氧合导向最佳呼气末正压对急性呼吸窘迫综合征犬肺局部气体分布和炎症反应的影响

目的 探讨氧合导向最佳呼气末正压(PEEP)对急性呼吸窘迫综合征(ARDS)犬肺组织局部气体分布和炎症反应的影响.方法 静脉注射油酸(油酸组,8只)、肺泡灌洗生理盐水(生理盐水组,8只)复制犬ARDS模型.模型成功后给予氧合导向最佳PEEP进行机械通气,基础状态、模型复制成功及机械通气4 h后均行肺部CT扫描,观察肺局部气体分布.4 h后处死犬,留取肺组织观察病理改变,凝胶迁移率改变电泳(EMSA)测肺组织NF-κB活性,比色法测肺组织髓过氧化物酶(MPO)和丙二醛(MDA)含量,ELISA测肺组织IL-6、IL-10含量.结果 (1)与基础状态比,2组犬模型复制成功后,总肺容积均显著减少,不通气区肺容积明显增加;与模型复制成功时比,2组犬在最佳氧合法确定PEEP水平,CT扫描显示低通气区及不通气区肺容积明显减少,正常通气肺组织增加,但过度膨胀区肺容积也显著增加,以腹侧(非重力依赖区)肺泡过度膨胀明显.与油酸组比,在最佳氧合法确定PEEP水平,生理盐水组过度膨胀区肺容积增多更显著.(2)2组犬肺右下叶腹侧组织损伤评分均明显高于右上叶,肺右下叶背侧组织损伤评分均明显高于右上叶、右下叶腹侧;肺右下叶背侧组织NF-κB活性均明显高于右上叶;肺右下叶背侧、右下叶腹侧组织MPO和MDA含量均明显高于右上叶;肺右下叶背侧组织IL-6、IL-10含量均明显高于右上叶、右下叶腹侧.结论 以氧合导向最佳PEEP致ARDS肺非重力依赖区过度膨胀,加重局部肺损伤.生理盐水组犬肺过度膨胀更显著.     

Respiratory system mechanics in acute respiratory distress syndrome

Respiratory mechanics research is important to the advancement of ARDS management. Twenty-eight years ago, research on the effects of PEEP and VT indicated that the lungs of ARDS patients did not behave in a manner consistent with homogenously distributed lung injury. Both Suter and colleagues] and Katz and colleagues reported that oxygenation continued to improve as PEEP increased (suggesting lung recruitment), even though static Crs decreased and dead-space ventilation increased (suggesting concurrent lung overdistension). This research strongly suggested that without VT reduction, the favorable effects of PEEP on lung recruitment are offset by lung overdistension at end-inspiration. The implications of these studies were not fully appreciated at that time, in part because the concept of ventilator-associated lung injury was in its nascent state. Ten years later. Gattinoni and colleagues compared measurements of static pressure-volume curves with FRC and CT scans of the chest in ARDS. They found that although PEEP recruits collapsed (primarily dorsal) lung segments, it simultaneously causes overdistension of non-dependent, inflated lung regions. Furthermore, the specific compliance of the aerated, residually healthy lung tissue is essentially normal. The main implication of these findings is that traditional mechanical ventilation practice was injecting excessive volumes of gas into functionally small lungs. Therefore, the emblematic low static Crs measured in ARDS reflects not only surface tension phenomena and recruitment of collapsed airspaces but also overdistension of the remaining healthy lung. The studies reviewed in this article support the concept that lung injury in ARDS is heterogeneously distributed, with resulting disparate mechanical stresses, and indicate the additional complexity from alterations in chest wall mechanics. Most of these studies, however, were published before lung-protective ventilation. Therefore, further studies are needed to refine the understanding of the mechanical effects of lung-protective ventilation. Although low-VT ventilation is becoming a standard of care for ARDS patients, many issues remain unresolved; among them are the role of PEEP and recruitment maneuvers in either preventing or promoting lung injury and the effects of respiratory rate and graded VT reduction on mechanical stress in the lungs. The authors believe that advances in mechanical ventilation that may further improve patient outcomes are likely to come from more sophisticated monitoring capabilities (ie, the ability to measure P1 or perhaps Cslice) than from the creation of new modes of ventilatory support.     

Adult respiratory distress syndrome profiles by computed tomography

Ten patients with full-blown ARDS, on mechanical ventilation with PEEP underwent lung CT. Seven normal subjects were also studied. Three tomographic levels (apex, hilum, and base) were selected. The most consistent morphologic finding in ARDS was the presence of densities in the dependent regions of the lung. Assuming that the three levels were a representative sample of the whole lung, the lung weight was computed from the mean CT number and lung gas volume. Analysis of the CT number frequency distribution revealed three definite patterns of distribution: type 1, bimodal, with one mode in the normal CT number range; type 2, unimodal narrow distribution, with the mode in the CT range of water; and type 3, unimodal broad distribution in the abnormal CT number range.     

Oleic acid vs saline solution lung lavage-induced acute lung injury: effects on lung morphology, pressure-volume relationships, and response to positive end-expiratory pressure

OBJECTIVE: To compare two lung injury models (oleic acid [OA] and saline solution washout [SW]) regarding lung morphology, regional inflation, and recruitment during static pressure-volume (PV) curves, and the effects of positive end-expiratory pressure (PEEP) below and above the lower inflection point (Pflex). METHODS: Fourteen adult pigs underwent OA or SW lung injury. Lung volumes were measured using CT. PV curves were obtained with simultaneous CT scanning at lung apex and base. Fractional inflation and recruitment were compared to data on PEEP above and below Pflex. RESULTS: Severity of lung injury was comparable. At zero PEEP, SW showed an increased amount of edema and poorly aerated lung volume, recruitment during inspiration, and a better oxygenation response with PEEP. Whole-lung PV curves were similar in both models, reflecting changes in alveolar inflation or deflation. On the inspiratory PV limb, recruitment and inflation were on the same line, while there was a substantial difference between deflation and derecruitment on the expiratory limb. PEEP-induced recruitment at lung apex and base was at or above the derecruitment line on the expiratory limb and showed no relationship to the whole-lung expiratory PV curve. CONCLUSIONS: The following conclusions were made: (1) OA and SW models are comparable in mechanics but not in lung injury characteristics; (2) neither inspiratory nor expiratory whole-lung PV curves are useful to select PEEP in order to optimize recruitment; and (3) after recruitment, there is no difference in derecruitment between the models at high PEEP, while more collapse occurs at lower PEEP in the basal sections of SW lungs.     

吸痰联合肺复张后不同PEEP水平对ARDS机械通气患者呼吸力学的影响

目的探讨吸痰联合肺复张后调整不同的呼气末正压(PEEP)水平对急性呼吸窘迫综合征(ARDS)机械通气患者呼吸力学的影响。方法选择22例ARDS机械通气患者,吸痰后给予肺复张,在原有PEEP水平(P0)基础上调整。于调整PEEP后10、30、60 min,监测患者各压力水平气道峰压(Ppeak)、平台压(Pplat)、肺实时顺应性(Cd)变化。结果与实验前比较,Cd在不同PEEP水平均显著升高(P均<0.05)。随着PEEP水平的不断增加,Cd也随之升高,与调整后其他PEEP水平相比,P0+4 cmH2O和P0+6 cmH2O测得Cd显著高于其他水平(P<0.05)。30 min Cd监测值显著高于10、60 min(P均<0.05)。与其他四组比较,P0+4 cmH2O和P0+6 cmH2O在30～60 min时段Cd下降趋势较小(P<0.05)。随着PEEP水平不断增加,Ppeak、Pplat也随之升高,但不同PEEP水平对Ppeak、Pplat的影响无统计学差异(P>0.05)。结论 ARDS机械通气患者在吸痰联合肺复张后选择在P0基础上增加4～6 cmH2O,有利于维持患者复张后肺顺应性,延缓肺泡去复张时间。     

Radiological imaging in acute lung injury and acute respiratory distress syndrome

Computed tomography (CT) has been utilized to study acute respiratory distress syndrome (ARDS) since the middle 1980s, when it revealed the inhomogeneous pattern of the lung lesion. Its advantages rely on the strict correlation between CT density and the lung physical density, allowing a quantification of lung compartments with different degrees of aeration. By CT scans, ARDS lung appeared to be "small" rather than "stiff," leading to the "baby lung" concept. The regional analysis revealed that this appearance derives from an evenly distributed lung edema, which tends, because of gravitational forces, to lie predominantly in the most dependent regions, leading to alveolar collapse. New data suggest that such a "sponge lung" is made by a "core," consolidated, lung portion, from which, through an inflammatory reaction, lung edema will spread, determining the collapsed and recruitable lung portion. The amount of recruitable lung varies among ARDS patients. This knowledge is necessary for a rational positive end-expiratory pressure (PEEP) setting because the amount of tissue maintained aerated by PEEP is closely associated with the amount of recruitable lung. CT scans may also help to diagnose ARDS because CT provides a good estimate of the high-permeability lung edema, the characteristic lesion of this syndrome.     

Recruitment and derecruitment during acute respiratory failure: a clinical study.

In a model of acute lung injury, we showed that positive end-expiratory pressure (PEEP) and tidal volume (VT) are interactive variables that determine the extent of lung recruitment, that recruitment occurs across the entire range of total lung capacity, and that superimposed pressure is a key determinant of lung collapse. Aiming to verify if the same rules apply in a clinical setting, we randomly ventilated five ALI/ARDS patients with 10, 15, 20, 30, 35, and 45 cm H2O plateau pressure and 5, 10, 15, and 20 cm H2O of PEEP. For each PEEP-VT condition, we obtained computed tomography at end inspiration and end expiration. We found that recruitment occurred along the entire volume-pressure curve, independent of lower and upper inflection points, and that estimated threshold opening pressures were normally distributed (mode = 20 cm H2O). Recruitment occurred progressively from nondependent to dependent lung regions. Overstretching was not associated with hyperinflation. Derecruitment did not parallel deflation, and estimated threshold closing pressures were normally distributed (mode = 5 cm H2O). End-inspiratory and end-expiratory collapse were correlated, suggesting a plateau-PEEP interaction. When superimposed gravitational pressure exceeded PEEP, end-expiratory collapse increased. We concluded that the rules governing recruitment and derecruitment equally apply in an oleic acid model and in human ALI/ARDS.     

Lung recruitment maneuvers in acute respiratory distress syndrome

In the experimental setting, repeated derecruitments of the lungs of ARDS models accentuate lung injury during mechanical ventilation, whereas open lung concept strategies can attenuate the injury. In the clinical setting, recruitment manuevers that use a continuous positive airway pressure of 40 cmH2O for 40 secs improve oxygenation in patients with early ARDS who do not have an impairment in the chest wall. High intermittent positive end-expiratory pressure (PEEP), intermitent sighs, or high-pressure controlled ventilation improves short-term oxygenation in ARDS patients. Both conventional and electrical impedance thoracictomography studies at the clinical setting indicate that high PEEP associated with low levels of pressure control ventilation recruit the collapsed portions of the ARDS lungs and that adequate PEEP levels are necessary to keep the ARDS lungs opened allowing a more homogenous ventilation. High PEEP/low tidal volume ventilation was seen to reduce inflammatory mediators in both bronchoalveolar lavage and plasma, compared to low PEEP/high tidal volume ventilation, after 36 hours of mechanical ventilation in ARDS patients. Recruitment maneuvers that used continuous positive airway pressure levels of 35-40 cmH2O for 40 secs, with PEEP set at 2 cmH2O above the lower inflection point of the pressure-volume curve, and tidal volume < 6 mL/kg were associated with a 28-day intensive care unit survival rate of 62%. This contrasted with a survival rate of only 29% with conventional ventilation (defined as the lowest PEEP for acceptable oxygenation without hemodynamic impairment with a tidal volume of 12 mL/kg), without recruitment manuevers (number needed to treat = 3; p < 0.001). In the near future, thoracic computed tomography associated with high-performance monitoring of regional ventilation may be used at the bedside to determine the optimal mechanical ventilation of the ARDS keeping an opened lung with a homogenous ventilation.     

Inflection point,positive end-expiratory pressure,and alveolar recruitment in acute respiratory distress syndrome

Summary Impaired arterial oxygenation due to a true intrapulmonary shunting is a key feature of the acute respiratory distress syndrome (ARDS), and every effort should be made to improve oxygen delivery to the body's tissues. In patients with ARDS an improvement in the arterial oxygenation can be obtained only by reopening previously closed airspaces, and the application of PEEP has been recognized, for a long time, as the method of choice to reach this goal. Therefore, the relationships between PEEP and alveolar recruitment are an issue of great clinical interest. Alveolar recruitment can be evaluated indirectly by recording the changes of several parameters, such as, the shunt fraction, the alveolar dead space, the functional residual capacity (FRC), the shape of the dynamic pressure-volume (P-V) curve, and the slope of the static P-V curve. This latter method, which consists of finding a lower inflection point on the total respiratory system P-V curve (P-V,rs), is one of the most employed methods in both the clinical practice and the research field. However, the relationship between a LIP on the P-V,rs curve and alveolar recruitment have recently been questioned. In fact a LIP can be found not only on the lung P-V curve, but also on the chest-wall P-V curve, and it has been shown that in some patients, the LIP seen on the P-V,rs is due to the chest-wall only and not to the lung. A quantitative estimation of the alveolar recruitment can be done by the analysis of the P-V curves drawn at different levels of PEEP, or by the a CT scan evaluation of the changes in gas distribution within the lung. Studies done with these methods have led to a demonstration of a weak relationship between the lower inflection point on the P-V,rs curve and the alveolar recruitment. In fact, it has been shown that a recruitment continues to occur even when PEEP is set beyond the LIP. These findings have a direct clinical implication in that a ventilatory strategy aimed at optimization of the alveolar recruitment must guarantee, at least in the early phase of the disease, an airway pressure high enough to overcome all the collapsing forces. Received: 16 October 1997 Accepted: 17 April 1998     

Best compliance during a decremental, but not incremental, positive end-expiratory pressure trial is related to open-lung positive end-expiratory pressure: a mathematical model of acute respiratory distress syndrome lungs

A mathematical model of the acute respiratory distress syndrome (ARDS) lung, incorporating simulated gravitational superimposed pressure and alveolar opening and closing pressures, was used to study the mean tidal pressure-volume (PV) slope ("effective compliance") during incremental and decremental positive end-expiratory pressure (PEEP) trials with constant tidal volume (VT) "ventilation." During incremental PEEP, the PEEP giving maximum mean tidal PV slope did not coincide with "open lung PEEP" (minimum PEEP preventing end expiratory collapse of 97.5% of alveoli inflated at end-inspiration), and it varied greatly with varying VT and "lung mechanics." Incremental PEEP with a low VT tests recruitment by the peak pressure, not prevention of collapse by PEEP. During decremental PEEP with a low VT, maximum mean tidal PV slope occurred with PEEP 2-3.5 cm H2O below open-lung PEEP, unless closing pressure was high. High VT, high "specific compliance," and high opening pressures caused slightly greater underestimation of open-lung PEEP. Maximum mean tidal PV slope was always higher (e.g., 93.7 versus 16.69 ml/cm H2O), and the variation in PV slope with PEEP was greater, during decremental PEEP. The maximum PV slope during a decremental PEEP trial with a low VT may be a useful method to determine open-lung PEEP in ARDS, and should be studied clinically.     

Ventilatory strategies in patients with sepsis and respiratory failure

Patients with sepsis may require mechanical ventilation due to the acute respiratory distress syndrome (ARDS). It has become increasingly accepted that mechanical ventilation can contribute to lung injury in these patients. The modern concept of ventilator-induced lung injury is described in the context of alveolar over-distention (volutrauma), alveolar de-recruitment (atelectrauma), and biochemical injury and inflammation to the lung parenchyma (biotrauma). To avoid over-distention lung injury, the tidal volume should be set at 6 mL/kg predicted body weight and plateau pressure should be limited to 30 cm H₂O. This has been shown to afford a survival benefit. Although setting positive end-expiratory pressure (PEEP) to zero is likely harmful during mechanical ventilation of patients with ARDS, evidence is lacking for a survival benefit if a high PEEP level is set compared with a modest level of PEEP. Although adjunctive measures such as recruitment maneuvers, prone position, and inhaled nitric oxide may improve oxygenation, evidence is lacking that these measures improve survival.     

Pulmonary and extrapulmonary forms of acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is usually viewed as the functional and morphological expression of a similar underlying lung injury caused by a variety of insults. However, the distinction between ARDS due to a direct (ARDSp) versus an indirect (ARDSexp) lung injury is gaining more attention as a means of better comprehending the pathophysiology of ARDS and for modifying ventilatory management. From the few published studies, we can summarize that: (1) the prevalent damage in early stages of a direct insult is intra-alveolar, whereas in indirect injury it is the interstitial edema. It is possible that the two insults may coexist (i.e., one lung with direct injury (as in pneumonia) and the other with indirect injury, through mediator release from the contralateral pneumonia); (2) the radiological pattern, by chest x-ray or computed tomography (CT), is different in ARDSp (characterized by prominent consolidation) and ARDSexp (characterized by prominent ground-glass opacification); (3) in ARDSp lung elastance is more markedly increased than in ARDSexp, where the main abnormality is the increase in chest wall elastance, due to abnormally high intra-abdominal pressure; (4) positive end-expiratory pressure (PEEP), inspiratory recruitment, and prone position are more effective to improve respiratory mechanics, alveolar recruitment, and gas-exchange in ARDSexp. Further studies are warranted to better define if the distinction between ARDS of different origins can improve clinical management and survival.     

Computed tomography assessment of positive end-expiratory pressure-induced alveolar recruitment in patients with acute respiratory distress syndrome

Computed tomography (CT) assessment of positive end-expiratory pressure (PEEP)-induced alveolar recruitment is classically achieved by quantifying the decrease in nonaerated lung parenchyma on a single juxtadiaphragmatic section (Gattinoni's method). This approach ignores the alveolar recruitment occurring in poorly aerated lung areas and may not reflect the alveolar recruitment of the entire lung. This study describes a new CT method in which PEEP-induced alveolar recruitment is computed as the volume of gas penetrating in poorly and nonaerated lung regions following PEEP. In 16 patients with acute respiratory distress syndrome a thoracic spiral CT scan was performed in ZEEP and PEEP 15 cm H(2)O. According to the new method, PEEP induced a 119% increase in functional residual capacity (FRC). PEEP-induced alveolar recruitment was 499 +/- 279 ml whereas distension and overdistension of previously aerated lung areas were 395 +/- 382 ml and 28 +/- 6 ml, respectively. The alveolar recruitment according to Gattinoni's method was 26 +/- 24 g and no correlation was found between both methods. A significant correlation was found between PEEP-induced alveolar recruitment and increase in Pa(O(2)) only when recruitment was assessed by the new method (Rho = 0.76, p = 0.003), suggesting that it may be more accurate than Gattinoni's method.     

Montelukast versus inhaled corticosteroids in the management of pediatric mild persistent asthma

Background

Lung tissue of patients with acute respiratory distress syndrome (ARDS) is heterogeneously damaged and prone to develop atelectasis. During inflation, atelectatic regions may exhibit alveolar recruitment accompanied by prolonged filling with air in contrast to regions with already open alveoli with a fast increase in regional aeration. During deflation, derecruitment of injured regions is possible with ongoing loss in regional aeration. The aim of our study was to assess the dynamics of regional lung aeration in mechanically ventilated patients with ARDS and its dependency on positive end-expiratory pressure (PEEP) using electrical impedance tomography (EIT).

Methods

Twelve lung healthy and twenty ARDS patients were examined by EIT during sustained step increases in airway pressure from 0, 8 and 15 cm H₂O to 35 cm H₂O and during subsequent step decrease to the corresponding PEEP. Regional EIT waveforms in the ventral and dorsal lung regions were fitted to bi-exponential equations. Regional fast and slow respiratory time constants and the sizes of the fast and slow compartments were subsequently calculated.

Results

ARDS patients exhibited significantly lower fast and slow time constants than the lung healthy patients in ventral and dorsal regions. The time constants were significantly affected by PEEP and differed between the regions. The size of the fast compartment was significantly lower in ARDS patients than in patients with healthy lung under all studied conditions.

Conclusion

These results show that regional lung mechanics can be assessed by EIT. They reflect the lower respiratory system compliance of injured lungs and imply more pronounced regional recruitment and derecruitment in ARDS patients.     

肺开放策略治疗急性呼吸窘迫综合征的临床研究

目的探讨压力控制法进行肺开放治疗急性呼吸窘迫综合征(ARDS)的临床疗效。方法 52例ARDS患者在肺保护通气的基础上采用压力控制法进行肺开放,将呼吸机调整到压力支持模式,个体化使用PEEP和支持压力水平,PEEP15～25 cm H2O,支持压力15～20 cm H2O,气道峰压不超过45 cm H2O,维持1分钟,肺开放后继续进行肺保护通气。动态观察肺开放策略实施前后氧合指标、呼吸力学指标及血流动力学指标的变化。结果 52例ARDS患者共进行164次肺开放,肺开放前后氧合功能障碍明显改善。结论肺开放策略治疗重症ARDS明显改善了肺的氧合功能和顺应性,对血流动力学影响小,相对安全,有效地提高了抢救成功率。     

急性呼吸窘迫综合征家兔肺不同区域有效血流灌注变化及肺保护性通气对其的影响

目的 通过观察家兔急性呼吸窘迫综合征(ARDS)模型肺不同区域有效血流灌注变化及肺保护性通气对其的影响,探讨ARDS所致严重低氧血症的发生机制。方法 采用静脉注射油酸的方法建立家兔ARDS模型,应用PIM-Ⅱ激光多普勒血流灌注扫描仪观察不同肺通气模式[(大潮气、小潮气 外源性呼气末正压(PEEP)、大潮气 俯卧位、俯卧位 小潮气 PEEP]下肺不同区域(肺上区、肺下区腹侧和肺下区背侧)局部有效血流灌注及动脉血气指标的变化。结果 家兔静脉注射油酸后,(1)肺不同区域氧合指数明显下降,应用肺保护性通气(小潮气 PEEP,俯卧位 小潮气 PEEP)后氧合指数明显改善;(2)肺不同区域局部有效血流灌注均有不同程度的下降,以肺下区背侧最为明显,肺下区腹侧次之,肺上区变化最小,应用肺保护性通气后,小潮气 PEEP对改善肺下区背侧胸膜下肺局部有效血流灌注的效果不如俯卧位 小潮气 PEEP。结论小潮气 PEEP、俯卧位 小潮气 PEEP均可良好改善肺局部有效血流灌注,其中俯卧位 小潮气 PEEP效果尤为明显;右-左分流导致的肺内分流可能是ARDS发生严重进行性低氧血症的主要原因之一。     

Comparison of Recruitment Manoeuvres in Ventilated Sheep with Acute Respiratory Distress Syndrome

Background

Recruitment manoeuvres are widely used in clinical practice to open the lung and prevent lung injury by derecruitment, although the evidence is still discussed. In this study two different recruitment manoeuvres were compared to no recruitment manoeuvres (control) in ventilated sheep with acute respiratory distress syndrome (ARDS), induced by lung lavage.

Methods

We performed a prospective, randomised study in 26 ventilated sheep with ARDS, to evaluate the effect of two different recruitment manoeuvres on gas exchange, blood pressure and lung injury. The two different recruitment manoeuvres, the high pressure recruitment manoeuvre (HPRM), with high peak pressure, and the smooth and moderate recruitment manoeuvre (SMRM), with lower peak pressure, were compared to controls (no recruitment) after disconnection. Oxygenation index and ventilation efficacy index were calculated to evaluate gas exchange. Lung injury was assessed by inflammatory response in broncho-alveolar lavage fluid (BALF) and blood and histology of the lung.

Results

Oxygenation index improved significantly after both recruitment manoeuvres compared with controls, but no significant difference was found between the recruitment manoeuvres. Blood pressure decreased after HPRM but not after SMRM. HPRM induced a higher number of total cells and more neutrophils in the BALF. In the histology of the lung, mean alveolar size was increased in the dorsocranial region of the lung of SMRM compared to controls.

Conclusion

Recruitment manoeuvres improved oxygenation, but SMRM was superior, with respect to hemodynamics and pulmonary inflammation, in ventilated sheep suffering from ARDS induced by lung lavage.     

应用肺动态压力-容积曲线低位转折点选择最佳呼气末正压的研究

目的探讨根据动态肺压力-容积曲线低位转折点压力(Pinf)选择急性呼吸窘迫综合征(ARDS)患者最佳呼气末正压(PEEP)的可行性.方法以8例早期ARDS患者为研究对象,测定动态肺压力-容积曲线及Pinfd.采用低流速法测定准静态肺压力-容积曲线,并确定静态肺压力-容积曲线低位转折点压力(Pinfs).调整PEEP水平,观察患者血流动力学、肺机械力学和氧代谢的变化.结果当PEEP从Pinfd-6cmH2O水平增加到Pinfd+6cmH2O时,动脉血氧分压、动脉血氧饱和度、气道平均压和气道峰压均显著增加.与Pinfd+6cmH2O比较,Pinfd-4cmH2O时的动态肺顺应性显著增高.Pinfd+6cmH2O时的心脏指数有降低趋势,Pinfd-4cmH2O时的氧输送有升高趋势.当Pinfd为(12.8±3.2)cmH2O,Pinfs为(11.0±3.2)cmH2O,两者具有正相关性(r=0.99,P《0.05).回归方程为Pinfd=1.66+1.01×Pinfs.结论当ARDS患者行机械通气治疗时,Pinfd-4cmH2O或Pinfs-2cmH2O为最佳PEEP,可获得最大氧输送.     

Recruitment maneuvers in acute lung injury

Maintaining optimal lung recruitment has a marked effect on the outcome of patients who suffer from ARDS. RMs superimposed on mechanical ventilation have the potential to recruit atelectatic lungs in the course of general anesthesia; however, the physiologic benefits are less evident in ARDS patients who are ventilated at low VT values and high PEEP levels. Currently, the following technical aspects warrant further investigation: optimal time (the first hours after intubation or the first days of ARDS), duration (from 15 seconds to 2 minutes), mode (continuous positive end-expiratory pressure or pressure controlled ventilation with high PEEP), and type of patients (pulmonary versus extrapulmonary ARDS). Before the routine implementation of RMs to recruit the lungs fully in ARDS patients, clinicians also need more information on side effects and contraindications. Although RMs are transient, they may be associated with complications such as hypotension, bradycardia, and barotrauma. Moreover, further studies are needed to compare the efficacy of periodic high-pressure RMs that are superimposed on mechanical ventilation with ventilation using high PEEP levels and low VT values without RMs in patients who have early ARDS after initial hemodynamic stabilization.     

Influence of tidal volume on alveolar recruitment. Respective role of PEEP and a recruitment maneuver

Both reduction in tidal volume (VT) and alveolar recruitment may be important to limit ventilator-associated lung injury during mechanical ventilation of patients with the acute respiratory distress syndrome (ARDS). The aim of this study was to assess the risk of alveolar derecruitment associated with VT reduction from 10 to 6 ml/kg. Whether this VT-related derecruitment could be reversed, either by a recruitment maneuver or by an increase in positive end-expiratory pressure (PEEP) level, was also investigated. Fifteen patients with ARDS were successively ventilated using conventional VT (CVT = 10 +/- 1 ml/kg) and low VT (LVT = 6 +/- 1 ml/ kg); total PEEP (PEEPtot) was individually set at the lower inflection point (Plip) of the pressure-volume curve (PEEPtot = 11 +/- 4 cm H(2)O). Pressure-volume curves were recorded from zero PEEP (ZEEP) and from PEEP, and recruited volume (Vrec) was calculated as the volume difference between the two curves for a given pressure. Despite a similar PEEPtot, Vrec was significantly lower with LVT than with CVT, indicating low VT-induced alveolar derecruitment. Reduction in VT was associated with a reduced Sa(O(2)). In 10 patients, Vrec was also measured before and after a recruitment maneuver (two sustained inflations at 45 cm H(2)O), and after an increase in PEEP (by 4 cm H(2)O). Low VT-induced derecruitment was reversed by a recruitment maneuver and by increasing PEEP. We conclude that a reduction in VT could be responsible for alveolar derecruitment, which may be transiently reversed by a reexpansion maneuver or prevented by a PEEP increase above Plip.