Mechanical ventilation in acute respiratory failure: recruitment and high positive end-expiratory pressure are necessary

PURPOSE OF REVIEW: To review as best the critical care clinicians can recruit the acute respiratory distress syndrome (ARDS) lungs and keep the lungs opened, assuring homogeneous ventilation, and to present the experimental and clinical results of these mechanical ventilation strategies, along with possible improvements in patient outcome based on selected published medical literature from 1972 to 2004 (highlighting the period from June 2003 to June 2004 and recent results of the authors' group research). RECENT FINDINGS: In the experimental setting, repeated derecruitments accentuate lung injury during mechanical ventilation, whereas open lung concept strategies can attenuate lung injury. In the clinical setting, recruitment maneuvers improve short-term oxygenation in ARDS patients. A recent prospective clinical trial showed that low versus intermediate positive end-expiratory pressure (PEEP) levels (8 vs 13 cm H2O) associated with low tidal ventilation had the same effect on ARDS patient survival. Nevertheless, both conventional and electrical impedance thoracic tomography studies indicate that stepwise PEEP recruitment maneuvers increase lung volume and the recruitment percentage of lung tissue, and higher levels of PEEP (18-26 cm H2O) are necessary to keep the ARDS lungs opened and assure a more homogeneous low tidal ventilation. SUMMARY: Stepwise PEEP recruitment maneuvers can open collapsed ARDS lungs. Higher levels of PEEP are necessary to maintain the lungs open and assure homogenous ventilation in ARDS. In the near future, thoracic CT associated with high-performance monitoring of regional ventilation (electrical impedance tomography) may be used at the bedside to determine the optimal mechanical ventilation of ARDS patients.     

How to set positive end-expiratory pressure

Application of positive end-expiratory pressure (PEEP) in acute lung injury patients under mechanical ventilation improves oxygenation and increases lung volume. The effect of PEEP is to recruit lung tissue in patients with diffuse lung edema. This effect is particularly important in patients ventilated with low tidal volumes. Measurement of respiratory system mechanics in patients with acute respiratory distress syndrome is important to assess the status of the disease and to choose appropriate ventilator settings that provide maximum alveolar recruitment while avoiding overdistention. In patients with acute respiratory distress syndrome in whom the lungs have been near-optimally recruited by PEEP and tidal volume, the use of recruitment maneuvers as adjuncts to mechanical ventilation remains controversial. The application of PEEP in patients with unilateral lung disease may be detrimental if PEEP hyperinflates normal lung regions, thus directing blood flow to diseased lung regions. In patients with air flow limitation and lung hyperinflation, the application of additional external PEEP to compensate for intrinsic PEEP and flow limitation frequently decreases the inspiratory effort to initiate an assisted breath, thus decreasing breathing work load.     

Postural therapy during mechanical pulmonary ventilation with PEEP in patients with unilateral lung damage

Mechanical ventilation of the lungs (MVL) with positive end expiratory pressure (PEEP) is difficult in patients with unilateral lung damage because of uneven distribution of volumes and pressures in the involved and intact lungs. Harmful effects are easier manifested under such conditions. Selective MVL with selective PEEP is widely used abroad for optimizing MVL, but this method is rather expensive and is not devoid of shortcomings. Our study carried out in 32 patients with unilateral lung involvement showed that traditional MVL with general PEEP can effectively (in 75% cases) regulate gaseous exchange and decrease its untoward effects if MVL is performed with the patient lying on the healthy side and not supine. MVL in patients with unilateral lung injury lying on the healthy side can be a simpler and cheaper alternative to selective MVL with selective PEEP.     

Optimization of oxygen transport in mechanically ventilated newborns using oximetry and pulsed Doppler-derived cardiac output

In respiratory distress syndrome (RDS), PEEP improves arterial oxygenation but may impair cardiac output. The effects of PEEP on gas exchange and hemodynamics were studied in 12 mechanically ventilated newborns in the acute phase of RDS. Stepwise increase in PEEP resulted in both a) a progressive increase in PaO2 and transcutaneous oxyhemoglobin saturation, and b) a depression of pulsed Doppler-measured cardiac output that was statistically significant at 9 cm H2O PEEP. Thus, averaged systemic oxygen delivery (DO2) was maintained with improved arterial oxygenation up to 6 cm H2O PEEP. Further increase in PEEP induced a significant fall in DO2. No variation was observed in heart rate and mean arterial pressure. The combined use of oximetry and pulsed Doppler echocardiography enables noninvasive optimization of mechanical ventilation and PEEP during the clinical course.     

气管插管后机械通气治疗危重支气管哮喘合并呼吸衰竭的疗效观察

目的探讨气管插管后机械通气对危重支气管哮喘合并呼吸衰竭的疗效。方法回顾性分析2002年1月~2008年4月收治的17例危重支气管哮喘合并呼吸衰竭患者,采用气管插管后机械通气。通气模式:同步间歇指令通气(SIMV)加低水平呼气末正压(PEEP)。根据患者病情及时调整呼吸机参数及考虑撤机,观察机械通气治疗前后血气及相关临床资料。结果机械通气治疗后,临床症状、体征改善明显,pH值、PaO2、PaCO2均恢复正常,顺利撤除呼吸机,与治疗前比较差异均有显著性意义(P<0.01)。结论危重支气管哮喘合并呼吸衰竭采用经气管插管后机械通气技术治疗效果确切,能迅速纠正呼吸衰竭,缓解临床症状,改善动脉血氧分压和通气,并能在短期内顺利撤机,值得临床推广。     

Clinical review: Positive end-expiratory pressure and cardiac output

In patients with acute lung injury, high levels of positive end-expiratory pressure (PEEP) may be necessary to maintain or restore oxygenation, despite the fact that 'aggressive' mechanical ventilation can markedly affect cardiac function in a complex and often unpredictable fashion. As heart rate usually does not change with PEEP, the entire fall in cardiac output is a consequence of a reduction in left ventricular stroke volume (SV). PEEP-induced changes in cardiac output are analyzed, therefore, in terms of changes in SV and its determinants (preload, afterload, contractility and ventricular compliance). Mechanical ventilation with PEEP, like any other active or passive ventilatory maneuver, primarily affects cardiac function by changing lung volume and intrathoracic pressure. In order to describe the direct cardiocirculatory consequences of respiratory failure necessitating mechanical ventilation and PEEP, this review will focus on the effects of changes in lung volume, factors controlling venous return, the diastolic interactions between the ventricles and the effects of intrathoracic pressure on cardiac function, specifically left ventricular function. Finally, the hemodynamic consequences of PEEP in patients with heart failure, chronic obstructive pulmonary disease and acute respiratory distress syndrome are discussed.     

呼气末正压对急性呼吸窘迫综合征绵羊内脏器官灌注的影响

目的　观察呼气末正压 (PEEP)对急性呼吸窘迫综合征 (ARDS)绵羊内脏器官灌注的影响。方法　内毒素 (LPS)静脉注射复制绵羊ARDS模型 ,维持心脏最佳前负荷 ,依次调整PEEP为 5、 10、15cmH2 O ,观察不同PEEP对血流动力学、呼吸力学、氧代谢及内脏器官灌注的影响。结果　与基础值(PEEP =0cmH2 O)比较 ,PEEP 5、 10、 15cmH2 O组心率、平均动脉压、肺动脉压、中心静脉压、肺动脉嵌顿压及心输出量差异无显著性意义 ,但PEEP 10、 15cmH2 0组动脉氧分压和动脉氧饱和度均同步明显增加 ,氧合指数也从 ( 10 4 6 4± 2 5 2 1)mmHg提高到 ( 136 2 5± 38 5 4 )和 ( 135 37± 37 5 6 )mmHg (P <0 0 5 ) ,PEEP 5、 10、 15cmH2 O组肠黏膜pH值 (pHi)与基础比较 ,差异无显著性意义 (P >0 0 5 )。各组肠黏膜与动脉二氧化碳分压差 (Pg aCO2 )也无明显差异。全身氧输送、血乳酸无明显改变 (P >0 0 5 )。与基础值比较 ,PEEP各组平均气道压、气道平台压及肺动态顺应性显著增加 ,PEEP 15cmH2 O组气道峰压也明显增高(P <0 0 5 )。结论　维持心脏最佳前负荷状态下 ,血流动力学和氧输送可保持稳定 ,PEEP在 15cmH2 O以下对ARDS绵羊内脏灌注无明显影响     

Partial liquid ventilation in severely surfactant-depleted, spontaneously breathing rabbits supported by proportional assist ventilation

OBJECTIVE: We hypothesized that partial liquid ventilation (PLV) would improve oxygenation in nonparalyzed, surfactant-deficient rabbits breathing spontaneously while supported by proportional assist ventilation (PAV). This ventilation mode compensates for low pulmonary compliance and high resistance and thereby facilitates spontaneous breathing. DESIGN: Randomized trial. SETTING: University animal research facility. SUBJECTS: Twenty-six anesthetized New Zealand white rabbits weighing 2592 +/- 237g (mean +/- sd). INTERVENTIONS: After pulmonary lavage (target Pao2 <100 mm Hg on mechanical ventilation with 6 cm H2O of positive end-expiratory pressure [PEEP] and an Fio2 of 1.0), rabbits were randomized to PAV (PEEP of 8 cm H2O) with or without PLV. PLV rabbits received 25 mL/kg of perfluorocarbon by intratracheal infusion (1 mL/kg/min). Pao2, Paco2, tidal volume, respiratory rate, minute ventilation, mean airway pressure, arterial blood pressure, heart rate, pulmonary compliance, and airway resistance were measured. Evaporated perfluorocarbon was refilled every 30 mins in PLV animals. After 5 hrs, animals were killed and lungs were removed. Lung injury was evaluated using a histologic score. MAIN RESULTS: Pao2 and compliance were significantly higher in PLV rabbits compared with controls (p <.05, analysis of variance for repeated measures). All other parameters were similar in both groups. CONCLUSIONS: PLV improved oxygenation and pulmonary compliance in spontaneously breathing, severely surfactant-depleted rabbits supported by PAV. The severity of lung injury by histology was unaffected.     

贵州省首例重症人感染高致病性H5N1亚型禽流感致急性呼吸窘迫综合征患者的机械通气策略探讨

目的 探讨重症高致病性H5N1人禽流感病例急性呼吸窘迫综合征(ARDS)机械通气策略.方法 对2009年1月15日本院收治的1例重症高致病性H5N1亚型禽流感感染患者的资料进行分析、总结.结果 患者男性,29岁,发病前有家禽宰杀史,以畏寒、发热起病,持续高热,继之出现进行性呼吸困难.1月19日(发病5 d)胸部影像学可见以左下肺为主的双肺炎症表现,迅速进展出现ARDS样肺部表现.立即给予机械通气为主的综合治疗措施,通气模式为同步间歇指令通气+压力支持+呼气末正压(SIMV+PS+PEEP),采用小潮气量肺通气保护策略,病情逐日好转,无多器官功能降碍发生,2月6日痊愈出院.结论 早发现、早诊断、早治疗是成功救治高致病性H5N1人禽流感的前提,小潮气量加最佳PEEP通气策略改善氧合是治疗的关键.     

俯卧位通气联合呼气末正压治疗急性呼吸窘迫综合征家猪的疗效研究

目的 探讨俯卧位通气联合呼气末正压(PEEP)治疗急性呼吸窘迫综合征(ARDS)的疗效及其机制.方法 12头家猪静脉注射油酸建立ARDS模型,分为仰卧位组和俯卧位组,均给予0(ZEEP)、10(PEEP10)、20 cm H2O(PEEP20,1 cm H2O=0.098 kPa)PEEP的机械通气15 min,监测家猪血流动力学、肺气体交换和呼吸力学指标;处死动物观察肺组织病理学变化.结果 俯卧位组ZEEP、PEEP10时氧合指数(PaO2/FiO2)明显优于仰卧位组[ZEEP:(234.00±72.55)mm Hg比(106.58±34.93)mm Hg,PEEP10:(342.97±60.15) mm Hg比(246.80±83.69)mm Hg,1 mm Hg=0.133 kPa,P均<0.05];PEEP20时两组PaO2/FiO2差异无统计学意义(P>0.05).PEEP10时两组肺复张容积(RV)差异无统计学意义(P>0.05);但PEEP20时俯卧位组RV显著高于仰卧位组[(378.55±101.80)ml比(302.95±34.31)ml,P<0.05].两组间心率(HR)、平均动脉压(MAP)、心排血指数(CI)、呼吸系统顺应性(Cst)及动脉血二氧化碳分压(PaCO2)差异均无统计学意义(P均>0.05);仰卧位组背侧肺组织的肺损伤总评分明显高于俯卧位组[(12.00±1.69)分比(6.03±1.56)分,P<0.05].结论 俯卧位通气联合合适的PEEP可改善ARDS家猪氧合,并且不影响血流动力学和呼吸力学,肺组织损伤的重新分布可能是其机制之一.     

Gastric intramucosal pH is stable during titration of positive end-expiratory pressure to improve oxygenation in acute respiratory distress syndrome

Background

Optimal positive end-expiratory pressure (PEEP) is an important component of adequate mechanical ventilation in acute lung injury and acute respiratory distress syndrome (ARDS). In the present study we tested the effect on gastric intramucosal pH of incremental increases in PEEP level (i.e. PEEP titration) to improve oxygenation in ARDS. Seventeen consecutive patients with ARDS, as defined by consensus criteria, were included in this clinical, prospective study. All patients were haemodynamically stable, and were not receiving vasopressors. From an initial level of 5 cmH₂O, PEEP was titrated at 2 cmH₂O increments until the partial arterial oxygen tension was 300 mmHg or greater, peak airway pressure was 45 cmH₂O or greater, or mean arterial blood pressure decreased by 20% or more of the baseline value. Optimal PEEP was defined as the level of PEEP that achieved the best oxygenation. The maximum PEEP was the highest PEEP level reached during titration in each patient.

Results

Gastric mucosal pH was measured using gastric tonometry at all levels of PEEP. The thermodilution technique was used for measurement of cardiac index. Gastric mucosal pH was similar at baseline and at optimal PEEP levels, but it was slightly reduced at maximum PEEP. Cardiac index and oxygen delivery remained stable at all PEEP levels.

Conclusion

Incremental titration of PEEP based on improvement in oxygenation does not decrease gastric intramucosal perfusion when cardiac output is preserved in patients with ARDS.     

呼气末正压对急性呼吸窘迫综合征肺复张容积及氧合影响的临床研究

目的　评价呼气末正压 (PEEP)对急性呼吸窘迫综合征 (ARDS)肺复张容积的影响 ,探讨ARDS患者 PEEP的选择方法。方法　以 11例血流动力学稳定、接受机械通气的 ARDS患者为研究对象 ,采用压力容积曲线法分别测定 PEEP为 5、10、15 cm H2 O(1cm H2 O=0 .0 98k Pa)时的肺复张容积 ,观察患者动脉血气、肺机械力学和血流动力学变化。结果　 PEEP分别 5、10和 15 cm H2 O时肺复张容积分别为 (4 0 .2±15 .3) ml、 (12 3.8± 4 3.1) ml和 (178.9± 4 3.5 ) m l,随着 PEEP水平的增加 ,肺复张容积亦明显增加 (P均 <0 .0 5 )。动脉氧合指数也随着 PEEP水平增加而增加 ,且其变化与肺复张容积呈正相关 (r=0 .4 83,P<0 .0 1)。不同 PEEP条件下 ,患者的肺静态顺应性无明显变化 (P>0 .0 5 )。将患者按有无低位转折点 (L IP)分为有 L IP组与无 L IP组 ,两组患者的肺复张容积都随着 PEEP水平的增加而增加 ,其中 PEEP15 cm H2 O时 L IP组患者的肺复张容积大于无 L IP组 (P<0 .0 5 )。结论　 PEEP水平越高 ,肺复张容积越大 ,肺复张容积增加与动脉氧合指数的变化呈正相关     

Gastric intramucosal pH is stable during titration of positive end-expiratory pressure to improve oxygenation in acute respiratory distress syndrome

Background  

Optimal positive end-expiratory pressure (PEEP) is an important component of adequate mechanical ventilation in acute lung injury and acute respiratory distress syndrome (ARDS). In the present study we tested the effect on gastric intramucosal pH of incremental increases in PEEP level (i.e. PEEP titration) to improve oxygenation in ARDS. Seventeen consecutive patients with ARDS, as defined by consensus criteria, were included in this clinical, prospective study. All patients were haemodynamically stable, and were not receiving vasopressors. From an initial level of 5 cmH₂O, PEEP was titrated at 2 cmH₂O increments until the partial arterial oxygen tension was 300 mmHg or greater, peak airway pressure was 45 cmH₂O or greater, or mean arterial blood pressure decreased by 20% or more of the baseline value. Optimal PEEP was defined as the level of PEEP that achieved the best oxygenation. The maximum PEEP was the highest PEEP level reached during titration in each patient.     

PEEP: its use in young patients with apparently normal lungs.

PEEP has been advocated for use in patients with the acute respiratory distress syndrome characterized by a marked reduction in FRC. It has not been advocated for patients with apparently normal lungs requiring prolonged mechanical ventilation. We have done inert gas washouts on five young patients comparing no PEEP to 10 cm H2O PEEP. Four of the five showed a significant improvement in PaO2, a decrease in AaDO2 and Qs/Qt, the fifth a slight improvement on PEEP. Arterial washouts were significantly faster on PEEP in all patients suggesting a decrease in intrapulmonary shunting. Airway washouts in the initial phase were faster off PEEP suggesting an increase in lung volume and FRC with PEEP. Later portions of the curve were faster on PEEP suggesting improved distribution of ventilation. These findings suggest that PEEP might be of significant value in treatment of patients requiring prolonged mechanical ventilation for reasons other than lung abnormalities.     

跨肺压法设置呼气末正压通气对急性呼吸窘迫综合征模型猪肺保护作用的研究

目的比较跨肺压法与最佳氧合法选择最佳呼气末正压通气（PEEP）,对急性呼吸窘迫综合征（ARDS）模型猪肺损伤作用的影响。 方法12只普通家猪随机分为跨肺压组和最佳氧合组,均给予有创通气、留置股动脉导管接PiCCO仪监测血流动力学及留置右颈内静脉导管测中心静脉压（CVP）,稳定30 min后,行0.9%氯化钠溶液肺泡灌洗复制猪ARDS模型。模型成功后,在充分肺复张的基础上,两组分别使用跨肺压法和最佳氧合法设置最佳PEEP,并以此维持通气4 h。观察并记录基础状态（PEEP 5 cmH₂O）（Tbase）、ARDS模型稳定（PEEP 5 cmH₂O）（T0）和最佳PEEP维持机械通气4 h期间（T1-T4）的肺毛细血管通透性指数（PVPI）、血管外肺水指数（EVLWI）及呼吸力学变化,并在Tbase、T0、T4 3个时间点采集血标本,酶联免疫吸附剂测定法（ELISA）测定血白介素1β（IL-1β）、白介素6（IL-6）炎症因子表达水平。实验结束处死动物,留取猪右上肺、右下肺背侧、右下肺腹侧,行免疫组化测肺组织核转录因子kappa B（NF-κB）、IL-1β、IL-6水平,比色法测肺组织抗髓过氧化物酶（MPO）活性,同时观察病理改变及测湿干比反应肺水含量。 结果呼吸力学方面：跨肺压组最佳PEEP、Pm、Paw-exp、Ptrans-exp明显低于最佳氧合组（P<0.05）,而跨肺压组Ptrans-ins在最佳PEEP通气第3小时、第4小时明显低于最佳氧合组（P<0.05）。炎症反应方面：右肺上叶肺组织NF-κB、右全肺肺组织IL-6、右肺下叶背侧及右全肺MPO表达跨肺压组均明显低于最佳氧合组（P<0.05）。肺水肿指标方面：两组最佳PEEP通气4h后PVPI、EVLWI以及各部位湿干比（W/D）差异无统计学意义（P>0.05）。病理方面：跨肺压组右肺上叶、下叶背侧及右全肺损伤病理评分低于最佳氧合组（P>0.05）。 结论通过跨肺压法设置最佳PEEP能够在维持肺泡开放状态的同时,减少肺炎症反应发生,预防肺损伤,达到肺保护作用。     

Therapeutic use of intrinsic positive end-expiratory pressure

A patient with acute hypoxemic respiratory failure undergoing mechanical ventilation with PEEP developed significant obstructive airway disease. We found that intrinsic PEEP, substituted for externally applied PEEP, could maintain oxygenation. The increased inspiratory/expiratory time ratio, which resulted in the development of intrinsic PEEP, beneficially reduced airway pressures.     

Assessment of electrical impedance tomography to set optimal positive end-expiratory pressure for veno-venous ECMO-treated severe ARDS patients

PurposeUltra-protective ventilation with low tidal volume is used in severe acute respiratory distress syndrome (ARDS) patients under extracorporeal membrane oxygenation (ECMO). However, the optimal positive end-expiratory pressure (PEEP) is unknown. The aim of our study was to assess electrical impedance tomography's (EIT) ability to choose the best PEEP for these patients.Materials and methodsA recruitment maneuver and after a decremental PEEP trial from 20 to 5 cmH₂0 were monitored by EIT, with lung images divided into four ventral-to-dorsal horizontal regions of interest. For each patient, three EIT-based PEEP were defined: PEEP ODCL_min (lowest pressure with the least EIT-based collapse lung [CL] and overdistension [OD]), PEEP ODCL₁₅ (lowest pressure able to limit EIT-based collapse to less than or equal to 15% with the least overdistension) and PEEP Comp (PEEP with the highest EIT-based compliance).ResultsHigh PEEP levels were significantly associated with more overdistension while decreasing PEEP led to more collapsed zones. PEEP ODCL₁₅ and PEEP Comp were in complete agreement with the reference Pulmonary PEEP (chosen according to usual respiratory clinical and ultrasound criteria), PEEP ODCLmin was in average agreement with the Pulmonary PEEP.ConclusionEIT may be a useful real-time monitoring technique to optimize the PEEP level in severe ARDS patients under ECMO.Take-home messageUltra-protective ventilation with low tidal volume is used in severe acute respiratory distress syndrome patients under extracorporeal membrane oxygenation (ECMO), but the optimal positive end-expiratory pressure is unknown. This trial shows that electrical impedance tomography may be an interesting non-invasive bedside tool to provide real-time monitoring of PEEP impact in severe ARDS patients under ECMO.The Pulmovista® electrical impedance tomography was provided by Dräger (Lübeck, Germany) during the study period. Dräger had no role in the study design, collection, analysis and interpretation of the data, writing the article, or the decision to submit the article for publication.     

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.     

The effect of positive end-expiratory pressure during partial liquid ventilation in acute lung injury in piglets.

OBJECTIVES: To investigate the effects of positive end-expiratory pressure (PEEP) application during partial liquid ventilation (PLV) on gas exchange, lung mechanics, and hemodynamics in acute lung injury. DESIGN: Prospective, randomized, experimental study. SETTING: University research laboratory. SUBJECTS: Six piglets weighing 7 to 12 kg. INTERVENTIONS: After induction of anesthesia, tracheostomy, and controlled mechanical ventilation, animals were instrumented with two central venous catheters, a pulmonary artery catheter and two arterial catheters, and an ultrasonic flow probe around the pulmonary artery. Acute lung injury was induced by the infusion of oleic acid (0.08 mL/kg) and repeated lung lavage procedures with 0.9% sodium chloride (20 mL/kg). The protocol consisted of four different PEEP levels (0, 5, 10, and 15 cm H2O) randomly applied during PLV. The oxygenated and warmed perfluorocarbon liquid (30 mL/kg) was instilled into the trachea over 5 mins without changing the ventilator settings. MEASUREMENTS AND MAIN RESULTS: Airway pressures, tidal volumes, dynamic and static pulmonary compliance, mean and expiratory airway resistances, and arterial blood gases were measured. In addition, dynamic pressure/volume loops were recorded. Hemodynamic monitoring included right atrial, mean pulmonary artery, pulmonary capillary wedge, and mean systemic arterial pressures and continuous flow recording at the pulmonary artery. The infusion of oleic acid combined with two to five lung lavage procedures induced a significant reduction in PaO2/FI(O2) from 485 +/- 28 torr (64 +/- 3.6 kPa) to 68 +/- 3.2 torr (9.0 +/- 0.4 kPa) (p < .01) and in static pulmonary compliance from 1.3 +/- 0.06 to 0.67 +/- 0.04 mL/cm H2O/kg (p < .01). During PLV, PaO2/FI(O2) increased significantly from 68 +/- 3.2 torr (8.9 +/- 0.4 kPa) to >200 torr (>26 kPa) (p < .01). The highest PaO2 values were observed during PLV with PEEP of 15 cm H2O. Deadspace ventilation was lower during PLV when PEEP levels of 10 to 15 cm H2O were applied. There were no differences in hemodynamic data during PLV with PEEP levels up to 10 cm H2O. However, PEEP levels of 15 cm H2O resulted in a significant decrease in cardiac output. Dynamic pressure/volume loops showed early inspiratory pressure spikes during PLV with PEEP levels of 0 and 5 cm H2O. CONCLUSIONS: Partial liquid ventilation is a useful technique to improve oxygenation in severe acute lung injury. The application of PEEP during PLV further improves oxygenation and lung mechanics. PEEP levels of 10 cm H2O seem to be optimal to improve oxygenation and lung mechanics.     

Lung recruitment during small tidal volume ventilation allows minimal positive end-expiratory pressure without augmenting lung injury.

OBJECTIVES: Ventilation with positive end-expiratory pressure (PEEP) above the inflection point (P(inf)) has been shown to reduce lung injury by recruiting previously closed alveolar regions; however, it carries the risk of hyperinflating the lungs. The present study examined the hypothesis that a new strategy of recruiting the lung with a sustained inflation (SI), followed by ventilation with small tidal volumes, would allow the maintenance of low PEEP levels ( P(inf). MEASUREMENTS AND MAIN RESULTS: In groups 2 and 4, static compliance decreased after ventilation (p < .01). Histologically, group 2 (PEEP < P(inf) without SI) showed significantly greater injury of small airways, but not of terminal respiratory units, compared with group 1. Group 3 (PEEP < P(inf) after a SI), but not group 4, showed significantly less injury of small airways and terminal respiratory units compared with group 2. CONCLUSIONS: We conclude that small tidal volume ventilation after a recruitment maneuver allows ventilation on the deflation limb of the pressure/volume curve of the lungs at a PEEP < P(inf). This strategy a) minimizes lung injury as well as, or better than, use of PEEP > P(inf), and b) ensures a lower PEEP, which may minimize the detrimental consequences of high lung volume ventilation.