Storyboard

Surgery is an intervention that physically reorganizes the body's structures: it removes, repairs or reconstructs tissues and organs. It causes an immediate systemic stress response (activation of the HPA axis, release of catecholamines, acute phase response) that is physiologically adaptive but may become excessive in major surgeries or in comorbid patients.

The endocrine response to surgical stress follows first-order kinetics: plasma cortisol rises up to 2001000 nmol/L during incision and general anesthesia (vs. 300700 nmol/L in severe hypoglycemia or sepsis), and declines with t½ 1.5 h. Cortisol mobilizes glucose (perioperative hyperglycemia), suppresses immunity, and increases protein catabolism. Regional anesthesia (epidural, intradural) partially blocks this response.

Wound healing follows a sequential process (hemostasis inflammation proliferation remodeling) that can be modeled as first-order kinetics: wound tension grows exponentially towards T_max ( 80% of the original tissue at 6 weeks). Barrier function is restored within 2448 h (epithelialization); sufficient mechanical strength to remove stitches requires 710 days; final strength is achieved in 36 months.

Intraoperative fluid balance is essential: hyper- and hypohydration have serious consequences. The third space (redistribution of fluid to the interstice of the surgical field, paralyzed intestine and traumatized areas) can subtract 0.51 L/h in major abdominal surgeries. Goal-directed fluid therapy (GDFT) uses dynamic parameters (PPV, SVV measured with arterial catheter) to guide replacement.

The Minimum Alveolar Concentration (MAC) of the inhaled anesthetic determines the anesthetic depth: MAC 1.0 inhibits movement in 50% of patients in response to the incision. Surgical risk is estimated with the ASA classification (I: healthy VI: brain dead organ donor) and with risk calculators such as NSQIP or EuroSCORE, which use multivariate logistic regression. An ASA III-IV with emergency surgery implies perioperative mortality of 515%.

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