A randomized clinical trial to compare the effects of a heat and moisture exchange filter with a heated humidifying system on the occurrence rate of ventilator-associated pneumonia<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Zheng Ruiqiang, Yang Congshan, Qiu Haibo, Yang Yi, Huang Yingzi.  Department of Critical Care Medicine, Nanjing Zhong-Da Hospital and School of Clinical Medicine, Institute of Emergency and Critical Care Medicine, Southeast University, Nanjing, 210009, China 

Abstract<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Objective：To compare the performance of heat and moisture exchange filters with heated humidifying systems in the mechanical ventilator circuit on the incidence of ventilator- associated pneumonia (VAP).

Methods：From January to June 2004, patients who required mechanical ventilation (MV) in the general intensive care unit (ICU) were randomized to either a heat and moisture exchange filters (HMEF) or a heated humidifying system (HHs) in the breathing circuit. Ventilator circuits were changed routinely every 7 days, HMEFs were changed every 24 hours, or more frequently if necessary. Single suction catheters were used, a specific endotracheal tube suction and lavage protocol was not employed.  Patients were dropped from the study if MV less than 48 hours.  The Centers for Disease Control and Prevention (CDC) criteria for diagnosis of pneumonia were used to diagnosis ventilator- associated pneumonia (VAP). The following risks were compared: age, sex, the underlying diseases of the patients at the time of admission to the ICU, acute physiology and chronic health evaluation Ⅱ (APACHE Ⅱ) score, ventilation days, the duration of enteral-feed and H2-antagonist. VAP rate, hospital mortality, peak inspriatory airway pressure (PIP), mean airway pressure (MAP) and tidal volume (before HMEF, after use HMEF 1 and 24 hours in HMEF group, at the same time in HHs group) were recorded.

Results：Eighty-two patients were involved in the study, twenty-two patients were excluded from the study because they were ventilated for less than 48 hours. Sixty patients who completed the study, thirty patients were in the HMEF group and another 30 patients in the HHs groups. Male patients constituted 51% in the HMEF group and 52% in the HHs group, there were no significant sex difference between two groups (P>0.05).  The mean (x±SD) for the age of the HMEF group was 64±12 years and of the HHs group was 68±10 years (P>0.05). The APACHEⅡ score, the time of VAP occurrence after MV, enteral feed days, and H2 antagonists days were no significant differences between the 2 groups (P>0.05).  The VAP rate of HMEF group was 28.6%, the rate of HHs group was 44.4%, the difference was statistically significant (P<0.05), The time of VAP occurrence after MV in HMEF group was no difference than that in HHs group (5.7±2.2 days vs. 4.7±1.7 days, P>0.05).  There were significant difference in duration of MV in HMEF group compare with HHs group (6.2±0.4 days vs 12.5±11.9 days, P<0.05).  The mortality was no significant difference between two groups (47% vs 56%, P>0.05).  Tidal volume, PIP and MAP did not change in HMEF group at different times, there were no difference compared with two groups.

Conclusion：HMEF could reduce the incidence of VAP and duration of MV, HMEF may be advantageous over than HHs. HMEF did not increase the airway pressure.

Key words：Mechanical ventilation; heated humidifying systems; heat and moisture exchange filters; ventilator- associated pneumonia. 

呼吸机相关肺炎是医院获得性感染的主要类型。人工气道丧失了上呼吸道加温加湿和过滤细菌的功能，建立人工气道的机械通气患者呼吸机相关肺炎(VAP)的发病率在20%到75%^[1～3]。为了替代上呼吸道，呼吸机装备了加温加湿器(HHs)，但患者气道分泌物可以通过呼吸机管路进入HHs，在温度和湿度适宜的条件下利于细菌生长繁殖，并在呼吸机送气时随气体进入患者肺内，造成VAP。<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

针对HHs的不足，具有细菌过滤功能的热湿交换器(HMEF)逐渐应用于临床。理论上，细菌过滤器放置在人工气道和呼吸机管路之间，既可以有效利用患者呼出气的温度和湿度，给吸入气体加温加湿，又可以过滤和吸附呼出气中的细菌，达到替代上呼吸道的功能，从而可能降低了VAP的发病率。目前国外的研究存在矛盾的结论^[1～4]，国内尚无报道，本研究旨在前瞻性随机研究HMEF对VAP患病率的影响。

材料与方法

1.病例选择与分组

2004年1月至6月收住东南大学附属中大医院危重病医学科，建立人工气道机械通气患者。患者入选后立即按随机数字表随机分为HMEF和HHs组，入选后机械通气时间不足48小时的患者予以排除。

2.研究方法

两组患者均应用一次性呼吸管路，呼吸管路吸气管和呼气管均配有冷凝水收集器，呼吸管路每7天更换一次。

两组患者都使用开放式一次性吸痰管，根据需要随时吸痰。吸痰时可根据情况每次向气道内注入无菌生理盐水10～20ml以稀释痰液。

　　两组患者呼吸支持模式均应用容量控制模式，调节潮气量保证动脉血二氧化碳分压(PaCO₂)在正常范围(35～45mmHg)，调节呼气末正压 (PEEP) 水平保证在吸氧浓度(FiO₂)小于60%条件下，动脉血氧分压(PaO₂)在60mmHg以上。

HMEF组患者在呼吸机管路与人工气道连接处装置HMEF，HMEF每24小时更换一次，如发现痰液堵塞HMEF时随时更换HMEF，每日更换HMEF超过三次的患者予以排除。

HHS组患者应用标准M730贮水罐，加热器温度设定在37℃，定期添加无菌蒸馏水保证贮水罐水量，定期清除吸气和呼气管路中冷凝水收集器中的冷凝水。

两组患者吸痰时、HMEF组更换HMEF和HHs组贮水罐加水时，操作人员均采取严格无菌操作，操作前洗手，操作时戴消毒无菌手套、口罩和帽子。

3.观察终点

患者撤离呼吸机后48小时或患者死亡。

4.VAP的诊断标准

采用美国疾病预防和控制中心(CDC)医院获得性肺炎诊断标准^[5]，同时符合以下标准之一，(1)脓性痰或痰液性状改变；(2)血培养阳性，且排除其他部位感染所致。

5.观察指标

记录两组患者年龄、性别、入住ICU的主要病因，APACHE II评分、鼻饲流质时间和抑制胃酸分泌药物使用时间等一般情况。所有患者均每日检查血常规，每两日检查床边胸片，入院当日及研究期间每两天经人工气道抽吸留取标本送检细菌培养。记录患者VAP患病率和发病时间、机械通气时间、机械通气潮气量和住院病死率。记录HMEF组患者应用HMEF前、应用HMEF1小时和24小时后的气道峰值压力 (PIP)和平均气道压力 (MAP)，记录HHs组患者相同时间点的上述压力指标。

6.统计学处理

以SPSS11.5统计软件包进行统计处理，所有计量资料以均数±标准差(x±s)表示。均数比较采用t检验，率的比较采用卡方检验，P<0.05为有统计学差异。

HMEF不增加气道阻力。本研究中HMEF组应用HMEF前后以及应用24小时后，HMEF组和HHs组在HMEF组应用HMEF1、24小时后的潮气量、气道峰值压力和气道平均压力都无明显统计学差异。HMEF本身是一种低阻力设备，HMEF组呼吸管路减少了连接HHs的管路，缩短管路长度，减低HHs相关管路的阻力，应用HMEF和应用HHs气道阻力无明显差异，应用HMEF24小时后更换并不增加气道阻力^[7]。<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

HMEF能够降低VAP患病率，缩短机械通气时间，满足加热加湿吸入气体的要求。临床操作简单安全，同时能够降低护士工作量，减少交叉感染机会，保护医护人员。具有一定应用前景。

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