日本未熟児新生児学会雑誌　第17巻　第2号　57～66頁（2005年）

日本未熟児新生児学会雑誌　17(2)：215-224；2005　

受理日：平成16．12．01

保育器内呼吸管理中の回路内加温加湿に関する実験的検討

Optimal Humidification for Mechanically Ventilated Neonates in Incubators

＊1現　名古屋市立大学大学院医学研究科先天異常・新生児・小児医学分野，＊2名古屋第二赤十字病院　小児科

Department of Pediatrics, Nagoya Daini Red-Cross Hospital

山田恭聖＊1・村松幹司＊2・田中太平＊2・佐野洋史＊2・横山岳彦＊2・岩佐充二＊2・安藤恒三郎＊2

Yasumasa YAMADA，Taihei TANAKA，Kanji MURAMATSU， Hirohumi SANO，Mitsuji IWASA，Tsunesaburou ANDOU

Key Words：humidity，airway obstruction，mechanical ventilation，secretion

　超早産児の急性期人工呼吸管理において，チューブトラブルは神経学的予後にも関わる重大な合併症で，その原因の一つに粘稠な喀痰によるチューブ閉塞がある。このような合併症は呼吸器からの吸気ガスの適切な加温加湿によりある程度予防できる可能性がある。保育器内での呼吸管理という特殊な環境下で，どのような環境因子が粘稠な喀痰に関係しているかを調べるために，喀痰溶解モデルを使用し検討した。
　モデルは超早産児の急性期を想定し，吸気ガスの湿度と温度を測定しながら，加温加湿器の設定，保育器の温度，気道温度プローブの位置を変更し，喀痰に見立てたイソジンゲルが気管モデル内でどの程度溶解するかを計測した。
　喀痰の溶解は気管モデルに入る直前の吸気ガスの絶対湿度に依存し，絶対湿度は吸気ガス温度が37～38℃以下であれば，吸気ガス温に正の相関を示した。さらに吸気ガス温は保育器の温度に依存していた。
　保育器の温度が比較的低い時，供給ガス温度は低下し，その結果絶対湿度も低下する。このため保育器温が低下した時に，粘稠な痰によるチューブ閉塞に注意が必要である。

　Tracheal tube occlusion-induced ischemic cerebral blood flow change may be associated with neurological complications including intraventricular hemorrhage, periventricular leukomalacia and other sequelae. Optimal humidity minimizes the risk of airway occlusion and the expenditure of energy used for growth and development. It is possible that optimally humidified ventilated gas prevents these critical complications. However, environmental factor in the NICU would make the delivery of optimal humidity difficult to achieve, because the warm ambient conditions generated by incubators should affect the ability of the humidifier and circuit to control humidity delivery. Therefore, we studied what environmental factor contributed optimally humidified ventilated gas to minimize the risk of tracheal tube occlusion.
　Three kinds of gasses with various humidifier settings were ventilated artificially through an endotrachial tube model in three different incubator temperatures. A brown water-soluble gel on dry filter paper was used as a substitute for secretions. Because the gel was hydrated by moisture from the delivered gas, the gel melted and a brown stain spread over the dry filter paper to the extent that the gas could hydrate the gel. The stains were measured and the stained area calculated by computer. Relative humidity, absolute humidity and gas temperature were measured immediately in front of the endotracheal tube model.
　We showed that gel hydrated area was dependent on absolute humidity of the gas delivered immediately in front of the endotracheal tube model. If delivered gas temperature was below 37～38℃, it was indicated that absolute humidity was almost directly proportional to gas temperature rather than circuits-configurations or humidifier setting. Furthermore, there was a positive correlation between gas temperature and incubator temperature.
　We concluded that drying secretion would occlude tracheal tube in comparatively low incubator temperature. Our result was limited in specific humidifier setting, incubator temperature and ventilator setting. Further research is required to investigate appropriate environmental factor to prevent airway occlusion.