不同潮气量机械通气对创伤后急性呼吸窘迫综合征疗效的影响

目的探讨小潮气量（LTV）加呼气末正压（PEEP）机械通气（MV）治疗创伤后急性呼吸窘迫综合征（ARDS）的疗效。方法以18例常规潮气量（8～l2ml／kg）MV为对照组，20例小潮气量（5～7ml／kg）加用PEEP的MV模式为观察组．比较两组间血气，RR、HR、MAP、CVP、呼吸机所致肺损伤（VILI）、多脏器功能不全（MODS）发生率及ARDS病死率。结果两组PaO2差异无显著性意义（P〉0．05）；观察组PaCO2高于对照组（P〈0．05）；观察组无VILI、MODS及死亡病例发生，对照组2例VILI、2例ARDS并发MODS死亡。结论在ARDS治疗中采用小潮气量加PEEP及允许范围内高碳酸血症（PHC）的保护性通气策略，可明显改善缺氧，减少VILI发生，从而降低其病死率。     

全身麻醉中应用小潮气量联合低水平呼气末正压通气对老年患者呼吸功能的影响

目的 观察全身麻醉中应用小潮气量(VT)联合低水平呼气末正压通气(PEEP)对老年患者呼吸功能的影响.方法 20例ASAⅠ或Ⅱ级上腹部手术老年患者,随机均分为A组和B组.A组,机械通气模式为间歇正压通气(IPPV)加5cm H2O PEEP,VT=6ml/kg,f=15次/分;B组,机械通气模式为IPPV,VT=9ml/kg,f=12次/分.观察术前(T1)、麻醉插管后30min(T2)、拔管后15min(T3)的动脉氧分压(PaO2)、动脉血二氧化碳分压(PaCO2)、肺泡-动脉氧分压差(A-aDO2)、MAP、CVP及术中的气道峰(Ppeak).结果 T3时,A PaO2较B组明显升高(P<0.05),A组A-aDO2较B组明显降低(P<0.05).其他各时点A、B两组PaO2、PaCO2、A-aDO2、MAP、CVP、Ppeak组间比较差异无统计学意义.结论 小潮气量联合低水平PEEP通气能够有效改善老年患者术后低氧血症,减少肺部并发症,更有利于老年患者呼吸功能的恢复,对老年患者血流动力学无明显影响.     

高呼气末正压小潮气量通气对肺功能正常患者血流动力学的影响

目的 观察肺功能正常的患者术后使用不同水平呼气末正压(PEEP)小潮气量通气对血流动力学的影响.方法 102例ASA Ⅰ或Ⅱ级,择期全麻下耳鼻喉科术后患者,随机均分为六组.研究组使用保护性肺通气模式,潮气量5 ml/kg,根据PEEP 0、5、10、15和20 emH2O分为P0、P5、P10、P15和P20.五组.对照组(C组)使用常规机械通气模式,潮气量10 ml/kg.观察保护性肺通气前(T1)及保护性肺通气30 min后(T2)的血流动力学的改变.结果 与C组及T1时比较,T2时加速度指数(ACI)在P0、P5、P10和P15组升高,P20组降低;心脏指数(CI)、左室做功指数(LCWI)、平均动脉压(MAP)在P20组降低(P＜0.05);胸腔液体水平(TFC)P10P15和P20组T2时明显低于T1时(P＜0.05).结论 对肺功能正常患者实施小潮气量的保护性肺通气,PEEP在0和5 cmH2O2水平,对血流动力学无明显影响;当PEEP在10和15 cmH2O冰平时ACI增强和TFC减少,有潜在血流动力学危害;当PEEP在20 cmH2O时CI和MAP均降低.有明显血流动力学波动.     

呼吸道高压、高潮气量PEEP对高充气压肺水肿的作用

大鼠在戊巴比妥麻醉下,通过气管切开通气,以便测定潮气量及呼吸道气压。全部动物均用~(125)碘标记白蛋白和~(99)锝标记红血球,以测定肺微血管渗漏;并分作5组:(Ⅰ)间歇正压通气(IPPV),吸气压力峰值7cmH_2O,潮气量13±3ml/kg;Ⅱ)高潮气量(HiV,40±3ml/kg)及高充气压(HiP,45cmH_2O);(Ⅲ)通气压峰值同第Ⅱ组;加用10cmH_2O的PEEP(潮气量为25±1ml/kg),Ⅳ)充气压为45cmH_2O的低潮气量(LoV,19±1ml/kg);(Ⅴ)负压吸气及高潮气量。各组肺脏均制成标本,在显微镜下作解剖学研究。动物在实验期间无死亡;但第Ⅴ组(Lop-HiV)皆呈垂死状态。第Ⅱ及第Ⅴ组(HiP-HiV及LoP-HiV)气管内出现水肿液体,肺部明     

不同机械通气模式对老年腹部手术患者细胞因子的影响

目的探讨不同机械通气模式对于老年腹部手术患者细胞因子的影响。方法 72例择期进行腹部手术全麻机械通气的老年患者(年龄65岁)分为6组,每组12例。A组:VCV(Vt 6 m L/kg)+PEEP 8 mm Hg+auto-flow模式;B组:VCV(Vt 6 m L/kg)+PEEP 8 mm Hg+const-flow模式;C组:VCV(Vt 6 m L/kg)+PEEP 12 mm Hg+auto-flow模式;D组:VCV(Vt 6 m L/kg)+PEEP 12mm Hg+const-flow模式;E组:VCV(Vt 10 m L/kg)+auto-flow模式;F组:VCV(Vt 10 m L/kg)+const-flow模式。6组患者全身麻醉气管插管后,均予以VCV(Vt 6 m L/kg)+const-flow模式通气60 min,再按分组的通气模式进行通气,总通气时间大于5 h。在通气1 h及5 h两个时间点,抽取静脉血和支气管肺泡灌洗液检测IL-8、IL-10、MMP-9、SP-A以及SF浓度。结果大潮气量组(E、F两组)较小潮气量四组(A、B、C、D四组)通气5 h后,血与BALF中测定的IL-8、MMP-9浓度以及血中测定的SP-A、SF浓度明显升高(P0.05),血与BALF中测定的IL-10浓度以及BALF中测定的SP-A浓度明显降低(P0.05)。通气5 h后F组较E组,血及BALF中IL-8以及MMP-9、血SF、血SP-A更高(P0.05),而BALF中SP-A则更低(P0.05)。结论 (1)大潮气量机械通气较小潮气量机械通气而言,更有利于促进IL-8、MMP-9、SF的分泌,抑制IL-10的释放,BALF中SP-A下降,血中SP-A升高,进一步加剧了VILI的程度。(2)就老年(年龄65岁)腹部手术患者而言,围手术期以VCV(Vt6 m L/kg)+PEEP 12 mm Hg+auto-flow模式机械通气较其他五种通气模式,更有利于减轻肺组织急性炎症反应及氧化应激反应的激活,减轻机械通气所致生物伤,从而减轻VILI的程度。     

肥胖因素对大鼠呼吸机相关性肺损伤的影响

目的评价肥胖因素对大鼠呼吸机相关性肺损伤(VILI)的影响。方法清洁级雄性SD大鼠45只,6～8周龄,按照体重分为3组(n=15):正常体重对照组(C组)、正常体重VILI组(CV组)和肥胖VILI组(FV组)。C组和CV组体重为233～267 g,FV组体重为288～332 g。C组潮气量VT 10 ml/kg,CV组和FV组潮气量VT 40 ml/kg,通气频率40次/min,吸呼比1∶ 2,PEEP 0 mmHg,FiO2 21%,机械通气4 h,制备大鼠VILI模型。分别于气管插管前即刻和机械通气4 h时采集动脉血样行血气分析,记录PaO2;剩余血样收集血浆。机械通气4 h时采血后处死大鼠,分离两侧肺组织,收集支气管肺泡灌洗液(BALF)。采用ELISA法检测血浆瘦素浓度、血浆及BALF中TNF-α、IL-1β、IL-6的浓度。测定肺组织湿重/干重(W/D)比值,HE染色后观察肺组织病理结果并进行肺损伤评分,采用Western blot法检测肺组织NF-κB p65表达水平。结果与C组和CV组比较,FV组血浆瘦素浓度升高(P<0.01)。与C组比较,CV组和FV组机械通气...     

不同潮气量联合低水平呼气末正压通气对老年腹内高压患者血气和血流动力的影响

目的 观察不同潮气量联合低水平呼气末正压通气(PEEP)对老年腹内高压(IAH)患者血气和血流动力的影响.方法 给予有创机械通气治疗的老年IAH患者44例,随机分为4组,每组11例.PEEP均设定为5cm H2O,潮气量分别为5、7、9、11ml/kg,呼吸频率分别为20、17、14、12次/分,于通气2h后检测血气分析、中心静脉压(CVP),心率(HR)、平均动脉压(MAP)、平台压(PPLAT,cm H2O),气道峰压(PPEAK,cm H2O).结果 ①与Ⅰ、Ⅱ组比较,Ⅲ、Ⅳ组的MAP值降低(P＜0.05),而且Ⅳ组下降得更为明显(P＜0.05),Ⅲ组及Ⅳ组较通气前MAP值下降(P＜0.05);HR 4组与通气前比较均下降,4组资料差异无统计学意义;与Ⅰ、Ⅱ组比较,Ⅲ、Ⅳ组的CVP值升高(P＜0.05),而且Ⅳ组较Ⅲ组升高得更为明显(P＜0.05),Ⅲ组及Ⅳ组较通气前CVP值升高(P＜0.05).②与Ⅰ、Ⅱ组比较,Ⅲ组及Ⅳ组的PPLAT值升高(P＜0.05),而且Ⅳ组较Ⅲ组升高得更为明显(P＜0.05);与Ⅰ、Ⅱ组比较,Ⅲ组及Ⅳ组的PPEAK值升高(P＜0.05),而且Ⅳ组较Ⅲ组升高得更为明显(P＜0.05);SpO2 4组与通气前比较均上升(P＜0.05),PaCO2值Ⅱ、Ⅲ及Ⅳ组与通气前比较均下降,而且Ⅳ组较Ⅲ组下降得更明显(P＜0.05);PaCO2值Ⅰ组与通气前比较升高(P＜0.05);PaO2 4组与通气前比较均上升(P＜0.05).结论老年IAH患者采用小潮气量通气(7ml/kg)配合低水平PEEP安全、有效.     

小潮气量联合PEEP对单肺通气时胸外科手术患者血管外肺水的影响

目的 探讨小潮气量联合呼气末正压(PEEP)对单肺通气时胸外科手术患者血管外肺水的影响.方法 食道癌手术患者40例,年龄45～80岁,体重48～83kg,性别不限,ASA分级Ⅰ或Ⅱ级,随机分为2组(n=20):传统模式单肺通气组(Ⅰ组)机械通气模式为间歇正压通气(IPPV),VT9 ml/kg,通气频率12次/min;小潮气量联合PEEP单肺通气组(Ⅱ组)机械通气模式为IPPV联合PEEP5 cm H2O,VT6 ml/kg,通气频率15次/min.于麻醉诱导前(T0)、双肺通气30 min(T1)、单肺通气30 min(T2)、单肺通气1 h(T3)、恢复双肺通气拔管前(T4)和术后18 h(T5)时,记录血管外肺水(EVLW)、血管外肺水指数(EVLWI)、肺血管通透性指数(PVPI)和心输出量(CO),于T1～4时记录气道峰压(Ppeak);取股动脉血样,进行血气分析,并计算氧合指数(OI).结果 与Ⅰ组比较,Ⅱ组单肺通气期间EVLWI和.PVPI升高(P＜0.05),其余指标比较差异无统计学意义(P＞0.05);两组各时点OI、CO和Poeak比较差异无统计学意义(P＞0.05);与T0时比较,Ⅰ组T1时PVPI升高(P＜0.05),其余时点PVPI、EVLW和EVLWI差异无统计学意义(P＞0.05),Ⅱ组T2时EVLW、T1～4时EVLWI和T1.2时PVPI升高(P＜0.05);与T1时比较,Ⅰ组T2～5时EVLW、EVLWI和PVPI差异无统计学意义,Ⅱ组T5时PVPI降低(P＜0.05).结论 采用VT6 ml/kg、PEEP 5 cm H2O的单肺通气可增加患者血管外肺水,未对肺功能产生有利作用.     

小潮气量联合低水平呼气末正压通气策略在妇科腹腔镜手术麻醉中的应用

目的观察小潮气量联合低水平呼气末正压通气策略应用于妇科腹腔镜手术的效果。方法随机将40例妇科腹腔镜手术患者均分为常规机械通气组(Ⅰ组)和小潮气量联合低水平PEEP通气组(Ⅱ组)。Ⅰ组新鲜气体流量2 L/min,VT 8 m L/kg,吸呼比1∶2。Ⅱ组新鲜气体流量2 L/min,VT 6 m L/kg,吸呼比为1∶2,PEEP 5 cm H2O。调整通气频率,维持PETCO235~45 mm Hg。于插管后5 min(T1)、气腹30 min(T2)和气腹结束后5 min(T3)时记录气道峰压(Ppeak)、气道平台压(Pplat)、动态肺顺应性(Cdyn)和气道阻力(Raw),并计算肺泡-动脉血氧分压差(A-a DO2)、氧合指数(Pa O2/Fi O2)、呼吸指数(RI)和死腔率(VD/VT)。记录拔管时间、术后48h内呼吸并发症发生情况和住院时间。结果与Ⅰ组比较,Ⅱ组T2时Ppeak和Pplat、T1、2时Raw降低,T2时Cdyn升高,T1~3时Pa O2/Fi O2升高(P0.05),RI、VD/VT和A-a DO2降低(P0.05)。2组各时点动脉血p H值、拔管时间、住院时间无显著差异(P0.05。Ⅱ组术后48 h内呼吸并发症发生率降低(P0.05)。结论小潮气量(6 m L/kg)联合低水平PEEP(5 cm H2O)通气是妇科腹腔镜手术麻醉较适宜的呼吸管理模式。     

参附注射液对大鼠机械通气相关性肺损伤的保护作用及其机制

目的 探讨参附注射液(Shenfu injection,SF)对大鼠机械通气(mechanical ventilation,MV)相关性肺损伤的保护作用及其机制. 方法 40只健康成年雄性Wister大鼠采用随机数字表法分为4组,每组10只:对照组(C组)、正常潮气量MV组(N组)、大潮气量MV组(L组)、大潮气量MV+SF处理组(SF组).C组保留自主呼吸;N组、L组和SF组MV4h,潮气量分别设置为8～10 ml/kg、40 ml/kg、40 ml/kg,SF组于MV前15 min静脉注射SF 10 ml/kg.实验结束处死动物,收集支气管肺泡灌洗液(bronchoalveolar lavage fluid,BALF),测定BALF中总蛋白、IL-1β、IL-18和TNF-α的浓度;取肺组织,测量湿/干重比(wet/dry,W/D),采用免疫组化法检测肺组织NF-κB的表达,观察病理学改变并进行肺损伤评分. 结果 SF组BALF中TNF-α、IL-1β、IL-18浓度分别为(65±11)、(47±9)、(58±8) ng/L,较L组(99±7)、(69±7)、(86±7) ng/L明显降低(P＜0.05);SF组大鼠肺损伤评分、W/D、肺组织NF-κB光密度值分别为(8.5±1.8)分、(5.0±1.6)、(0.32±0.28),较L组(14.1±2.7)分、(5.5±1.8)、(0.54±0.33)均明显降低(P＜0.05). 结论 SF可减轻大鼠MV相关性肺损伤,其机制可能与SF抑制肺内NF-κB通路的活性且降低肺内炎性因子的释放有关.     

Alveolar Recruitment in Pulmonary and Extrapulmonary Acute Respiratory Distress Syndrome: Comparison Using Pressure-Volume Curve or Static Compliance

Background: Alveolar recruitment in response to positive end-expiratory pressure (PEEP) may differ between pulmonary and extrapulmonary acute respiratory distress syndrome (ARDS), and alveolar recruitment values may differ when measured by pressure-volume curve compared with static compliance.

Methods: The authors compared PEEP-induced alveolar recruitment in 71 consecutive patients identified in a database. Patients were classified as having pulmonary, extrapulmonary, or mixed/uncertain ARDS. Pressure-volume curves with and without PEEP were available for all patients, and pressure-volume curves with two PEEP levels were available for 44 patients. Static compliance was calculated as tidal volume divided by pressure change for tidal volumes of 400 and 700 ml. Recruited volume was measured at an elastic pressure of 15 cm H2O.

Results: Volume recruited by PEEP (10 +/- 3 cm H2O) was 223 +/- 111 ml in the pulmonary ARDS group (29 patients), 206 +/- 164 ml in the extrapulmonary group (16 patients), and 242 +/- 176 ml in the mixed/uncertain group (26 patients) (P = 0.75). At high PEEP (14 +/- 2 cmH2O, 44 patients), recruited volumes were also similar (P = 0.60). With static compliance, recruitment was markedly underestimated and was dependent on tidal volume (226 +/- 148 ml using pressure-volume curve, 95 +/- 185 ml for a tidal volume of 400 ml, and 23 +/- 169 ml for 700 ml; P < 0.001).     

Alveolar recruitment in pulmonary and extrapulmonary acute respiratory distress syndrome: comparison using pressure-volume curve or static compliance

BACKGROUND: Alveolar recruitment in response to positive end-expiratory pressure (PEEP) may differ between pulmonary and extrapulmonary acute respiratory distress syndrome (ARDS), and alveolar recruitment values may differ when measured by pressure-volume curve compared with static compliance. METHODS: The authors compared PEEP-induced alveolar recruitment in 71 consecutive patients identified in a database. Patients were classified as having pulmonary, extrapulmonary, or mixed/uncertain ARDS. Pressure-volume curves with and without PEEP were available for all patients, and pressure-volume curves with two PEEP levels were available for 44 patients. Static compliance was calculated as tidal volume divided by pressure change for tidal volumes of 400 and 700 ml. Recruited volume was measured at an elastic pressure of 15 cm H2O. RESULTS: Volume recruited by PEEP (10 +/- 3 cm H2O) was 223 +/- 111 ml in the pulmonary ARDS group (29 patients), 206 +/- 164 ml in the extrapulmonary group (16 patients), and 242 +/- 176 ml in the mixed/uncertain group (26 patients) (P = 0.75). At high PEEP (14 +/- 2 cmH2O, 44 patients), recruited volumes were also similar (P = 0.60). With static compliance, recruitment was markedly underestimated and was dependent on tidal volume (226 +/- 148 ml using pressure-volume curve, 95 +/- 185 ml for a tidal volume of 400 ml, and 23 +/- 169 ml for 700 ml; P < 0.001). CONCLUSION: In a large sample of patients, classification of ARDS was uncertain in more than one third of patients, and alveolar recruitment was similar in pulmonary and extrapulmonary ARDS. PEEP levels should not be determined based on cause of ARDS.     

How to prevent ventilator-induced lung injury?

The experimental evidence that ventilator could injure lungs through the application of excessive end-inspiratory volumes and transpulmonary pressures has led to major changes in the clinical management of patients suffering from the acute respiratory distress syndrome (ARDS). The prevention of ventilator-induced lung injury has become one of the main goals of current ventilator strategies for patients with ARDS as well as for patients with normal lungs that require mechanical ventilation. Tidal volume reduction allowed for a reduction in mortality that confirmed the clinical relevance of ventilator-induced lung injury. In contrast, strategies for setting positive end-expiratory pressure (PEEP) have been proposed but the optimal PEEP level remains unsettled. Considerable efforts have been made within the last decades to try to develop new ventilator strategies as well as pharmacological and mechanical measures in order to prevent VILI and further improve the outcome of ARDS patients. This review will strive to describe seminal experimental and clinical studies that aimed at preventing the development of VILI.     

高频振荡通气在成年人急性呼吸窘迫综合征的临床应用

背景 高频振荡通气(high-frequency oscillatory ventilation,HFOV)作为一种新的通气模式,具有高频率、小潮气量、高平均气道压的特点,近年来被成功应用于成年人急性呼吸窘迫综合征(acute respiratory distress syndrome,ARDS)的治疗.研究表明,HFOV在改善氧合、减少呼吸机相关性肺损伤(ventilator associated lung injury,VILI)方面较常规机械通气(conventional mechanical ventilation,CMV)具有优势.但其对ARDS病死率的影响尚不明确. 目的 通过归纳HFOV在成年人ARDS中的临床应用揭示HFOV的优势和缺陷. 内容 HFOV能够高效改善氧合、减少VILI,但不能减少ARDS的病死率.HFOV技术的最适患者的筛选、最佳使用时机、最佳参数的设定以及与其他治疗手段联用等问题有待进一步探索. 趋向 HFOV应用于ARDS的治疗需要更加深入的研究和探索.     

小潮气量结合肺复张术对食管癌开胸术后早期急性呼吸窘迫综合征患者的疗效

目的 观察小潮气量(VT)结合肺复张术对食管癌开胸术后早期急性呼吸窘迫综合征(ARDS)患者的疗效与可能出现的不良反应.方法 2007年1月1日至2009年9月30日收治食管癌开胸术后早期ARDS患者26例,男性20例,女性6例;年龄51～76岁,平均65.5岁.患者术后循环稳定,因ARDS而不能脱离机械通气.监测并持续记录无创血压、脉搏氧饱和度,实行小VT通气结合呼吸末正压(PEEP)递增法进行肺复张.记录肺复张前及两次肺复张后30 min的PEEP水平及吸入氧浓度(FiO2);监测静态肺顺应性(CLS)及动脉血气分析.结果 26例患者共实施肺复张术52次,全部患者在肺复张术后,FiO2减低,CLS增加,动脉血气分析改善.所有病例均顺利出院,未发生气压伤或其他并发症.结论 小VT结合肺复张策略可以有效改善食管癌开胸术后早期ARDS患者的低氧血症.     

Visual validation of the mechanical stabilizing effects of positive end-expiratory pressure at the alveolar level

BACKGROUND: Positive end-expiratory pressure (PEEP) reduces ventilator-induced lung injury (VILI), presumably by mechanically stabilizing alveoli and decreasing intrapulmonary shear. Although there is indirect support for this concept in the literature, direct evidence is lacking. In a surfactant depletion model of acute lung injury we observed unstable alveolar mechanics referred to as repeated alveolar collapse and expansion (RACE) as measured by changes in alveolar area from inspiration to expiration (I - E(Delta)). We tested the hypothesis that over a range of tidal volumes PEEP would prevent RACE by mechanically stabilizing alveoli. MATERIALS AND METHODS: Yorkshire pigs were randomized to three groups: control (n = 4), Tween (surfactant-deactivating detergent) (n = 4), and Tween + PEEP (7 cm H(2)O) (n = 4). Using in vivo video microscopy individual alveolar areas were measured with computer image analysis at end inspiration and expiration over consecutive increases in tidal volume (7, 10, 15, 20, and 30 cc/kg.) I - E(Delta) was calculated for each alveolus. RESULTS: Surfactant deactivation significantly increased I - E(Delta) at every tidal volume compared to controls (P < 0.05). PEEP prevented this change, returning I - E(Delta) to control levels over a spectrum of tidal volumes. CONCLUSIONS: RACE occurs in our surfactant deactivation model of acute lung injury. PEEP mechanically stabilizes alveoli and prevents RACE over a range of tidal volumes. This is the first study to visually document the existence of RACE and the mechanical stabilizing effects of PEEP at the alveolar level. The ability of PEEP to stabilize alveoli and reduce shear during mechanical ventilation has important implications for therapeutic strategies directed at VILI and acute respiratory distress syndrome.     

The preventive role of higher PEEP in treating severely hypoxemic ARDS

This review summarizes knowledge and evidence on the use of positive end-expiratory pressure (PEEP) in patients with severely hypoxemic acute respiratory distress syndrome (ARDS). More specifically, it documents the current evidence on the effects of higher PEEP in preventing (or attenuating) lung damage during the ventilatory management of patients with severely hypoxemic ARDS. No established threshold has been set to define severely hypoxemic ARDS and higher PEEP. In this review, those variables are defined as PaO(2)/F(I)O(2) ≤100 mm Hg and ≥15 cm H(2)O, respectively. In ARDS, the intensity of hypoxemia correlated with the amount of lung recruitability. In ARDS, the primary objective of PEEP is to increase the amount of non-aerated lung at the end of expiration. In early ARDS with a diffuse pattern and severe hypoxemia, higher PEEP contributes to lung recruitment by maintaining lung recruitment elicited by tidal breath and recruitment maneuvers as well as minimizes the repeated opening and closure with no significant overdistension. Three clinical trials comparing high PEEP + low tidal volume to low PEEP + large tidal volume found benefits favoring the former combination. Three large multicenter randomized controlled trials did not demonstrate a significant effect on patient outcome of higher or lower PEEP at a fixed low tidal volume. The meta-analysis on individual data of these three studies showed that the hospital mortality was not significantly different between the two groups of patients, was significantly lower in the higher PEEP group in the subset of ARDS patients (PaO(2)/F(I)O(2) ≤200 mm Hg), and tended to be higher in the higher PEEP group in the subset of patients with acute lung injury (200< PaO(2)/F(I)O(2) ≤300 mm Hg). Therefore, higher PEEP should be used in patients with the highest lung recruitability and in the most hypoxemic patients. Higher PEEP should be used with caution in patients less severe hypoxemic (acute lung injury).To deliver optimal PEEP to those ARDS patients with the highest lung recruitability, this technique should be monitored at the bedside. Alternative methods are under investigation as part of a decremental PEEP trial.     

Mechanical ventilation in acute respiratory distress syndrome. New Trends

Adult Respiratory Distress Syndrome (ARDS) is characterized by an inflammatory process affecting endothelial and epithelial lung tissue, with occurrence of hypoxemia, bilateral X-ray infiltrates, in absence of cardiogenic edema. The introduction of Computerized Tomography brought some improvements in understanding the ARDS lung, leading to a pulmonary model made up of three zones: 1) normally inflated, 2) recruitable and 3) consolidated. It has now been well established that mechanical ventilation of ARDS lung presents some iatrogenic effects that may affect mortality. Several mechanisms are considered responsible of ventilator-associated lung injury (VALI): high inspired oxygen fraction, high inspiratory plateau pressure and large tidal volume, and intratidal collapse and reinflation of alveolar units. In these years, different ventilatory strategies in the treatment of ARDS patients have been suggested to decrease and to prevent VALI. The most important one seems to be the application of an appropriate value of tidal volume and positive end-expiratory pressure (PEEP). Several randomized studies, which compared low versus high tidal volumes, have recently been finished. Despite some differences, it seems that a ventilatory management limiting inspiratory plateau pressure to 35 cmH2O or lower may be useful to reduce VALI and mortality, also in association with a PEEP level sufficient to decrease the end-expiratory collapse. Another useful ventilatory tool for improving gas exchange and decreasing VALI in ARDS patients is likely the prone positioning, even if further studies are necessary to understand how this maneuver may really affect mortality. Another therapeutic instrument for improving oxygenation in ARDS patients is the inhalation of NO. Unfortunately, this pharmacological agent does not seem to affect the outcome of these patients.     

Early application of the lung protective ventilation strategy at different stages in two ARDS patients

We experienced 2 patients with acute respiratory distress syndrome (ARDS) from pneumonia after intervention for subarachnoidal hemorrhage. We applied lung protective ventilation strategy (LPVS) on both cases: a tidal volume less than 6 ml x kg(-1) ideal body weight and PEEP at 10-15 cmH2O. Although etiology and degree of hypoxia were very similar in two patients when ARDS was diagnosed, clinical course was quite different. The patient in whom LPVS had been started on the 5th day of ARDS required mechanical ventilation of 23 days. In contrast, another patient in whom LPVS had been started on the 16th day of ARDS required mechanical ventilation of 219 days. PaCO2 during LPVS with permissive hypercapnia in the latter patient increased up to 161 mmHg but no adverse effect was observed. These cases suggest that early application of the LPVS may be important to improve respiratory outcomes of ARDS patients.