From the March 6, 2003 issue
Has your double check system ever failed, leading to
a medication error that escaped your detection and ultimately
reached a patient? If you answered yes to this
question, youre not alone. Heres one recent example.
A pharmacist correctly calculated the dose and volume of interferon
for an infant, but entered 0.68 mL into the computer instead
of the correct volume of 0.068 mL (a common mistake documented
in the literature). A second pharmacist double checked the
calculation. He arrived at the correct volume of 0.068, but
misread the computer entry of 0.68 by the first pharmacist
as 0.068 due to confirmation bias seeing only what
one expects to see and overlooking any disconfirming evidence.
As this example shows, theres no question that double
checks carried out by people fail at times. But have these
failures led you to doubt the overall value of double check
systems? Given how busy healthcare professionals are, do
you wonder if this error reduction strategy is even worth
your time to carry out? We asked Dr. Anthony Grasha, Professor
of Psychology at the University of Cincinnati, to offer
comment on this issue.
Research shows that people find about 95% of all mistakes
when checking the work of others.1,2 Mathematically, the
benefit of double checks can be demonstrated by multiplying
this 5% error rate during the checking process and the rate
in which errors occur with the task itself (the checking
error rate x the task error rate). For example, if a pharmacy
dispensing error rate is 5% (based on research findings),
and a double check occurs before medications are dispensed,
then the actual chance of a dispensing error reaching the
patient is 5% of 5%, or only 0.25%.
Human factors suggest that double checks are more effective
if they are performed independently. For example, an error
in the concentration of a drug will be detected more often
if the person checking the product performs all calculations
independently, without knowledge of any prior calculations.
In fact, sharing prior calculations or performing a double
check together with the person who originally completed
the task is fraught with problems. In these instances, if
a mistake is present, the person checking the work is more
easily drawn into the same mistake, especially if it appears
to be correct at first glance (e.g., numbers correct but
decimal point placement wrong, correct drug but wrong concentration
selected during PCA pump set-up).
Dr. Grasha also points out that the effectiveness of double
check systems depends on training staff to carry them out
properly as an independent cognitive task, not a
superficial routine task. And with workload issues looming
heavily over practitioners, double checks should only be
applied strategically to situations that most warrant their
use prescribing, dispensing, and administering select
high alert medications. These have the greatest chance of
harming patients if misused. Fewer well-placed double checks
will be much more successful than an overabundance of double
References: 1) Grasha AF, et. al. Delayed verification
errors in community pharmacy. Tech Report Number 112101.
Cognitive Systems performance Lab. Contact: Tony.Grasha@UC.Edu.
2) Campbell GM. and Facchinetti N. Using process control
charts to monitor dispensing and checking errors. Am J Health-Syst
Pharm 2000; 55: 946-952.