血管加壓素 / 抗利尿激素
**血管加壓素 (Vasopressin)**，又稱抗利尿激素 (ADH)，是一種在下視丘合成並儲存於腦下垂體後葉的內源性胜肽荷爾蒙。在獸醫學中，它具有幾個關鍵作用： * **診斷試劑**：主要用於限水試驗中，以區分中樞性與腎性尿崩症。 * **急診與重症照護**：越來越多被用作血管擴張性休克及心肺腦復甦術 (CPCR) 的輔助治療。 > **臨床要點**：在嚴重休克或心搏驟停（心室性心搏停止/無脈性電氣活動）的情況下，血管加壓素比腎上腺素具有明顯優勢。即使在酸中毒環境中，它也能引起強烈的血管收縮，並能保留冠狀動脈和腎臟的血管系統（改善心肌灌注），且不具有與兒茶酚胺相關的致心律不整和變時性副作用。 過去曾用於治療中樞性尿崩症，但由於長效油性製劑已停產，目前長期管理已大多被合成類似物 **去氨加壓素 (Desmopressin, DDAVP)** 所取代。
作用機制: Vasopressin exerts its effects via multiple receptor subtypes: * **V1 Receptors (Vascular Smooth Muscle)**: Mediates profound vasoconstriction. At high doses, it causes contraction of capillaries and small arterioles, increasing systemic vascular resistance and blood pressure. It also stimulates smooth muscle in the bladder, gallbladder, and GI tract. * **V2 Receptors (Renal Collecting Ducts)**: Mediates antidiuretic effects. Vasopressin binds to V2 receptors → activates adenylate cyclase → increases **cAMP** → promotes the insertion of **aquaporin-2 channels** into the luminal membrane → increases water permeability and reabsorption of solute-free water → concentrates urine and decreases urine flow. * **V3 Receptors (Pituitary)**: Stimulates the release of corticotropin (ACTH). * **Oxytocin & Purinergic (P2) Receptors**: Minimal oxytocic effects at standard doses, but massive doses can stimulate uterine contraction.
各物種劑量
- Diagnostic agent (after water deprivation test) · 0.5 U/kg IM · IM · Once · Empty bladder and determine specific gravity at 30, 60, and 120 minutes after administration.
- Adjunctive treatment of vasodilatory shock (unresponsive to fluids/catecholamines) · 0.01-0.04 Units/minute IV · IV · CRI
- CPCR (pulseless electrical activity or ventricular asystole) · 0.2-0.8 Units/kg, IV once · IV · Once · May be beneficial for myocardial and cerebral blood flow.
- Diagnostic agent (Exogenous vasopressin test after water deprivation test) · 2.5 mU/kg IV over one hour · IV · Once · 1 hour · Give aqueous vasopressin in D5W. Empty bladder and collect urine at 30, 60, and 90 minutes.
- Adjunctive treatment of vasodilatory shock (unresponsive to fluids/catecholamines) · 0.01-0.04 Units/minute IV · IV · CRI · Dose is not dependent upon patient weight. DO NOT exceed 0.04 Units/minute (risk of myocardial ischemia). DO NOT use in cardiogenic shock.
- CPCR (pulseless electrical activity or ventricular asystole) · 0.2-0.8 Units/kg, IV once · IV · Once · May be beneficial for myocardial and cerebral blood flow.
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給藥途徑
禁忌症
- Known hypersensitivity to vasopressin
- Chronic nephritis until nitrogen retention is resolved to reasonable levels
- Cardiogenic shock (due to risk of myocardial ischemia)
不良反應
- Local irritation at the injection site
- Sterile abscesses
- Skin reactions
- Platelet aggregation
- Bilirubinemia
- Abdominal pain
- Hematuria
- Hypersensitivity (urticarial) reactions
- Water intoxication (with overdosage)
藥物相互作用
- Alcohol · May inhibit the antidiuretic activity of vasopressin
- Demeclocycline · May inhibit the antidiuretic activity of vasopressin
- Epinephrine (large doses) · May inhibit the antidiuretic activity of vasopressin
- Heparin · May inhibit the antidiuretic activity of vasopressin
- Norepinephrine (large doses) · May inhibit the antidiuretic activity of vasopressin
- Antidepressants, Tricyclic · May potentiate the antidiuretic effects of vasopressin
- Carbamazepine · May potentiate the antidiuretic effects of vasopressin
- Chlorpropamide · May potentiate the antidiuretic effects of vasopressin
- Clofibrate · May potentiate the antidiuretic effects of vasopressin
- Fludrocortisone · May potentiate the antidiuretic effects of vasopressin
- Phenformin · May potentiate the antidiuretic effects of vasopressin
- Urea · May potentiate the antidiuretic effects of vasopressin
監測
- Urine output and frequency
- Water consumption
- Urine specific gravity
- Urine osmolality
- Blood pressure and ECG (when used for shock/CPCR)
過量
### Water Intoxication Overdosage of vasopressin leads to excessive water retention and subsequent **water intoxication** (dilutional hyponatremia). * **Early Signs**: Listlessness, depression, and lethargy. * **Severe Signs**: Coma, seizures, and eventually death due to cerebral edema. **Treatment**: * *Mild Intoxication*: Discontinue vasopressin therapy and strictly restrict water access until clinical signs resolve. * *Severe Intoxication*: May require the administration of osmotic diuretics (e.g., mannitol, urea, or dextrose) with or without a loop diuretic like furosemide to rapidly excrete excess free water.
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