Todd D A, John E, Osborn R A
Department of Pediatrics, Westmead Hospital, NSW, Australia.
Crit Care Med. 1991 Oct;19(10):1310-6. doi: 10.1097/00003246-199110000-00014.
To compare the degree of tracheobronchial damage in newborn lambs ventilated for 6 hrs with relative humidities of 30% or 90% and continuous positive airway pressure breathing, conventional mechanical ventilation of 25 and 60 breaths/min, or high frequency flow-interrupted ventilation at 600 breaths/min.
Tracheobronchial damage secondary to mechanical ventilation remains a major iatrogenic lesion of the newborn despite substantial advances in both mechanical design and ventilatory techniques. A histologic scoring system was used to compare the damage noted in the tracheobronchial epithelium of newborn lambs after 6 hrs of conventional mechanical ventilation or high-frequency flow-interrupted ventilation at two relative humidities. Three groups of animals were ventilated for 6 hrs with an FIO2 of 0.21 at 36.0 degrees C and relative humidity of 90%. The first group received continuous positive airway pressure of 4 cm H2O, the second group received slow rate, conventional mechanical ventilation at 25 breaths/min, and the third group received fast rate, conventional mechanical ventilation at 60 breaths/min. Two other groups of animals were ventilated for 6 hrs with an FIO2 of 0.21 at 36.0 degrees C and relative humidity of 30%. The first group was ventilated with high-frequency flow-interrupted ventilation at 600 breaths/min and the second group with slow rate, conventional mechanical ventilation at 25 breaths/min. Two additional groups served as nonintubated controls; one group was killed immediately after sedation and the other group was killed after 6 hrs of sedation.
The damage was mild but significantly different from controls when 90% humidity was used and there was no difference in the histology score between continuous positive airway pressure breathing and conventional mechanical ventilation at 25 or 60 breaths/min. Significant inflammation, erosion, necrosis, and blistering occurred with both conventional mechanical ventilation at 25 breaths/min and high-frequency flow-interrupted ventilation at 600 breaths/min when 30% humidity was used. The damage was only found 5 mm below the tip of the endotracheal tube and not at 3.5 cm beyond the endotrachea tube in the trachea nor in the right main bronchus.
These data indicate that endotracheal intubation and mechanical ventilation, regardless of the method of ventilation, cause damage to the tracheal mucosa, but that poorly humidified inspired gases cause significantly greater damage.
比较在相对湿度为30%或90%的条件下，对新生羔羊进行6小时持续气道正压通气、25次/分钟和60次/分钟的传统机械通气或600次/分钟的高频气流阻断通气时，气管支气管的损伤程度。
尽管在机械设计和通气技术方面取得了重大进展，但机械通气继发的气管支气管损伤仍然是新生儿主要的医源性损伤。采用组织学评分系统比较在两种相对湿度下，新生羔羊经6小时传统机械通气或高频气流阻断通气后，气管支气管上皮的损伤情况。三组动物在36.0℃、FIO2为0.21、相对湿度为90%的条件下通气6小时。第一组接受4 cm H2O的持续气道正压通气，第二组接受25次/分钟的慢速传统机械通气，第三组接受60次/分钟的快速传统机械通气。另外两组动物在36.0℃、FIO2为0.21、相对湿度为30%的条件下通气6小时。第一组采用600次/分钟的高频气流阻断通气，第二组采用25次/分钟的慢速传统机械通气。另有两组作为未插管对照；一组在镇静后立即处死，另一组在镇静6小时后处死。
当使用90%的湿度时，损伤较轻，但与对照组有显著差异，持续气道正压通气与25次/分钟或60次/分钟的传统机械通气在组织学评分上没有差异。当使用30%的湿度时，25次/分钟的传统机械通气和600次/分钟的高频气流阻断通气均出现显著的炎症、糜烂、坏死和水疱形成。损伤仅出现在气管插管尖端下方5 mm处，在气管内及右主支气管中插管尖端3.5 cm以外未发现损伤。
这些数据表明，气管插管和机械通气，无论通气方法如何，都会导致气管黏膜损伤，但吸入气体湿化不良会造成更严重的损伤。
