A recent case involving a preventable medical error that resulted in death was the product of cognitive bias.

Cognitive bias, also referred to as confirmation bias, occurs when a practitioner sees what he/she expects to see, rather than what is actually there.

In the case at issue, reported by Liz Kowalczyk in The Boston Globe (“Surgical error at Tufts prompts widespread changes,” August 2014) a patient was undergoing a procedure to relieve pain from a back injury. The physician ordered a dye to be injected into the patient’s spine in order to test the location of tubing which had been threaded into her spine.

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However, the pharmacy did not have the dye that the physician had ordered, and provided a different one. Unfortunately, the dye’s label clearly warned against use inside the spine.

The surgeon was handed the dye by a nurse and according to hospital executives, looked at the label, and then injected the dye into the patient’s back. The patient died the next day as a result of the error. There are differing accounts of what exactly happened, but the investigators agreed that cognitive bias was responsible.

According to the surgeon’s account, a pharmacist told the nurse that the operating room pharmacy did not carry the dye that he had ordered, and instead the pharmacist handed her two bottles of a different dye.

The nurse handed the dye to the surgeon, telling him “this is what we have,” The surgeon claims that he took the bottles and used them without looking at them.

Patrick Croskerry, MD, PhD, a specialist on cognitive errors told The Boston Globe, “The surgeon trusted the person who handed him the vial. You expect them to be correct. What you expect to happen will happen because most of the time it actually does.”

Unfortunately, in this case it did not. Hospital executives were reported to believe that the surgeon did look at the vials of dye, but saw what he expected to see, the correct dye, rather than the warning label that stated the dye should not be used in the spine.

In an analysis by personal-injury attorney Rick Shapiro in The Legal Examiner (“A new concern in the cause of hospital errors: cognitive bias,” September 3, 2014), Shapiro warned that cognitive bias and confirmation bias contribute to medication errors and surgical mistakes; they contribute even more to diagnostic errors, where a practitioner may see what he or she expects to see, rather than what is really there.

Shapiro suggested that second opinions and decision-making protocols can help to reduce errors, as well as having more than one person check a medication before administering it to a patient.