Objective and subjective measures of sleepiness, and their associations with on-road driving events in shift workers SUZANNE FTOUNI 1 , TRACEY L. SLETTEN 1 , MARK HOWARD 2 , CLARE ANDERSON 1,3,4 , MICHAEL G. LENNE ´ 5 , STEVEN W. LOCKLEY 1,3,4 and SHANTHA M. W. RAJARATNAM 1,3,4 1 School of Psychology and Psychiatry, Monash University, Clayton, Vic., Australia, 2 Institute for Breathing and Sleep, Austin Hospital, Heidelberg, Vic., Australia, 3 Division of Sleep Medicine, Department of Medicine, Brigham and WomenÕs Hospital, Boston, MA, USA, 4 Division of Sleep Medicine, Department of Medicine, Harvard Medical School, Boston, MA, USA and 5 Monash University Accident Research Centre, Monash University, Clayton, Vic., Australia Keywords accidents, drowsy driving, nurses, safety, shift work, sleepiness Correspondence Shantha Rajaratnam, PhD, School of Psychology and Psychiatry, Monash University, Building 17, Wellington Road, Clayton, 3800 Vic., Australia. Tel.: +61 3 9905 3934; fax: +61 3 9905 3948; e-mail: shantha.rajaratnam@monash.edu Accepted in revised form 15 June 2012; received 1 March 2012 DOI: 10.1111/j.1365-2869.2012.01038.x SUMMARY To assess the relationships between sleepiness and the incidence of adverse driving events in nurses commuting to and from night and rotating shifts, 27 rotating and permanent night shift-working nurses were asked to complete daily sleep and duty logs, and wear wrist-activity monitors for 2 weeks (369 driving sessions). During all commutes, ocular measures of drowsiness, including the Johns Drowsiness Scale score, were assessed using the Optalertä system. Participants self-reported their subjective sleepiness at the beginning and end of each drive, and any events that occurred during the drive. Rotating shift nurses reported higher levels of sleepiness compared with permanent night shift nurses. In both shift-working groups, self-reported sleepiness, drowsiness and drive events were significantly higher during commutes following night shifts compared with commutes before night shifts. Strong associations were found between objective drowsiness and increased odds of driving events during commutes following night shifts. Maximum total blink duration (mean = 7.96 s) during the drive and pre-drive Karolinska Sleepiness Scale (mean = 5.0) were associated with greater incidence of sleep-related events [OR, 5.35 (95% CI, 1.32, 21.60), OR, 1.69 (95% CI, 1.04, 2.73), respectively]. Inattention was strongly associated with a Johns Drowsiness Scale score equal to or above 4.5 [OR, 4.58 (95% CI, 1.26–16.69)]. Hazardous driving events were more likely to occur when drivers had been awake for 16 h or more [OR, 4.50 (95% CI, 1.81, 11.16)]. Under real-world driving conditions, shift-working nurses experience high levels of drowsiness as indicated by ocular measures, which are associated with impaired driving performance following night shift work. INTRODUCTION Approximately 15–20% of motor vehicle crashes (MVC) are attributed to sleepiness and fatigue in the USA and Australia (Austroads, 2005; Teff, 2010), making it one of the most common preventable causes of death on the roads (Dobbie, 2002; Maclean et al., 2003). Shift workers are overrepresented in sleepiness-related MVCs (Crummy et al., 2008), which often occur during the commute from work following the night shift (Barger et al., 2005; Crummy et al., 2008). Sleepiness-related MVCs result from a critical combination of sleep deficiency and circadian misalignment (Arendt, 2010; Dijk and Czeisler, 1994). Night shift workers are particularly vulnerable to sleepiness, particularly towards the end of their shift, due to the interaction of circadian (approx- imately 24 h) and homeostatic factors, which combine in a multiplicative manner. In addition, night shift work is often J. Sleep Res. (2013) 22, 58–69 Measures of sleepiness 58 ª 2012 European Sleep Research Society