亜酸化窒素 (笑気)
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.
動物種別の用量
- 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.
用量は獣医療従事者向けの臨床リファレンスです。必ず最新の添付文書と個々の患者で確認してください。
投与経路
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)
モニタリング
- Inspired oxygen concentration (FiO2) - especially in rebreathing circuits
- Pulse oximetry (SpO2)
- Capnography (ETCO2)
- Respiratory rate and effort
- Cardiovascular parameters (HR, BP)
過量投与
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.
VetSheet の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。