Testing Treating & Tracking Railway Drivers to Enhance Safety (part 4)

by | Jun 6, 2016 | Uncategorized

Making our railways safer

Given the high costs of railway disasters, applying a multimodal approach towards preventing accidents is prudent. A comprehensive approach should include testing for the presence of sleep apnea, evaluation for signs of functional impairment, and worker education to prevent and counteract sleepiness during work.

Railway workers provide an invaluable service, and their own lives as well as the lives of others are often dependent on their ability to drive a train while fully functional, at any time. Several technologies such as Positive Train Control (PTC) Systems have been developed and can provide one mechanism of improving safety. Still, a great deal of accidents are attributed to fatigue. Given the high prevalence of sleep apnea in railway drivers, the need for a comprehensive approach to screening is urgent.

With respect to rail, how would any OSA regulations and the current PTC requirements interrelate?

PTC systems can act as safety measures to improve overall railway safety. These devices can increase train safety through automation, such as technology that slows trains moving too fast around a curved section of rail. Despite this technology, it is of utmost importance to ensure the highest level of human performance because railway workers play an essential role in the safety of trains.

Objective sleep apnea testing for all workers

Which categories of transportation workers with safety sensitive duties should be required to undergo screening for OSA? On what basis did you identify those workers?

All transportation workers with safety sensitive duties should undergo sleep testing. The unique risks posed by railway workers in safety sensitive positions, especially drivers, as well as the great human and financial costs involved in each wreck justify screening every worker. However, unlike traditional assessments which rely strongly on patient self-report of symptoms, screening transportation workers should rely strongly on objective testing such as polysomnography, home sleep testing, maintenance of wakefulness testing and driving simulators.

Research has repeatedly demonstrated an inability for medical examiners to reliably elicit symptoms from transportation workers by traditional history (i.e. questions and answers). Establishing screening programs in these workers, therefore, needs to rely upon objective testing. This would provide for the safest and most prudent approach. It would also be the simplest to implement. Every worker with a need for sustained attention (i.e. drivers) should undergo diagnostic testing for sleep apnea such as home sleep testing or polysomnography. These tests will usually identify the presence of latent sleep apnea, which is undiagnosed in 40% to 80% of individuals who have the disease. In certain circumstances a polysomnogram, which is a more sensitive for the detection of sleep apnea, may be the preferred test.

The American Academy of Sleep Medicine (AASM) guidelines of 20091 are relied upon by the Federal Aviation Administration for their guide for medical examiners to screen for sleep apnea. While the AASM guidelines do consider “driving populations” as high-risk populations, the guidelines were geared towards an evaluation of the general population and therefore were not specifically devised for transportation workers.

Traditional sleep apnea evaluations that rely on subjective symptom reporting are unreliable in evaluating transportation workers. In clinical practice, the most commonly reported symptoms of sleep apnea include snoring and excessive sleepiness. Sleepiness is often self-reported or elicited and quantified through the use of surveys, such as the Epworth Sleepiness Scale (ESS). On average, individuals who are excessively sleepy have an ESS score of 10 or above and those with sleep apnea have an average ESS score of about 13. However, when transportation workers, such as commercial drivers, are surveyed at driver certification exams, they report very low ESS scores, that are, in fact, lower than the general community. Some drivers with OSA evidence “deception,” reporting even lower ESS scores than drivers without OSA .2 Similar observations about sleepiness were made in the cohort of Greek railway drivers (cited above) who had moderate to severe sleep apnea, but reported normal ESS scores. The drivers with the most severe cases of sleep apnea (mean AHI = 68) reported even lower ESS scores than the drivers with moderate apnea.3   Therefore, in lieu of using an ESS and other subjective measurements or self-reports to assess sleepiness due to the limitations mentioned above, the Maintenance of Wakefulness test (MWT) can be used 4 for greater accuracy.

Maintenance of Wakefulness Testing

What alternative forms and degrees of restriction could the  the Federal Motor Carrier Safety Administration (FMCSA) and the Federal Railway Administration (FRA), place on the performance of safety-sensitive duties by transportation workers with moderate-to-severe OSA?

The MWT is the gold standard objective, a valid and reliable measure of excessive daytime sleepiness in clinical practice, which tests the ability of a subject to maintain wakefulness while engaging in a quiet and boring situation (i.e. sitting on a comfortable chair in a semi-dark room).5 The MWT can discriminate between sleepy and alert drivers with OSA. Research has found an association between drivers with OSA who are “sleepy” on MWT and those who perform poorly on driving simulators, suggesting that other factors play a role in poor real time driving performance. 6

The sleepier a driver is, the more likely their performance will suffer. In addition to sleep apnea, risk factors for fatigue among workers include uncertain shift times, long commutes, sub-optimal terminal sleeping conditions, and insufficient sleep before a night shift. Similar to reports from other shift workers, train drivers beginning their shift between 10 PM and 4 AM have reported sleeping insufficiently (fewer than 6 hours a day on average), which leaves them sleep deprived. 7 A relationship also exists between age and sleepiness; older patients with OSA are more likely to exhibit excessive sleepiness on an MWT. 8

While some individuals with OSA or who are sleep restricted are consistently impaired on driving simulators, others routinely function normally on a driving simulator. This suggests that genetic factors may play a role in determining a subset of individuals who are most likely to be impaired by OSA.6 Since the neurobehavioral response to sleep disruption cannot be solely accounted for by the presence of OSA or its severity, other objective testing is needed to establish that individuals are fit to drive trains.

Psychomotor vigilance testing

The Psychomotor Vigilance Test (PVT) is a sustained attention psychometric test that has not yet been established to predict poor driving performance. The PVT measures the reaction time of a subject’s response to visual stimuli. In sleep research it has been used to identify drowsiness secondary to disturbed or insufficient sleep.  The advantage of this test is that it can generally be performed in less than 10 minutes and provide immediate feedback regarding attention levels. However, we could not find any data during our review of related literature establishing that poor performance on the PVT can be used to predict impaired driving.  Further research is required to identify whether PVT or another short duration psychometric test might be utilized to identify drivers who are more likely to be impaired as a result of sleep deprivation or OSA.

Driving Simulators

Railway driving simulators or railway driving data analysis may offer the best possible tool to identify drivers who are impaired by OSA or other causes. While MWT indirectly gauges risk though identifying an individual’s ability to stay awake, driving simulation pinpoints performance that is impaired even when a driver is “awake.” Research looking at MWT to evaluate its ability to assess driver impairment has frequently compared MWT results to driving simulator performance.6, 9-13 Most of these studies have looked at the driving of an automobile, measuring steering deviation, lane deviation and crashes. In some studies, simulators have been set up to mimic nighttime driving.6 Simulators for railway driving track features such as speed approach of the crossing, head movements, and stopping compliance.14 Furthermore, some of the research that establishes that MWT could be used to assess driving ability in untreated patients with OSA analyzes actual driving session data.13 The best tool to identify drivers who are fit-for-duty or to flag drivers who have an underlying sleep disorder may be to utilize current railway simulators to mimic nighttime driving situations, which is when most railway accidents take place, or review driver data to track safety and performance metrics.

Fit for Duty

An important part of fatigue management is ensuring that all operators are ready to perform and fit for duty. Treating OSA may relieve the root cause of sleepiness in a driver. However, the only way to ensure that a driver is able to perform is to test their ability to stay awake and perform. Therefore, restrictions should focus on ensuring that those with OSA are treated and, perhaps equally important, that they are able to perform without the adverse effects of sleepiness.

All individuals who are diagnosed with mild, moderate or severe OSA and treated with Continuous Positive Airway Pressure (CPAP) should demonstrate that they are adherent to treatment. This is accomplished by CPAP devices that track compliance data as well as the efficacy of treatment. Individuals who undergo treatment with an oral appliance must undergo a sleep study to demonstrate that their device is effective to relieve the apnea. If effective, it is also important to ensure compliance. Recently developed technology allows compliance data to be tracked in oral appliances.

All individuals diagnosed with OSA, even those who deny any sleepiness and those who are treated successfully with CPAP or an oral appliance, should routinely demonstrate through an approved driving simulation or MWT that they are fit to drive in situations that require sustained attention.

How effective would these restrictions be in improving transportation safety?

Data from driving simulators and crash data have demonstrated that driving capabilities return in patients with OSA that are treated with CPAP. In motor vehicles, baseline performance has been shown to return within a matter of days. 15,16 It is advised that a screening program in railway drivers should also collect and continue to monitor safety data for continuous evaluation, quality control and program improvement.

The difference between mild, moderate and severe sleep apnea

Should any regulations differentiate requirements for patients with moderate, as opposed to severe, OSA?

Excessive sleepiness can be observed at any level of sleep apnea and is not limited to moderate-to-severe OSA. The most commonly utilized parameter to categorize the severity of sleep apnea is the apnea-hypopnea-index or the AHI. An AHI of < 5 is normal, 5-14 is considered to be mild sleep apnea, 15-29 is considered moderate, and 30 or more is considered to be severe OSA.  In fact, excessive sleepiness may even be present in patients with disordered breathing who might not be diagnosed with “mild” sleep apnea using the AHI, but would be diagnosed utilizing the respiratory disturbance index (RDI) that includes respiratory effort related arousals in the detection of abnormal events. While an AHI of 20 or greater has been shown as an independent risk factor for excessive sleepiness in some studies, 17 numerous studies have shown excessive sleepiness in patients with mild forms of OSA. For example, in the study of rail workers from Brazil mentioned above, 54.4% of those with OSA had a mild form that was associated with excessive sleepiness. Therefore, limiting regulations to those with moderate or severe OSA could leave a substantial portion of patients who have excessive sleepiness undetected even though their AHI might only qualify them as having “mild” sleep apnea (AHI <15). Furthermore, the use of HST, which is advocated for herein, reduces the accuracy of discriminating between mild and moderate sleep apnea or between moderate to severe apnea, as it tends to underestimate the total severity of sleep apnea.

References:

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