Stress Response to Surgery
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Direct answer
Surgery is a controlled injury, and the body mounts the same neuroendocrine and inflammatory response it would to trauma, scaled to the insult. Afferent nociceptive signals and cytokines activate the pituitary-adrenal axis: cortisol, ACTH, growth hormone and prolactin rise, vasopressin and aldosterone retain sodium and water while potassium is lost, and catecholamines surge. Counter-regulatory hormones dominate insulin — the "diabetes of injury" — alongside glycogenolysis, gluconeogenesis, lipolysis and negative nitrogen balance peaking around day three. Cuthbertson's classical description divides this into an ebb phase (hours of hypometabolic shock physiology) and a flow phase (days of catabolism followed by anabolic recovery); the entire modern ERAS apparatus — regional analgesia, minimal access surgery, early feeding — exists to blunt precisely this response.
What you must remember
- Ebb and flow (Cuthbertson, 1932): ebb phase — first hours, low cardiac output, hypothermia, hypometabolism; flow phase — catabolic days 1-3 with raised metabolic rate, then anabolic recovery over weeks as nitrogen balance turns positive.
- Four counter-regulatory hormones: cortisol, glucagon, growth hormone and catecholamines — they oppose insulin, and together with inflammatory cytokines produce postoperative insulin resistance and hyperglycaemia.
- Endocrine signature: ACTH and cortisol up; ADH and aldosterone up (sodium and water retention, oliguria, potassium loss); growth hormone and prolactin up; insulin first suppressed, then resisted; TSH changes minor.
- Inflammatory arm: interleukin-1 and interleukin-6 (IL-6 peaks within hours and tracks the magnitude of insult — laparoscopic operations generate far less than open), tumour necrosis factor-alpha driving the acute-phase response — CRP peaks around 48 hours, fibrinogen rises, albumin falls.
- Metabolic sequence: liver glycogen exhausts within a day, gluconeogenesis from alanine, glutamine, lactate (Cori cycle) and glycerol takes over, fat becomes the major fuel, and muscle breakdown yields 10-15 g of urinary nitrogen daily at peak.
- Magnitude is proportional to injury: burns and open laparotomy at the top, laparoscopic and peripheral procedures at the bottom — the physiological justification for minimal access surgery.
- Modulators with exam weight: thoracic epidural blunts the afferent catecholamine and cortisol surge (Kehlet's work underlies ERAS), preoperative carbohydrate drinks reduce insulin resistance, and early enteral feeding shortens catabolism.
Tracing the response hour by hour
Follow a patient through open right hemicolectomy. In the first hours, the ebb picture: vasoconstriction, cold peripheries, oliguria driven by ADH and aldosterone, a stress leucocytosis and a modest temperature — the ward mistake is chasing this early fever with antibiotics when it is cytokine-mediated. By day one, flow begins: glucose drifts up despite fasting, sodium and water retention add two or three kilograms of fluid weight, and potassium still needs supplementing because intracellular losses continue despite rising serum values. CRP peaks at 48 hours — a CRP now climbing on day five is a signal, not a residue. Nitrogen losses peak around day three to seven; with early enteral nutrition and epidural analgesia the patient reaches positive balance within the week, while a complication such as an anastomotic leak re-ignites the cascade at greater amplitude — deteriorating glucose control on day six is a soft sign of leak. Every ERAS element — preoperative carbohydrate loading, regional blocks, early feeding — is a targeted strike on one limb of this physiology.
Perspective: how the exam frames it
The viva tests reasoning: why is the postoperative patient hyponatraemic (dilutional, from ADH — do not chase it with saline reflexively), why does a diabetic's insulin requirement rise (insulin resistance of injury), and why does epidural analgesia reduce catabolism (afferent blockade of the neural limb). The classic confusion is between stress-induced hyperglycaemia and unmasked diabetes — the safe answer is that transient peri-operative hyperglycaemia in a non-diabetic reflects counter-regulatory dominance and needs monitoring, not a lifelong label. A favourite Indian viva tail: why does prolonged "starvation till flatus" after abdominal surgery worsen outcomes — prolonged catabolism, glutamine depletion and delayed recovery, the physiology ERAS reverses.
Frequently asked questions
What are the ebb and flow phases of the stress response?
The ebb phase is the initial hours of hypometabolism, vasoconstriction and low cardiac output; the flow phase is the subsequent catabolic surge — raised metabolism, negative nitrogen balance — followed by anabolic recovery.
Which hormones mediate the metabolic response to surgery?
Cortisol, catecholamines, glucagon and growth hormone oppose insulin, while ADH and aldosterone retain salt and water — together they generate hyperglycaemia, oliguria and potassium loss.
Why does hyperglycaemia occur after surgery even in non-diabetics?
Counter-regulatory hormones plus cytokine-mediated insulin resistance produce the "diabetes of injury"; transient peri-operative hyperglycaemia does not by itself diagnose diabetes mellitus.
What role does interleukin-6 play postoperatively?
IL-6 rises within hours in proportion to tissue injury, drives the acute-phase response (CRP peaking near 48 hours), and is markedly lower after laparoscopic than open surgery.
How does ERAS blunt the stress response?
Regional analgesia blocks afferent nociceptive signalling, preoperative carbohydrates and early feeding limit insulin resistance and catabolism, minimal access surgery reduces the injury burden, and normothermia and early mobilisation complete the attenuation.