Night Shift Decreases Cognitive Performance of ICU Physicians


Night Shift Decreases Cognitive Performance of ICU Physicians

Maltese. Intensive Care Medicine (2016) 42:393-400 DOI 10.1007/s00134-4115-4

Clinical Question

  • In Intensive care doctors what is the impact of night shift work on cognitive performance?


  • Prospective, observational, comparative, randomised, cross-over study
  • Four cognitive skills were tested on ICU doctors following night shift (NS) and following a night of rest (NR) at home
  • Randomisation was used to determine the order of evaluation of the two conditions (NS or NR first) to minimise a possible training bias of doing the tests twice and the content of the tests were changed between the first and second evaluation


  • 3 different intensive care units in one hospital (North Hospital), Marseille, France
  • October 2012 – October 2013


  • Inclusion: Intensive Care Doctors (staff physicians or residents)
  • Exclusion: Unwilling to participate, or incomplete participation due to shift allocation
  • 58 doctors contacted; 51 participated (27 residents, 21 physicians), 4 refused, 3 incomplete participation


  • Evaluation was conducted by the same psychologist in a quiet office between 10am-noon
  • Assessment commenced with a demographic and lifestyle questionnaire with self-assessment of attentional capacity or tiredness using visual analogue scales
  • 4 cognitive tasks were then completed using the Wechsler Adult Intelligence Scale and the Wisconsin Card Sorting Test to assess verbal comprehension, working memory, processing speed and perceptual reasoning
  • Each doctor had 2 evaluations separated by a period of at least 7 days. The NR condition took place at least 3 days after the last on-duty shift. The NS evaluation occurred following a 14 hour night shift which followed a 10 hour working day (participants could have a nap during the day preceding night shift).
  • The influence of professional experience and the amount of sleep on cognitive performance was also investigated


  • The participants were their own control and the comparison was made between cognitive performance after night shift and cognitive performance after a night of rest at home


  • All cognitive abilities declined after night shift
    • Working memory capacity(WMC)
      • 9.5% lower after night shift (p<0.001)
      • Although the working memory capacity was higher in the physicians than the residents after a night of rest, there was no difference after a night shift
      • The number of hours slept on the night shift (<2, 2-4 or >4 hours) did not impact WMC
    • Information processing speed (IPS)
      • 12.5% lower after night shift (p<0.001)
      • IPS was similar in physicians and residents after NR and NS
      • The number of hours slept on the night shift did not impact IPS
    • Perceptual reasoning (PR)
      • 6.5% lower after night shift (p<0.002)
      • PR was significantly lower in residents compared with physicians after NS
      • The number of hours slept on night shift did not impact PR
    • Cognitive flexibility (CF)
      • not statistically significantly lower after night shift (p=0.063)
      • CF was significantly less in residents after NSCF was significantly less in physicians if sleep time was <2hrs on night shift
  • A correlation analysis was performed between the self-reported tiredness or attentional abilities by physicians and their actual performance. There was no significant correlation between the self-report and the cognitive evaluation

Authors’ Conclusions

  • All cognitive abilities worsened after night shift. The level of impairment did not differ based on seniority of the doctor or the hours of sleep obtained on the night shift. Doctors were found to be poor at self-evaluating their level of fatigue


  • Prospective, observational trial of an important issue of workplace safety
  • The tools used for the assessment were a validated technique for measuring cognitive function
  • Having the participant as their own control was an effective way of detecting any change following night shift
  • Randomisation of participants to do the first testing either after NS or after NR minimised the impact of ‘learning how to do the test’ on the results


  • The study did not aim to correlate decline in cognition and its relationship to quality of patient care and the chance of error
  • The cognitive tests represented a moment in time, and may not accurately reflect the real world where chronic sleep deprivation may impact on functional capacity. Protracted periods of time on night shift may alter the cognitive performance further

The Bottom Line

  • Night shift reduces the cognitive ability of physicians. Awareness of this may be a trigger to improve patient safety such that delaying non-urgent procedures or decisions until daylight hours is prioritised

External Links


Summary author: Celia Bradford
Summary date: February 18th 2016
Peer-review editor: Steve Mathieu

One comment

  • Jon Hilton

    Wouldn’t a better control have been testing the doctors cognitive abilities after a 12 hour day shift?

    Is it the length of shift which impact cognition or working at night?

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