Disease (νοσοσ) is not only suffering (παθοσ): it is also toil (πονοσ). Hippocrates Introduction Reacting when facing a threat to homeostasis is a common and primeval pattern of behavior in living beings, that involves a number of complex endocrine and metabolic functions. The reaction to surgical stress is an example of this primordial behaviour. Stress response is also the pathway along which both aging and illnesses occur. Surgery for which older patients are scheduled can be more or less invasive and more or less demanding in terms of energy expenditure, thus causing stressing effects that go beyond that of the underlying surgical condition. On the other hand, aging processes, the way in which functional reserves are affected by aging, and the number and severity of associated conditions substantially modulate the effectiveness of the individual response to surgical aggression. When intense and prolonged external stressors superimpose on a state of vulnerability induced by aging processes and comorbidity, severe post-operative complications may originate, such as myocardial ischemia, post-operative delirium, respiratory insufficiency, deep metabolic alterations, intense deconditioning and consequent functional impairment. As a consequence of both the stress intensity and duration and the effectiveness of defensive reaction, different trajectories are possible. Stress response: stages and determinants The concept of stress as general adaptation syndrome (GAS) was defined by Seyle in the last century (Seyle 1936). Since its definition, the conceptual model of stress as GAS has provided a paradigm for interpreting and understanding this complex defensive reaction under multiple aspects. Essentially, in an attempt to counteract aggression, the organism starts providing extraordinary performance, continues opposing strong resistance and, when the aggression persists for too long, ends up self-harming. Stages of stress Independently from the nature of the stressor applied, Seyle individuated a typical sequence in biological answers to stress: alarm, resistance and exhaustion. Important endocrine mechanisms are involved. Alarm During the “alarm” stage, the stressor is recognized as a threat. Stress hormones are produced in response, such as adrenaline, noradrenaline and cortisol. This enables the body to perform extraordinary activities, but at the cost of heavy energy consumption and consequent tissue damage.
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