Anaes SAQs · Anaesthetic adjuncts

Vasopressin — pharmacology and clinical use

Final SAQ — vasopressin (antidiuretic hormone, ADH) as the endogenous posterior-pituitary PEPTIDE hormone that is fundamentally NOT a catecholamine and acts through a completely separate, non-adrenergic receptor family: V1 (V1a, Gq, vascular smooth muscle vasoconstriction), V2 (Gs, renal collecting duct water reabsorption via aquaporin-2) and V3 (V1b, Gq, anterior pituitary ACTH release, taught stress-axis integration). As a vasopressor it works through V1 INDEPENDENT of adrenergic receptors — effective when adrenergic receptors are downregulated in septic shock and vasoplegia; the catecholamine-sparing, catecholamine-resistant agent (Hiroto 2026). Principal use is SECOND-LINE in septic shock, added to noradrenaline at a FIXED dose of 0.03 to 0.04 units per min (taught formulary; NOT titrated to effect), catecholamine-sparing — reduces noradrenaline requirement (Hiroto 2026); also vasoplegia post-CPB (Torre 2026). Given by IV infusion. Adverse effects: peripheral, digital and MESENTERIC ISCHAEMIA (V1, taught mapping), HYPONATRAEMIA (V2 water retention at high or prolonged doses, taught), decreased CO from increased afterload, reflex bradycardia (no beta-1 counterbalance, taught). Desmopressin (DDAVP) = synthetic V2-SELECTIVE analogue, minimal V1, NO vasoconstriction — central diabetes insipidus, haemophilia/von Willebrand disease (factor VIII and vWF release). Versus noradrenaline (non-adrenergic V1 versus alpha-plus-beta-1 adrenergic, no tachyarrhythmia, effective when adrenergic downregulated, used TOGETHER, fixed-dose versus titrated); versus adrenaline (peptide versus catecholamine, completely different mechanism). delirium-null in older adults (Dong 2026, vasopressin not studied); neonatal septic shock adjunct (Yahya 2026, 4-RCT scope).