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June 1999
Volume 63 |
Number 6
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RESIDENTS' REVIEW
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| 'What Is the Evidence?' |
The-Hung Edward Nguyen, M.D.
"Residents' Review" Editor
It's late Friday evening and you are in the last operating room
running. The surgeons have finished closing and your patient has
a rapid, shallow spontaneous breathing pattern. Your attending
trots into the room, looks around, and asks, "Do you want to extubate?"
Like a stellar resident you run though all the routine criteria
for extubation which the patient has met. "I don't think he's
quite there yet," you hesitantly reply. "Oh really? So you have
a low pretest probability for successful extubation," says your
attending with a grin in his/her eyes, arms crossed and foot tapping.
"I know you and I don't think he's ready, but what's the evidence?"
You note the patient is breathing 30 times a minute with tidal
volumes of 0.12 liters. After a quick mental calculation, you
mention an article that discussed the frequency to tidal volume
(f/Vt) ratio and its utility in predicting success in weaning
and extubation from mechanical ventilation.1
A patient whose f/Vt ratio was greater than 100 breaths per minute
per liter had a 95 percent likelihood of failure to wean. Your
attending knowingly nods, "Ah, yes - the 'Tobin index.' That study
was in the setting of the ICU but perhaps those data could be
applicable here. OK, we'll wait."
The above scenario demonstrated the use of evidence-based medicine
(EBM) in clinical practice. While many anesthesiologists utilize
this approach routinely, it has only recently been defined as
a new paradigm in patient care. Evidence-based medicine is "an
approach to caring for patients that involves the explicit and
judicious use of the clinical research literature combined with
an understanding of pathophysiology, our clinical experience and
patient preferences to aid in clinical decision making."2
EBM has its roots in internal medicine and is gaining a stronger
foothold in anesthesiology and critical care. Since certain common
processes in critical care, such as sepsis and adult respiratory
distress syndrome, are so hard to define and that much of operating
room anesthesiology is based on "style" and individual practice
techniques, it has been difficult to implement EBM into our specialty.
However, EBM represents a thought process that is applicable to
all fields of medicine. It forces us to define explicitly patients'
problems, assign a pre-test probability and examine the sensitivities
and specificities of tests or interventions that we perform in
order to aid us in improving patient outcome. It also teaches
us to critically examine the literature to determine if a study
was well performed so that we can incorporate it into our daily
practice.
Practicing EBM means we have to know the best current literature.
As a resident, this can be difficult. But there are many resources
such as Web sites and computerized databases that can help expedite
our survey of the literature and can give more detailed information
on EBM.3,4,5 We also have to keep
in mind that knowledge of the gold-standard "double-blind randomized
prospective placebo-controlled study" has to be used in the setting
of strong clinical expertise. Individual patient differences and
the generalization of a study always have to be kept in mind.
Furthermore, we must make a distinction between there being a
lack of studies that show an intervention changes outcome (no
evidence of effect) versus there being documented studies that
show an intervention has no change in outcome (evidence of no
effect).
As a resident, I am no expert practitioner of EBM, but at least
I have found that the framework of EBM has helped my thought process
and has given me something to strive for in terms of improving
my own clinical practice. Whenever I examine a patient, order
a test or perform an intervention, I try to take a second to ask,
"What is the evidence?"
References:
- Yang KL, Tobin MJ. A prospective study
of indexes predicting the outcome of trials of weaning from
mechanical ventilation. N Engl J Med. 1991; 324:1445-1450.
- Pronovost P, Angus DC. Evidence Based
Critical Care. In: Sackett DL, Richardson WS, Rosenberg W, Haynes
RB, eds. Evidence-Based Medicine: How to practice and teach
EBM. Edinburgh: Churchill Livingstone; 1999.
- Cochrane Collaboration: hiru.mcmaster.ca/cochrane
- Evidence Based Medicine Resource Center: www.nyam.org/library/teach.html
- Centre for Evidence-Based Medicine: <cebm.jr2.ox.ac.uk>
The-Hung Edward Nguyen, M.D., is a CA-1
anesthesiology resident, Johns Hopkins School of Medicine, Baltimore,
Maryland.
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