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5 SBAs on endocrine, metabolism and temperature
Viva
5 viva questions
Why is the shock of adrenal failure resistant to noradrenaline?
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Cortisol is permissive for the vascular response to catecholamines: it maintains adrenoceptor expression and the downstream signalling that produces vasoconstriction. Without it the vessel does not respond however much agonist is given, so the correct treatment is hydrocortisone rather than more noradrenaline.
A patient is deeply hyponatraemic with a normal potassium and no hyperpigmentation. Can this still be adrenal insufficiency?
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Yes — secondary or tertiary. Aldosterone is preserved because it is driven by renin–angiotensin rather than ACTH, so the potassium is normal; ACTH is low, so there is no hyperpigmentation. The hyponatraemia arises because cortisol normally restrains ADH release, and without that restraint water is retained.
Where in the axis does long-term prednisolone act?
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At both feedback sites: it suppresses CRH release from the hypothalamus and ACTH release from the anterior pituitary. Loss of ACTH drive causes adrenocortical atrophy, so recovery on withdrawal is slow — the pituitary recovers before the adrenal, and full recovery can take months. That is why steroids are tapered rather than stopped.
Why does neuraxial blockade attenuate the stress response to a hip replacement but not to an oesophagectomy?
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It blocks the neural afferent limb, and for surgery below the umbilicus that limb carries most of the signal. Upper abdominal and thoracic surgery generates a much larger cytokine limb — IL-6 and TNF-α reaching the hypothalamus by the bloodstream — which no regional block can interrupt. The block also rarely covers the full dermatomal range of the injury.
What single induction agent will suppress this axis, and by what mechanism?
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Etomidate, by inhibiting 11β-hydroxylase in the adrenal cortex, reducing both cortisol and aldosterone synthesis for up to 8 hours after a single dose. Continuous infusion for sedation increased mortality and was abandoned; a single induction dose has not been shown to.