Our photo-periodic health or circadian rhythms are entrained by the paired suprachiasmatic nuclei (SCN) of the anterior hypothalamus which regulate a host of diverse physiologic processes from sleep, behavioural activity and appetite, through to hormone and steroid production and function, hepatic activity and renal excretion. Interference of these rhythms are associated with many pathological conditions; simple disturbances of sleep or in sleep quality results in excessive daytime sleepiness is referred to as “chrono-fatigue” or “Shift Maladaptation Syndrome,” however, increasingly more significant conditions such as cancer, metabolic syndrome, cardiovascular disease, diabetes, depression, arthritis and asthma have been recognised. The effect of shift or night work has been demonstrated for example, to effect gene expression at the level of the SCN and influences release of various hormones, protein products and cytokines. To take mental illness as an example; chronic stress as experienced by emergency or regular night work has been shown to reduce Brain Derived Neurotrophic Factor (BDNF), which provides feedback from the periphery to the SCN, and a link between chronic stress and BDNF levels with anxiety and depression in people has been demonstrated . Whilst the incidence of cancer among veterinary surgeons in general is unknown, the incidence of depression and mental disorders is above national averages.
Furthermore and importantly, to improve the clinical prognosis of any patient, the ability of the clinician, especially those where work is out-with normal hours, and almost by definition of a stressful nature, to maintain objective and rational cognitive decisions is vital in allowing correct diagnosis, implementation of appropriate therapy and avoidance of medical error. Unsurprisingly, cognitive function is most efficient when well rested. Whilst fatigue can occur independently of sleep deprivation, for example during high stress periods; it often arises due to the nature of equine veterinary work and can lead to error. Diagnostic error can be categorized into 3 major groupings: no-fault, systemic and cognitive. No fault errors occur when disease is silent or atypical, systemic errors are attributed to system failures but it is in the human-factors and individual characteristics influencing cognitive and affective behaviour and decision making that is most influenced by day/night influence or chronobiology. Under conditions of stress, including fatigue, the manner in which a clinician differentiates and implements diagnostic or therapeutic protocols depends and is determined by a variety of factors and it is the summation of these factors which leads, hopefully, to one or a limited number of cognitive dispositions to respond (CDRs) and a diagnostic and therapeutic protocol (Figure 1).
Figure 1: CDR determining factors and actions. From et al (2005). Advances in Patient Safety: From Research to Implementation
As highlighted there are a number of determinants of CDRs but they largely fall into 3 groupings: ambient conditions, past experience and impact of affective state, and arguably all three can be influenced by chronobiology. For example; temperature, activity level, motivation and other variables that may affect clinical performance are influenced by diurnal phase in many individuals. Premenopausal women may be subject to mood variations, circannual influences such as winter darkness can exert a negative influence on affective state, and the circadian -synchronicity that results from shift work, common in equine veterinary medicine, can predispose to depressive-like symptoms. These various influences are collectively referred to as affective dispositions to respond (ADRs) and compromise cognitive control and therefore the efficacy of clinical decision making (Table 1):
Table 1: Potential Chronobiological Influences on Affective Dispositions to Respond
1. Specific affective biases in decision making
2. Endogenous affective disorders within the clinician
• Depressive disorders
• Anxiety disorders
• Manic disorders
3. Emotional dysregulation in clinicians
• Unconscious defences, avoidance, anxiety
• Emotional involvement or detachment
Adapted from Henriksen et al (2005). Advances in Patient Safety: From Research to Implementation.
Long hours of work, sleep deprivation, stress and accumulated sleep debt are common in the equine veterinary workplace. Generally, the longer people stay awake, the sleepier they become and their cognitive and psychomotor performance is impaired reaching its nadir between 3-4 am when cognitive performance is the equivalent of being intoxicated. This brings in to sharp focus veterinary actions to perform intricate surgery, or make life-influencing decisions, during those hours or, perhaps suggesting that postponement to daylight hours is preferential.
There has long been an association between sleep deprivation and medical error, and was found to have the greatest impact on diagnostic error with interns making substantially more serious errors when they worked frequent shifts of 24 hours or more than when working shorter shifts. This was supported in later studies which also identified additional effects including a higher predisposition to road traffic accidents, a highly relevant finding for the ambulatory vet.
Interestingly people are recognized as demonstrating different chronotypes, with their sleep-wake cycle to the light-dark cycle differing between individuals. This is generally expressed as “larks” for early chronotypes and as “owls” for late ones and can be quantified perhaps suggesting the possibility of selecting people more suited to certain shifted roles.
Whilst a number of chemical aids have been used to alleviate fatigue and psychophysiological performance their effects were limited and more work needs to be directed at management with preventative strategies and protocols implemented to reduce the potential for diagnostic error addressing both CDRs and ADRs. These may include heightened metacognition, simulation training and development of cognitive forcing strategies but could just as well be asking for a few more hours in bed.