亜酸化窒素 (笑気)
Nitrous oxide
Dinitrogen monoxide (N2O)
別名: Entonox · Laughing gas · N2O · Dinitrogen monoxide · Nitrogen oxide
VetSheet 獣医チームが監修更新日 2026年4月5日エビデンスに基づく獣医学リファレンス
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
動物種別用量
🌎 NA — North America🌍 EU — Europe
犬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Adjunct for induction and maintenance of anaesthesia | Inspired concentrations of 50-70% | Inhalational | Continuous during anaesthesia | Duration of procedure | 🌍 EU |
- Adjunct for induction and maintenance of anaesthesia: Must be administered with a minimum of 30% oxygen.
猫
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Adjunct for induction and maintenance of anaesthesia | Inspired concentrations of 50-70% | Inhalational | Continuous during anaesthesia | Duration of procedure | 🌍 EU |
- Adjunct for induction and maintenance of anaesthesia: Must be administered with a minimum of 30% oxygen.
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
概要
亜酸化窒素（N2O）は、イソフルランなどの揮発性麻酔薬の導入および維持を補助するために酸素とともに使用される吸入ガスです。主要な吸入麻酔薬の必要濃度を低下させ、第2ガス効果および濃度効果により、安定した麻酔深度への到達を早めます。
臨床上の警告： N2Oは体内のガスが充満した空間を急速に膨張させ、体積や圧力を増加させます。気胸や胃拡張・捻転（GDV）の患者には絶対禁忌です。
臨床上の警告： N2Oの使用中止後は、拡散性低酸素症を防ぐために5〜10分間酸素を補充する必要があります。
作用機序
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.
安全性・警告
禁忌
- 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)
有害事象
- 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)
注意事項
Human Safety & Scavenging: Prolonged exposure can have serious adverse effects on human health. Active scavenging is essential.
Important: N2O is not absorbed by activated charcoal in passive scavenging systems.
Hypoxia Risk: A minimum oxygen concentration of 30% is required during anaesthesia. The inspired concentration of oxygen may fall to critically low levels when N2O is used in rebreathing circuits during low flow rates. Do not use in such systems unless the inspired oxygen concentration can be measured on a breath-by-breath basis.
Diffusion Hypoxia: Always supplement with 100% oxygen for 5-10 minutes after turning off N2O.
監視
- Inspired oxygen concentration (FiO2) - especially in rebreathing circuits
- Pulse oximetry (SpO2)
- Capnography (ETCO2)
- Respiratory rate and effort
- Cardiovascular parameters (HR, BP)
薬物動態
半減期
吸収
Rapidly absorbed across the alveolar membrane into the blood.
分布
Distributes rapidly to highly perfused tissues including the brain.
代謝
Virtually no biotransformation; the cobalt ion in vitamin B12 is oxidized by N2O, inhibiting methionine synthase.
消失
Rapidly excreted unchanged via the lungs upon discontinuation.
過剰投与
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.
製品
製剤
- 100% nitrous oxide (N2O) gas
- Nitrous oxide plus oxygen (Entonox)
動物用医薬品
- Nitrous oxide medical gas cylinders
ヒト用医薬品
- Entonox (50% N2O / 50% O2) cylinders
- Nitrous oxide medical gas cylinders
規制ステータス
Regulated as a medical gas.
POM (Prescription Only Medicine)
POM-V. Strict regulations regarding occupational exposure and scavenging apply.
規制データなし: 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
保管・安定性
Store in pressurized medical gas cylinders in a cool, dry, well-ventilated area away from combustible materials. Cylinders must be secured to prevent falling.
飼主向け情報
亜酸化窒素（通称：笑気ガス）は、全身麻酔中に獣医師が安全かつ一般的に使用するガスです。酸素や他の麻酔薬と併用することで、手術中のペットを確実に眠らせ、痛みを感じさせないようにします。主要な麻酔薬の効き目を早め、他の薬の投与量を減らすことができます。手術が終わると体から非常に早く排出されるため、スムーズな覚醒が期待できます。
VetSheet医薬品リファレンスは獣医専門家の臨床意思決定支援を目的としており、専門的判断または製造業者の最新医薬品情報の代替にはなりません。