機(jī)械通氣的氣道濕化
在正常生理狀態(tài)下，吸入氣體通過(guò)上呼吸道加溫加濕作用達(dá)到BTPS狀態(tài)，即氣體溫度達(dá)到37℃, 絕對(duì)濕度44mgH2O/L，相對(duì)濕度100%。而在正壓通氣或建立人工氣道的情況下，呼吸機(jī)通過(guò)高壓或高流速輸送的氣體較為干燥，使上呼吸道生理性加溫加濕功能負(fù)擔(dān)加重，此時(shí)，使用呼吸濕化器提供足夠的濕化補(bǔ)償就顯得尤為必要。
上呼吸道可以提供吸入氣體75%的濕度。在進(jìn)行有創(chuàng)機(jī)械通氣時(shí)，因人工氣道的建立，上呼吸道被旁路，不能對(duì)吸入氣體進(jìn)行加溫加濕時(shí)，濕化器就需要補(bǔ)償丟失的這部分溫度和濕度。吸入氣體總的濕度需求是44mg/L，被旁路的75%氣道濕化功能需要濕化器進(jìn)行補(bǔ)償，即0.75*44mg/L=33mg/L。因此，對(duì)有創(chuàng)通氣患者進(jìn)行主動(dòng)濕化達(dá)到理想BTPS狀態(tài)時(shí)，濕化器需要提供33-44mg/L 的濕度，對(duì)應(yīng)的氣體溫度在34-41℃之間，相對(duì)濕度達(dá)100%來(lái)維持正常呼吸道的生理功能。
盡管呼吸濕化器可以保證Y型管處的氣體溫度達(dá)到41℃，依據(jù)ARRC指南建議Y型管處的最高氣體溫度是37℃，相對(duì)濕度是100%。ISO 組織認(rèn)為：輸送的氣體溫度持續(xù)在41℃以上會(huì)對(duì)患者帶來(lái)潛在的熱損傷，并把43℃作為熱損傷的高溫報(bào)警臨界點(diǎn)。
在進(jìn)行無(wú)創(chuàng)機(jī)械通氣時(shí)，盡管上呼吸道的生理濕化功能保留，由于漏氣通氣的特點(diǎn)，單位時(shí)間內(nèi)經(jīng)過(guò)連接界面處的氣流加大，使得患者上呼吸道水分丟失，導(dǎo)致上呼吸道濕化的負(fù)荷加重，黏膜濕度不足。此時(shí)，使用呼吸濕化器可顯著提升吸入氣體的溫度及濕度，增加患者的依從性和舒適度，從而提高無(wú)創(chuàng)通氣的成功率。
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