Mayday, Mayday, Mayday: Using salivary cortisol to detect distress (and eustress!) in critical incident training

The understanding of stress and its impact on human performance is crucial to mitigate human error in the face of a threat. This is especially the case for critical incidents on a ship bridge, where human error can easily lead to severe danger for crew, cargo, and other vessels. To overcome the current limitations of robust objective stress measures that reliably detect (di-)stress under highly noisy conditions, we set out to explore whether salivary cortisol – the stress biomarker in medicine and psychology – is a valuable complementary assessment tool in a high-stress/emergency context. In a controlled within-subjects experiment (N = 12) using a ship bridge simulator, we measured stress levels under three conditions (80 min each): baseline, low stress (open water navigation task in autopilot), and high stress (open water emergency scenario). We sampled salivary cortisol at 10 min intervals in conjunction with heart rate (variability) monitoring, and subjective stress assessments from both participants and expert evaluators. Results validate salivary cortisol as a successful tool for detecting distress. Unlike the other stress measures, salivary cortisol strongly correlated with expert stress assessments (r = 0.856) and overt stress behavior like instances of freezing and missing response cues. Surprisingly, data further revealed decreased salivary cortisol across periods of self-assessed improved performance (i.e., eustress). In fact, data suggests an inverted u-relationship between performance and salivary cortisol. The findings have direct implications for the vast field of emergency training, and serve as a first important validation and benchmark to proceed with real life applications.