Surgery, in general , is a disruption to the body and triggers a series of events that are very broadly referred to as the stress response. It is a normal reaction of great importance in both nature and medicine. The natural stress response in man is designed to first protect against threats and is highlighted by the surge of hormones needed to either “fight or run”. This initial response is then followed by a response designed to promote survival , including activation of the immune system to promote wound healing and protect against infection. The surgical stress response has three key components: stimulation of the sympathetic nervous system, activation of endocrine system, and triggering of the immune system. The sympathetic nervous system can be equated to car’s gas pedal. [2] It provides the body with a burst of energy so that it can respond to danger or injury, primarily by releasing the hormone adrenaline into the bloodstream. As adrenaline circulates through the body, the heart beats faster allowing more blood to be delivered to muscles and vital organs. Other changes include dilation of the airways in the lungs so that more oxygen is taken in with every breath and release of glucose (sugar) and fats from storage sites in order to provide needed energy. Activation of the endocrine system is primarily manifested as hormonal changes including increases in growth hormone, arginine vasopressin, cortisol , and aldosterone and decreases in insulin and thyroxine. The net effect of these hormonal changes can include a slowdown of gut motility; water and salt retention; increased energy expenditure; high glucose levels due to release from storage sites, new production from amino acids broken down from muscle protein, and insulin resistance; increased use of fats as an energy source; and increased tendency toward blood clotting. [3]
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