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A Surgeon discusses his experiences using BIS
Dr. Lewis Kaplan is Associate Professor of Surgery and Director,
Emergency General Surgery Section of Trauma and Critical Care at
Yale University School of Medicine. Prior to coming to Yale, Dr.
Kaplan was Associate Professor of Surgery in the Division of Trauma
and Surgical Critical Care at the Medical College of Pennsylvania-Hahnemann
University.
Aspect: You believe Aspect's BIS monitor is a valuable tool in the
ICU, but you weren't convinced at first. Why were you skeptical?
LK:
I was a clinical fellow when I first encountered the BIS in
the ICU. My skepticism was that the BIS is a form of processed EEG.
EEGs are completely uninterpretable by the average physician - you
need a neurologist - so translating the EEG into an objective sedation
scale seemed to me far-fetched.
Aspect:
What observations led you to the conclusion that BIS monitoring
had clinical value in the ICU?
LK:
Over the course of a couple of months, as I observed patients
who were paralyzed and sedated, I noticed that as we would lighten
their sedation the BIS value would rise. The correlation between
BIS values and what I observed clinically convinced me that this
was more than just artifact. There was a close correlation between
the BIS value and patient status.
Aspect:
In what types of ICU cases do you find the BIS monitor
most useful?
LK:
All patients who receive paralytic sedation should have the
monitor as a standard because there is no other tool for assessing
their sedation level. We find that BIS is also very useful in patients
maintained on sedative infusions so we can accurately evaluate how
deep they are and avoid oversedation. A third group for whom we find
BIS very valuable is patients maintained on continuous infusions
of sedatives and analgesics as part of a post-operative regimen.
We don't want them heavily sedated, but we also don't want them
roaming all over the bed. In those cases we want to assure they're
at an acceptable sedation level where they're controllable, and
not so heavily sedated that it takes days to wake them up.
Aspect: Any others?
LK:
Yes. BIS is very useful for patients in a drug-induced coma,
such as with pentobarbital or propofol. The goal is to maintain
a burst-suppression EEG pattern. Before the BIS this could be quite
complicated, as it often required getting an EEG monitor & technician
and a neurologist. There were also prolonged gaps when we had no
data due to the need to transport the patient out of the ICU for
other tests such as a CT scan of the brain. And after a CT scan,
the EEG leads need to be reapplied. The BIS monitor, on the other
hand, is compact, takes up very little space, and there's only one
sensor that's easily applied. Average clinicians are able to easily
interpret the patient's response to treatment and can titrate sedatives
to the BIS value and suppression ratio recommended by the neurology
team. You don't need the EEG technician to operate the BIS, and
you may not need as many visits from the neurologist. Further, there's
a clinical benefit to the continuous availability of data, which
enables clinicians to evaluate and titrate to maintain a consistent
burst suppression pattern.
Aspect:
How big a problem is oversedation in the ICU?
LK:
Consistency of sedation is a problem in the ICU. To make sure
the patient is comfortable we tend to err on the side of too much
rather than too little sedation. When patients receive more sedation
than is necessary, they become more difficult to assess and manage.
Our data, published in Critical Care 2000, revealed that more than
69% of paralyzed patients on sedative infusions were found to be
inappropriately sedated. The majority, or 54%, were oversedated.
Aspect:
What are some of the consequences of oversedation?
LK:
It's not uncommon to embark on a neurologic work-up consisting
of additional labs, perhaps an additional CT-scan, and a neurologic
consultation, all as a result of oversedation. Some patients develop
an acidosis from the vehicle in which some of the sedatives are
mixed. Oversedated patients are unable to participate in their care,
are weaker, and stay on the ventilator longer. They may not be able
to change position in bed so they can develop pressure ulcerations,
and they are at risk for infections, including ventilator-associated
pneumonia. Oversedated patients also have longer ICU stays and longer
hospital stays, all of which means increased costs and use of precious
resources. Those patients who have been on paralytics may develop
a prolonged neuromuscular blockade syndrome even after the agent
is withdrawn. You also need to consider the high cost of sedative
drugs when patients are oversedated. In our study, we were able
to achieve an 18% decrease in the cost of sedative drugs for an
average of $150 per patient by adding BIS monitoring to assess and
titrate sedatives.
Aspect:
Undersedation also has its costs and risks.
LK:
Yes. If a patient has acute respiratory distress syndrome and
you leave them undersedated, they may become agitated and might
pull out the endotracheal tube and get hypoxic. Unintended medical
device removal has implications involving cost, nursing resources
and patient outcomes. There are also the consequences of recall
of unpleasant experiences. In our study, we achieved a 78% reduction
in patient recall of unpleasant experiences in paralyzed patients
when sedatives were titrated to BIS values rather than hemodynamic
parameters.
Aspect:
What is the role of BIS, then, in trying to achieve the
right balance in each patient?
LK:
The right balance is patient-dependent and will change over time
throughout the course of their care and as their goals for care
change. One of the ways we determine whether a patient is adequately
sedated is by following both baseline and stimulated BIS values.
In other words, we assess what happens to the BIS value when the
patient is suctioned, or a tube is manipulated, when they are rolled
over for their bath, or their fractured extremity is moved. As long
as we maintain adequate analgesia, they're not so deep that I have
to worry about over-medication, but not so light that talking around
them or suctioning them is going to provoke them to a BIS value
in the 90s where they might pull their tube out. BIS gives you an
objective measure to titrate sedatives to a physiologically defined
endpoint, as compared to a subjective idea of how much medication
a patient should receive. It also allows us to better manage the
balance between sedation and analgesia. With BIS, we've been able
to cut across very different training backgrounds, different perspectives
and different biases, and achieve some parity in care across shifts.
BIS provides an easy-to-follow common point of reference.
Aspect:
Given your familiarity with the BIS monitor, what other
possible applications do you think it has?
LK:
For many conscious sedation procedures there hasn't been a good
way of evaluating how deeply sedated a patient has become. From
a safety and medical error perspective, incorporating BIS into moderate
or conscious sedation protocols would seem to make it safer for
the patient and help caregivers achieve the results they are looking
for: a calm, co-operative patient that isn't oversedated and maintains
their airway. BIS seems to be an intelligent way of handling some
of the concerns the Joint Commission has articulated while ensuring
quality care and avoiding what is an area of intense scrutiny: avoidable
medical errors. BIS can have a huge impact in this regard. There
may also be future value in the use of BIS on patients who enter
the emergency department with altered levels of consciousness. There
are certainly numerous avenues to explore.
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