腎上腺素
**腎上腺素**（Adrenaline）是由腎上腺髓質產生的強效內源性兒茶酚胺。它是交感神經系統主要的「戰鬥或逃跑」荷爾蒙。 在獸醫學中，它是一種關鍵的救命急救藥物，主要用於： * **心肺腦復甦術 (CPCR)：** 在心搏停止（心室靜止）時恢復自主循環。 * **嚴重過敏性休克：** 透過誘發支氣管擴張和血管收縮，迅速逆轉危及生命的過敏反應。 * **局部麻醉輔助劑：** 添加於局部麻醉劑（如利多卡因）中以引起局部血管收縮，從而延緩全身吸收、延長麻醉效果並減少注射部位出血。 > **臨床要點：** 腎上腺素效力極強且治療指數非常狹窄。必須極度小心確保使用正確的濃度。**切勿將 1:1,000 (1 mg/mL) 濃度與 1:10,000 (0.1 mg/mL) 濃度混淆。**
作用機制: Epinephrine is a direct-acting, non-selective adrenergic agonist that stimulates both alpha (α) and beta (β) receptors via G-protein coupled pathways (activating **adenylyl cyclase** → ↑ **cAMP**). * **α1-receptors:** → Induces profound smooth muscle contraction and vasoconstriction, increasing systemic vascular resistance and blood pressure. * **β1-receptors:** → Directly stimulates the heart, increasing both chronotropy (heart rate) and inotropy (contractility), which increases cardiac output and myocardial oxygen demand. * **β2-receptors:** → Relaxes smooth muscle, leading to profound bronchodilation (relieving bronchospasm in anaphylaxis), vasodilation in skeletal muscle, and increased glycogenolysis (raising blood sugar). * **Histamine Antagonism:** Physiologically antagonizes the effects of histamine released during anaphylaxis. *Hemodynamic effects depend on the route and rate of administration:* Rapid IV injection causes direct cardiac stimulation and increased systolic BP. Slow IV infusion produces a modest rise in systolic pressure, a decrease in diastolic pressure, and decreased total peripheral resistance due to dominant β2 effects.
各物種劑量
- Anaphylaxis · 0.5-1 mL/100 lbs. body weight of 1:1,000 (dilute to 1:10,000 if using IV) · SC, IM, IV · may be repeated at 15 minute intervals · Often used in conjunction with corticosteroids and diphenhydramine.
- Anaphylaxis · 0.5-1 mL/100 lbs. body weight of 1:1,000 (dilute to 1:10,000 if using IV) · SC, IM, IV · may be repeated at 15 minute intervals · Often used in conjunction with corticosteroids and diphenhydramine.
- Cardiac resuscitation (asystole) · 0.01 mg/kg · IV · Repeat every 3-5 minutes if no return of spontaneous circulation (ROSC) · Part of CPCR protocol after ABCs. Vasopressin may be alternated.
- Cardiac resuscitation · 0.1-0.2 mg/kg (high dose) or 0.01-0.02 mg/kg (low dose) · IV or IO · Repeat at 3-5 minute intervals if no response · Low dose generally attempted first.
- Cardiac resuscitation · 0.01-0.02 mg/kg (IV) or 0.03-0.1 mg/kg (IT) · IV, IT · every 3-5 minutes · For IT, dilute in 5-10 mL of sterile water or normal saline.
- Neonatal resuscitation (when respiratory support/compressions fail) · 0.1-0.3 mg/kg · IV or IO
- Anaphylaxis · 0.01-0.02 mg/kg · IV, IT, IM, SC · Dosage may be doubled and given via endotracheal tube if IV line not established. Less severe cases may use IM or SC.
- Anaphylaxis · 0.2-0.5 mg (total dose) · SC or IM
給藥途徑
禁忌症
- Narrow-angle glaucoma
- Hypersensitivity to epinephrine
- Shock due to non-anaphylactoid causes
- During general anesthesia with halogenated hydrocarbons or cyclopropane
- During labor (may delay the second stage)
- Cardiac dilatation or coronary insufficiency
- Conditions where vasopressors are contraindicated (e.g., thyrotoxicosis, diabetes, hypertension, toxemia of pregnancy)
- Injection with local anesthetics into small appendages (toes, ears, etc.) due to risk of necrosis
不良反應
- Anxiety and fear
- Tremors and excitability
- Vomiting
- Hypertension (especially with overdosage)
- Cardiac arrhythmias (especially with pre-existing heart disease)
- Hyperuricemia
- Lactic acidosis (with prolonged use or overdose)
- Tissue necrosis and sloughing at the injection site (with repeated injections or injection into small appendages)
藥物相互作用
- Alpha-blockers (phentolamine, phenoxybenzamine, prazosin) · May negate the therapeutic effects of epinephrine.
- Alpha-2 agonists (detomidine, dexmedetomidine, xylazine) · Do NOT use epinephrine to treat cardiac effects caused by alpha-2 agonists; may worsen hemodynamics.
- General Anesthetics (halogenated hydrocarbons, cyclopropane) · Increased risk of developing severe arrhythmias. Propranolol may be used to treat if they occur.
- Antihistamines (diphenhydramine, chlorpheniramine) · May potentiate the effects of epinephrine.
- Beta-blockers (propranolol) · May potentiate hypertension and antagonize epinephrine's cardiac and bronchodilating effects.
- Digoxin · Increased risk of arrhythmias if used concurrently.
- Nitrates · May reverse the pressor effects of epinephrine.
- Levothyroxine · May potentiate the effects of epinephrine.
- Oxytocic agents · Hypertension may result if used concurrently. · moderate
- Other Sympathomimetic agents (isoproterenol) · Should not be administered together as increased toxicity may result.
- Phenothiazines · May reverse the pressor effects of epinephrine.
- Reserpine · May potentiate the pressor effects of epinephrine.
監測
- Cardiac rate and rhythm (ECG)
- Respiratory rate and auscultation (especially during anaphylaxis)
- Urine flow (if possible)
- Blood pressure
- Blood gases (if indicated and possible)
過量
Clinical signs of overdosage or inadvertent IV administration of SC/IM doses include: * Sharp rises in systolic, diastolic, and venous blood pressures * Cardiac arrhythmias * Pulmonary edema and dyspnea * Vomiting, headache, and chest pain * Cerebral hemorrhages (due to severe hypertension) * Renal failure, metabolic acidosis, and cold skin **Treatment:** Because epinephrine has a relatively short duration of effect, treatment is mainly supportive. If necessary, an alpha-adrenergic blocker (e.g., phentolamine) or a beta-adrenergic blocker (e.g., propranolol) can be used to treat severe hypertension and cardiac arrhythmias. Prolonged periods of hypotension may follow, requiring treatment with norepinephrine.
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