一氧化二氮 (笑氣)
一氧化二氮（N2O，俗稱笑氣）是一種吸入性氣體，通常與氧氣混合使用，作為揮發性麻醉劑（如異氟醚）的輔助藥物，用於全身麻醉的誘導與維持。它能降低主要吸入性麻醉劑的需求濃度，並透過**第二氣體效應 (second gas effect)**與**濃度效應 (concentration effect)**加速達到穩定的麻醉深度。 > **臨床警告：** N2O 會導致體內任何充滿氣體的空間迅速擴張，增加體積或壓力。對於患有氣胸或胃擴張扭轉 (GDV) 的病患絕對禁用。 > **臨床警告：** 停止使用 N2O 後，必須持續補充氧氣 5-10 分鐘，以防止**擴散性缺氧 (diffusion hypoxia)**。
作用機制: Nitrous oxide causes generalized **CNS depression**. When administered at the beginning of volatile agent anaesthesia, it increases the speed of uptake of the volatile agent from the alveoli → **second gas effect** and **concentration effect** → hastens attainment of a stable plane of anaesthesia. It has minimal direct respiratory and cardiovascular effects.
各物種劑量
- Adjunct for induction and maintenance of anaesthesia · Inspired concentrations of 50-70% · Inhalational · Continuous during anaesthesia · Duration of procedure · Must be administered with a minimum of 30% oxygen.
- Adjunct for induction and maintenance of anaesthesia · Inspired concentrations of 50-70% · Inhalational · Continuous during anaesthesia · Duration of procedure · Must be administered with a minimum of 30% oxygen.
劑量為持牌獸醫專業人員的臨床參考。請務必對照最新藥品說明書及個別病患確認。
給藥途徑
禁忌症
- Patients with air-filled spaces within the body (e.g., pneumothorax, gastric dilatation/GDV, intestinal obstruction)
- Marked respiratory compromise (due to hypoxia risks)
- Raised intracranial pressure (due to associated increases in cerebral blood flow)
不良反應
- Diffusion hypoxia (if oxygen is not supplemented upon discontinuation)
- Megaloblastic changes in bone marrow (with exposure lasting a few hours)
- Agranulocytosis (with prolonged exposure of a few days)
監測
- Inspired oxygen concentration (FiO2) - especially in rebreathing circuits
- Pulse oximetry (SpO2)
- Capnography (ETCO2)
- Respiratory rate and effort
- Cardiovascular parameters (HR, BP)
過量
Overdosage primarily presents as **hypoxia** if the inspired oxygen concentration falls below 30%. Treatment consists of immediately discontinuing nitrous oxide and providing 100% oxygen via positive pressure ventilation if necessary.
VetSheet 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。