Abstract

Occupational sleep medicine is a new field within the specialty of sleep medicine. It is developing from multiple basic and clinical strands yielding applications in both operational (normative, workplace) and clinical environments. In its most basic form, occupational sleep medicine studies work as it affects sleep and sleep-related physiology both in terms of direct effects on performance and in terms of direct and indirect (through impaired safety) effects on health. Good performance translates into safety and productivity. All the chapters in this occupational sleep medicine section discuss the sleep and circadian rhythm effects variously on performance, productivity, safety (and, thus, indirectly on health), and well-being in the operational (workplace) context. Several of the chapters touch on the direct effects of sleep on health (see Chapters 71, Chapter 72, and Chapter 74). Three chapters outside of this section have a primary focus on the direct effects of sleep on health (see Chapters 25 to Chapter 27). Occupational sleep medicine will likely contribute to and be in part enabled by the development and implementation of individual, continuous, unobtrusive biomedical status monitoring, including in all probability monitoring of sleep–wake history, for use as input to biomathematical modeling predicting performance. We envision occupational sleep medicine being integrated into enterprise-wide systems of fatigue risk management (see Chapters 66 and 70). In the modern corporate environment, fatigue risk management is typically folded into safety management. Occupational sleep medicine will develop as a subset of sleep medicine with ties to occupational medicine and industrial and organizational psychology.

Occupational sleep medicine is concerned with performance, productivity, safety, health, and well-being in the workplace or operational environment as affected by sleep restriction, circadian rhythm phase, and workload. The operational environment is defined as a work setting in which human performance plays a critical role and there is a high risk that if human performance degrades the system will fail. In the operational environment, the human in the operational loop has limited time to decide and act upon a course of action.¹ Operational environments include military operations, maritime (including intracoastal and riverine) operations, medicine, the various modes of land transportation, aviation, security work, energy generation, resource extraction (mining, drilling), financial markets, and industrial production. In these settings, operational demands (shift timing and duration; work intensity, difficulty, and complexity) degrade performance directly through the effects of workload and circadian timing and indirectly by reducing the amount of time available for sleep, and thus total sleep time, a primary determinant of alertness and performance.¹

Fatigue as a Function of Sleep–Wake History, Circadian Rhythm, and Work Load

In the workplace, termed here the operational environment, we speak of fatigue defined subjectively by self-report and objectively as degraded performance. Fatigue, so defined, is the end result of a common pathway integrating multiple factors. These factors include time awake (sleep–wake history), time of day (circadian rhythm), and workload (time on task, task intensity, and task complexity) (see Chapter 65). Also relevant to the generation of fatigue in the workplace are the clinical causes of excessive work-shift sleepiness (see Chapters 4 to Chapter 6, Chapter 57, and Chapter 75). Effective implementation of fatigue risk management in the operational environment will require a systematic understanding of the interaction of the multiple factors causing fatigue, perhaps by means of integrating these factors into biomathematical models predicting performance. In evaluating fatigue and excessive work-shift sleepiness in the workplace, the occupational sleep medicine physician should screen for and treat the clinical causes of sleepiness and fatigue, including obstructive sleep apnea, other sleep disorders, and insomnia (see Sections 10 and 13) in addition to providing a broader occupational consultation.

Managing Sleep and Circadian Rhythm–Related Fatigue Risk

Fatigue-related performance decrements include lapses in attention, slowed reaction time, and impaired anticipation, planning, and judgment (see Chapter 66). Fatigue degrades the ability to observe, orient, decide, and act (OODA). The concept of the OODA loop was developed as a tool for analyzing relative advantage in air-to-air combat and has been extended to operational performance in general.^2,3 Biomathematical models integrating circadian variations in alertness and its mirror, sleep propensity, with homeostatic sleep–wake regulation and sleep inertia—in effect encapsulating what is currently known in the science of sleep, circadian rhythms, and fatigue—have been effective in predicting operational performance, which is useful in comparing one potential schedule to another and could be integrated into software systems for rostering and scheduling to manage fatigue and its operational consequences in the workplace.

Fatigue as a function of extended work hours and shift work is ubiquitous, and fatigue-related degradation in cognitive performance is common. Yet errors and incidents are uncommon and accidents are, fortunately, rare. How are we to understand this? A reasonable hypothesis is that the outcome of human performance is stochastic, depending upon both variability in internal state and variability in environmental demands. Thus, only when the internal stochastic process of lapsed attention or slowed response coincides with a period of high cognitive demand will an error occur, and only if this error is system critical will an incident or accident occur (see Chapter 67). This concept of the intersection of lapsing of attention or slowing of response time (or both) with a critical event is important operationally and clinically and suggests that past avoidance of accidents in the fatigued state does not guarantee future safety.

Fatigue risk management is emerging as the applied, normative arm of occupational sleep medicine. Fatigue in the workplace has been traditionally—and is still to this day—managed with one-size-fits-all prescriptive hours-of-service rules that specify shift duration, between-shift intervals, and within-shift breaks. These hours-of-service rules are typically blind to the human circadian rhythm in sleep propensity and performance and the increasing homeostatic drive for sleep from extended waking, and they are thus likely to be overly restrictive at some times and unsafe at other times. Hours of service represent a single and brittle line of defense against fatigue-related error, incident, and accident. Fatigue risk management is based on the scientific understanding of the dynamics of sleep loss and recovery and provides an alternative to the prescriptive hours-of-service approach (see Chapter 68).

Fatigue risk management is a layered defense in depth against error, incident, and accident. In its basic form, fatigue risk management ensures an adequate sleep opportunity in terms of duration and placement with respect to the circadian rhythm; ensures that personnel are making good use of the sleep opportunity; and evaluates, given the sleep opportunity and the use made of it, how well personnel are performing in the workplace. Unlike hours-of-service regulations, fatigue risk management is evidence based and entails iterative evaluation and improvement. As our understanding of the dynamics of sleep and performance becomes deeper and more comprehensive, including, for example, the effects of workload and individual differences in response to fatigue-related factors, our ability to implement fatigue risk management will correspondingly improve.