Night-Shift Nap Awakens ER Residents and Nurses

STANFORD, Calif., Nov. 3 -- Allowed a 40-minute nap midway through 12-hour night shifts, emergency room residents and nurses responded with more vigilance and vigor, found researchers here.

Nevertheless, the randomized study that compared nappers with non-nappers working the night shift at a Stanford hospital ER was not all positive. The nappers did not exceed the nonnappers in all parameters, and during post-shift driving simulator tests even the nappers had catastrophic lapses in motor skills.

In the driving tests, simulating a commute home after work, cars left the road or crashed into oncoming vehicles, Rebecca Smith-Coggins, M.D., of Stanford, and colleagues, reported in the November issue of the Annals of Emergency Medicine.

Night shifts interfere with circadian rhythms so that even adequate daytime sleep before a night shift may not be protective, the researchers said. Even worse, being up for 24 hours has the same effect as being legally drunk, said co-author Steven Howard, M.D.

In the night-shift study of 42 residents and nurses (occupations equally divided) who worked three consecutive night shifts, 21 participants were randomized to a control group (no nap) and 21 to a 40-minute nap opportunity at 3 a.m.

All participants were free of sleep disorders at the start of the study and completed sleep-wake diaries for a total of 11 days, including two testing days. As a whole, the group reported that their optimum sleep time was a mean of nine hours.

The participants were instructed not to drink caffeine during the study. For a first night-shift, all participants worked as usual and kept sleep logs, and worked as usual again on a second night shift. On the third consecutive night shift, they were randomized to a nap or no-nap schedule. The nap opportunity occurred in a dark quiet room away from clinical sites. The non-nappers worked as usual.

According to polysomnographic data, 90% of the nappers were able to catch a few winks for an average of 24.8 minutes (SD 11.1). All completed performance tests three times during each study shift (preshift, 4 a.m., and 7:30 a.m.).

As measured by the Psychomotor Vigilance Test (a test of sustained attention and simple visual reaction time), at 7:30 a.m., the nap group had fewer performance lapses (nap 3.13 vs. no-nap 4.12; P<0.03; mean difference 0.99; 95% CI: -0.1-2.08).

In the mood profile test, the nappers reported more vigor (nap 4.44 vs. no-nap 2.39; P<0.03; mean difference 2.05 CI: 0.63-3.47), less fatigue (nap 7.4 vs. no-nap 10.43; P<0.05; mean difference 3.03; CI: 1.11-4.95), and less sleepiness (nap 5.36 vs. no-nap 6.48; P< 0.03; mean difference 1.12; CI: 0.41-1.83).

However, measures of tension, depression, confusion, and anger, were the same for both groups, the investigators said.

A nap increased the speed by 20 seconds with which the participants completed a simulated intravenous insertion (nap 66.40 sec versus no-nap 86.48 sec; P<0.10; mean difference 20.08 sec.; CI: 4.64-35.52).

There were no differences by occupation, sex, time of day, or in number of hematomas or attempts. Although this represents a non-significant finding empirically, clinically, a patient might find an extra-20 second experience of intravenous placement quite significant, Dr. Smith-Coggins said.

Immediately after the nap at 4 a.m., the still-sleepy nappers did less well on a memory test (the Probed Recall Memory test). The score for the nappers was 2.76, compared with 3.7 for the no-nap group (P<0.05; mean difference 0.94; CI: 0.20-1.68). However, the investigators said that this finding reversed by the end of the night shift and was probably due to temporary grogginess, suggesting the importance of a wake-up period after a nap to address potential sleep inertia.

A 40-minute simulation of a drive home at 8 a.m. after the night shift and videotaped for behavioral signs of sleepiness and driving accuracy produced somewhat alarming results.

Although there were no aggregate differences in driving performance between the two groups, the researchers said, there were a substantial number of occurrences of dangerous driving in both groups. Across all participants, such events occurred during approximately 8% of the drive, each event potentially lethal.

However, a comparison of dangerous driving in the same individual between shifts showed that the driving of non-nappers worsened on night three, whereas that of napping subjects improved slightly. Analysis of driver alertness also showed trends suggesting the nap helped. Some improved and none got worse, they reported.

Several outliers in the nap group were individuals with a higher percentage of eyes closed while driving even on the second night before randomization. Therefore the nap group may have included a disproportionate number of individuals intrinsically prone to sleepiness, the researchers said. This cluster of subjects supports the possibility that individual "traits" might be as important as group state or interventions because they affect sleepiness and fatigue-related performance, Dr. Smith-Coggins said.

Limitations of the study included the fact that the driving simulator lacked the usual noises, vibrations, and lights of a real environment. Moreover participants knew there was no real risk of falling asleep. Thus, driving performance may have been reduced to a common poor quality in both groups. There was also no baseline measure of driving performance obtained when the participants were fully rested.

The limit on caffeine usage limits the generalizability of the study, the researchers said, but banning caffeine was necessary to ensure that all subjects were equivalent.

This study reported the first randomized trial of a nap intervention during the night shift for physicians and nurses, Dr. Smith-Coggins wrote. Evaluating the costs and safety of napping will be difficult and will depend on the work and staffing demands of each clinical setting. There may be substantial and sometimes hidden costs to individuals and society from inefficient care provided by fatigued physicians, she added.

This study is important and timely in light of recent literature on health care professionals' long work hours, sleep, and performance, the researchers said. The impact of work-hour reduction and schedule changes on attention failures, medical errors, and intern sleep have gained wide attention, they added.

The authors wrote that they hope that by providing scientific data that support the benefit of napping, hospitals and other employers will consider policy changes that include nap breaks to help improve safety and performance. "Relevant issues related to implementing nap intervention require further explorations, though models exist in other work settings," they concluded.