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June 1996
Volume 60 |
Number 6
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| The Changing Pattern
of Anesthesia-Related Adverse Events |
Frederick W. Cheney, M.D., Director
ASA Closed Claims Project
The ASA Closed Claims Project database is a standardized collection
of case summaries of adverse anesthesia-related outcomes derived
from professional liability closed claims files. This project,
which has been ongoing since 1985, reflects to some extent the
safety of anesthesia practice in the United States.
Presently, there are 3,533 closed claims collected from 35 insurance
organizations that insure approximately 14,500 anesthesiologists.
Claims for Death, Brain Damage and Nerve Injury [Figure
1]
In the overall database, the most frequent complications are
death (34 percent), nerve damage (16 percent) and patient brain
damage (12 percent). If claims for death and brain damage are
taken as an indication of the severity of injury, analysis of
the data by the year the adverse outcome occurred makes it apparent
that the severity of injury has been decreasing over time. In
the 1970s, 56 percent of claims were for death and brain damage
as compared to only 45 percent in the 1980s and 31 percent in
the 1990s. The incidence of nerve injury, a far less serious complication
than the other two, has remained relatively constant over the
years.
Claims for Respiratory System Damaging Events [Figure
2]
The most common damaging events or mechanisms of injury are those
involving the respiratory system. These data are also changing
over time. In the 1970s, 36 percent of the injuries were respiratory
in nature. The incidence of respiratory-related damaging events
decreased to 27 percent in the 1980s and 15 percent in the 1990s.
Since pulse oximetry (SpO2) and capnography (ETCO2)
have been in use since the mid-1980s, we further analyzed the
data to determine if we could identify an early trend of the impact
of these monitoring modalities on the decrease in respiratory
system damaging events. In order to focus on circumstances where
SpO2 and ETCO2 would be expected to have
the most impact, we examined only 1,729 claims in which the adverse
event occurred intraoperatively during general anesthesia. In
8 percent (n=138) of these 1,729 claims, SpO2 (without
ETCO2) was in use, and in another 8.2 percent (n=142),
both SpO2 and ETCO2 were in use. In the
remainder of the claims (83.8 percent), neither monitor was in
use.
Claims Related to Respiratory, Cardiovascular and Equipment Damaging
Events [Figure 3]
Respiratory-related damaging events led to the injuries in 42
percent of the no SpO2/ETCO2 claims, 29
percent of the SpO2 claims and 20 percent of the SpO2
+ ETCO2 claims. The next most frequent but far less
common damaging events in the no SpO2/ETCO2
claims were cardiovascular- and equipment-related. Cardiovascular
damaging events were more common in both the SpO2 and
SpO2 + ETCO2 groups, compared with those
claims in which neither monitor was in use. In the 142 claims
in which both monitors were in use, respiratory and cardiovascular
damaging events each represented 20 percent of claims, compared
with 42 percent for respiratory claims and 9 percent for cardiovascular
claims in the no SpO2/ETCO2 group. The occurrence
of equipment-related damaging events was not influenced by the
use of SpO2 and ETCO2 monitoring.
Claims Involving Inadequate Ventilation, Esophageal Intubation,
Difficult Intubation [Figure
4]
Among the claims in the respiratory system category in which
SpO2 and ETCO2 were not monitored, the most
common specific damaging events were inadequate ventilation, esophageal
intubation and difficult intubation. These three damaging events
combined to represent 71 percent of the claims in that group.
In the SpO2 group, there were 40 respiratory-related
damaging events, most of which were due to difficult intubation
and esophageal intubation. Of the 12 esophageal intubations in
the SpO2 group, hypoxemia was apparent in most cases,
but the correct diagnosis was made too late to prevent brain damage
or death.
In most cases, over-reliance on auscultation of the lungs, disregard
of the SpO2 values or failure to observe the pulse
oximeter with the alarms turned off were the reasons for the adverse
outcome. There were only two damaging events attributed to inadequate
ventilation in the SpO2 group.
Of the 28 respiratory-related damaging events in the SpO2
+ ETCO2 group, there were six esophageal intubations
and one claim due to inadequate ventilation. In the SpO2
+ ETCO2 group, as in the SpO2 group, difficult
intubation was the most common damaging event. The esophageal
intubations in the claims in which ETCO2 was in use
were due to a combination of factors, including misinterpretation
of an ETCO2 reading of zero as machine failure or disregard
of the capnographic readings.
The incidence of severe injury (brain damage and death) in the
three most frequent respiratory system damaging events was comparable
between the no SpO2/ETCO2 group (83 percent)
and the two groups in which some combination of these monitors
was in use (77 percent). Therefore, when adverse outcomes occurred
with these monitors in use, the monitor did not seem to reduce
the severity of injury.
The almost total lack of inadequate ventilation damaging events
in claims in which either SpO2 or SpO2 +
ETCO2 were in use suggests that these two monitors
may have an impact on this mechanism of patient injury. The near
absence of any inadequate ventilation claims in the SpO2
group suggests that most of the adverse outcomes attributed to
inadequate ventilation in the group with no SpO2 monitoring
may have been due to inadequate "oxygenation."
The relative increase in cardiovascular system damaging events
and decrease in inadequate ventilation damaging events in the
groups where SpO2 or SpO2 + ETCO2
were in use also suggests that many of the adverse events attributed
to inadequate ventilation in the no SpO2/ETCO2
group may well have been cardiovascular in origin. The
fact that difficult intubation is still a frequently cited respiratory
damaging event in a group of claims where SpO2 and/or
ETCO2 monitors were in use is not surprising
since the monitors themselves do not intubate tracheas.
Conclusion
The preliminary data presented may reflect a changing profile
of anesthesia-related injury due to adverse respiratory events.
This profile may change as more claims for injuries occurring
in the 1990s are processed. From the data available to date, it
is obvious that in order to be effective, the monitors must be
properly used and interpreted. Utilization of the ASA Practice
Guidelines for Management of the Difficult Airway may lead to
a reduction in patient injury due to this mechanism of injury.
Whatever the reason, it is encouraging that severe-injury claims
for death or brain damage seem to be decreasing. Because of this,
nerve injury may well assume the position as the leading cause
of anesthesia-related injury for which a malpractice claim is
made. Since preventative strategies for nerve injury are not apparent,
claims for this injury may be expected to remain constant while
those for death and brain damage are concurrently decreasing.
Frederick W. Cheney, M.D., is Professor
and Chair, Department of Anesthesiology, University of Washington
School of Medicine, Seattle, Washington.
Send e-mail to Dr. Cheney
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