One response to management fatigue has been to consider what factors promote crew endurance, with the United States Coast Guard adopting Crew Endurance Management Practices. Crew endurance is defined as ’the ability to maintain performance within safety limits while enduring job-related physical, psychological and environmental challenges’12 (p XV). Crew Endurance Management (CEM) is defined as ’a system for managing the risk factors that can lead to human error and performance degradation in maritime work environments’12 (p XVI). While CEM considers a range of factors including, for instance, temperature extremes, stress, caffeine use, extended separations from family, one of the mainstays of the approach is sleep management. This remains a critical factor affecting the health and performance of crews on merchant ships.
Extensive research on sleep has demonstrated that brain activity during sleep progresses through distinct stages (see 13). In Stage One, in the first 5-10 minutes brain activity slows, but if roused during this stage people often feel they have not slept at all. At Stage Two, after 10-15 minutes sleep deepens further. In Stage Three, also called slow-wave sleep, a person aroused will feel quite sluggish and take several minutes to ‘come to’. However, after 20-30 minutes of slow-wave sleep, the person then returns to a Stage Two sleep pattern, which is subsequently followed by Rapid Eye Movement (REM) sleep. This is thought to be the most regenerative stage of sleep and is characterised by rapid eye movements, little muscle tone, and very active brain activity – this is when you dream. The full cycle repeats itself several times a night, with the crucial REM periods lengthening as the cycle proceeds. The first REM episode may only last for 5-10 minutes. If the cycle is interrupted, it resets from the beginning again. Crew who do not have sufficient sleep periods and/or have their sleep frequently interrupted will develop a ‘sleep debt’ which can have the same effects as being drunk on alcohol in terms of their ability to work machinery, navigate and so on. The only effective ‘treatment’ for a lack of sleep is, more sleep! Individuals keeping sleep logs can be a useful way of monitoring sleep.
A further challenge in the maritime environment is not just the total amount of sleep, or of REM sleep, but also when sleep occurs. The body’s ability to regulate its hormones, alertness and temperature is mediated by circadian rhythms. This ‘ebb and flow’ of body energy and alertness is a natural bodily activity that usually occurs in a predictable manner over a 24 hour period and is synchronised by the amount of light people experience. Circadian desynchronosis results in jet-lag type symptoms when people see light (natural or artificial) at the wrong time of day (when it should be dark, according to their ‘body clock’).
The inevitable consequences of sleep debt and circadian desynchronisation is that cognitive performance deteriorates, the body is put under greater stress, more errors in performance occur, and these may include, for instance, arithmetical errors in navigation, less vigilance when using machinery, being less likely to identify a hazard and slower reaction times. This combination of being more likely to make mistakes, less likely to detect them and less able to correct them, can of course be disastrous in the engine room, on deck or in the Bridge on watch. Sleep debt (getting less than 7-8 hours of continuous sleep a day) can also be associated with reduced energy, apathy, withdrawal and depression. Sleep debt will accumulate and the effects spread further into the day from just after wakening, up to many hours later, and possibly even the whole waking period. While brief planned napping can be helpful on a short term basis, it will not address the fundamental sleep debt problem of a lack of REM sleep. The use of medications, either to delay or to bring on sleep, should be avoided except in the most extreme situations and for short periods of time, as they mask and interfere with the body’s ability to regulate itself and may have negative performance, mood and other health-related effects. They may be particularly problematic if a heavily sedated person is awoken to deal with an emergency situation.