Any stress, including that from a precise procedure, causes a dramatic release of adrenocorticotropic hormone (ACTH) from the anterior pituitary that, in turn, directs the release of cortisol from the adrenal cortex. The circulating cortisol level remains elevated to two to five times the normal level for approximately 24 hours after the procedure52 and acts upon skeletal tissue to bring about breakdown of skeletal muscle tissue proteins into amino acids for localized wound healing and for glucose production by the liver.
Concomitantly, epinephrine and norepinephrine are released and remain elevated for 48 hours, stimulating breakdown of liver glycogen with release of glucose for cellular energy needs through the immediate postoperative period.53 The upsurge in epinephrine suppresses release of insulin,54 glucagon concentrations rise,55 and the liver is stimulated to start gluconeogenesis to go back to preoperative levels and to aid the power requirements of the healing process. Additional reactions to surgery include alterations in water regulation mediated by release of antidiuretic hormone and aldosterone, which increases water reabsorption in the renal collecting ducts and increases sodium retention in the renal tubules, respectively.56,57 It is thought that the release of the hormones is stimulated by signals from blood pressure– and osmolarity-sensitive receptors.53 This diminished capability to excrete water in the early postoperative period results in temporary weight gain and a come back to normal blood volume.58 After the above mentioned events, the patient enters a metabolic transition period of 1 or 2 days in which the human body begins to turn from corticosteroid- and epinephrine-initiated breakdown to rebuilding and healing. During this time period, shedding of the retained water is effected, while conserving nitrogen and potassium. The slow procedure for healing and regaining weight may now begin and is marked by protein synthesis, wound healing, buildup of muscle tissue, and increasing strength.53 Many of these processes occur with a fair degree of predictability in the adequately nourished adult patient. The procedure is imperiled, as could be the prognosis for full recovery, if the adult is elderly or malnourished.