|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Scientists are discovering the importance of adequate sleep to allow normal human performance. A consensus report[347] by the leaders in the field of sleep medicine stated:
[we] evaluated scientific and technical reports on the distribution throughout the 24-h day of medical incidents (such as heart attack and stroke) and performance failures (such as vehicular accidents and human errors in industrial and technical operations that can affect public safety). We found that these events occur most often at times of day coincident with the temporal pattern of brain processes associated with sleep. It thus appears that the occurrence of a wide range of catastrophic phenomena are influenced by sleep-related processes in ways heretofore not fully appreciated.This report goes on to give many examples of catastrophes that have occurred at least in part because of the effects of sleep deprivation and fatigue.
Investigations in other complex industries (aviation, nuclear power, maritime, long-haul trucking) have identified fatigue as the probable cause of, or a contributing factor in, many accidents. Unlike health care,
Based on these findings, it is likely that chronic sleep deprivation, circadian rhythm abnormalities, and fatigue can be blamed for some iatrogenic adverse patient outcomes. As previously mentioned, the IOM report published in 1999 revealed that thousands of patients are harmed each year by preventable error. Some of these errors may have fatigue as a causative factor, and this should be an area of active study. However, it is difficult to determine the degree to which this is true. Although these factors have long been minimized or ignored by health care professionals, an understanding of them is critical to maximize patient safety. This is reflected by recently published reviews.[223] [348] [349]
Carskadon and Dement[350] referred to sleep as a reversible behavioral state of perceptual disengagement from and unresponsiveness to the environment that is usually accompanied by postural recumbency, quiescence, closed eyes, and other indicators commonly associated with sleeping. Sleep can be thought of as a physiologic drive state similar to hunger or thirst and is necessary for the maintenance of alertness, performance, and overall well-being. The intensity of this drive can be inferred from noting how quickly an individual falls asleep. Just as eating and drinking satiate hunger and thirst states, sleeping reverses the desire to sleep.
The amount of sleep required by any individual is that which allows him or her to be awake and alert throughout the day. The average sleep time for young adults is 7 to 8 hours in a 24-hour period, with an approximately 15% inter-individual variation. These sleep requirements do not change with age and humans can do little to train their physiology to function optimally on less sleep than what is required.
If adequate sleep is not obtained for whatever reason, daytime sleepiness and impaired performance ensue. Sleep loss is cumulative, resulting in what is referred to as a sleep debt. The individual who has obtained an optimal amount of sleep is better prepared to perform long periods of sustained work compared with one who is operating from a sleep debt.
Because of the additive effects of chronic partial sleep loss, even minor sleep restriction on a nightly basis can insidiously accumulate into a substantial sleep debt.[351] It is important that the only way to pay back a sleep debt is with sleep.
Sleep debts are commonplace in our culture. Shift work, long and irregular work hours, and the demands of family and recreation lead to irregular sleep patterns and prevent restful sleep. This is particularly true for physicians, who often work in shifts, have long duty periods, and must frequently care for patients beyond normal working hours.
Rhythms that fluctuate on a 24-hour time scale are known as circadian rhythms. The biologic clock that is responsible for these rhythms is located in the suprachiasmatic nucleus in the human brain. The best-known circadian rhythms are those of body temperature, hormone secretion, metabolism, and the sleep/wake cycle. The circadian system is synchronized to the 24-hour day by external stimuli referred to as zeitgebers, the most influential of which is the light/dark cycle of day and night.
The circadian system is biphasic, producing a state of increased sleep tendency and decreased performance capacity during two periods throughout the 24-hour day—from 2 AM to 6 AM and from 2 PM to 6 PM. These periods are sometimes referred to as circadian lulls. The circadian clock is very resistant to alterations, and it does not adjust rapidly to changes such as that produced by jet lag or shift work. Disruption of the normal circadian rhythm or incomplete circadian adaptation leads to acute and chronic sleep deprivation, decreased alertness, increased subjective fatigue, and decreased physical and mental performance.[352]
Sleepiness and alertness are at opposite ends of a continuum. Daytime sleepiness is the most obvious effect of failing to obtain adequate sleep. Healthy adults are maximally alert by midmorning. This is sequentially followed by a circadian lull in the early afternoon (causing some cultures to incorporate an afternoon "siesta"), increased alertness in the early evening, and finally increased sleepiness that normally results in falling asleep at night.
The most extreme periods of sleepiness become manifest when one is required to remain awake when one would normally be asleep (2 AM to 6 AM). Data from the U.S. Department of Transportation reveal that the greatest numbers of single-vehicle accidents take place during the early morning hours when people are at a circadian lull of alertness. These accidents are thought to be due to inadvertent lapses in driver attention brought about by extremes of sleepiness.
The major factors causing sleepiness are decreased quantity of sleep, poor quality of sleep (sleep fragmentation resulting from multiple awakenings or abnormal progression of sleep states and stages), disrupted circadian rhythms, and the use of certain medications. The amount of sleep obtained is directly related to daytime sleepiness. If sleep is restricted in healthy adults, daytime sleepiness can be demonstrated the following day.[351] [353] If one is allowed to extend sleep beyond the usual sleep time, increased alertness can be demonstrated in the laboratory.[349] [354] Sleep quality is affected by many factors. Sleep fragmentation affects the elderly and patients with sleep disorders such as sleep apnea and periodic limb movements.
Caffeine[355] [356] and other stronger stimulants are known to reduce nocturnal sleep if ingested close to bedtime, hence decreasing sleep quantity and quality. Potent stimulants such as amphetamines do produce increased alertness and performance, but they have significant side effects and are not an option for health care personnel (e.g., the individual must undergo a substantial amount of recovery sleep ("crash") after their effect is gone). Newer, non-amphetamine alertness-enhancing drugs (e.g., modafinil) are currently under study in shift workers, including health care workers (see Countermeasures).
Long work hours, fatigue, and sleep deprivation have also been shown to bring about dramatic changes in mood and emotions.[357] [358] Depression, anxiety, irritability, anger, and depersonalization have all been shown to increase during testing of chronically fatigued house staff. These emotions are an obvious source of stress between anesthetists and their coworkers, patients, and families. The relationship of mood, performance, and patient safety has yet to be determined.
Vigilance, the centerpiece of the ASA logo, is defined as "the ability to remain alertly watchful especially to avoid danger."[359] Vigilance is critical, although studies of the performance of anesthesiologists make it clear that vigilance is not the only key characteristic of the careful anesthesiologist. Vigilance is a necessary but not sufficient condition to permit the safe passage of a patient through the perioperative period. If vigilance and other aspects of decision-making are impaired by performance-shaping factors such as sleep deprivation and fatigue, there is a greater likelihood of an adverse patient outcome.
Monitoring of slowly changing stimuli is a classic vigilance task, which makes up a significant proportion of the anesthetist's work. This type of task is the most sensitive to the degrading effects of sleepiness and fatigue. During the performance of lengthy vigilance tasks, the most common types of decrements include increased reaction time, lapses (transient periods of unawareness), and a reduction in the probability of detecting an alarm.[360] This type of performance impairment has been documented after as little as 30 minutes of time on a task, and the decrement is even more pronounced if the individual is physiologically sleepy at the beginning of the task.
The most extreme cause of impaired vigilance is the occurrence of actual sleep episodes (microsleeps) encroaching into periods of wakefulness. Microsleep events typically last a few seconds to a few minutes. They are intermittent in onset, and their impending occurrence is difficult for the individual to predict. Most individuals underestimate their level of sleepiness when they can be objectively shown to be extremely sleepy, thus making this problem even more insidious. In other words, one can fall asleep and not be perceptually aware of it. This has significant meaning both in the workplace and when driving home after long work periods.
Microsleeps are a sign of extreme sleepiness and are harbingers of the onset of longer sleep periods. Typically they occur during periods of low workload or stimulation and when an individual is maximally sleepy. In addition, an individual's performance between microsleep episodes is impaired. Frequent and longer microsleeps increase the number of errors of omission.
Driving while drowsy may be less forgiving than practicing medicine while drowsy. It is easy to imagine that if a driver has a microsleep for only seconds while traveling at 60 miles per hour there is a high likelihood of an accident. Although the anesthetist's work environment does not (usually) evolve as fast as that of the driver, the safety implications of falling asleep while providing care are similarly obvious.[361]
Scientists at the NASA Ames Research Center studied the occurrence of microsleep episodes on pilots during transmeridian flights.[362] These flights involve multiple time zone changes with long, irregular work schedules and a resultant disruption of circadian rhythms. This situation causes fatigue, sleepiness, and decreased performance, which are believed to have an impact on flight safety. This particular protocol compared two pilot groups flying equivalent flights: a control (non-nap) group and a nap group. EEG monitoring of the pilots was performed to determine the extent of microsleep episodes and also to document whether pilots were actually able to nap if given the opportunity. In brief, the study revealed that (1) crew members were able to nap seated in the cockpit if given the opportunity, (2) the non-nap crew had significantly more microsleep episodes during critical phases of flight when compared with the crew that had napped, and (3) performance on a standardized test of visual reaction time was impaired in the non-nap group when compared with the group that had napped. This study demonstrated that microsleeps do occur even in a work environment in which sleep is strictly forbidden and in which work hours are tightly regulated. Napping appears to be a reasonable countermeasure to decrease the likelihood of microsleeps and improve performance. Other work on napping supports these conclusions.
Do anesthetists suffer microsleep events? The answer almost certainly is yes. Anecdotal evidence as well as unpublished reports from our own surveys suggest that these events do occur from time to time.[361] This was formally evaluated recently in a study of anesthesiologists using a patient simulator.[190]
From a practical standpoint, shift work will remain a common method to provide 24-hour care in the hospital setting. Workers and managers should learn how circadian factors, sleep-related factors, and social factors affect the lives of workers and their families.[237] Hospital organizations should make it a priority to establish that workers are appropriately rested, just as they try to ensure that workers are not impaired by drugs or alcohol on the job.
|
|
|
|
|
|
|
|
|
|
|
|
|
