Occupational Medicine 2016;66:2–7 doi:10.1093/occmed/kqv195
EDITORIALS
The hidden burden of OSA in safety critical workers: how should we deal with it? severity of OSA that could impact on diagnosis. Some workers had not completed their formal assessment for OSA and there were no clear criteria for commencing treatment with CPAP or data on adherence to treatment. Nevertheless, the study provides valuable insights into the feasibility of introducing simple objective screening for OSA in an occupational setting and its impact on identification and treatment of OSA. While the prevalence of diagnosed OSA increased up to 7% using the new screening criteria, it is still less than expected. General population studies have identified a prevalence of at least mild OSA of over 24% in adult males, with a prevalence of over 50% in male predominant occupations with a high rate of obesity [3,5]. As pointed out by Colquhoun and Casolin, the screening process that was introduced had a high specificity (>90% that screened positive had OSA); however, the sensitivity of this approach is unknown. Combining BMI with age, gender and symptoms for occupational screening for OSA can produce a sensitivity and specificity of 81 and 73%, respectively, increasing to 91% for both when combined with overnight oximetry [6], an approach that also appears to be cost-effective when the costs related to crash risk are taken into account [7]. This method relies upon accurate reporting of symptoms; however, symptoms of OSA appear to have been substantially underreported by the rail workers during their occupational medical assessment and had little influence on the decision to undertake further investigation. The new rail workers’ criteria relied heavily on very high BMIs to trigger further investigation for OSA. The criteria would be expected to provide a low false-positive rate, as reported, but is likely to have had a modest sensitivity missing some workers with OSA. Reducing the BMI cut-offs in the screening criteria would likely improve the sensitivity of screening, but at the same time reduce specificity with many more workers undertaking unnecessary investigations. A potential alternative is screening for OSA using home monitoring, such as nocturnal oximetry. However, this does not substantially improve the accuracy of diagnosis compared with a well-designed process that combines initial screening based on personal characteristics followed by oximetry in those at high risk and is less costeffective [6]. Although the prevalence of OSA is high in some occupational groups, it is almost certainly not necessary to treat every safety critical worker with OSA. There
© The Author 2016. Published by Oxford University Press on behalf of the Society of Occupational Medicine. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://occmed.oxfordjournals.org/ by guest on February 16, 2016
Sleepiness due to inadequate sleep, circadian effects (usually at night) or sleep disorders is the main cause of the 20% of crashes attributed to fatigue. Obstructive sleep apnoea (OSA) is the most common sleep disorder contributing to this toll, resulting in a 2- to 3-fold increase in risk [1], although this has not been clearly substantiated among professional drivers [2]. Much of the literature addressing the prevalence and impact of OSA on safety critical work is drawn from the road transport industry but similar impacts would be expected in occupations such as rail workers. While OSA is a common disorder, present in 24% of men and 9% of women, it can remain unrecognized and untreated for prolonged periods, making it potentially appropriate for screening and treatment programmes. The prevalence appears particularly high in some occupational groups, such as truck drivers, where there is a male predominance and high prevalence of obesity that increases the risk of OSA [3]. How best to identify and treat at risk individuals in safety critical occupations and so mitigate accident risk is the subject of intense research and debate. In this issue of the journal, Colquhoun and Casolin [4] evaluated the impact of introducing objective measures to screen for sleep apnoea in Australian rail workers’ health assessments and identified a large number of workers with previously undiagnosed OSA. The new objective criteria required any of (i) a body mass index (BMI) over 40 kg/m2, (ii) a BMI over 35 kg/m2 in conjunction with hypertension, diabetes or OSA symptoms or (iii) self-reported excessive sleepiness. Previously identification of sleep apnoea had relied on self-report of sleepiness alone. The proportion of rail workers with diagnosed OSA increased from 2 to 7% after introducing the new criteria in this population of over 4000 workers. Following clinical assessment, more than half of these workers were treated with continuous positive airways pressure (CPAP). Self-reported sleepiness and the frequency of self-reported symptoms of OSA (apnoeas during sleep) were dramatically lower than expected based on similar populations and appear to have been substantially under-reported [3]. The study highlights the inadequacy of using subjective measures to identify sleepiness and OSA in occupational settings but also raises the question as to whether all safety critical workers found to have OSA by screening require treatment. This was a retrospective cross-sectional study and there was variability in the techniques for measuring and assessing the
Editorials 3
to a level close to that of the general population, although some can have residual sleepiness despite good adherence to treatment. Mandibular advancement splints are a reasonable alternative to CPAP for managing mild-tomoderate OSA providing similar control of respiratory events at night and symptoms. Their impact on crash risk has not been studied. Colquhoun and Casolin’s study highlights the substantial hidden burden of undetected OSA in safety critical workers and the challenges in identifying it given that sleepiness and apnoea symptoms appear to be dramatically under-reported. The objective screening criteria adopted in the recent Australian rail medical standards resulted in a marked increase in the identification and treatment of OSA in rail workers with a low false-positive rate, albeit acknowledging that some with sleep apnoea would have been missed. Adjusting the screening criteria to improve the sensitivity by lowering the BMI criteria would increase the detection of OSA but it would also increase the false-positive rate. More workers would undergo unnecessary investigations and some would be diagnosed with OSA that may not require treatment. The challenge remains to accurately and objectively assess the impact of OSA on sleepiness and accident risk to ensure that those at high risk in safety critical industries are treated, while those who are not at risk can continue to work unimpeded. Mark E. Howard Institute for Breathing & Sleep and Austin Health, Heidelberg,Victoria 3084, Australia e-mail: [email protected]
Fergal J. O’Donoghue Institute for Breathing & Sleep and Austin Health Heidelberg,Victoria 3084, Australia e-mail: Fergal.O’[email protected]
Conflicts of interest M.E.H. is conducting research sponsored by the Co-operative Research Centre for alertness, safety and productivity and Prevention Express.
References 1. Tregear S, Reston J, Schoelles K, Phillips B. Obstructive sleep apnea and risk of motor vehicle crash: systematic review and meta-analysis. J Clin Sleep Med 2009;5:573–581. 2. Stevenson MR, Elkington J, Sharwood L et al. The role of sleepiness, sleep disorders, and the work environment on
Downloaded from http://occmed.oxfordjournals.org/ by guest on February 16, 2016
is significant variability in individual responses both to restricted sleep and OSA [8,9]. Some have substantially greater cognitive impairment and sleepiness than others despite the same degree of sleep restriction or sleep apnoea. For example, although 59% of Australian road transport drivers have at least mild OSA on nocturnal monitoring, 16% have OSA combined with excessive sleepiness when reported anonymously [3]. Consistent with this concept, there is only a modest relationship between OSA severity and crash risk [1]. While this raises the possibility that safety critical workers such as rail workers might self-select to be more resistant to conditions that cause sleepiness, this does not appear to be the case [10]. The clinical decision to treat safety critical workers for OSA should take into account the impact on sleepiness and cognitive function. In confidential settings, subjective sleepiness and self-reported sleepiness while driving are linked to crash risk [3,11]. However, as suggested by the very low subjective sleepiness scores in the current study, self-reported sleepiness appears unreliable in the occupational setting when licensing may be affected. The Maintenance of Wakefulness Test (MWT) evaluates the ability to stay awake in a laboratory environment and is currently used as an objective method to assess sleepiness for safety critical work. Those who fall asleep more quickly have impaired real-life driving performance [12], although there is only a weak relationship to crash risk in the limited studies to date [13]. In the study by Colquhoun and Casolin, four drivers who were reluctant to be treated with CPAP had MWTs, which were all normal, and remained under observation rather than commencing treatment. While this supports the concept of individual differences in the response to OSA, clinicians need to remain cautious when using the MWT as it is prone to motivational effects when used for licensing assessment [14]. The longer 40 minute version is preferable for this purpose. Other methods, such as reaction time and driving simulation, have been proposed as an alternative to the MWT for assessing the impacts of sleepiness in safety critical workers; however, at present, there is inadequate scientific support to recommend their use [13]. Robust measures of sleepiness need to be developed that can predict the longer term risk of sleepiness-related impairment and accidents at work. Many other factors may affect sleepiness and safety in the occupational setting. Shift duration, circadian misalignment on night shift, sleep restriction and sedating drugs including alcohol all influence sleepiness and crash risk [15]. Their influence on sleepiness and the fact that these factors may fluctuate rapidly need to be considered as part of clinical assessment. These factors also enhance the impact of OSA on sleepiness and impaired perform ance [16] and should be considered as part of managing OSA in safety critical workers. Treatment with nocturnal nasal CPAP improves sleepiness, simulated driving performance and crash risk [17]. Crash risk appears to fall
4 OCCupational medicine
performance during sleep deprivation is similar in professional and nonprofessional drivers. Traffic Inj Prev 2014;15:132–137. 11. Lloberes P, Levy G, Descals C et al. Self-reported sleepiness while driving as a risk factor for traffic accidents in patients with obstructive sleep apnoea syndrome and in non-apnoeic snorers. Respir Med 2000;94:971–976. 12. Philip P, Sagaspe P, Taillard J et al. Maintenance of Wakefulness Test, obstructive sleep apnea syndrome, and driving risk. Ann Neurol 2008;64:410–416. 13. Kingshott RN, Cowan JO, Jones DR et al. The role of sleepdisordered breathing, daytime sleepiness, and impaired performance in motor vehicle crashes—a case control study. Sleep Breath 2004;8:61–72. 14. Arzi L, Shreter R, El-Ad B, Peled R, Pillar G. Forty- versus 20-minute trials of the maintenance of wakefulness test regimen for licensing of drivers. J Clin Sleep Med 2009;5:57–62. 15. Philip P, Akerstedt T. Transport and industrial safety, how are they affected by sleepiness and sleep restriction? Sleep Med Rev 2006;10:347–356. 16. Vakulin A, Baulk SD, Catcheside PG et al. Effects of alcohol and sleep restriction on simulated driving performance in untreated patients with obstructive sleep apnea. Ann Intern Med 2009;151:447–455. 17. Tregear S, Reston J, Schoelles K, Phillips B. Contin uous positive airway pressure reduces risk of motor veh icle crash among drivers with obstructive sleep apnea: systematic review and meta-analysis. Sleep 2010; 33:1373–1380.
doi:10.1093/occmed/kqv163
Ebola—what have we learned from the recent outbreak? Many occupational physicians have been touched by the most recent outbreak of Ebola virus in West Africa, which was declared a ‘public health emergency of international concern’ by the World Health Organization (WHO) in August 2014 [1]. While many UK-based companies and their employees faced limited direct effects from the outbreak, it was still widely recognized as a humanitarian crisis threatening international security and global growth [2,3]. In many ways, the Ebola outbreak was just the latest wake-up call for international organizations, businesses and healthcare professionals to recognize the global health impact on work and workers of an increasingly connected world. This awakening follows the increasing trend for businesses to extend their scope into
developing countries where there may be challenges in physical and social infrastructure [4]. Hot on the heels of Severe Acute Respiratory Syndrome (SARS), pandemic flu, and concurrent with the grumbling appendix that is Middle East Respiratory Syndrome (MERS Co-V), Ebola demonstrated how infectious diseases pay scant regard to national or commercial borders. Businesses with international operations in the most affected countries (Sierra Leone, Liberia and Guinea) and those working in specific employment sectors such as transportation, oil and gas, extractive industries and healthcare were particularly affected [3]. During infectious disease outbreaks, occupational physicians may be called upon to swiftly assess risks using limited and
Downloaded from http://occmed.oxfordjournals.org/ by guest on February 16, 2016
heavy-vehicle crashes in 2 Australian states. Am J Epidemiol 2014;179:594–601. 3. Howard ME, Desai AV, Grunstein RR et al. Sleepiness, sleep-disordered breathing, and accident risk factors in commercial vehicle drivers. Am J Respir Crit Care Med 2004;170:1014–1021. 4. Colquhuon CP, Casolin A. Impact of rail medical standards on obstructive sleep apnoea prevalence. Occup Med (Lond) 2016;66:62–68. 5. Young T, Palta M, Dempsey J, Skatrud J, Weber S, Badr S. The occurrence of sleep-disordered breathing among middle-aged adults. N Engl J Med 1993;328:1230–1235. 6. Gurubhagavatula I, Maislin G, Nkwuo JE, Pack AI. Occupational screening for obstructive sleep apnea in commercial drivers. Am J Respir Crit Care Med 2004;170:371–376. 7. Gurubhagavatula I, Nkwuo JE, Maislin G, Pack AI. Estimated cost of crashes in commercial drivers supports screening and treatment of obstructive sleep apnea. Accid Anal Prev 2008;40:104–115. 8. Vakulin A, Catcheside PG, Baulk SD et al. Individual variability and predictors of driving simulator impairment in patients with obstructive sleep apnea. J Clin Sleep Med 2014;10:647–655. 9. Van Dongen HP, Baynard MD, Maislin G, Dinges DF. Systematic interindividual differences in neurobehavioral impairment from sleep loss: evidence of trait-like differential vulnerability. Sleep 2004;27:423–433. 10. Howard ME, Jackson ML, Swann P, Berlowitz DJ, Grunstein RR, Pierce RJ. Deterioration in driving
EDITORIALS
The hidden burden of OSA in safety critical workers: how should we deal with it? severity of OSA that could impact on diagnosis. Some workers had not completed their formal assessment for OSA and there were no clear criteria for commencing treatment with CPAP or data on adherence to treatment. Nevertheless, the study provides valuable insights into the feasibility of introducing simple objective screening for OSA in an occupational setting and its impact on identification and treatment of OSA. While the prevalence of diagnosed OSA increased up to 7% using the new screening criteria, it is still less than expected. General population studies have identified a prevalence of at least mild OSA of over 24% in adult males, with a prevalence of over 50% in male predominant occupations with a high rate of obesity [3,5]. As pointed out by Colquhoun and Casolin, the screening process that was introduced had a high specificity (>90% that screened positive had OSA); however, the sensitivity of this approach is unknown. Combining BMI with age, gender and symptoms for occupational screening for OSA can produce a sensitivity and specificity of 81 and 73%, respectively, increasing to 91% for both when combined with overnight oximetry [6], an approach that also appears to be cost-effective when the costs related to crash risk are taken into account [7]. This method relies upon accurate reporting of symptoms; however, symptoms of OSA appear to have been substantially underreported by the rail workers during their occupational medical assessment and had little influence on the decision to undertake further investigation. The new rail workers’ criteria relied heavily on very high BMIs to trigger further investigation for OSA. The criteria would be expected to provide a low false-positive rate, as reported, but is likely to have had a modest sensitivity missing some workers with OSA. Reducing the BMI cut-offs in the screening criteria would likely improve the sensitivity of screening, but at the same time reduce specificity with many more workers undertaking unnecessary investigations. A potential alternative is screening for OSA using home monitoring, such as nocturnal oximetry. However, this does not substantially improve the accuracy of diagnosis compared with a well-designed process that combines initial screening based on personal characteristics followed by oximetry in those at high risk and is less costeffective [6]. Although the prevalence of OSA is high in some occupational groups, it is almost certainly not necessary to treat every safety critical worker with OSA. There
© The Author 2016. Published by Oxford University Press on behalf of the Society of Occupational Medicine. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://occmed.oxfordjournals.org/ by guest on February 16, 2016
Sleepiness due to inadequate sleep, circadian effects (usually at night) or sleep disorders is the main cause of the 20% of crashes attributed to fatigue. Obstructive sleep apnoea (OSA) is the most common sleep disorder contributing to this toll, resulting in a 2- to 3-fold increase in risk [1], although this has not been clearly substantiated among professional drivers [2]. Much of the literature addressing the prevalence and impact of OSA on safety critical work is drawn from the road transport industry but similar impacts would be expected in occupations such as rail workers. While OSA is a common disorder, present in 24% of men and 9% of women, it can remain unrecognized and untreated for prolonged periods, making it potentially appropriate for screening and treatment programmes. The prevalence appears particularly high in some occupational groups, such as truck drivers, where there is a male predominance and high prevalence of obesity that increases the risk of OSA [3]. How best to identify and treat at risk individuals in safety critical occupations and so mitigate accident risk is the subject of intense research and debate. In this issue of the journal, Colquhoun and Casolin [4] evaluated the impact of introducing objective measures to screen for sleep apnoea in Australian rail workers’ health assessments and identified a large number of workers with previously undiagnosed OSA. The new objective criteria required any of (i) a body mass index (BMI) over 40 kg/m2, (ii) a BMI over 35 kg/m2 in conjunction with hypertension, diabetes or OSA symptoms or (iii) self-reported excessive sleepiness. Previously identification of sleep apnoea had relied on self-report of sleepiness alone. The proportion of rail workers with diagnosed OSA increased from 2 to 7% after introducing the new criteria in this population of over 4000 workers. Following clinical assessment, more than half of these workers were treated with continuous positive airways pressure (CPAP). Self-reported sleepiness and the frequency of self-reported symptoms of OSA (apnoeas during sleep) were dramatically lower than expected based on similar populations and appear to have been substantially under-reported [3]. The study highlights the inadequacy of using subjective measures to identify sleepiness and OSA in occupational settings but also raises the question as to whether all safety critical workers found to have OSA by screening require treatment. This was a retrospective cross-sectional study and there was variability in the techniques for measuring and assessing the
Editorials 3
to a level close to that of the general population, although some can have residual sleepiness despite good adherence to treatment. Mandibular advancement splints are a reasonable alternative to CPAP for managing mild-tomoderate OSA providing similar control of respiratory events at night and symptoms. Their impact on crash risk has not been studied. Colquhoun and Casolin’s study highlights the substantial hidden burden of undetected OSA in safety critical workers and the challenges in identifying it given that sleepiness and apnoea symptoms appear to be dramatically under-reported. The objective screening criteria adopted in the recent Australian rail medical standards resulted in a marked increase in the identification and treatment of OSA in rail workers with a low false-positive rate, albeit acknowledging that some with sleep apnoea would have been missed. Adjusting the screening criteria to improve the sensitivity by lowering the BMI criteria would increase the detection of OSA but it would also increase the false-positive rate. More workers would undergo unnecessary investigations and some would be diagnosed with OSA that may not require treatment. The challenge remains to accurately and objectively assess the impact of OSA on sleepiness and accident risk to ensure that those at high risk in safety critical industries are treated, while those who are not at risk can continue to work unimpeded. Mark E. Howard Institute for Breathing & Sleep and Austin Health, Heidelberg,Victoria 3084, Australia e-mail: [email protected]
Fergal J. O’Donoghue Institute for Breathing & Sleep and Austin Health Heidelberg,Victoria 3084, Australia e-mail: Fergal.O’[email protected]
Conflicts of interest M.E.H. is conducting research sponsored by the Co-operative Research Centre for alertness, safety and productivity and Prevention Express.
References 1. Tregear S, Reston J, Schoelles K, Phillips B. Obstructive sleep apnea and risk of motor vehicle crash: systematic review and meta-analysis. J Clin Sleep Med 2009;5:573–581. 2. Stevenson MR, Elkington J, Sharwood L et al. The role of sleepiness, sleep disorders, and the work environment on
Downloaded from http://occmed.oxfordjournals.org/ by guest on February 16, 2016
is significant variability in individual responses both to restricted sleep and OSA [8,9]. Some have substantially greater cognitive impairment and sleepiness than others despite the same degree of sleep restriction or sleep apnoea. For example, although 59% of Australian road transport drivers have at least mild OSA on nocturnal monitoring, 16% have OSA combined with excessive sleepiness when reported anonymously [3]. Consistent with this concept, there is only a modest relationship between OSA severity and crash risk [1]. While this raises the possibility that safety critical workers such as rail workers might self-select to be more resistant to conditions that cause sleepiness, this does not appear to be the case [10]. The clinical decision to treat safety critical workers for OSA should take into account the impact on sleepiness and cognitive function. In confidential settings, subjective sleepiness and self-reported sleepiness while driving are linked to crash risk [3,11]. However, as suggested by the very low subjective sleepiness scores in the current study, self-reported sleepiness appears unreliable in the occupational setting when licensing may be affected. The Maintenance of Wakefulness Test (MWT) evaluates the ability to stay awake in a laboratory environment and is currently used as an objective method to assess sleepiness for safety critical work. Those who fall asleep more quickly have impaired real-life driving performance [12], although there is only a weak relationship to crash risk in the limited studies to date [13]. In the study by Colquhoun and Casolin, four drivers who were reluctant to be treated with CPAP had MWTs, which were all normal, and remained under observation rather than commencing treatment. While this supports the concept of individual differences in the response to OSA, clinicians need to remain cautious when using the MWT as it is prone to motivational effects when used for licensing assessment [14]. The longer 40 minute version is preferable for this purpose. Other methods, such as reaction time and driving simulation, have been proposed as an alternative to the MWT for assessing the impacts of sleepiness in safety critical workers; however, at present, there is inadequate scientific support to recommend their use [13]. Robust measures of sleepiness need to be developed that can predict the longer term risk of sleepiness-related impairment and accidents at work. Many other factors may affect sleepiness and safety in the occupational setting. Shift duration, circadian misalignment on night shift, sleep restriction and sedating drugs including alcohol all influence sleepiness and crash risk [15]. Their influence on sleepiness and the fact that these factors may fluctuate rapidly need to be considered as part of clinical assessment. These factors also enhance the impact of OSA on sleepiness and impaired perform ance [16] and should be considered as part of managing OSA in safety critical workers. Treatment with nocturnal nasal CPAP improves sleepiness, simulated driving performance and crash risk [17]. Crash risk appears to fall
4 OCCupational medicine
performance during sleep deprivation is similar in professional and nonprofessional drivers. Traffic Inj Prev 2014;15:132–137. 11. Lloberes P, Levy G, Descals C et al. Self-reported sleepiness while driving as a risk factor for traffic accidents in patients with obstructive sleep apnoea syndrome and in non-apnoeic snorers. Respir Med 2000;94:971–976. 12. Philip P, Sagaspe P, Taillard J et al. Maintenance of Wakefulness Test, obstructive sleep apnea syndrome, and driving risk. Ann Neurol 2008;64:410–416. 13. Kingshott RN, Cowan JO, Jones DR et al. The role of sleepdisordered breathing, daytime sleepiness, and impaired performance in motor vehicle crashes—a case control study. Sleep Breath 2004;8:61–72. 14. Arzi L, Shreter R, El-Ad B, Peled R, Pillar G. Forty- versus 20-minute trials of the maintenance of wakefulness test regimen for licensing of drivers. J Clin Sleep Med 2009;5:57–62. 15. Philip P, Akerstedt T. Transport and industrial safety, how are they affected by sleepiness and sleep restriction? Sleep Med Rev 2006;10:347–356. 16. Vakulin A, Baulk SD, Catcheside PG et al. Effects of alcohol and sleep restriction on simulated driving performance in untreated patients with obstructive sleep apnea. Ann Intern Med 2009;151:447–455. 17. Tregear S, Reston J, Schoelles K, Phillips B. Contin uous positive airway pressure reduces risk of motor veh icle crash among drivers with obstructive sleep apnea: systematic review and meta-analysis. Sleep 2010; 33:1373–1380.
doi:10.1093/occmed/kqv163
Ebola—what have we learned from the recent outbreak? Many occupational physicians have been touched by the most recent outbreak of Ebola virus in West Africa, which was declared a ‘public health emergency of international concern’ by the World Health Organization (WHO) in August 2014 [1]. While many UK-based companies and their employees faced limited direct effects from the outbreak, it was still widely recognized as a humanitarian crisis threatening international security and global growth [2,3]. In many ways, the Ebola outbreak was just the latest wake-up call for international organizations, businesses and healthcare professionals to recognize the global health impact on work and workers of an increasingly connected world. This awakening follows the increasing trend for businesses to extend their scope into
developing countries where there may be challenges in physical and social infrastructure [4]. Hot on the heels of Severe Acute Respiratory Syndrome (SARS), pandemic flu, and concurrent with the grumbling appendix that is Middle East Respiratory Syndrome (MERS Co-V), Ebola demonstrated how infectious diseases pay scant regard to national or commercial borders. Businesses with international operations in the most affected countries (Sierra Leone, Liberia and Guinea) and those working in specific employment sectors such as transportation, oil and gas, extractive industries and healthcare were particularly affected [3]. During infectious disease outbreaks, occupational physicians may be called upon to swiftly assess risks using limited and
Downloaded from http://occmed.oxfordjournals.org/ by guest on February 16, 2016
heavy-vehicle crashes in 2 Australian states. Am J Epidemiol 2014;179:594–601. 3. Howard ME, Desai AV, Grunstein RR et al. Sleepiness, sleep-disordered breathing, and accident risk factors in commercial vehicle drivers. Am J Respir Crit Care Med 2004;170:1014–1021. 4. Colquhuon CP, Casolin A. Impact of rail medical standards on obstructive sleep apnoea prevalence. Occup Med (Lond) 2016;66:62–68. 5. Young T, Palta M, Dempsey J, Skatrud J, Weber S, Badr S. The occurrence of sleep-disordered breathing among middle-aged adults. N Engl J Med 1993;328:1230–1235. 6. Gurubhagavatula I, Maislin G, Nkwuo JE, Pack AI. Occupational screening for obstructive sleep apnea in commercial drivers. Am J Respir Crit Care Med 2004;170:371–376. 7. Gurubhagavatula I, Nkwuo JE, Maislin G, Pack AI. Estimated cost of crashes in commercial drivers supports screening and treatment of obstructive sleep apnea. Accid Anal Prev 2008;40:104–115. 8. Vakulin A, Catcheside PG, Baulk SD et al. Individual variability and predictors of driving simulator impairment in patients with obstructive sleep apnea. J Clin Sleep Med 2014;10:647–655. 9. Van Dongen HP, Baynard MD, Maislin G, Dinges DF. Systematic interindividual differences in neurobehavioral impairment from sleep loss: evidence of trait-like differential vulnerability. Sleep 2004;27:423–433. 10. Howard ME, Jackson ML, Swann P, Berlowitz DJ, Grunstein RR, Pierce RJ. Deterioration in driving
