February 2001
Volume 65 |
Number 2
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| The
Anesthesiologist and Fatigue |
Steven K. Howard, M.D.
For a variety of complex reasons, health care personnel have
traditionally worked long hours. Fatigue among resident physicians
has been studied for many years, but the results of these studies
have been mixed, especially regarding the effect of fatigue on
performance. No studies have been performed on different age groups
of anesthesiologists after residency training, and to summarize
in detail the results of the many published articles is beyond
the scope of this article. In general, as the hours of sustained
wakefulness increase, the studies have shown major detrimental
effects on mood, subjective sleepiness (how sleepy you feel) and
subtle detrimental effects on psychomotor performance. This has
obvious operational implications, as patients rely on us to provide
safe care both day and night.
Determinants of Sleepiness
The major determinants of sleepiness are sleep quantity and sleep
quality, circadian influences and the use of certain medications.
If sleep is restricted below an individual's average normal requirement
(which for most adults is greater than eight hours of sleep per
24 hours), then daytime sleepiness will result. This resultant
sleep debt builds and continues to pressure the brain physiologically
to fall asleep. Superimposed on this is the effect of the biphasic
circadian clock that produces a state of increased sleep tendency
and decreased performance capacity during two periods in the 24-hour
day from about 2 a.m. to 6 a.m. and from about 2 p.m. to 6 p.m.
Central nervous system (CNS) depressants (e.g., alcohol) can exacerbate
latent sleepiness while CNS stimulants (e.g., caffeine) can mask
it. However, the only way to actually pay back the sleep debt
is by acquiring adequate sleep.
That sleepiness can have real-world operational importance is
supported by recent evidence from other domains. Many studies
have shown that automobile accidents oscillate with circadian-induced
sleepiness. Studies from the National Aeronautics and Space Administration
reveal pilots having microsleeps in the cockpit during critical
portions of flight. Similar analysis has rarely been performed
for health care accidents, but there is no reason to think that
health care workers will be immune to the impairing effects of
fatigue.
My laboratory has performed two studies of fatigue in resident
anesthesiologists. The investigations include 1) a study of daytime
sleepiness and 2) a study of performance using a realistic patient
simulator. What follows is a brief description of the two experiments.
Measurement of Daytime Sleepiness
Daytime sleepiness was measured in a group of anesthesiology
residents. Daytime sleepiness is routinely measured in sleep laboratories
to evaluate patients for sleep disorders such as obstructive sleep
apnea and narcolepsy. Daytime sleepiness is measured by a test
called the multiple sleep latency test (MSLT). The MSLT measures
the ease of falling asleep over the course of a day and is based
on the firmly established principle that the sleepier you are,
the faster you fall asleep. The sleep latency (time to fall asleep)
is determined using specific electroencephalography (EEG) criteria.
The MSLT score is the average latency across five attempts to
fall asleep over the course of a day. Pathologic MSLT scores are
< 5 minutes and are seen commonly in patients with sleep disorders
and in healthy people who have been sleep-deprived for 24 hours.
Normal MSLT scores are > 10 minutes.
In this study, each subject was observed in each of three conditions.
In the baseline condition, the subjects were on typical operating
room rotations and had not had an on-call period for at least
48 hours. In the post-call condition, the subjects were on a demanding
clinical rotation and were studied immediately after a 24-hour,
in-hospital on-call period. In the sleep-extended condition, the
subjects were required to extend and maximize their sleep for
four consecutive days prior to being tested.
The residents’ average total sleep time (hours ± standard deviation)
for the four nights prior to the study period were: baseline 7.1
± 1.5; post-call 6.3 ± 1.9; and sleep-extended 8.8 ± 1. In this
study, subjects were found to have daytime sleepiness at or near
pathologic levels in both the post-call condition (4.9 ± 4.7 minutes)
and the baseline (6.7 ± 5.3 minutes) condition. The figure shows
these data graphically over the course of the day. This documents
a previously unknown level of chronic sleep debt in our subjects
in the baseline condition even though subjects were averaging
over seven hours of sleep per night. It is important to note that
this level of daytime sleepiness was reversible, as shown for
the sleep-extended condition. When the same subjects were allowed
to obtain more sleep, the MSLT scores were normal (12.0 ± 6.4
minutes).
This study also revealed that subjects had poor ability to subjectively
perceive their actual level of physiologic sleepiness as measured
by the MSLT. They also had trouble perceiving that they had actually
fallen asleep even when sleep was recorded unambiguously by the
EEG. The study's findings suggest that there may be situations
during our clinical work where we become vulnerable to falling
asleep, are unable to perceive that this is occurring and do not
even know that we have nodded off. This can only increase the
risk to our patients or indeed to ourselves as we drive ourselves
home.
Figure 1
Simulator Study
The next logical experiment was to test the effects of fatigue
on performance using a patient simulator in a realistic environment.
We asked the question: How does sleepiness and fatigue affect
our ability to perform our job as anesthesiologists? Simulation
is a useful technique for studying this question since it poses
no risk to patients and allows for extensive manipulation of both
the subject and the environment. Simulation also allows for the
experiment to be controlled and reproduced between subjects, which
is impossible to do with real patients.
We evaluated simulator performance of resident anesthesiologists
in each of two conditions. In the sleep-deprived condition, the
subjects were kept awake for 24 hours. This replicates a common
clinical practice for some experienced anesthesiologists who provide
anesthesia care for patients during the day after a busy on-call
period. In the sleep-extended condition, the subjects were required
to extend their sleep for four consecutive days prior to being
tested in the simulator.
The simulations consisted of matched laparoscopic cases of four-hour
duration beginning at 9 a.m. and ending at 1:30 p.m. Twenty-seven
probes of vigilance were introduced into the scenario at randomly
distributed times as were two subtle clinical events per case.
All simulations were videotaped for retrospective analysis.
In this complex study, subjects had slightly slower average
response times to vigilance probes in the fatigued condition,
and certain subjects completely missed some probes because they
were clearly asleep. An extensive analysis of 96 hours of the
study’s videotapes was performed to quantify profoundly sleepy
behaviors (i.e., head nodding or obvious sleep episodes). We found
a far greater number and duration of the sleepy episodes in the
sleep-deprived group. Two subjects during the experiment had profound
sleepiness for a total of more than 25 percent of the four-hour
scenario (essentially asleep for one hour!). While all subjects
often cycled rapidly between awake and sleepy behaviors, these
subjects had several continuous episodes of sleep lasting more
than five minutes.
Sleepiness and Fatigue in Society
Throughout the industrialized world and in virtually all transport
industries where impaired performance translates into risk of
death or injuries, work hours are controlled by regulation to
mitigate the effects of sleep loss, fatigue and circadian disruption.
In these industries, accidents related to fatigue are not considered
isolated occurrences but rather as the expected result of errors
and incidents induced by human physiological limitations. The
National Transportation Safety Board (NTSB) examines the sleep/wake
history of any crew member involved in an accident, and fatigue
has been formally identified as a contributing factor and probable
cause in major transportation accidents.
In contrast, within health care in the United States, regulation
of work hours, schedules and rest requirements are either nonexistent
or are markedly less than those considered appropriate by the
rest of our society. Great Britain and Australia have addressed
the work hours of junior doctors, which has had a significant
impact on how physicians are trained in those countries. In many
cases, the trainees’ mentors now do the after hours work previously
done by trainees. So now who is being sleep deprived?
Unlike pilots, nuclear power plant operators, truck drivers or
train engineers, there is no U.S. federal regulatory body that
has oversight responsibility for the work/rest practices of physicians.
The incentives and disincentives to work while sleepy change with
the practice setting. No doubt, trainees look at working the day
after-call differently than does an experienced practitioner who
is getting paid an incremental fee to care for a patient. This
is a complicated issue, and answers to this problem have not and
will not come easily.
Generally, the burden of proof has been placed on clinicians
and investigators to prove that working long shifts (24-36 hours)
and irregular on-call schedules is not safe for patients or clinicians.
The case examples in which sleep loss and physician fatigue have
been identified as important contributing factors to medical error
have been treated as isolated individual lapses rather than as
the tip of the iceberg of a widespread and serious risk. Perhaps
the time has come for us to reverse the burden of proof in the
interests of safety. The life we save might be our own.
Bibliography:
Howard SK, Gaba DM. Human performance and patient safety. In:
Morrell RC, Eichhorn JH, eds. A Manual of Patient Safety in Anesthesia.
New York: Churchill Livingstone; 1997.
Howard SK, Gaba DM, Rosekind MR, Zarcone VP. Excessive daytime
sleepiness in resident physicians: Risks, intervention, and implications.
Sleep. 2000 (submitted).
Howard SK, Smith BE, Gaba DM, Rosekind MR. Performance of well-rested
vs. highly-fatigued residents: A simulator study. Anesthesiology.
1997; A-943.
Howard SK, Keshavacharya S, Smith BE, et al. Behavioral evidence
of fatigue during a simulator experiment. Anesthesiology. 1998;
A-1236.
Horne J, Reyner L. Sleep-related vehicle accidents. Br Med J.
1995; 310:565-567.
Pack AI, Pack AM, Rodgman E, et al. Characteristics of crashes
attributed to the driver having fallen asleep. Accid Anal Prev.
1995; 27:769-775.
Rosekind M, Graeber R, Dinges D, et al. Crew factors in flight
operations: IX. Effects of preplanned cockpit rest on crew performance
and alertness in long-haul operations. Vol. NASA Technical Memorandum
108839. Moffett Field, CA: NASA Ames Research Center; 1995.
Mitler M, Dement D, Dement W. Sleep medicine, public policy,
and public health. In: Kryger M, Roth T, Dement W, eds. Principles
and Practice of Sleep Medicine. 3rd ed. Philadelphia, PA: W.B.
Saunders Co; 2000:580-588.
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Steven K. Howard,
M.D., is Staff Physician, V.A. Palo Alto Health Care System
and Associate Professor, Stanford University School of Medicine,
Palo Alto, California |
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