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.     

Measuring intra-esophageal pressure to assess transmural pulmonary arterial occlusion pressure in patients with acute lung injury: a case series and review

BACKGROUND: Positive end-expiratory pressure (PEEP) may interfere with accurate assessment of cardiac function. PEEP may decrease left ventricular volume by lowering the transmural gradient between ventricular and pleural surface pressure (P(PL)) around the heart while raising the absolute pulmonary arterial occlusion pressure (PAOP). Clinical formulas used to predict the transmural PAOP (PAOP(TM)) require subtracting 25-50% of the PEEP level from the PAOP. However, both PAOP and P(PL) are influenced by transmitted PEEP and transmitted intra-abdominal pressure (IAP). We compared PAOP(TM) calculated by measuring intra-esophageal pressure (P(ES)) with PAOP(TM) estimated by clinical formulas. METHODS: Twenty-two P(ES) measurements were made with a bedside pulmonary mechanics monitor (BICORE CP-100) on 11 patients with acute lung injury who had an elevated PAOP (mean +/- standard deviation) of 21.1 +/- 6.2 mm Hg and PEEP of 13.0 +/- 3.8 mm Hg. Paired comparisons were made with the Wilcoxon signed-rank test and multiple comparisons were made using one-way analysis of variance (ANOVA) and the Student-Newman-Keuls test. Pearson product-moment correlation coefficients were calculated. A MEDLINE literature search was done to survey the reported range of PEEP transmitted to P(PL). RESULTS: P(ES) (14.6 +/- 5.0 mm Hg) exceeded PEEP; 9 of 11 patients had clinical evidence of increased IAP. PAOP(TM) predicted by clinical formulas were 13.5-17.7 mm Hg, whereas PAOP(TM) calculated by P(ES) was 6.2 +/- 3.6 mm Hg (p < 0.05). Linear regression revealed a moderate correlation between PAOP and PEEP (r = 0.49, p = 0.02). In contrast, there was a strong correlation between PAOP and P(ES) (r = 0.83, p < 0.0001). A review of data derived from the literature did not show a consistent pattern of PEEP transmission. CONCLUSION: PAOP(TM) calculated by P(ES) may reflect transmitted IAP to the pleural surface. Using P(ES) to calculate PAOP(TM) may provide a more accurate assessment of hemodynamic status than predicting PAOP(TM) using clinical formulas based solely on estimated PEEP transmission.     

Effect of end-inspiratory pause duration on plateau pressure in mechanically ventilated patients

OBJECTIVE: To compare the values of plateau pressure (Pplat) recorded at different times after end-inspiratory occlusion and those of static elastance (Est,rs) and total resistance (Rrs) of the respiratory system. DESIGN: Physiological study. SETTING: Medical intensive care unit of a university hospital. PATIENTS: Eleven patients with ARDS and ten patients with COPD requiring tracheal intubation and mechanical ventilation were investigated. COPD patients were investigated on zero end-expiratory pressure (ZEEP) and ARDS patients on both ZEEP and positive end-expiratory pressure (PEEP). MEASUREMENTS AND RESULTS: Respiratory mechanics were assessed using the rapid airway occlusion technique. Tracheal pressure (Ptr) was measured downstream the endotracheal tube. Ptr was recorded 0.5 s, 1 s, 2 s, 3 s, and 5 s after a 5-s end-inspiratory occlusion. Est,rs and Rrs were computed at the same times using standard formula. In ARDS patients on ZEEP, Pplat amounted to 20+/-5, 20+/-5, 19+/-5, 19+/-5, and 18+/-5 cmH(2)O at 0.5, 1, 2, 3 and 5 s, respectively (P <0.001). In COPD patients, these values were 18+/-4 cmH(2)O, 17+/-4 cmH(2)O, 17+/-4 cmH(2)O, 16+/-4 cmH(2)O, and 16+/-4 cmH(2)O (P <0.001). Except for one ARDS patient on PEEP, Pplat was always less than 35 cmH(2)O, regardless of the time of measurement. As compared to 5 s, measurements at 0.5 s resulted in overestimation of Est,rs by 14% and 29% and in underestimation of Rrs by 34% and 24%, in ARDS and COPD patients, respectively. CONCLUSIONS: Very early post-occlusion values of Pplat were statistically greater than at 3 s or 5 s. This probably has no major impact on the occurrence of volutrauma. Clinicians must be aware, however, that Est,rs and Rrs are greatly modified by the time of recording of Pplat.     

Estimating cardiac filling pressure in mechanically ventilated patients with hyperinflation

OBJECTIVE: When positive end-expiratory pressure (PEEP) is applied, the intracavitary left ventricular end-diastolic pressure (LVEDP) exceeds the LV filling pressure because pericardial pressure exceeds 0 at end-expiration. Under those conditions, the LV filling pressure is itself better reflected by the transmural LVEDP (tLVEDP) (LVEDP minus pericardial pressure). By extension, end-expiratory pulmonary artery occlusion pressure (eePAOP), as an estimate of end-expiratory LVEDP, overestimates LV filling pressure when pericardial pressure is >0, because it occurs when PEEP is present. We hypothesized that LV filling pressure could be measured from eePAOP by also knowing the proportional transmission of alveolar pressure to pulmonary vessels calculated as index of transmission = (end-inspiratory PAOP--eePAOP)/(plateau pressure--total PEEP). We calculated transmural pulmonary artery occlusion pressure (tPAOP) with this equation: tPAOP = eePAOP--(index of transmission x total PEEP). We compared tPAOP with airway disconnection nadir PAOP measured during rapid airway disconnection in subjects undergoing PEEP with and without evidence of dynamic pulmonary hyperinflation. DESIGN: Prospective study. SETTING: Medical intensive care unit of a university hospital. PATIENTS: We studied 107 patients mechanically ventilated with PEEP for acute respiratory failure. Patients without dynamic pulmonary hyperinflation (group A; n = 58) were analyzed separately from patients with dynamic pulmonary hyperinflation (group B; n = 49). INTERVENTION: Transient airway disconnection. MEASUREMENTS AND MAIN RESULTS: In group A, tPAOP (8.5+/-6.0 mm Hg) and nadir PAOP (8.6+/-6.0 mm Hg) did not differ from each other but were lower than eePAOP (12.4+/-5.6 mm Hg; p < .05). The agreement between tPAOP and nadir PAOP was good (bias, 0.15 mm Hg; limits of agreement, -1.5-1.8 mm Hg). In group B, tPAOP (9.7+/-5.4 mm Hg) was lower than both nadir PAOP and eePAOP (12.1+/-5.4 and 13.9+/-5.2 mm Hg, respectively; p < .05 for both comparisons). The agreement between tPAOP and nadir PAOP was poor (bias, 2.3 mm Hg; limits of agreement, -0.2-4.8 mm Hg). CONCLUSIONS: Indexing the transmission of proportional alveolar pressure to PAOP in the estimation of LV filling pressure is equivalent to the nadir method in patients without dynamic pulmonary hyperinflation and may be more reliable than the nadir PAOP method in patients with dynamic pulmonary hyperinflation.     

Vascular pedicle width in acute lung injury: correlation with intravascular pressures and ability to discriminate fluid status

Introduction

Conservative fluid management in patients with acute lung injury (ALI) increases time alive and free from mechanical ventilation. Vascular pedicle width (VPW) is a non-invasive measurement of intravascular volume status. The VPW was studied in ALI patients to determine the correlation between VPW and intravascular pressure measurements and whether VPW could predict fluid status.

Methods

This retrospective cohort study involved 152 patients with ALI enrolled in the Fluid and Catheter Treatment Trial (FACTT) from five NHLBI ARDS (Acute Respiratory Distress Syndrome) Network sites. VPW and central venous pressure (CVP) or pulmonary artery occlusion pressure (PAOP) from the first four study days were correlated. The relationships between VPW, positive end-expiratory pressure (PEEP), cumulative fluid balance, and PAOP were also evaluated. Receiver operator characteristic (ROC) curves were used to determine the ability of VPW to detect PAOP <8 mmHg and PAOP ≥18 mm Hg.

Results

A total of 71 and 152 patients provided 118 and 276 paired VPW/PAOP and VPW/CVP measurements, respectively. VPW correlated with PAOP (r = 0.41; P < 0.001) and less well with CVP (r = 0.21; P = 0.001). In linear regression, VPW correlated with PAOP 1.5-fold better than cumulative fluid balance and 2.5-fold better than PEEP. VPW discriminated achievement of PAOP <8 mm Hg (AUC = 0.73; P = 0.04) with VPW ≤67 mm demonstrating 71% sensitivity (95% CI 30 to 95%) and 68% specificity (95% CI 59 to 75%). For discriminating a hydrostatic component of the edema (that is, PAOP ≥18 mm Hg), VPW ≥72 mm demonstrated 61.4% sensitivity (95% CI 47 to 74%) and 61% specificity (49 to 71%) (area under the curve (AUC) 0.69; P = 0.001).

Conclusions

VPW correlates with PAOP better than CVP in patients with ALI. Due to its only moderate sensitivity and specificity, the ability of VPW to discriminate fluid status in patients with acute lung injury is limited and should only be considered when intravascular pressures are unavailable.     

Prone position improves mechanics and alveolar ventilation in acute respiratory distress syndrome

Objective We tested the hypothesis that ventilation in the prone position might improve homogenization of tidal ventilation by reducing time-constant inequalities, and thus improving alveolar ventilation. We have recently reported in ARDS patients that these inequalities are responsible for the presence of a slow compartment, excluded from tidal ventilation at supportive respiratory rate.Design In 11 ARDS patients treated by ventilation in the prone position because of a major oxygenation impairment (PaO₂/FIO₂100 mm Hg) we studied mechanical and blood gas changes produced by a low PEEP (6±1 cm H₂O), ventilation in the prone position, and the two combined.Results Ventilation in the prone position significantly reduced the expiratory time constant from 1.98±0.53 s at baseline with ZEEP to 1.53±0.34 s, and significantly decreased PaCO₂ from 55±11 mm Hg at baseline with ZEEP to 50±7 mm Hg. This improvement in alveolar ventilation was accompanied by a significant improvement in respiratory system mechanics, and in arterial oxygenation, the latter being markedly increased by application of a low PEEP (PaO₂/FIO₂ increasing from 64±19 mm Hg in supine position with ZEEP to 137±88 mm Hg in prone with a low PEEP).Conclusion In severely hypoxemic patients, prone position was able to improve alveolar ventilation significantly by reducing the expiratory time constant.     

Translaryngeal tracheostomy in acute respiratory distress syndrome patients

OBJECTIVE: To prevent gas exchange deterioration during translaryngeal tracheostomy (TLT) in patients with acute respiratory distress syndrome (ARDS) ventilation is maintained through a small diameter endotracheal tube (ETT; 4.0 mm i.d.) advanced beyond the tracheostoma. We report on the feasibility of uninterrupted ventilation delivered through a high-resistance ETT in ARDS patients, and relevant ventilatory adjustments and monitoring. DESIGN AND SETTING: Prospective, observational clinical study in an eight-bed intensive care unit of a university hospital. Patients: Eight consecutive ARDS patients scheduled for tracheostomy. INTERVENTIONS: During TLT volume control ventilation was maintained through the 4.0-mm i.d. ETT. Tidal volume, respiratory rate, and inspiratory to expiratory ratio were kept constant. Fractional inspiratory oxygen was 1. Positive end expiratory pressure (PEEP) set on the ventilator (PEEP(vent)) was reduced to maintain total PEEP (PEEP(tot)) at baseline level according to the measured intrinsic PEEP (auto-PEEP). MEASUREMENTS AND MAIN RESULTS: Data were collected before tracheostomy and while on mechanical ventilation with the 4.0-mm i.d. ETT. Neither PaCO(2) nor PaO(2) changed significantly (54.5+/-10.0 vs. 56.4+/-7.0 and 137+/-69 vs. 140+/-59 mmHg, respectively). Auto-PEEP increased from 0.6+/-1.1 to 9.8+/-6.5 cmH(2)O during ventilation with the 4.0-mm i.d. ETT. By decreasing PEEP(vent) we obtained a stable PEEP(tot) (11.4+/-4.3 vs. 11.8+/-4.3 cmH(2)O), and end-inspiratory occlusion pressure (26.7+/-7.4 vs. 28.0+/-6.6 cmH(2)O). Peak inspiratory pressure rose from 33.8+/-8.1 to 77.8+/-12.7 cmH(2)O. CONCLUSIONS: The high-resistance ETT allows ventilatory assistance during the whole TLT procedure. Assessment of stability in plateau pressure and PEEP(tot) by end-inspiratory and end-expiratory occlusions prevent hyperinflation and possibly barotrauma.     

A high positive end-expiratory pressure, low tidal volume ventilatory strategy improves outcome in persistent acute respiratory distress syndrome: a randomized, controlled trial

OBJECTIVE: It has been shown in a two-center study that high positive end-expiratory pressure (PEEP) and low tidal volume (LTV) improved outcome in ARDS. However, that study involved patients with underlying diseases unique to the study area, was conducted at only two centers, and enrolled a small number of patients. We similarly hypothesized that a ventilatory strategy based on PEEP above the lower inflection point of the pressure volume curve of the respiratory system (Pflex) set on day 1 with a low tidal volume would result in improved outcome in patients with severe and persistent acute respiratory distress syndrome (ARDS). DESIGN: Randomized, controlled clinical trial. SETTING: Network of eight Spanish multidisciplinary intensive care units (ICUs) under the acronym of ARIES (Acute Respiratory Insufficiency: Espa?a Study). PATIENTS: All consecutive patients admitted into participating Spanish ICUs from March 1999 to March 2001 with a diagnosis of ARDS were considered for the study. If 24 hrs after meeting ARDS criteria, the Pao2/Fio2 remained < or =200 mm Hg on standard ventilator settings, patients were randomized into two groups: control and Pflex/LTV. INTERVENTIONS: In the control group, tidal volume was 9-11 mL/kg of predicted body weight (PBW) and PEEP > or =5 cm H2O. In the Pflex/LTV group, tidal volume was 5-8 mL/kg PBW and PEEP was set on day 1 at Pflex + 2 cm H2O. In both groups, Fio2 was set to maintain arterial oxygen saturation >90% and Pao2 70-100 mm Hg, and respiratory rate was adjusted to maintain Paco2 between 35 and 50 mm Hg. MEASUREMENTS AND MAIN RESULTS: The study was stopped early based on an efficacy stopping rule as described in the methods. Of 103 patients who were enrolled (50 control and 53 Pflex), eight patients (five in control, three in Pflex) were excluded from the final evaluation because the random group assignment was not performed in one center according to protocol. Main outcome measures were ICU and hospital mortality, ventilator-free days, and nonpulmonary organ dysfunction. ICU mortality (24 of 45 [53.3%] vs. 16 of 50 [32%], p = .040), hospital mortality (25 of 45 [55.5%] vs. 17 of 50 [34%], p = .041), and ventilator-free days at day 28 (6.02 +/- 7.95 in control and 10.90 +/- 9.45 in Pflex/LTV, p = .008) all favored Pflex/LTV. The mean difference in the number of additional organ failures postrandomization was higher in the control group (p < .001). CONCLUSIONS: A mechanical ventilation strategy with a PEEP level set on day 1 above Pflex and a low tidal volume compared with a strategy with a higher tidal volume and relatively low PEEP has a beneficial impact on outcome in patients with severe and persistent ARDS.     

Effects of positive end-expiratory pressure in an experimental model of acute myocardial infarct in wistar rats

ABSTRACT: Our purpose in this study was to access the pulmonary effects of mechanical ventilation with positive end-expiratory pressure (PEEP; 10 cmH2O) or without PEEP (zero PEEP-ZEEP) in a rat model of acute myocardial infarction that resulted in hypotension but not in pulmonary congestion. METHODS: Wistar rats were anesthetized (1.5% isoflurane) and myocardial infarct was induced by ligature of the anterior interventricular coronary artery. Rats with myocardial infarct were compared with sham-operated (Sham) and closed thorax groups. RESULTS AND CONCLUSION: There was a significant decrease in MAP in the acute myocardial infarct group (92.5 +/- 4.2 mmHg) when compared with closed chest group (113.0 +/- 4.4 mmHg). There was no significant difference between acute myocardial infarct and Sham groups in PEEP or ZEEP. Mechanical ventilation for 120 min resulted in a significant increase in respiratory system elastance in the groups ventilated with ZEEP (2.59 +/- 0.17 and 2.32 +/- 0.17 cmH2O.mL, Sham and acute myocardial infarct groups, respectively). This effect of mechanical ventilation was not observed in the presence of PEEP in both groups. There was no significant increase in the amount of perivascular pulmonary edema measured in all groups studied. Mean airspace linear intercept and lung tissue distortion index also did not show statistically significant difference between Sham and acute myocardial infarct groups. We conclude that in this experimental model of acute myocardial infarct (12.4 +/- 4.1% area of necrotic tissue and 26.4 +/- 4.0% area of ischemic tissue), there was a protective pulmonary effect of 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。     

评分法选择PEEP对ARDS病人的临床价值

目的：研究评分法选择PEEP对ARDS病人的临床价值。方法：对1999年～2004年88例ARDS病人随机使用两种方法选择PEEP进行机械通气。其中评分组（实验组）51例，根据评分法四项指标得分数总和，如评分大于等于6分则PEEP用20-25cmHO；3～5分则PEEP用12～20cmH2O；评分小于等于2分则PEEP用5～12cmH2O；传统方法组（对照组）37例，PEEP均使用5～12cmH2O。分别检测两组病例通气开始时、通气后24h时的血气分析，计算两组病例入ICU30d时病死率，观察其并发症发生情况。结果：实验组较对照组痛死率明显下降，具有极显著差异，P〈0．01；且实验组中采用低PEEP小组的病死率亦较对照组低，具有显著差异，P〈0．05。实验组与对照组在通气24h时都能较通气开始时改善病人的血气情况，且实验组较对照组PaO2升高更明显，具有极显著差异，P〈0．001，而pH、PaCO2在两组无显著差异，P〉0．05。两组均未发生气压伤，实验组较对照组并发MOF的发生率低，具有显著差异，P〈0．05；血压明显下降的发生率高，具有显著差异，P〈0．05，但能纠正。结论：采用评分法选择PEEP较传统方法有更高的临床价值，可明显降低削RDS病人痛死率，改善病人的氧合情况，并且并发症较少或可控制。     

Pulmonary capillary pressures during the acute respiratory distress syndrome

Objectives (1)To describe the evolution of pulmonary capillary pressure (Pcap) and of the pressure drop across the pulmonary venous bed from early to established acute respiratory distress syndrome (ARDS), (2) to assess Pcap under different levels of positive end-expiratory pressure (PEEP) and (3) to compare the visual method and a mathematical model to determine Pcap.Design Prospective, intervention study.Setting Intensive care unit in a teaching institution.Patients Nine ARDS patients, according to the ARDS Consensus Conference criteria.Interventions Pulmonary arterial pressures were measured during routine respiratory mechanics measurements throughout ARDS. Four PEEP levels (6, 9, 12 and 15 cmH₂O) were studied.Measurements and results Pulmonary artery occlusions were made in triplicate at each PEEP level. Pcap was determined for every occlusion trace by three observers (visual method) and a mathematical model. Diastolic pulmonary artery pressure (PAPd) and pulmonary artery occlusion pressure (PAOP) were measured. The visually determined Pcap showed a bias of 2.5±2.1 mmHg as compared to the mathematical estimation. PAPd, Pcap and PAOP tended to decrease from early to late ARDS (p=0.128, 0.265, 0.121). Pcap–PAOP (6.3±2.7 mmHg) did not change throughout ARDS. Higher PEEP levels were associated with increased PAPd, Pcap and PAOP, as well as with larger Pcap–PAOP throughout ARDS.Conclusions Pulmonary capillary pressure cannot be predicted from PAOP during early and established ARDS. The high variability in Pcap–PAOP increases the risk for underestimation of filtration pressures and consequently the risk for lung edema. Pcap can be estimated at the bedside by either the visual or mathematical methods.     

密闭式吸痰对急性呼吸窘迫综合征小猪呼吸及循环系统的影响

[目的]探讨密闭式吸痰对急性呼吸窘迫综合征(ARDS)小猪动脉血气、呼吸力学和心率(HR)、血压的影响。[方法]先制作小猪ARDS模型,模型成功后将其随机分为呼气末正压(PEEP)5cmH2O组和10cmH2O组,予机械通气30min后进行密闭式吸痰。监测吸痰前1min及吸痰后1min、3min、5min、10min动脉血气、呼吸力学及HR、血压的变化。[结果]两组在密闭式吸痰后动脉血氧分压(PaO2)和动脉血氧饱和度(SaO2)均下降,直到吸痰后10min仍低于吸痰前基线水平(P<0.05),而吸痰后舒张压(DBP)与吸痰前比较均无差异(P>0.05);在PEEP5cmH2O组,吸痰后气道峰压(Ppeak)、平台压(Pplat)、平均气道压(Pmean)均升高,持续到吸痰后10min仍显著高于吸痰前基线水平(P<0.05);肺静态顺应性(Cs)、平均动脉压(MAP)、收缩压(SBP)均降低,持续到吸痰后10min仍低于吸痰前基线水平(P<0.05);在PEEP10cmH2O组,吸痰后1min及3minPpeak显著升高(P<0.05),持续到吸痰后10min仍高于吸痰前基线水平但差异无统计学意义(P>0.05);Pplat、Pmean在吸痰后1min显著增高,在吸痰后3min、5min、10min仍高于吸痰前基线水平但无统计学差异(P>0.05),同时在吸痰后1min及3minCs显著下降(P<0.05),持续到吸痰后10min仍低于吸痰前基线水平但差异无统计学意义(P>0.05)。[结论]不论在PEEP5cmH2O还是10cmH2O水平,密闭式吸痰可引起ARDS小猪较严重的低氧血症,使气道压力增高、肺顺应性降低、血压下降。但在PEEP5cmH2O组,吸痰所引起的缺氧、气道高压及低血压持续时间较长。     

Effects of positive end-expiratory pressure on gas exchange and expiratory flow limitation in adult respiratory distress syndrome

OBJECTIVE: To assess the effects of different positive end-expiratory pressure (PEEP) levels (0, 5, 10, and 15 cm H2O) on tidal expiratory flow limitation (FL), regional intrinsic positive end-expiratory pressure (PEEPi) inhomogeneity, alveolar recruited volume (Vrec), respiratory mechanics, and arterial blood gases in mechanically ventilated patients with acute respiratory distress syndrome (ARDS). DESIGN: Prospective clinical study. SETTING: Multidisciplinary intensive care unit of a university hospital. PATIENTS: Thirteen sedated, mechanically ventilated patients during the first 2 days of ARDS. INTERVENTIONS: Detection of tidal FL and evaluation of total dynamic PEEP (PEEPt,dyn), total static PEEP (PEEPt,st), respiratory mechanics, and Vrec from pressure, flow, and volume traces provided by the ventilator. The average (+/-sd) tidal volume was 7.1 +/- 1.5 mL/kg, the total cycle duration was 2.9 +/- 0.45 secs, and the duty cycle was 0.35 +/- 0.05. MEASUREMENTS: Tidal FL was assessed using the negative expiratory pressure technique. Regional PEEPi inhomogeneity was assessed as the ratio of PEEPt,dyn to PEEPt,st (PEEPi inequality index), and Vrec was quantified as the difference in lung volume at the same airway pressure between quasi-static inflation volume-pressure curves on zero end-expiratory pressure (ZEEP) and PEEP. RESULTS: On ZEEP, seven patients exhibited FL amounting to 31 +/- 8% of tidal volume. They had higher PEEPt,st and PEEPi,st ( p<.001) and lower PEEPi inequality index ( p<.001) than the six nonflow-limited (NFL) patients. Two FL patients became NFL with PEEP of 5 cm H2O and five with PEEP of 10 cm H2O. In both groups, PaO2 increased progressively with PEEP. In the FL group, there was a significant correlation of PaO2 to PEEPi inequality index ( p=.002). For a given PEEP, Vrec was greater in NFL than FL patients, and a significant correlation of Pao to Vrec ( p<.001) was found only in the NFL group. CONCLUSIONS: We conclude that on ZEEP, tidal FL is common in ARDS patients and is associated with greater regional PEEPi inhomogeneity than in NFL patients. With PEEP of 10 cm H2O, flow limitation with concurrent cyclic dynamic airway compression and re-expansion and the risk of "low lung volume injury" were absent in all patients. In FL patients, PEEP induced a significant increase in PaO2, mainly because of the reduction of regional PEEPi inequality, whereas in the NFL group, arterial oxygenation was improved satisfactorily because of alveolar recruitment.     

Adapting prognostic respiratory variables of ARDS in children to small-scale community needs

PURPOSE: The clinical literature on the incidence and subsequent mortality of adult respiratory distress syndrome (ARDS) has come primarily from the experiences of large tertiary referral centers, particularly in Western Europe and North America. Consequently, very little has been published on the incidence, management, and outcome of ARDS in smaller community-based intensive care units. We aimed to delineate early clinical respiratory predictors of death in children with ARDS on the modest scale of a community hospital. MATERIALS AND METHODS: A retrospective chart review of children with ARDS needing conventional mechanical ventilation admitted to our pediatric intensive care unit from 1984 to 1997. The diagnosis of ARDS was based on acute onset of diffuse, bilateral pulmonary infiltrates of noncardiac origin and severe hypoxemia defined by partial pressure of oxygen <200 mm Hg during positive end-expiratory pressure (PEEP) of 6 cm H2O or greater for a minimum of 24 hours. Demographic, clinical, and physiological data including PaO2/ FIO2, A-aDo2, and ventilation index were retrieved. RESULTS: Fifty-six children with ARDS aged 8 +/- 5.5 years (range, 50 days to 21 years) were identified. The mortality rate was 50%. Early predictors of death included the peak inspiratory pressure (PIP), ventilation index, and PEEP on the third day after diagnosis: Nonsurvivors had significantly higher PIP (35.3 +/- 10.5 cm H2O vs 44.4 +/- 10.7 cm H2O, P < .001), PEEP (8 +/- 2.8 cm H2O vs 10.7.0 +/- 3.5 cm H2O, P < .01), and ventilation index (49.14 +/- 20.4 mm Hg x cm H2O/minute vs 61.6 +/- 51.1 mm Hg cm H2O/minute) than survivors. In contrast, PAO2/FIO2 and A-a DO2 were capable of predicting outcome by day 5 and thereafter. CONCLUSIONS: A small-scale mortality outcome for ARDS is comparable to large tertiary referral institutions. The PIP, PEEP, and ventilation index are valuable for predicting outcome in ARDS by the third day of conventional therapy. The development of a local risk profile may assist in decision-making of early application of supportive therapies in this population.     

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     

Oxygen delivery-consumption relationship in adult respiratory distress syndrome patients: The effects of sepsis

The oxygen consumption-delivery relationship (VO2/ O₂) was studied in 15 sedated paralyzed patients with the adult respiratory distress syndrome (ARDS) due to multiple trauma and in whom sepsis was absent. Different levels (0 to 15 cm H2O) of positive end-expiratory pressure (PEEP) were applied. Oxygen delivery was calculated from cardiac index (thermodilution technique) and arterial oxygen content measurements. Oxygen consumption was calculated using Fick's equation. Regression lines were obtained for each patient. Oxygen supply dependency was defined as a significant (P < .05) relationship between changes in O2 and O₂ with PEEP. Results were compared with those obtained in 18 ARDS patients in whom ARDS was due to sepsis. In nonseptic ARDS patients no significant relationship between changes in VO2 and O₂ with PEEP was found within the experimental range of O₂ on zero end-expiratory pressure (ZEEP) (347 to 845 mL/min/m²). None of these patients had multiple organ system failure (MOSF), and 73% survived. In ARDS patients in whom sepsis was present, supply dependency was present only when O₂ on ZEEP ranged between 330 and 640 mL/min/m². All these patients developed MOSF and died. When O₂ on ZEEP ranged between 686 and 951 mL/min/m² in septic ARDS patients, the supply dependency phenomenon was absent and only three patients developed MOSF and died (70% survivors). In almost all patients PEEP reduced O₂ and therefore worsened OZ balance by either increasing OZ extraction ratio and approaching the critical threshold for supply dependency or dismissing O₂ from the range of non-supply dependency.     

Positive end-expiratory pressure titration in acute respiratory distress syndrome patients: impact on right ventricular outflow impedance evaluated by pulmonary artery Doppler flow velocity measurements

OBJECTIVE: Positive end-expiratory pressure (PEEP) titration in acute respiratory distress syndrome patients remains debatable. We used two mechanical approaches, calculation of the compliance of the respiratory system and determination of the lower inflexion point of the pressure-volume curve of the respiratory system, to identify specific PEEPs (PEEPS and PEEPA) whose impact on right ventricular (RV) outflow was compared with Doppler analysis of pulmonary artery flow velocity. DESIGN: Prospective, open, clinical study. SETTING: Medical intensive care unit of a university hospital. PATIENTS: Sixteen consecutive ventilator-dependent acute respiratory distress syndrome patients. INTERVENTIONS: Two PEEPs were determined: PEEPS was the highest PEEP associated with the highest value of respiratory compliance, and PEEPA was the coordinate of the lower inflexion point of the inspiratory pressure-volume curve on the pressure axis plus 2 cm H2O. MEASUREMENTS AND MAIN RESULTS: We observed a large difference between the two PEEPs, with PEEPA (13 + 4 cm H2O) > PEEPS (6 + 3 cm H2O). Changes in RV outflow impedance produced by tidal ventilation with zero end-expiratory pressure (ZEEP) and after application of these two PEEPs were assessed by Doppler study of pulmonary artery flow velocity obtained by a transesophageal approach, with particular reference to the end-expiratory and end-inspiratory pulmonary artery velocity-time integral, as reflecting RV stroke output, and mean acceleration as reflecting RV outflow impedance during an unchanged flow period. A significant inspiratory reduction in pulmonary artery velocity-time integral (from 11.8 + 0.3 to 10.0 + 0.3 cm) and mean acceleration (from 11.9 + 0.9 to 8.0 + 0.9 m/sec2) was observed with ZEEP, showing a reduction in RV stroke index (from 29.0 + 0.9 to 26.0 + 0.6 cm3/m2) by a sudden increase in outflow impedance during tidal ventilation. Application of PEEPA, which improved Pao2 (102 + 40 vs. 65 + 18 torr with ZEEP), worsened the inspiratory drop in RV stroke index (21.6 + 0.8 cm3/m2), resulting in a significant reduction in cardiac index compared with ZEEP (from 3.0 + 1.0 to 2.7 + 1.1). Application of PEEPS, which also significantly improved Pao2 (81 + 21 torr), was associated with a lesser impact on RV outflow impedance (inspiratory mean acceleration: 9.5 + 1 m/sec2) and cardiac index (3.2 + 1.0) than PEEPA. CONCLUSION: RV outflow impedance evaluated by the Doppler technique appeared sensitive to PEEP titration. Application of PEEPA worsened RV systolic function impairment produced by tidal ventilation. Conversely, application of PEEPS reduced RV systolic function impairment, suggesting an association with a lower pulmonary vascular resistance.     

Right atrial pressure predicts hemodynamic response to apneic positive airway pressure

OBJECTIVE: To evaluate if the preexistant filling state, assessed by right atrial pressure (RAP), pulmonary artery occlusion pressure (PAOP), and right ventricular end-diastolic volume index (EDVI), would define the subsequent hemodynamic effects of increases in airway pressure (Paw). DESIGN: Prospective open clinical study. SETTING: Postoperative intensive care unit, university hospital. PATIENTS: Twenty-two consecutive ventilator-dependent patients with mild to severe acute lung injury with Murray scores (scoring infiltrates on chest radiograph, oxygenation index, lung compliance, and the level of positive end-expiratory pressure) ranging from 0.5 to 3.0 without history of preexisting cardiopulmonary disease. INTERVENTIONS: Paw varied during apnea from 0 to 10, 20, and 30 cm H2O using inspiratory hold maneuvers of 15 secs. MEASUREMENTS AND MAIN RESULTS: Cardiac index and right ventricular ejection fraction were measured by the thermodilution technique. We made measurements in triplicate using manual injection of iced saline. Right ventricular volumes were calculated. Increasing Paw induced variable changes in cardiac index among subjects (+6% to -43% change from baseline 0 cm H2O Paw values), which correlated with percentage changes in both stroke index (r2 = .89) and right ventricular EDVI (r2 = .75), whereas heart rate and right ventricular ejection fraction did not change. The change in cardiac index from 0 to 30 cm H2O Paw correlated with baseline values for RAP, PAOP, and right ventricular EDVI (r2 = .68, .43, and .34, respectively, p < 0.01). Increases in RAP correlated with lung compliance if baseline RAP was >10 mm Hg but did not if it was < or =10 mm Hg. Similarly, patients with baseline RAP < or =10 mm Hg had a greater decrease in cardiac index than patients with a RAP >10 mm Hg (for 30 cm H2O Paw: -30% +/- 9% vs. -8% +/- 7%, p < .01). CONCLUSIONS: Apneic positive Paw decreased cardiac output mainly by reducing venous return. From the investigated filling variables, RAP was most sensitive in predicting the hemodynamic response, followed by PAOP and right ventricular EDVI. Patients with RAP < or =10 mm Hg, if subjected to aggressive positive pressure ventilation, are at risk of hemodynamic deterioration and organ hypoperfusion.