Incidence and regional distribution of lung overinflation during mechanical ventilation with positive end-expiratory pressure

OBJECTIVE: In patients with acute lung injury, alveolar recruitment resulting from positive end-expiratory pressure (PEEP) may be associated with overinflation of previously aerated lung regions. The aim of this study was to assess the incidence and regional distribution of lung overinflation resulting from mechanical ventilation with PEEP. DESIGN: Reanalysis with a specific software including a color-coding system of quantitative lung computed tomography data obtained in four previous prospective studies. SETTING: A 20-bed surgical intensive care unit of a Parisian university hospital. PATIENTS: Thirty-two patients with acute lung injury in whom computed tomography of the whole lung was obtained at zero end-expiratory pressure (ZEEP) and PEEP 15 cm H2O. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Total lung recruitment was measured as the reaeration of poorly aerated (computed tomography attenuations ranging between -500 and -100 Hounsfield units) and nonaerated (computed tomography attenuations > or = -100 Hounsfield units) lung areas, and overinflation was measured as the lung volume characterized by computed tomography attenuations < or = -900 Hounsfield units. PEEP was associated with a significant alveolar recruitment (423 +/- 178 mL). Concomitantly, a lung overinflation of 123 +/- 138 mL was found in 14 patients (44%). In eight patients without chronic obstructive pulmonary disease, lung overinflation was predominantly found in nondependent lung regions located beneath the dome of diaphragm. In six patients with a past history of chronic obstructive pulmonary disease, PEEP increased the volume of emphysematous areas present in apical lung regions and produced an overinflation of nondependent lung regions located beneath the dome of diaphragm. CONCLUSION: Lung overinflation resulting from mechanical ventilation with PEEP is observed in more than one third of patients with acute lung injury lying supine and predominates in caudal and nondependent lung regions. Furthermore, in patients with a history of chronic obstructive pulmonary disease, PEEP markedly increases the volume of emphysematous lung regions.     

Lung collapse during low tidal volume ventilation in acute respiratory distress syndrome

BACKGROUND: Current ventilator management for acute respiratory distress syndrome (ARDS) incorporates low tidal volume (V(T)) ventilation in order to limit ventilator-induced lung injury. Low V(T) ventilation in supine patients, without the use of intermittent hyperinflations, may cause small airway closure, progressive atelectasis, and secretion retention. Use of high positive end-expiratory pressure (PEEP) levels with low V(T) ventilation may not counter this effect, because regional differences in intra-abdominal hydrostatic pressure may diminish the volume-stabilizing effects of PEEP. CASE SUMMARY: A 35-year-old man with abdominal compartment syndrome (intra-abdominal pressure > 48 cm H2O developed ARDS and was treated with V(T) of 4.5 mL/kg and PEEP of 20 cm H2O. Despite aggressive fluid therapy, appropriate airway humidification and tracheal suctioning, the patient developed complete bronchial obstruction, involving the entire right lung and left upper lobe. After bronchoscopy the patient was placed on a higher V(T) (7.0 mL/kg). Intermittent PEEP was instituted at 30 cm H2O for 2 breaths every 3 minutes. This intermittently raised the end-inspiratory plateau pressure from 38 cm H2O to 50 cm H2O. With the same airway humidity and tracheal suctioning practices bronchial obstruction did not reoccur. CONCLUSION: Low V(T) ventilation in ARDS may increase the risk of small airway closure and retained secretions. This adverse effect highlights the importance of pulmonary hygiene measures in ARDS during lung-protective ventilation.     

Alveolar recruitment in combination with sufficient positive end-expiratory pressure increases oxygenation and lung aeration in patients with severe chest trauma

OBJECTIVE: Investigation of oxygenation and lung aeration during mechanical ventilation according to the open lung concept in patients with acute lung injury or acute respiratory distress syndrome. DESIGN: Retrospective analysis. SETTING: Surgical intensive care unit of a university hospital. PATIENTS: We retrospectively identified 17 patients with acute lung injury/acute respiratory distress syndrome due to pulmonary contusion who had thoracic helical computed tomography scans before and after ventilation with the open lung concept. INTERVENTIONS: Baseline ventilation consisted of low tidal volumes (< or =6 mL/kg) and positive end-expiratory pressure (PEEP; 5-17 cm H2O). We briefly applied high inspiratory pressures for opening up collapsed alveoli. External PEEP and intrinsic PEEP were combined to keep recruited lung units open. We generated intrinsic PEEP by pressure-cycled high-frequency inverse ratio ventilation (80 min, inspiratory/expiratory ratio 2:1) and maintained our ventilatory strategy for 24 hrs. Then, after reducing total PEEP by decreasing respiratory rate, Pao2/Fio2 ratio was reevaluated. If it remained >300 mm Hg, weaning was started. If not, previous ventilator settings were resumed for another 24 hrs after recruiting the lungs once again. MEASUREMENTS AND MAIN RESULTS: Physiologic variables and ventilator settings were obtained from routine charts. Data from computed tomography before and after the open lung concept were analyzed for volumetric quantification of lung aeration and collapse. All results are presented as median and range. During baseline ventilation, PEEP was 10 (range, 5-17) cm H2O and after recruitment 21 (range, 18-26) cm H2O. Opening pressures were 65 (range, 50-80) cm H2O. After recruitment, Pao2/Fio2 ratio was higher in all patients. Total lung volume increased from 2915 (range, 1952-4941) to 4247 (range, 2285-6355) mL and normally aerated volume from 1742 (range, 774-2941) to 2971 (range, 1270-5232) mL. Atelectasis decreased significantly from 604 (range, 147-1538) to 106 (range, 0-736) mL. Hyperinflation increased significantly from 5 (range, 0-188) to 62 (range, 1-424) mL, whereas poor aeration did not change substantially from 649 (range, 302-1292) to 757 (range, 350-1613) mL. No hemodynamic problems occurred. CONCLUSIONS: Lung recruitment increased arterial oxygenation, normally aerated lung volume, and total lung volume while decreasing the amount of collapsed tissue. These results indicate that the open lung concept is a reasonable mode of ventilation for patients with severe chest trauma.     

机械通气治疗重症哮喘过程中发生气压伤的相关因素分析

目的：分析机械通气治疗重症哮喘过程中发生气压伤的相关因素，提高机械通气治疗重症哮喘的疗效。方法：将45例无气压伤发生和6例发生气压伤的重症哮喘患者就通气模式、潮气量、吸气峰压、平台压、呼气末正压、吸气流量、肺顺应性、呼吸频率等指标进行回顾性分析。结果：6例气压伤患者中4例机械通气的平台压大于35cm H2O，其中3例有肺大泡。结论：平台压过高是重症哮喘机械通气中致气压伤的关键因素，合理的调控平台压是防止气压伤发生的关键。     

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.     

Low spatial resolution computed tomography underestimates lung overinflation resulting from positive pressure ventilation

OBJECTIVE: In acute lung injury, lung overinflation resulting from mechanical ventilation with positive end-expiratory pressure (PEEP) can be assessed using lung computed tomography. The goal of this study was to compare lung overinflation measured on low and high spatial resolution computed tomography sections. DESIGN: Lung overinflation was measured on thick (10-mm) and thin (1.5-mm) computed tomography sections obtained at zero end-expiratory pressure (ZEEP) and PEEP 10 cm H2O using a software including a color-coding system. SETTING: A 20-bed surgical intensive care unit of a university hospital. PATIENTS: Thirty mechanically ventilated patients with acute lung injury. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Overinflated lung volume was measured as the end-expiratory volume of lung regions with computed tomography attenuations <-900 Hounsfield units. Lung overinflation, expressed in percentage of the total lung volume, was significantly underestimated by thick computed tomography sections compared with thin computed tomography sections (0.4 +/- 1.6% vs. 3.0 +/- 4.0% in ZEEP and 1.9 +/- 4% vs. 6.8 +/- 7.3% in PEEP, p < .01). In patients with a diffuse loss of aeration, the overinflated lung volumes of thick and thin computed tomography sections were, respectively, 0.6 +/- 0.8 mL vs. 16 +/- 10 mL in ZEEP (p < .01) and 8 +/- 9 mL vs. 73 +/- 62 mL in PEEP (p < .05). In patients with a focal loss of aeration, this underestimation was more pronounced: 18 +/- 56 mL vs. 127 +/- 140 mL in ZEEP (p < .01) and 85 +/- 161 mL vs. 322 +/- 292 mL in PEEP (p < .01). CONCLUSIONS: In patients with acute lung injury, an accurate computed tomography estimation of lung overinflation resulting from positive pressure mechanical ventilation requires high spatial resolution computed tomography sections, particularly when the lung morphology shows a focal loss of aeration.     

Customization of an open-lung ventilation strategy to treat a case of life-threatening acute respiratory distress syndrome

The ARDS Network low-tidal-volume protocol is considered the standard of care for patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). The protocol is built on the foundation of low-tidal-volume ventilation, use of a combined PEEP and F(IO(2)) table, and managing alveolar end-inspiratory pressure by limiting the plateau airway pressure to ≤ 30 cm H(2)O. Although this strategy, to date, is the only method that significantly improves ALI/ARDS survival, alternative methods of improving hypoxemia and minimizing ventilator-induced lung injury, in conjunction with low-tidal-volume ventilation, can be used for life-threatening ARDS. We present a case in which we customized the use of alveolar recruitment maneuvers by analyzing the hysteresis of the pressure-volume curve to assess lung recruitability, decremental PEEP to sustain lung recruitment, and careful use of plateau pressure ≥ 30 cm H(2)O, which improved our patient's life-threatening hypoxemia within the first 36 min of arrival to our ICU.     

Lung computed tomography during a lung recruitment maneuver in patients with acute lung injury

OBJECTIVE: To assess the acute effect of a lung recruitment maneuver (LRM) on lung morphology in patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). PATIENTS: Ten patients with ALI/ARDS on mechanical ventilation. DESIGN: Prospective clinical study. SETTING: Computed tomography (CT) scan facility in a teaching hospital. INTERVENTIONS: An LRM performed by stepwise increases in positive end-expiratory pressure (PEEP) of up to 30-40 cm H(2)O. Lung basal CT sections were taken at end-expiration (patients 1 to 5), and at end-expiration and end-inspiration (patients 6 to 10). Arterial blood gases and static compliance (C(st)) were measured before, during and after the LRM. MEASUREMENTS AND MAIN RESULTS: Poorly aerated and non-aerated tissue at PEEP 10 cm H(2)O accounted for 60.0+/-29.1% of lung parenchyma, while only 1.1+/-1.8% was hyperinflated. Increasing PEEP to 20 and 30 cm H(2)O, compared to PEEP 10 cm H(2)O, decreased poorly aerated and non-aerated tissue by 16.2+/-28.0% and 33.4+/-13.8%, respectively ( p<0.05). This was associated with an increase in PaO(2) and a decrease in total static compliance. Inspiration increased alveolar recruitment at all PEEP levels. Hyperinflated tissue increased up to 2.9+/-4.0% with PEEP 30 cm H(2)O, and to a lesser degree with inspiration. No barotrauma or severe hypotension occurred. CONCLUSIONS: Lung recruitment maneuvers improve oxygenation by expanding collapsed alveoli without inducing too much hyperinflation in ALI/ARDS patients. An LRM during the CT scan gives morphologic and functional information that could be useful in setting ventilatory parameters.     

Effects of ventilatory pattern on experimental lung injury caused by high airway pressure

OBJECTIVE: To determine the influence of clinician-adjustable ventilator settings on the development of ventilator-induced lung injury, as assessed by changes in gas exchange (Pao2), compliance, functional residual capacity, and wet weight to dry weight ratio. DESIGN: Randomized in vivo rabbit study. SETTING: Hospital research laboratory. SUBJECTS: Forty-four anesthetized, mechanically ventilated adult rabbits. INTERVENTIONS: Ventilation for 2 hrs with pressure control ventilation at 45 cm H2O, Fio2 = 0.6, and randomization to one of five ventilatory strategies using combinations of positive end-expiratory pressure (3 or 12 cm H2O), inspiratory time (0.45, 1.0, or 2.0 secs), and frequency (9 or 23/min). MEASUREMENTS AND MAIN RESULTS: Among the ventilator strategies applied, PEEP at 12 cm H2O (elevated positive end-expiratory pressure) and inspiratory time at 0.45 secs (reduced inspiratory time) best preserved Pao2 (p <.003) and compliance (p <.035). During injury development, two consistent changes were observed: Tidal volume increased, and airway pressure waveform was transformed by extending the time to attain target pressure. CONCLUSIONS: In this preclinical model, lung injury was attenuated by decreasing inspiratory time. As lung injury occurred, tidal volume increased and airway pressure waveform changed.     

急性心源性肺水肿机械通气患者呼气末正压设定的临床研究

目的探讨急性心源性肺水肿(ACPE)时不同呼气末正压(PEEP)水平对血流动力学与肺参数的影响。方法39例呼吸衰竭机械通气患者根据心排血指数(CI)分为两组。观察心功能正常组(n=18,CI≥2.0L·min-1·m-2)与心功能低下组(n=21,CI<2.0L·min-1·m-2)在双水平气道正压通气(BIPAP)模式下不同PEEP水平对血流动力学〔心排血量(CO)、CI、肺毛细血管血流(PCBF)、中心静脉压(CVP)、外周血管阻力(SVR)〕、肺参数〔内源性呼气末正压(PEEPi)、气道峰压(Ppeak)、平均气道压(Pmean)、每分通气量(MV)、肺泡通气量(Vtalv)〕及经皮血氧饱和度(SpO2)、血压(BP)、心率(HR)等的变化。结果心功能正常组PEEP在0～13cmH2O(1cmH2O=0.098kPa)对血流动力学无明显影响,肺参数中Ppeak、PEEPi随着PEEP增高而相应增高,气道阻力(R)下降;心功能低下组随着PEEP变化SVR、CO、CI呈曲线性变化,以PEEP0～7cmH2O时CO、CI值较高而SVR较低,10～13cmH2OCO、CI值较低而SVR较高,对肺参数影响以PEEP5～7cmH2O时PEEPi较小。结论ACPE患者机械通气调节应结合血流动力学变化并兼顾肺机械参数变化,PEEP使用具有明显个体化倾向,以PEEP5～7cmH2O(一般<10cmH2O)为宜。     

适当呼气末正压及不同通气模式对肝移植患者血流动力学和氧代谢动力学的影响

目的 寻找适宜的呼气末正压(PEEP),研究不同机械通气方式对肝移植术后患者血流动力学及氧代谢动力学的影响.方法 采用随机、单盲、交叉试验方法.选取11例背驮式肝移植术后呼吸机辅助通气患者为观察对象,经漂浮导管、桡动脉导管进行持续心排血量(CO)、平均肺动脉压(MPAP)、平均动脉血压(MABP)、中心静脉压(CVP)和气道压力监测.压力调节容量控制通气(PRVCV)的PEEP定为0、5、10和15 cm H2O(1 cm H2O=0.098 kPa),不同水平PEEP各用30 min;交替使用PRVCV和压力控制同步间歇指令通气加压力支持通气(PC-SIMV+PSV)各60 min;观察4种PEEP水平和两种通气模式下血流动力学和氧代谢动力学指标的变化.结果 不同水平PEEP时肝移植术后患者气道峰压、平均气道压、CVP及MPAP差异均有显著性,其中在PEEP为10 cm H2O和15 cm H2O时显著高于PEEP为0和5 cm H2O时;不同水平PEEP对pH、动脉血二氧化碳分压(PaCO2)、动脉血氧分压(PaO2)、动脉血氧饱和度(SaO2)、氧供给(DO2)、氧消耗(VO2)、氧摄取率(O2ER)均无明显影响.PRVCV模式时平均气道压明显低于PC-SIMV+PSV模式[(8.78±1.53)cm H2O比(11.64±3.30)cm H2O,P＜0.05];PRVCV模式时VO2虽低于PC-SIMV+PSV模式,但差异无显著性.两种通气模式对患者的其他血流动力学指标以及氧代谢动力学指标并无显著影响.结论 为减少对患者体循环及移植肝脏血液回流的影响,肝移植术后患者通气支持时宜选用5 cm H2O的低水平PEEP.PRVCV模式可作为肝移植术后患者呼吸支持和脱机过渡较为理想的通气模式.     

Phase-related changes in right ventricular cardiac output under volume-controlled mechanical ventilation with positive end-expiratory pressure.

OBJECTIVE: To examine determinants of right ventricular function throughout the ventilatory cycle under volume-controlled mechanical ventilation with various positive end-expiratory pressure (PEEP) stages. DESIGN: Prospective observational animal pilot study. SETTING: Animal research laboratory at a university hospital. SUBJECTS: Eight healthy swine under volume- controlled mechanical ventilation. INTERVENTIONS: Flow probes were implanted in eight swine in order to continuously measure blood flow in the pulmonary artery and inferior vena cava. After a recovery phase of 14 days, the swine were subjected to various PEEP stages (0, 5, 10 cm H2O) during volume-controlled positive pressure ventilation. MEASUREMENTS AND MAIN RESULTS: Continuous flow measurement took place in the pulmonary artery and inferior vena cava. Data on standard hemodynamic parameters were additionally acquired. Respiration-phase-specific analysis of right ventricular cardiac output and of additional hemodynamic function parameters followed, after calculation of mean values throughout five respiration cycles. PEEP at 5 cm H2O led to significant decreases in inferior vena cava flow (4.1%), and in right ventricular cardiac output (5.2%); the respective decreases at PEEP 10 cm H2O were 13.9% and 18.3%. In the inspiration phase at PEEP 10 cm H2O, results revealed an overproportionally pronounced decrease in comparison with the expiration phase in inferior vena cava flow (-24.6% vs. -10%) and right ventricular cardiac output (-35% vs. -13.5%). This phenomenon is presumably caused by a PEEP-related increase in mean airway pressure by the amount of 10.7 cm H2O in inspiration. CONCLUSIONS: Increases in PEEP during volume-controlled mechanical ventilation leads to respiration-phase-specific reduction of right ventricular cardiac output, with a significantly pronounced decrease during the inspiration phase. This decrease in cardiac output should be taken into particular consideration for patients with already critically reduced cardiac output.     

Airway pressure release ventilation during acute lung injury: a prospective multicenter trial

OBJECTIVE: To evaluate the feasibility of airway pressure release ventilation (APRV) in providing ventilatory support to patients with acute lung injury of diverse etiology and mild-to-moderate severity. DESIGN: Prospective, multicenter, nonrandomized crossover trial. SETTING: ICUs in six major referral hospitals. PATIENTS: Fifty adult patients with respiratory failure requiring mechanical ventilation and positive end-expiratory airway pressure. INTERVENTIONS: After optimization of continuous positive airway pressure (CPAP), conventional ventilation and APRV were administered sequentially for 30 mins. During APRV, the CPAP level and airway pressure release level were adjusted to prevent hypoxemia, while the degree of ventilatory support was adjusted by altering the frequency of pressure release. MEASUREMENTS AND MAIN RESULTS: Circulatory and ventilatory pressures, arterial blood gases and pH, heart rate, and respiratory rate were measured. Alveolar ventilation was augmented adequately in 47 of 50 patients by APRV. Adjustment of APRV required an increase in mean CPAP from 13 +/- 3 (SD) to 21 +/- 9 cm H2O and a release pressure of 6 +/- 5 cm H2O. This airway pressure pattern produced a mean airway pressure comparable to that pressure achieved during conventional ventilation. Failure of APRV in three patients could be attributed to an inadequate level of CPAP or an inadequate APRV rate. While maintaining oxygenation of arterial blood and circulatory function, APRV allowed a substantial (55 +/- 17%; p less than .0001) reduction in peak airway pressure compared with conventional positive pressure ventilation adjusted to deliver a comparable or lower level of ventilatory support. CONCLUSIONS: APRV is a feasible alternative to conventional mechanical ventilation for augmentation of alveolar ventilation in patients with acute lung injury of mild-to-moderate severity.     

Position of exhalation port and mask design affect CO2 rebreathing during noninvasive positive pressure ventilation

OBJECTIVE: Noninvasive positive pressure ventilation may be considered a first line intervention to treat patients with hypercapnic respiratory failure. However, CO2 rebreathing from the ventilator circuit or mask may impair CO2 elimination and load the ventilatory muscles. This study was conducted to evaluate the effect of exhalation port location and mask design on CO2 rebreathing during noninvasive positive pressure ventilation. DESIGN: Lung model evaluation. SETTING: Experimental laboratory of a large university-affiliated hospital. SUBJECTS: A dual-chamber test lung was used to simulate the ventilatory mechanics of a patient with obstructive lung disease. INTERVENTION: Hypercapnic respiratory failure (end-tidal CO2 of 75 mm Hg) and obstructive lung disease were simulated in a double-chamber lung model. A facial mask (inner volume of 165 mL) with exhalation port within the mask (Facial-MEP) or the same mask with exhalation port in the ventilator circuit (Facial-WS) and a total face mask with exhalation port within the mask (inner volume 875 mL, Total Face) were tested during continuous positive airway pressure and pressure support ventilation provided by a single-limb circuit ventilator at the same frequency and tidal volume. MEASUREMENTS AND MAIN RESULTS: A capnometer and a flow transducer were placed in the lung model upper airway to measure the volume of CO2 rebreathed and tidal volume (Vt). The inspiratory load was estimated from the pressure variation in the lung model driving chamber (PDR). Volume of CO2 rebreathed was smaller during Facial-MEP compared with the other masks in all tested conditions (p <.001). The Vt and PDR necessary to decrease end-tidal CO2 20% (from 75 to 60 mm Hg) was different among the tested masks (Facial-MEP, Vt 701 +/- 9 mL, PDR 8.1 +/- 0.1 cm H2O/sec; Facial-WS, Vt 745 +/- 9 mL, PDR 10.2 +/- 0.1 cm H2O/sec; Total Face, Vt 790 +/- 12 mL, PDR 11.4 +/- 0.2 cm H2O/sec, p <.001). CONCLUSION: Facial-MEP with its exhalation port within the mask and the smallest mask volume demonstrated less rebreathed CO2 and a lower PDR than either the Facial-WS or Total Face masks. Additional studies are necessary to confirm if mask design can clinically affect patient's inspiratory effort during noninvasive positive pressure ventilation.     

呼气末正压对机械通气患者中心静脉压及髂总静脉压的影响

目的 观察不同呼气末正压(PEEP)水平对机械通气患者中心静脉压(CVP)和髂总静脉压(CIVP)及两者相关关系的影响.方法 将2007年2-8月收住重症加强治疗病房(ICU),无心肺疾患、循环稳定、无腹胀、无凝血功能异常,需机械通气的20例成年患者列为观察对象,采用自身对照,随机加用0、5和10 cm HzO(1 am H2O=0.098 kPa)PEEP,评估在此条件下,CVP、CIVP和两者压力阶差变化及其与机械通气压力变化间的相关关系.结果 CVP及CIVP随PEEP增加而增高,差异有统计学意义(P0.05);CVP及CIVP与机械通气各压力值变化呈正相关,但CVP及CIVP仅与平均气道压(Pmean)及PEEP有统计学意义(CVP与PEEP r=0.751,CIVP与PEEP r=0.685,CVP与Pmean r=0.634,CIVP与Pmena r=0.603,P均相似文献   

体外膜肺氧合支持下甲型H1N1流感的肺保护策略探讨

目的 观察体外膜肺氧合(ECMO)用于甲型H1N1流感所致重症肺炎时,如何通过肺休息实施肺保护策略.方法 对5例甲型H1N1流感所致重症肺炎患者应用ECMO支持和不同机械通气策略进行治疗.其中2例死亡患者均采用同步间歇指令通气(SIMV)及双水平气道正压(BiPAP)通气模式,同时利用气道压力释放通气(APRV)模式进行控制性肺膨胀,复张压力设定在40 cm H_2O(1 cm H_2O=0.098 kPa).3例存活患者均应用肺休息策略,即逐渐抬高呼气末正压(PEEP),通过最佳顺应性寻找最佳PEEP,然后通过BiPAP模式将高水平压力(Phigh)设定为20 cm H_2O进行观察.结果 死亡2例,其中1例因肺损伤反复出现自发性气胸伴脓毒症死亡;另1例死于多器官功能障碍综合征.3例采用肺休息治疗策略,最终康复.结论 甲型H1N1流感所致重症肺炎患者应用ECMO治疗时,通过肺休息实施肺保护策略,可以明显改善预后,减少肺损伤的发生.     

Partial liquid ventilation and positive end-expiratory pressure reduce ventilator-induced lung injury in an ovine model of acute respiratory failure

OBJECTIVE: To examine the isolated and combined effects of positive end-expiratory pressure (PEEP) and partial liquid ventilation (PLV) on the development of ventilator-induced lung injury in an ovine model. DESIGN: Prospective controlled animal study. SETTING: University-based cardiovascular animal physiology laboratory. SUBJECTS: Thirty-eight anesthetized supine sheep weighing 22.3 +/- 2.2 kg. INTERVENTIONS: Animals were ventilated for 6 hrs (respiratory rate, 15; FIO2, 1.0, inspiratory/expiratory ratio, 1:1) with one of five pressure-controlled strategies, expressed as peak inspiratory pressure (PIP)/PEEP: low-PIP, 25/5 cm H2O (n = 8); high-PIP, 50/5 cm H2O (n = 8); high-PIP-PLV, 50/5 cm H2O-PLV (n = 8); high-PEEP, 50/20 cm H2O (n = 7); and high-PEEP-PLV, 50/20 cm H2O-PLV (n = 7). MEASUREMENTS AND MAIN RESULTS: Compared with the low-PIP control, high-PIP ventilation increased airleak, shunt, histologic evidence of lung injury, neutrophil infiltrates, and wet lung weight. Maintaining PEEP at 20 cm H2O or adding PLV reduced the development of physiologic shunt and dependent histologic injury indexes. Neither higher PEEP nor PLV reduced the high incidence of barotrauma observed in high-PIP animals. CONCLUSIONS: We conclude that application of PLV or PEEP at 20 cm H2O may improve gas exchange and afford lung protection from ventilator-induced lung injury during high-pressure mechanical ventilation in this model.     

外源性呼气末正压对气道压力的影响

目的探讨外源性呼气末正压（PEEP）对气过压力影响的规律。方法通过模拟肺（静态顺应性为28ml／cmH2O,气道阻力为0．8cmH2O·L－1·S-1）试验,设置不同的PEEP,观察气道压力（修压、平均压、平台压）的变化。结果外源性PEEP从0增加至3cmH2O时,气过压力增幅最大,平均每增加1cmH2OPEEP,气道峰压、平台压增加3．5～4．1cmH2O,当PEEP增加至12cmH2O时,气道峰压和平台压增加了20cmH2O以上。结论外源性PEEP对气造压力的影响,可产生一种“扩大”效应,这种“扩大”效应在低水平的PEEP时尤为显著。在使用人工机械通气时,如需设置外源性PEEP时,必须严密监测气道压力的变化,以防止肺损伤。     

Gas exchange during conventional and high-frequency pulse ventilation in the surfactant-deficient lung: influence of positive end-expiratory pressure

High-frequency pulse ventilation (HFPV) was compared to conventional ventilation (CV) in a model of severe respiratory failure induced by serial lung lavages with warm saline in 8 mongrel dogs. Before the lavage, during HFPV at 4 Hz with a pulse volume (PV) of 125 ml, mean PaO2 was 107 torr and mean PaCO2 was 34 torr. After the last lavage, during CV at an inspired oxygen fraction FIO2 of 1.0 and a tidal volume (VT) of 535 ml, the PaO2 averaged 60 torr and PaCO2 was 45 torr. At an FIO2 of 0.21, 20 cm H2O of positive end-expiratory pressure (PEEP) was applied to prevent hypoxemia. The resulting PaO2 was 87 torr; PaCO2 was 40 torr. Peak airway pressure (Ppa) rose from 21 to 51 cm H2O. When ventilation was switched to HFPV on room air, a PV similar to the control levels was associated with severe hypoxemia (PaO2 less than 45 torr, PaCO2 greater than 50 torr). As PV was increased PaO2 improved, reaching 113 torr at a PV of about 470 ml. The corresponding mean airway pressure (Paw) was about 20 cm H2O. Thus, application of PEEP during HFPV at low PV did not improve PaO2 even when measured Paw approximated 20 cm H2O. This suggests that HFPV with high PV is more effective than either CV with PEEP, or HFPV with low PV and PEEP.