肺复张治疗肺外源性急性呼吸窘迫综合征的效果评价

目的 观察肺复张对肺外源性急性呼吸窘迫综合征(ARDS)患者氧合指数[氧分压(PaO2)/吸入氧气浓度(FiO2)]、呼吸力学及血流动力学的影响.方法 14例肺外源性ARDS患者行保护性肺通气,稳定后开始肺复张治疗.实施控制性肺膨胀(SI)进行肺复张,每8小时进行1次,共3天,纪录每天第1次患者治疗前及治疗后1小时的血气指标、呼吸机参数及肺复张前后的血流动力学指标.结果 1、2、3天肺复张治疗后1小时患者PaO2/FiO2较治疗前均有上升,(162.6±19.80)mmHg vs(220.93±34.10)mmHg,(195.6±24.40) mmHg vs (243.3±34.60)mmHg,(222.57±27.40) mmHg vs(254.71±38.90)mmHg(P＜0.05或＜0.0l);气道峰压[PIP:(35.64±2.71)cmH2O vs(34.07±2.58)cmH2O,(32.86±3.30)cmH2O vs(30.93±3.15)cmH2O,(30.14±2.66)cmH2O vs (28.07±3.27)cmH2O,P＜0.01]、气道平台压[Pplat:(31.29±2.49)cmH2O vs (28.93±2.63) cmH2O,(28.79±3.02) cmH2O vs(26.86±3.13)cmH2O,(25.71±2.09)cmH2O vs(23.57±2.34)cmH2O,P＜0.01]在肺复张治疗后均下降,呼吸系统静态顺应性(Cst)在肺复张治疗后改善,且整体呈升高趋势[(26.21±3.26)ml/cmH2O vs (30.14±3.70) ml/cmH2O,(29.36±4.25) ml/cmH2O vs (33.64±5.30) ml/cmH2O,(32.14±5.05) ml/cmH2O vs (35.57±5.57)ml/cmH2O,P＜0.01)];14例患者中有9例在肺复张过程中心率升高、血压下降,但均能于复张后3分钟恢复至复张前水平,余患者肺复张过程中心率、血压未见明显波动,14例患者均无心律失常发生.结论 对于肺外源性ARDS,肺复张可明显改善氧合,改善呼吸系统顺应性,对血流动力学影响轻徽.     

A comparative study of the cardiorespiratory effects of continuous positive airway pressure breathing and continuous positive pressure ventilation in acute respiratory failure

Positive end expiratory pressure (PEEP) produces cardiopulmonary effects whether administered by controlled positive pressure ventilation (CPPV) or continuous positive airway pressure (CPAP). In eight patients with acute respiratory failure, the effects of 20 cm PEEP administered via CPPV and CPAP were compared. An esophageal balloon was used to calculate the transmural vascular pressures. The control values under mechanical ventilation with no PEEP (IPPV) for PaO₂ and QS/QT (FiO₂ being 1.0) were respectively 132±15 mmHg and 31±3%; CPPV gave a PaO₂ of 369±27 mmHg and QS/QT fo 14±1.6%, CPAP 365±18 mmHg and 18±1.3% respectively. The two different modes of ventilation (CPPV and CPAP) gave identical blood gas improvement through the same level of end expiratory transpulmonary pressure despite marked differences between absolute mean airway and esophageal pressures. Conversely, hemodynamic tolerance was very different from one technique to the other: CPPV depressed cardiac index from 3.4±0.3 to 2.4±0.2 l/min/m² as well as decreasing transmural filling pressures, suggesting a reduction in venous return. Conversely, filling pressures maintained at control values during CPAP and cardiac indexes were unchanged.Abbreviations IPPV intermittent positive pressure ventilation; mechanical ventilation (controlled mode) with zero end expiratory pressure (ZEEP) - CPPV continuous positive pressure ventilation: mechanical ventilation (controlled mode) with a positive pressure during expiration - CPAP continuous positive airway pressure; spontaneous ventilation with a positive pressure maintained during expiration - PEEP positive end expiratory pressure, whatever the ventilatory mode; spontaneous (CPAP) or mechanical (CPPV) Presented in part at the 44 th annual meeting of American College of Chest Physicians, Washington DC, October 1978     

Experimental results of using the "open lung concept"

Several elements of the "open lung concept", like ventilation with small tidal volumes, were incorporated into various ventilatory strategies. Our study demonstrates how the whole concept can be applied in an animal model using a standardized protocol with the following possible results. Eighteen pigs weighing between 30 and 45 kg were anaesthetized, tracheotomized and ventilated. Acute lung injury was induced by surfactant washout. Blood gases were monitored via a continuous arterial sensor system (Trendcare system). After washout, the ventilatory pattern of the American "ARDS Network study" was applied (PEEP = 9 cmH2O, volume controlled mode with a tidal volume of 6 ml/kg body weight and a respiratory rate of 25 breaths per minute). Afterwards, the opening pressure and the pressure at which the lung collapses were titrated. Both levels were used as the basis for adjusting the recruitment pressure and PEEP, which was necessary to keep the lung open. The respiratory rate was chosen in such a way that at a low intrapulmonary pressure difference between inspiration and expiration as well as normocapnia was reached. After induction of an acute lung injury by surfactant washout, the oxygenation index (OI) dropped from 556 +/- 54 to 176 +/- 89 mmHg. In the "ARDS Network" mode, OI increased to 285 +/- 49 mmHg. After alveolar recruitment with a peak pressure of 53 +/- 7 cmH2O and application of a median PEEP of 17 +/- 3 cmH2O, oxygenation returned close to baseline. A pCO2 of 33 +/- 4 mmHg resulted after using a respiratory rate of 39 breaths per minute. The median tidal volume was 8 ml/kg body weight. Despite a short arterial systolic blood pressure drop of 23 +/- 11 mmHg during recruitment, no significant difference was detectable afterwards compared to the baseline. Using low tidal volumes alone, complete reopening was not achieved in an experimentally induced acute lung injury. After recruitment manoeuvres, it was possible to reopen the lung and keep it open by application of a sufficient PEEP.     

最佳氧合法导向的PEEP对ARDS绵羊血流动力学和气体交换的影响

目的探讨最佳氧合法导向的呼气末正压(PEEP)对急性呼吸窘迫综合征(ARDS)绵羊血流动力学和气体交换的影响。方法肺泡灌洗法复制绵羊ARDS模型(n=6),在充分肺复张的基础上,利用最佳氧合法滴定最佳PEEP,并维持通气2 h。观察基础状态(PEEP 5 cmH2O)、ARDS模型稳定(PEEP 5 cmH2O)和最佳PEEP维持通气2 h的血流动力学、气体交换和呼吸力学变化。结果最佳氧合法滴定的最佳PEEP为(18±2)cmH2O。与ARDS模型比较,最佳PEEP维持通气期间心率(HR)、平均动脉压(MAP)、心脏指数(CI)、每搏指数(SVI)、中心静脉压(CVP)、平均肺动脉压(MPAP)、肺动脉嵌顿压(PAWP)和肺循环阻力指数(PVRI)差异无统计学意义(P>0.05),CVP、MPAP、PAWP和PVRI较基础状态明显升高(P<0.05)。与ARDS模型稳定时比较,最佳PEEP维持通气期间动脉血二氧化碳分压(PaCO2)明显降低(P<0.05),氧合指数(PaO2/FiO2)和氧输送(DO2I)显著升高(P<0.05),肺内分流率(Qs/Qt)明显改善(P<0.05),且PaCO2、PaO2/FiO2、DO2I和Qs/Qt均接近基础状态(P>0.05)。与ARDS模型稳定时比较,最佳PEEP维持通气期间的平均气道压(Pm)明显升高(P<0.05)、平台压力(Pplat)无明显变化(P>0.05)、肺动态顺应性(Cdyn)明显增加(P<0.05)。结论最佳氧合法导向的PEEP能有效地减少ARDS绵羊的肺内分流、改善氧合和肺顺应性,对血流动力学无明显影响。     

不同呼气末正压对ARDS犬肺复张后氧输送的影响

目的 探讨在急性呼吸窘迫综合征(ARDS)肺复张(RM)后不同呼气末正压(PEEP)对氧输送(DO2)影响.方法 复制15只犬油酸ARDS模型,低流速法描记静态压力容积(p-V)曲线,双向回归法计算吸气支低位拐点(LIP),压力控制法行RM,RM后按随机表调整PEEP分别为8(A),12(B),16 cmH2O(C)组(大致相当P-V曲线低位拐点以下4 cmH2O、拐点处和+4 cmH2O水平)(1 cmH2O=0.098 kPa).监测15 min时呼吸力学和P-V曲线法测定复张容积.同时观察RM前、RM完成后0,5,10和15 min时动脉血气、血流动力学,计算DO2.多组间单因素比较采用单因素方差分析,两独立样本间比较用t检验.结果 A组PaO2在RM后5,10和15 min[(257±23)mmHg,(253±21)mmHg,(255±19)mmHg]较0 min(322±20)mmHg(1 mmHg=0.133 kPa)有显著下降(P＜0.05);B和C组PaO2在RM后差异无统计学意义,两组间相比差异无统计学意义,但均显著高于A组(P＜0.05).静态顺应性在A,B组[(14.3±2.2)mL/cmH2O vs.(17.2±1.4)mL/cmH2O]之间差异无统计学意义(P＞0.05),但C组的静态顺应性(10.5±0.9)mL/cmH2O比其他组显著降低.复张容积则随PEEP水平的增高而增加[(50±12)mL,(124±15)mL,(157±10)mL],相对于PEEP A升到B组,从B到C组复张容积增加量明显降低(P＜0.05).以RM后与RM前氧输送的比值变化反映RM后不同PEEP水平对DO2的影响,复张后B组0,5,10,15 min时DO2(1.15±0.11),(1.14±0.12),(1.14±0.12),(1.16±0.11)较RM前DO2(1.00±0.09)显著增加(P＜0.05),而在其他组与RM前相比DO2无显著增加(P＞0.05).结论 LIP附近压力为ARDS RM后的PEEP比较合适,可以维持肺复张后氧合与复张容积,并改善肺顺应性,增加氧输送.

Abstract：

Objective To explore the effect of different positive end expiratory pressures (PEEP) on oxygen delivery (DO2) after recruitment maneuvers (RM) in dogs with acute respiratory distress syndrome (ARDS). Method After ARDS models established in 15 dogs by oleic acid, static P-V (pressure-volume) curves were determined by low flow technique. Lower inflection point (LIP) was set by two-way linear regression methods. RM was operated with the pressure control method. ARDS dog models were randomly divided into three groups, namely PEEP 8 cmH2O group (group A), 12 cmH2O group (group B) and 16cmH2O group (group C) after RM (equivalent to pressure at4 cmH2O under LIP, 4 cmH2O near LIP, and 4 cmH2O above LIP, respectively). Hemodynamics and arterial blood gas analysis were monitored before RM, 0, 5, 10 and 15 min after RM. The recruited volume was measured by P-V curve method 15 min after RM and respiratory mechanics was also observed at the same time. Then DO2 was calculated. The quantitative variables were summarized as the mean and SD. The t-test was used to compare continuous variables between the two independent samples. One-way analysis of variance was used to compare variables among three groups. The level of significance was set at P＜0.05 for all the tests. Results In group A, the levels of PaO2 were significantly reduced 5 min, 10 min and 15 min after RM[(257 ± 23 )mmHg, (253±21)mmHg, and (255±19)mmHg] compared with PaO2 at 0 min [(322 ± 20) mmHg] (P＜0.05).But in group B and group C, the levels of PaO2 5 min, 10 min and 15 min after RM were not lower than level of PaO2 at 0 min after RM (P＞0.05 ). The levels of PaO2 in groups B and C were higher than that in group A at the same time (P＜0.05). The recruited volume distinctly increased with PEEP levels escalated [(50±12 ) mL, (124 ±15) mL, and ( 157 ±10)mL](P＜0.05). However, the increment in the recruited volume from PEEP 8 cmH2O to 12 cmH2O was dramatically greater than that from PEEP 12 cmH2O to 16 cmH2O.There was no significant difference in static compliance between group A and B [(14.3 ± 2.2) mL/cmH2O vs. (17.2±1.4)mL/cmH2O] (P ＞ 0.05 ). But compared with groups A and B, the static compliance in the group C significantly reduced(10.5 ± 0.9) mL/cmH2O ( P ＜ 0.05 ). The ratios of DO2 after RM to DO2 before RM were different at different levels of PEEP. The levels of DO2 after RM[( 1.15 ± 0. 11 ),( 1. 14 ± 0.12), ( 1.14 ± 0. 12) and ( 1.16 ± 0.11 )] increased more greatly than that before RM ( 1.00 ±0.09) in the group B (P ＜ 0.05 ). It did not occurred in the groups A and C. Conclusions The PEEP 12 cmH2O set at near the LIP after RM could be the optimal PEEP. Not only can it improve DO2 and the static compliance, but also maintain oxygenation and the recruited volume after RM.     

Transpulmonary pressure measurements and lung mechanics in patients with early ARDS and SARS-CoV-2

PurposeAcute Respiratory Distress Syndrome (ARDS) secondary to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has demonstrated variable oxygenation and respiratory-system mechanics without investigation of transpulmonary and chest-wall mechanics. This study describes lung, chest wall and respiratory-system mechanics in patients with SARS-CoV-2 and ARDS.MethodsData was collected from forty patients with confirmed SARS-CoV-2 and ARDS at Beth Israel Deaconess Medical Center in Boston, Massachusetts. Esophageal balloons were placed to estimate pleural and transpulmonary pressures. Clinical characteristics, respiratory-system, transpulmonary, and chest-wall mechanics were measured over the first week.ResultsPatients had moderate-severe ARDS (PaO₂/FiO₂ 123[98–149]) and were critically ill (APACHE IV 108 [94–128] and SOFA 12 [11–13]). PaO₂/FiO₂ improved over the first week (150 mmHg [122.9–182] to 185 mmHg [138–228] (p = 0.035)). Respiratory system (30–35 ml/cm H₂O), lung (40–50 ml/cm H₂O) and chest wall (120–150 ml/cm H₂O) compliance remained similar over the first week. Elevated basal pleural pressures correlated with BMI. Patients required prolonged mechanical ventilation (14.5 days [9.5–19.0]), with a mortality of 32.5%.ConclusionsPatients displayed normal chest-wall mechanics, with increased basal pleural pressure. Respiratory system and lung mechanics were similar to known existing ARDS cohorts. The wide range of respiratory system mechanics illustrates the inherent heterogeneity that is consistent with typical ARDS.     

肝移植术后腹压监测的临床研究

目的 研究腹压（intraabdominal pressure,IAP）增高对肝移植术后患者尿量、平均动脉压（MAP）和中心静脉压（CVP）的影响。方法 对105例肝移植患者进行腹压监测;根据腹压情况将患者分为两组：腹压正常组53例（IAP〈20cm H2O,1cmH2O=0．098kPa）和腹压异常组52例（≥20cmH2O）,其中又将腹压异常组分为20～〈30cmH2O（42例）、30～〈40cmH2O（4例）、≥40cmH2O（6例）3个亚组。患者入ICU后即测量基础腹腔压力,平均每8～12h测量1次,当腹压≥20cmH2O时每4h监测1次。结果 正常腹压组患者的MAP、CVP、尿量与腹压改变无相关性（P〉0．05）;异常腹压组患者的尿量与腹压呈显著负相关（P〈0．05）,同时MAP、CVP上升;当腹压升至30～40cmH2O且尿量减少时,MAP、CVP也下降（P〈0．01）。结论 正常腹压不影响肝移植患者尿量和循环稳定性;腹压增高导致少尿,而且腹压增高患者的CVP、MAP呈现双相变化。     

Ability of dynamic airway pressure curve profile and elastance for positive end-expiratory pressure titration

OBJECTIVE: To evaluate the ability of three indices derived from the airway pressure curve for titrating positive end-expiratory pressure (PEEP) to minimize mechanical stress while improving lung aeration assessed by computed tomography (CT). DESIGN: Prospective, experimental study. SETTING: University research facilities. SUBJECTS: Twelve pigs. INTERVENTIONS: Animals were anesthetized and mechanically ventilated with tidal volume of 7 ml kg(-1). In non-injured lungs (n = 6), PEEP was set at 16 cmH(2)O and stepwise decreased until zero. Acute lung injury was then induced either with oleic acid (n = 6) or surfactant depletion (n = 6). A recruitment maneuver was performed, the PEEP set at 26 cmH(2)O and decreased stepwise until zero. CT scans were obtained at end-expiratory and end-inspiratory pauses. The elastance of the respiratory system (Ers), the stress index and the percentage of volume-dependent elastance (%E (2)) were estimated. MEASUREMENTS AND MAIN RESULTS: In non-injured and injured lungs, the PEEP at which Ers was lowest (8-4 and 16-12 cmH(2)O, respectively) corresponded to the best compromise between recruitment/hyperinflation. In non-injured lungs, stress index and %E (2) correlated with tidal recruitment and hyperinflation. In injured lungs, stress index and %E (2) suggested overdistension at all PEEP levels, whereas the CT scans evidenced tidal recruitment and hyperinflation simultaneously. CONCLUSION: During ventilation with low tidal volumes, Ers seems to be useful for guiding PEEP titration in non-injured and injured lungs, while stress index and %E (2) are useful in non-injured lungs only. Our results suggest that Ers can be superior to the stress index and %E (2) to guide PEEP titration in focal loss of lung aeration.     

氧合导向肺外源性急性呼吸窘迫综合征最佳呼气末正压选择与最大肺静态顺应性相关性研究

目的 研究氧合导向肺外源性急性呼吸窘迫综合征(ARDS)最佳呼气末正压(PEEP)选择与最大肺静态顺应性(Cst)的相关性.方法 14例肺外源性ARDS患者充分肺复张后,采用最佳氧合法指导患者PEEP选择,每日进行1次,共3天,观察患者呼吸力学、血流动力学、肺气体交换指标的变化.结果 最佳氧合法选择的PEEP计算出的Cst低于最大Cst,差异有统计学意义,第1天对比:(30.14±3.70) ml/cmH2O vs (33.57±4.43) ml/cmH2O(P＜0.05);第2天对比:(32.93±5.05) ml/cmH2O vs (37.71±6.13) ml/cmH2O(P＜0.05);第3天对比:(34.50±4.55) ml/cmH2O vs(39.07±6.44) ml/cmH2O(P＜0.05).最大Cst对应的PEEP低于最佳氧合法选择的PEEP,差异有统计学意义,第1天对比:(11.71±2.33)cmH2O vs( 14.85±2.45) cmH2O(均P＜0.01);第2天对比:(11.57±3.06) cmH2O vs( 14.14±2.88) cmH2O(P＜0.05);第3天对比:(10.86±2.45) cmH2O vs (13.29±2.43) cmH2O(P＜0.05).结论 最佳氧合法选择的PEEP未使Cst最大化,可能与造成部分肺泡过度膨胀有关,虽然能明显改善氧合,但也可能加重局部肺损伤.     

Pulmonary lactate release in patients with acute lung injury is not attributable to lung tissue hypoxia

OBJECTIVE: To determine whether pulmonary lactate production in patients with acute lung injury is attributable to lung tissue hypoxia. DESIGN: Prospective, controlled, clinical study. SETTING: A multidisciplinary university intensive care unit in a general hospital. PATIENTS: Seventy consecutive critically ill patients requiring mechanical ventilation and invasive hemodynamic monitoring. Of these patients, 18 had no acute lung injury (no ALI); 33 had acute lung injury (ALI) (Lung Injury Score [LIS] < or =2.5); and 19 had acute respiratory distress syndrome (ARDS) (LIS >2.5). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: After hemodynamic measurements, lactate and pyruvate concentrations were assessed in simultaneously drawn arterial (a) and mixed venous (v) blood samples. Pulmonary lactate release was calculated as the product of transpulmonary a-v lactate difference (L[a-v]) times the cardiac index. Two indices of anaerobic metabolism of the lung, i.e., the transpulmonary a-v difference of lactate pyruvate ratio (L/P[a-v]) and excess lactate formation across the lungs (XL), were calculated. L(a-v) and pulmonary lactate release were higher in patients with ARDS than in the other groups (p<.001), and they were also higher in patients with ALI compared with patients with no ALI (p<.001). In patients with ALI and ARDS (n = 52), pulmonary lactate release correlated significantly with LIS (r2 = .14, p<.01) and venous admixture (r2 = .13, p<.01). When all patients were lumped together (n = 70), pulmonary lactate release directly correlated with LIS (r2 = .30, p<.001), venous admixture (r2 = .26, p<.001), and P(A-a)O2 (r2 = .14, p<.01). Neither L/P(a-v) nor XL was significantly different among the three groups. CONCLUSION: The lungs of patients with ALI produce lactate that is proportional to the severity of lung injury. This lactate production does not seem to be attributable to lung tissue hypoxia.     

机械通气对急性肺损伤大鼠细胞凋亡的影响

目的 研究不同潮气量及不同呼气末正压(PEEP)水平对急性肺损伤(AU)大鼠支气管和肺组织细胞凋亡的影响,并初步探讨细胞凋亡在呼吸机相关性肺损伤(VILI)中的作用机制.方法 选用40只SD大鼠,制作ALI模型,随机(随机数字法)分为:(1)小潮气量组(LV组),潮气量8 mL/kg,不加PEEP;(2)大潮气量组,潮气量30 mL./kg,不加PEEP;(3)小潮气量+ 2PEEP组(LV2P组),潮气量8 mL/kg,同时给PEEP 2 cmH2O(1 crnH2O =0.098 kPa);(4)小潮气量+5PEEP组(LV5P组),潮气量8 mL/kg,同时给PEEP 5 cmH2O;(5)小潮气量+8PEEP组(LV8P组),潮气量8 mL/kg,同时给PEEP 8 cmH2O.通气2h后处死动物,留取肺标本.用脱氧核糖核苷酸末端转移酶介导的末端标记法(TUNEL)分析肺组织中的细胞凋亡情况,用免疫组化法检测肺组织中caspase-3蛋白的表达及分布.结果 大潮气量组支气管和肺组织细胞凋亡的明显增加(P＜0.01),caspase-3蛋白酶表达最强.采用PEEP后,支气管和肺组织细胞凋亡减少,capase-3蛋白酶表达弱阳性,以LV5P组最为显著(P＜0.01).结论 小潮气量对肺组织有保护作用,采用PEEP后保护作用更加明显,细胞凋亡在VILI的发生中有重要作用.     

控制性肺膨胀对急性呼吸窘迫综合征绵羊肺力学和肺损伤的影响

目的：探讨控制性肺膨胀（SI）与肺保护性通气策略联合应用时，对急性呼吸窘迫综合征（ARDS）的肺泡复张作用及其安全性。方法：利用内毒秀导的绵羊ARDS模型，观察实施SI[2.94kPa(1kPa=10.20cmH2O)，屏气时间20秒]后绵羊的肺力学和组织病理学改变。结果：实施SI后，绵羊的动态肺顺应性和肺容积显著增加，气道峰值压、平台压和平均气道压均显著降低（P均＜0．05），并可维持3－4小时。与未应用SI的绵羊比较，实施SI后的绵羊肺损伤减轻，肺不张改善。结论：SI具有肺复张和肺保护作用，是肺保护性通气策略的重要补充。     

胸甲型负压通气机对肺功能正常受试者和阻塞性通气功能障碍患者通气功能的影响

目的：探讨影响胸甲型负压通气机临床疗效的因素。方法：选取10例阻 塞性通气功能障碍患者和20例肺功能正常受试者，观察不同负压水平时受试者通气量的变化。结果：肺功能正常受试者的潮气量在负压为－10cmH2O时与自主呼吸时比较差异无显著性意义，但阻塞性通气功能障碍患者潮气量在负压为－10cmH2O时小于自主呼吸时（P＜0．05）；肺功能正常受试者的潮气量大于自主呼吸时（P＜0．05），而阻塞性通气功能障碍患者潮气量与自主呼吸比较差异无显著性意义。结论：胸甲型负压通气机在适当的压力水平可提高肺无病变受试者的通气量；通过对胸甲型负压通气机的适当改进，有望在一定程度上增加阻塞性通气功能障碍患者潮气量,为伴有呼吸肌疲劳的呼吸功能不全患者的康复治疗提供一种新的手段。     

Assessment of airway closure from deflation lung volume–pressure curve: sigmoidal equation revisited

OBJECTIVE: To assess a sigmoidal equation for describing airway closure. DESIGN: Experimental study. SETTING: University laboratory. PARTICIPANTS: Eight piglets mechanically ventilated on zero end-expiratory pressure (ZEEP). INTERVENTIONS: Control and lung saline lavage. MEASUREMENTS AND RESULTS: Lungs were inflated up to transpulmonary pressure of 30 cmH(2)O at constant flow (0.12l s(-1)) then deflated at the same flow rate up to the point at which oesophageal pressure was constant, which was assumed to represent complete airway closure. The deflation volume-transpulmonary pressure curve was fitted to: (1) a sigmoidal equation focusing on inflexion point and pressure at maximal compliance increase and (2) an exponential equation above an inflexion point determined by eyeballing. Data deviate from the exponential equation at the point of airway closure onset. The zero-volume intercept was determined. Complete airway closure was reached at -8.3+/-3.5cmH(2)O in control conditions and at -1.3+/-3.7 cmH(2)O after lavage (p < 0.05). Between control and lavage, onset of airway closure was 3.0+/-1.9 vs. 6.0+/-2.8 cmH(2)O (p <0.05), inflexion point 3.2+/-1.8 vs. 7.7+/-2.6 cmH(2)O (p <0.001), pressure at maximal compliance increase -1.9+/-0.7 vs. -0.03+/-2.1cmH(2)O (p <0.05) and zero-volume intercept -1.5+/-1.4 vs. 0.3+/-2.3cmH(2)O (p <0.05). CONCLUSIONS: During mechanical ventilation airways stay open and close around ZEEP in control but are closed above ZEEP after lavage. Inflexion point might reflect onset of airways closure in control. Pressure at maximal compliance increase was not a marker of complete airways closure. In control and lavage, pressure at maximal compliance increase and zero-volume intercept were reasonably equivalent.     

Relationship between ventilatory settings and barotrauma in the acute respiratory distress syndrome

OBJECTIVE: High pressures or volumes may increase the risk of barotrauma in the acute respiratory distress syndrome (ARDS). METHODS: The first part of the study analyzed data from a prospective trial of two ventilation strategies in 116 patients with ARDS retrospectively, and ventilatory pressures and volumes were compared in patients with or without pneumothorax. The second part consisted of a literature analysis of prospective trials (14 clinical studies, 2270 patients) describing incidence and risk factors for barotrauma in ARDS patients, and mean values of ventilatory parameters were plotted against incidence of barotrauma. RESULTS: In our clinical trial comparing two tidal volumes, 15 patients (12.3%) developed pneumothorax. There was no significant difference in any pressure or volume between these patients and the rest of the population, including end-inspiratory plateau pressure (P(plat)), driving pressure (P(plat)-PEEP), respiratory rate and compliance. Multiple trauma was more frequent among patients with pneumothorax (27%) than in those without (7%). Duration of mechanical ventilation tended to be longer with pneumothorax. In the literature review, the incidence of barotrauma varied between 0% and 49%, and correlated strongly with P(plat), with a high incidence above 35 cmH(2)O, and with compliance, with a high incidence below 30 ml/cmH(2)O. CONCLUSION: Clinical studies maintaining P(plat) lower than 35 cmH(2)O found no apparent relationship between ventilatory parameters and pneumothorax. Analysis of the literature suggests a correlation when patients receive mechanical ventilation with P(plat) levels exceeding 35 cmH(2)O.     

吸入氧浓度对急性呼吸窘迫综合征诊断的影响

目的 探讨吸入氧浓度(FiO2)对急性呼吸窘迫综合征(ARDS)患者氧合指数(P/F=PaO2/FiO2)的影响及其临床意义.方法 采用前瞻性研究,选择16例PEEP≥5 cmH2O(1 mmHg=0.098 kPa)时P/F为100～200 mmHg(1 mmHg=0.133 kPa)需机械通气的ARDS患者,实施肺复张(BIPAP,PH 40 cmH2O,40 s)后维持基线通气,稳定30 min后,按随机顺序设定FiO2为0.5,0.6,0.7,0.8,0.9和1.采用SPSS 13.0统计软件比较不同FiO2下患者呼吸力学、血气及血流动力学各指标的变化及其相关性.结果 随FiO2增加P/F逐渐增加,FiO2增加至0.7以上,P/F增加更加明显,FiO2分别为0.5和1.0两组进行比较,P/F的变化为24.70%±23.36%;6例(37.5%)患者FiO2为0.5时P/F＜200,而FiO2为1.0时P/F＞200;FiO2与Qs/Qt呈负相关(r=-0.390,P=0.027),吸入氧浓度越高,分流越小,FiO2为0.5和1.0时△Qs/Qt与△P/F呈正相关(r=0.82,P=0.005).结论 吸入氧浓度影响ARDS患者的氧合指数,从而可能影响ARDS的诊断,这与其对肺内分流的影响有关.

Abstract：

Objective To investigate the influence of inspired oxygen fraction (FiO2) on the ratio of PaO2/FiO2(P/F) during the implementation of lung protective ventilation strategy in patients with acute respiratory distress syndrome(ARDS) in order to unravel its clinical significance. Method This was a prospective study of 16 selected patients with ARDS treated with mechanical ventilation ( MV ) to get ratio of P/F in range of 100 to 200 by PEEP≥5 cmH2O and high inspired oxygen. After lung recruitment maneuvers by BiPAP with high pressure (PH) of 40 cmH2O for40 s, the MV was maintained the basic requirement for stabilizing the patients for 30 minutes. A series of FiO2 were set at fractions of 0.5,0.6,0.7,0.8,0.9 and 1in random sequence, and the changes of respiratory mechanics, blood gas and hemodynamics under the different concentrations of FiO2 were analyzed by using SPSS version 13.0 software. Results ( 1 ) The ratio of P/F increased as FiO2 increased, and it's significant as FiO2 increased to 0.7 or above. As the fractions of FiO2 were set at 0.5 and 1. O, the ratios of P/F changed in 24.70% ± 23.36% respectively. ( 2 ) Of them,6 patients ( 37.5% ) treated with FiO2 set at 0.5 had the ratio of P/F ＜ 200, and the fraction of FiO2 was increased to 1.0, the P/F ＞ 200. (3) FiO2 and Qs/Qt were negatively correlated ( r = - 0.390, P = O. 027 ),the higher inspired oxygen fraction, the lower shunt. When the fractions of FiO2 were set at 0.5 and 1.0 ,there was a positive correlation between △Qs/Qt and △P/F( r = 0.82, P = 0.005 ). Conclusions The inspired oxygen fraction affects the ratio of P/F, which may be resulted from shunt and it may influence the diagnosis of ARDS.     

The upper inflection point of the pressure-volume curve. Influence of methodology and of different modes of ventilation

OBJECTIVE: The pressure-volume (P/V) curve has been proposed as a tool to adjust the ventilatory settings in cases of acute respiratory distress syndrome (ARDS). The aim of this study was to test the influence of P/V tracing methodology on the presence and value of the upper inflection point (UIP). METHODS: In 13 medical ARDS patients, the interruption and the automated low flow inflation methods were compared while the patients were ventilated at conventional (10-12 ml/kg) and at low (5-6 ml/kg) tidal volume (Vt). Two levels of inspiratory flow and insufflation time were used (3 and 6 s). RESULTS: No significant difference in UIP was found between the static and the dynamic methods, whatever the flow used. At Vt 10-12 ml/kg, the static and dynamic UIPs were 22.4 +/- 4.4 cmH(2)O and 22.1 +/- 4.5 cmH(2)O ( p = 0.86), respectively; at Vt of 5-6 ml/kg, the static and dynamic UIPs were 26.6 +/- 4.1 cmH(2)O and 25.5 +/- 5 cmH(2)O ( p = 0.34), respectively. Significant differences in UIP were found, in the static and dynamic conditions, between the two levels of Vt ( p < 0.005): it was lower with the higher Vt, suggesting that UIP is dependent on previous tidal alveolar recruitment. CONCLUSION: Interruption and continuous flow techniques gave similar results, but the previous Vt influences the pressure value of the UIP.     

肿瘤术后急性呼吸窘迫综合征行肺复张不同模式的疗效及安全性

目的探讨控制性肺膨胀（SI）和压力控制（PCV）两种肺复张对肿瘤术后急性呼吸窘迫综合征（ARDS）患者的影响。方法采用随机对照病例研究方法,选择肿瘤术后ARDS患者22例,随机分为sI组和PCV组,每组11例。SI组呼吸机模式改为CPAP模式、压力设为40cmH2O进行机械通气,持续40s。PCV组呼吸机模式改为压力控制,吸气压力（PressureabovePEEP）20cmH2O,I：E=1：1,持续2min。收集2组患者肺复张前、复张后30min、2h、6h各时间点氧合指数（PaO2／FiO2）、静态肺顺应性（Cst）;监测每次肺复张前后血流动力学变化。结果治疗后2组患者PaO2／FiO2、Cst均呈上升趋势（P〈0．01）,但在各时间点两组比较差异无统计学意义（P〉0．05）。两组患者在肺复张后心率升高,平均动脉压下降,与复张前比较差异有统计学意义（P〈0．05）,PCV组心率和平均动脉压波动幅度低于sI组,差异有统计学意义（P〈0．05）。结论sI与PCV两种肺复张均能改善肺氧合及肺顺应性,PCV肺复张对血流动力学影响低于SI。     

Prevalence, etiologies and outcome of the acute respiratory distress syndrome among hypoxemic ventilated patients

Objective: To evaluate the prevalence and outcome of the acute respiratory distress syndrome (ARDS) among patients requiring mechanical ventilation. Design: A prospective, multi-institutional, initial cohort study including 28-day follow-up. Settings: Thirty-six French intensive care units (ICUs) from a working group of the French Intensive Care Society (SRLF). Patients: All the patients entering the ICUs during a 14-day period were screened prospectively. Hypoxemic patients, defined as having a PaO₂/FIO₂ ratio (P/F) of 300 mmHg or less and receiving mechanical ventilation, were classified into three groups, according to the Consensus Conference on ARDS: group 1 refers to ARDS (P/F: 200 mmHg or less and bilateral infiltrates on the chest X-ray); group 2 to acute lung injury (ALI) without having criteria for ARDS (200 < P/F ≤ 300 mmHg and bilateral infiltrates) and group 3 to patients with P/F of 300 mmHg or less but having exclusion criteria from the previous groups. Results: Nine hundred seventy-six patients entered the ICUs during the study period, 43 % of them being mechanically ventilated and 213 (22 %) meeting the criteria for one of the three groups. Among all the ICU admissions, ARDS, ALI and group 3 patients amounted, respectively, to 6.9 % (67), 1.8 % (17) and 13.3 % (129) of the patients, and represented 31.5 %, 8.1 % and 60.2 % of the hypoxemic, ventilated patients. The overall mortality rate was 41 % and was significantly higher in ARDS patients than in the others (60 % vs 31 % p < 0.01). In group 3, 42 patients had P/F less than 200 mmHg associated with unilateral lung injury; mortality was significantly lower (40.5 %) than in the ARDS group. In the whole group of hypoxemic, ventilated patients, septic shock and severity indices but not oxygenation indices were significantly associated with mortality, while the association with immunosuppression revealed only a trend (p = 0.06). Conclusions: In this survey we found that very few patients fulfilled the ALI non-ARDS criteria and that the mortality of the group with ARDS was high. Received: 21 September 1998 Final revision received: 3 February 1999 Accepted: 3 May 1999     

肺复张和保护性肺通气在急性肺损伤救治中的护理

目的探讨肺复张联合保护性肺通气策略治疗急性肺损伤患者的疗效及护理。方法对42例急性肺损伤/急性呼吸窘迫综合征(ALI/ARDS)患者均采用保护性机械通气,并联合肺复张手法,给予35 cmH2O的气道压力,持续30 s后,恢复原通气模式及条件。结果 31例患者成功撤机,临床症状明显好转,治愈出院,成功率73.8%。死亡11例,病死率26.2%。结论肺复张和保护性肺通气策略是治疗急性肺损伤的主要手段。做好保护性机械通气期间的护理及严密监测是治疗成功的关键。