probability argument all the way down and her miss rate on this particular failure wasn't one in twenty. It was one in one. Everything she was assigned to verify was correct. No amount of diligence, no quantity of care or experience or sleep, would have found insulin in a syringe nobody had asked her to look at.
ISMP uses the term independent double check, and independence has a specific meaning. The second person is supposed to arrive at the answer without being told what the answer is. Being pulled into a task already in progress and asked to confirm somebody else's number is not that. It's confirmation. And everyone in that room believed a verification had taken place.
Another nurse in the thread said it plainly. She used to co-sign insulin without really looking. Then a colleague asked her to co-sign ten units for hyperkalemia and she noticed the colleague had drawn up the full three-milliliter vial. She caught it. Now she looks at the lab, the order, and the syringe every time.
Same policy. Different behavior. Nothing changed but her, which is another way of saying that the policy had never specified any of it.
I Am Not Telling You to Stop Double-Checking
Toyota still runs a final inspection at the end of its assembly lines. After all these decades of building quality into the process, they have decided that catching a defect is better than shipping one. Nobody there believes that's where the quality comes from.
In Lean Hospitals I described the inspection steps in medication administration as required waste. Required, because the process that precedes them can still produce a defect. Waste, because a better process wouldn't need them. Don't remove an inspection until you've replaced it with something that makes the error impossible, and if what you've built isn't fully error-proofed, keep the inspection.
Deming's line is cease dependence on inspection. The word people skip is dependence.
So keep the co-sign. What I'd stop doing is treating it as a solution to the vials.
What a Check Does to the People Upstream of It
Karen Martin, on my podcast, described what happens upstream of a final inspection. When there's a final inspection at the end, people upstream relax. “Someone else will catch it.” She used herself as the example. As an author, knowing her own editor reads the manuscript next, she has caught herself being less diligent than she'd otherwise be, and she has to stop herself.
Now put that in a room with two clear liquids in it.
The first nurse drew both medications alone, before anyone else was in the room, knowing that someone was coming to check her. Would she have done it that way if nobody were coming to check her? I don't know. She doesn't either, probably. But a check is not a neutral observer standing outside the process. It's inside the process, and it changes what happens before it runs.
Rhode Island Hospital had three wrong-side brain surgeries in 2007. After the first two, the hospital said it had put safeguards in place, including a policy directing a second physician to review the correct site and side before surgery. An inspection, bolted onto a process that had produced a defect. In November, a chief resident began operating on the wrong side of an 82-year-old patient's head.
Adding an inspector is also a countermeasure you can finish by Friday.
When the Mix-Up Happens Before the Unit Ever Sees It
The nurse in that room could at least have looked at the vials. Sometimes the vials are gone by the time anyone downstream is involved.
On August 14, four patients at Ascension Saint Thomas Hospital Midtown in Nashville received potassium phosphate instead of mepivacaine. According to local coverage of the state survey report released this week, investigators reviewed surveillance video showing a pharmacy technician filling syringes with potassium phosphate and labeling them as mepivacaine, and found that the pharmacy system allowed technicians to override barcode scanning and enter medication information manually. Everything after that point was a correctly printed label on a clear syringe.
The insulin error harmed one patient because one act produced one syringe. A compounding step is not shaped that way. One act produces many, all identical, all labeled according to the record. That is why the count was four.
My previous post: Four Patients Got the Wrong Drug in Nashville. Ask a Better Question.
Watching the Drug Leave the Vial
An Australian nurse in the thread described how it works where she practices. Two nurses stand at the medication together and both physically look at the vial. They say the drug and the dose out loud. Then it's drawn up, in front of both of them. If more than one drug is going, the syringe gets labeled and signed. Then they administer it together.
That isn't a better inspection. It isn't an inspection. Both nurses are standing there during the only moment when the error can exist, the moment the drug leaves the vial. There is no object to examine afterward. The check happened while the drug was moving.
Her account of it isn't triumphant. Errors still happen, she says, and it's extremely time consuming.
I believe both halves of that sentence, and the second half is why almost nobody does it. Doing it that way costs nursing time which is the scarcest thing on any unit, and the cost shows up on the schedule while the benefit is an event that didn't occur.
Two other people in the thread got somewhere similar on their own. A nurse anesthetist in training described checking three times: when she picks up the vial, when she draws from the vial into a syringe she has already labeled, and once more before she throws the vial away. Look at the middle one. Vial against labeled syringe. She writes on her syringes. Nobody made her.
A CRNA replied that she has thrown away perfectly good medications because her mind wandered while she was drawing them up. She doesn't trust the check. She trusts the trash.
And then a small strange thing, a few comments down. A nurse said that when he co-signs a narcotic waste, the other nurse watches him like a hawk, every last drop into the bin. When he administers a medication, he wishes somebody would look that closely.
Same policy manual. Same building. The waste is witnessed because a missing controlled substance is a legal problem for the hospital with a federal agency attached to it. The insulin co-sign is a patient problem. I don't think anybody in that building sat down and decided to care more about one than the other. Something in the system decided it, though, and everyone on the floor can feel which check is real.
The vials are still the same size. They were the same size the week before, and they were the same size the following morning, when two other nurses stood in front of them with a policy that told them to check the insulin.
