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.     

呼气末压力为零时的静态压力容积曲线在急性呼吸窘迫综合征患者控制性肺膨胀中的应用

目的　评价呼气末压力为零 (ZEEP)时静态压力 容积 (P V)曲线在预测急性呼吸窘迫综合征 (ARDS)患者对控制性肺膨胀 (SI)反应性的作用。方法　 2 0例ARDS患者进行机械通气并测量ZEEP时的静态P V曲线 ,在使用呼气末正压通气 (PEEP) 2h后进行SI。根据 2 0例患者使用SI后改良氧合指数 (PaO2 /FiO2 )进行分组 ,增加≥ 2 0 %为SI反应组 (A组 ) ,<2 0 %为SI无反应组 (B组 )。结果　(1)A组ZEEP时静态P V曲线参数c - 2d≥ 0cmH2 O(1cmH2 O =0 0 98kPa) ,且c≥ 18cmH2 O ,呈向上凹的形态 ;而B组c - 2d <0cmH2 O或c <18cmH2 O ,呈向上凸的形态或一直线。 (2 )使用SI后 ,A组患者可减少肺内分流 (P =0 0 0 6 ) ,而B组不减少肺内分流 (P =0 339)。相同吸气压下的肺容积增加 ,A、B组间比较差异有显著性 [(2 4 1± 111)ml,(2 9± 4 6 )ml,P =0 0 36 ]。结论ARDS患者在ZEEP时静态P V曲线具有不同的形态 ,使用曲线参数的c - 2d及c值可迅速判断静态P V曲线形态 ,对指导预测ARDS患者中SI治疗具有一定的意义。     

Expiratory washout versus optimization of mechanical ventilation during permissive hypercapnia in patients with severe acute respiratory distress syndrome.

The aim of this study was to compare three ventilatory techniques for reducing PaCO2 in patients with severe acute respiratory distress syndrome treated with permissive hypercapnia: (1) expiratory washout alone at a flow of 15 L/min, (2) optimized mechanical ventilation defined as an increase in the respiratory frequency to the maximal rate possible without development of intrinsic positive end- expiratory pressure (PEEP) combined with a reduction of the instrumental dead space, and (3) the combination of both methods. Tidal volume was set according to the pressure-volume curve in order to obtain an inspiratory plateau airway pressure equal to the upper inflection point minus 2 cm H2O after setting the PEEP at 2 cm H2O above the lower inflection point and was kept constant throughout the study. The three modalities were compared at the same inspiratory plateau airway pressure through an adjustment of the extrinsic PEEP. During conventional mechanical ventilation using a respiratory frequency of 18 breaths/min, respiratory acidosis (PaCO2 = 84 +/- 24 mm Hg and pH = 7.21 +/- 0.12) was observed. Expiratory washout and optimized mechanical ventilation (respiratory frequency of 30 +/- 4 breaths/min) had similar effects on CO2 elimination (DeltaPaCO2 = -28 +/- 11% versus -27 +/- 12%). A further decrease in PaCO2 was observed when both methods were combined (DeltaPaCO2 = -46 +/- 7%). Extrinsic PEEP had to be reduced by 5.3 +/- 2.1 cm H2O during expiratory washout and by 7.3 +/- 1.3 cm H2O during the combination of the two modes, whereas it remained unchanged during optimized mechanical ventilation alone. In conclusion, increasing respiratory rate and reducing instrumental dead space during conventional mechanical ventilation is as efficient as expiratory washout to reduce PaCO2 in patients with severe ARDS and permissive hypercapnia. When used in combination, both techniques have additive effects and result in PaCO2 levels close to normal values.     

压力-容量曲线对急性肺损伤家兔实行个体化保护性通气的应用

目的研究以压力容量（P-V）曲线确定通气参数对急性肺损伤家兔肺的保护作用。方法新西兰家兔24只,随机分为4组（V1P1、V1P2、V2P1、V2P2）,每组4只。用油酸复制急性肺损伤模型,测定P-V曲线,以下曲点压力（Pinf）和上曲点压力（Pdef）分别选择呼气末正压（PEEP）的两水平：P1＝PinfP2＝Pinf－3cmH2O,潮气量（VT）两水平：V1＝15ml／kg,V2下调使平台压小于上曲点压力（Pplat＜Pdef）。观察肺力学、血气、血循环及肺病理改变。结果4组氧合效果基本相同,动脉血二氧化碳分压（PaCO2）和pH主要受VT影响。平均动脉压在大PEEP和（或）大VT时有所下降。呼吸系统静态顺应性（Cst）则以PEEP为Pinf时改善最明显,但大VT抵消了其作用且对肺泡有明显的损伤。小PEEP组肺泡透明膜变加重。结论以呼吸系统P-V曲线选择PEEP和VT进行个体化通气,对肺的力学特性和肺的病理性损伤有明显的保护作用,可能有利于改善急性肺损伤的预后。     

个体化通气在急性呼吸窘迫综合征机械通气中的应用

目的探讨急性呼吸窘迫综合征(ARDS)患者小潮气量肺保护性通气之上,进一步减轻呼吸机相关性肺损伤及改善患者预后的方法。方法北京协和医院加强医疗科2004年7月至2005年6月30例ARDS患者,根据随机表分为小潮气量组(LTV组,14例)和个体化通气组(Ⅳ组, 16例)。其中LTV组采用6 ml／kg的潮气量及高呼气末正压(PEEP)治疗策略。而IV组以监测静态压力容积(P-V)曲线为基础设定参数,以呼气相曲线参数b为PEEP,结合吸气相曲线高位转折点并限制潮气量≤8 ml／kg,用吸气相和呼气相参数b的差值(Ab)评估肺复张潜能并指导肺复张操作。比较两种通气策略对患者临床疗效、肺损伤程度以及预后等方面的影响。结果Ⅳ组28 d患者病死率(35．7％)与LTV组(57．2％)比较差异无统计学意义(X2=1．265,P>0．05)。Ⅳ组患者第3天和第7天的血浆表面活性蛋白D(SP-D)水平[154(91～217)、149(91～206)mg／L]与入组前[140(80～200)mg／L]比较差异无统计学意义(Z分别为1．079、1．741,P均>0．05);而第3天和第7天的白细胞介素8(IL-8)表达[179(122～236)、210(100～321)ng／L]与入组前[210(132～289)ng／L]比较差异亦无统计学意义(Z分别为-0．879、0．471,P均>0．05)。Ⅳ组患者28 d内脱离ICU时间[11(5～16)d]显著高于LTV组[3(0～8)d,Z=-2．277,P<0．05];无肺外器官衰竭时间[13(6～18)d]亦显著高于LTV组[3(0～7)d,Z=-2．372,P<0．05]。Ⅳ组患者前3 d PEEP水平,潮气量,动脉血二氧化碳分压(PaCO2)、气道平台压力(Pplat)[(11±2)cm H2O(1 cm H2O=0．098 kPa),(511±66)ml, (37±5)mm Hg(1 mm Hg=0．133 kPa),(21±5)cm H2O]与LTV组[(16±3)cm H2O,(407±58)ml, (47±8)mm Hg,(26±4)cm H2O]比较差异均有统计学意义(t分别为-8．019、6．501、-4．311、-4．823,P均<0．01)。结论个体化通气治疗与小潮气量高PEEP通气策略相比,更适合患者呼吸力学特征,可减少不必要的PEEP应用,改善顺应性,避免CO2潴留;可避免血SP-D及IL-8的升高而保护肺功能;并可延长28 d内脱离ICU的时间和无肺外器官衰竭时间,具有更佳的临床应用前景。     

呼气末正压通气在肺灌洗中的选择和应用

目的探讨呼气末正压(PEEP)通气在肺灌洗中的选择和应用。方法选择14例行全肺灌洗术的肺泡蛋白沉积症患者。随机分为实验组和对照组,各7例,实验组根据每个患者灌洗肺通气时的压力-容积曲线(P-V曲线)中吸气支的低拐点来确定PEEP值;对照组选择PEEP 5cmH2O通气。观察患者在使用PEEP前、PEEP通气30min、使用PEEP后的心率(HR)、有创平均动脉压(MAP)、中心静脉压(CVP)、心搏出量(CO)、每搏量(SV)、外周血管阻力指数(SVRI)、胸液成分(TFC)、心肌加速度指数(ACI)、呼气末二氧化碳(PetCO2)、气道峰压(Peak)、气道平台压(Plat)、动态肺顺应性、气道阻力以及血气分析值的变化。结果对照组各观察值在PEEP通气前后变化无统计学意义(P>0.05);在PEEP通气时,实验组的MAP降低、CVP和SPO2增高、TFC增高、PetCO2降低、Plat增高(P<0.05)。与PEEP通气前比较,实验组在PEEP通气后的PaCO2降低、SaO2增高(P<0.05)。与对照组比较,实验组在PEEP通气时的MAP降低、CVP、SPO2、PetCO2增高(P<0.05)。结论根据P-V曲线中吸气支的低拐点来确定PEEP值能使肺灌洗患者术中改善氧合。     

Titration of PEEP by the arterial minus end-tidal carbon dioxide gradient

It was shown in dogs that intrapulmonary physiologic shunt (Qsp/Qt), arterial oxygen tension (PaO2), total static respiratory compliance (CT), oxygen delivery (O2AV), cardiac output (Qt), and arterial minus end-tidal carbon dioxide gradient (PaCO2-PetCO2) undergo statistically significant deterioration when oleic acid is injected into the pulmonary artery. Positive end-expiratory pressure (PEEP) therapy reduced Qsp/Qt and PaCO2-PetCO2 gradient and increased PaO2. The CT did not show any consistent pattern of improvement with the application of PEEP. The Qt and the O2AV progressively decreased as PEEP was increased. The application of additional PEEP beyond that which minimized the PaCO2-PetCO2 gradient produced a statistically significant increase in the PaCO2-PetCO2 gradient, but this was not reflected by concomitant changes in Qsp/Qt or PaO2 in spite of a further decrease in Qt. Thus, the PaCO2-PetCO2 gradient may be a more sensitive indicator of excessive PEEP than is Qst/Qt or PaO2, since it should be smallest when there is maximal recruitment of perfused or functional gas units without overdistention of alveolar areas contributing to dead space. Also, the use of the PaCO2-PetCO2 gradient permits the rapid titration of PEEP without the need for a pulmonary artery catheter.     

A decremental PEEP trial for determining open-lung PEEP in a rabbit model of acute lung injury

A positive end-expiratory pressure (PEEP) above the lower inflection point (LIP) of the pressure-volume curve has been thought necessary to maintain recruited lung volume in acute lung injury (ALI). We used a strategy to identify the level of open-lung PEEP (OLP) by detecting the maximum tidal compliance during a decremental PEEP trial (DPT). We performed a randomized controlled study to compare the effect of the OLP to PEEP above LIP and zero PEEP on pulmonary mechanics, gas exchange, hemodynamic change, and lung injury in 26 rabbits with ALI. After recruitment maneuver, the lavage-injured rabbits received DPTs to identify the OLP. Animals were randomized to receive volume controlled ventilation with either: (a) PEEP = 0 cm H2O (ZEEP); (b) PEEP = 2 cm H2O above OLP (OLP + 2); or (c) PEEP = 2 cm H2O above LIP (LIP + 2). Peak inspiratory pressure and mean airway pressure were recorded and arterial blood gases were analyzed every 30 min. Mean blood pressure and heart rate were monitored continuously. Lung injury severity was assessed by lung wet/dry weight ratio. Animals in OLP + 2 group had less lung injury as well as relatively better compliance, more stable pH, and less hypercapnia compared to the LIP + 2 and ZEEP groups. We concluded that setting PEEP according to the OLP identified by DPTs is an effective method to attenuate lung injury. This strategy could be used as an indicator for optimal PEEP. The approach is simple and noninvasive and may be of clinical interest.     

压力—容量曲线对急性肺损伤家兔实行个体化保护性通气？…

OBJECTIVE: To explore the lung-protective effect of ventilation with tidal volume and PEEP determined on pressure-volume curve in oleic acid rabbit models of acute lung injury. METHODS: 24 New Zealand rabbits were randomly divided into 4 groups (V1P1, V1P2, V2P1, V2P2). After inducing lung injury, the P-V curves were measured and drawn. The low and upper inflection point pressure (Pinf and Pdef respectively) were manually determined. Two levels of tidal volume (V1 = 15 ml/kg, V2 reduced for Pplat < Pdef) and two levels of PEEP (P1 = Pinf, P2 = Pinf - 3 cm H2O) were selected. The peak airway pressure (PIP), plateau pressure (Pplat), mean pressure (PAW), static compliance (Cst), heart rate, arterial blood pressure and blood-gas analysis were measured. The lung tissues were pathologically analyzed with light microscope. RESULTS: The oxygenation was not significantly different among 4 groups. The reduced VT significantly raised PaCO2 and lowered pH. Larger VT reduced arterial blood pressure. VT and PEEP synergetically raised airway pressure. Larger PEEP improved Cst, which was counteracted by larger VT. Reduced VT significantly lessened alveolar barotrauma. Larger PEEP lightened alveolar hyaline membrane formation and hemorrhage. CONCLUSION: The ventilation with VT and PEEP determined on P-V curve has significant protective effect on the acutely injured lung.     

Alveolar derecruitment at decremental positive end-expiratory pressure levels in acute lung injury: comparison with the lower inflection point, oxygenation, and compliance.

We examined the hypothesis that recording multiple elastic pressure-volume (Pel/V) curves and calculating alveolar derecruitment (V(DER)) induced by decreasing positive end-expiratory pressure (PEEP) may allow determination of alveolar closing pressures, thus helping to select the optimal PEEP level. V(DER) measured in 16 patients with acute lung injury (ALI) was compared with the lower inflection point (LIP) and oxygenation changes. A modified automated method was used to record multiple Pel/V curves at low constant flow. PEEP was decreased in 5-cm H(2)O steps, from 20 or 15 cm H(2)O to 0 cm H(2)O (ZEEP). V(DER) was the volume loss between the curves recorded from PEEP and from ZEEP at the same Pel. Derecruitment occurred at each PEEP decrement, being spread almost uniformly over the 20/15 to 0 cm H(2)O range. V(DER) was not correlated with LIP. V(DER) changes correlated with Pa(O(2))/FI(O(2)) changes (rho = 0.6, p = 0.02). Linear compliance at ZEEP was correlated to V(DER) at PEEP 15 cm H(2)O (rho = 0.9, p = 0.001), suggesting that compliance above LIP may reflect the amount of recruitable lung. Thus, alveolar closure in ALI occurs over a wide range of pressures, and LIP is a poor predictor of alveolar closure.     

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.     

Effects of PEEP on respiratory mechanics after open heart surgery.

Respiratory dysfunction, particularly atelectasis, is common after open heart surgery. Routine use of PEEP (5 to 10 cm H2O) in these patients has been advocated. We studied the effects of different levels of PEEP on respiratory mechanics in ten mechanically ventilated open heart surgery patients in the immediate postoperative period. PEEP was studied in increasing increments and decreasing decrements. This procedure was repeated three times. Flow, tidal volume, and airway pressure were measured. We used the rapid airway occlusion technique to determine static compliance of the respiratory system (Cst,rs) and intrinsic PEEP (PEEPi). The changes in end-expiratory lung volume (delta EELV) were measured with respiratory inductive plethysmography. Recruitment of lung units (Vrec) was estimated as the difference in lung volume between PEEP and zero end-expiratory (ZEEP) for the same static inflation pressure (15 cm H2O). We found that (1) Cst,rs at ZEEP was significantly reduced (60 +/- 2 ml/cm H2O); (2) while PEEP of 5 cm H2O did not cause significant recruitment, higher levels of PEEP (10 to 15 cm H2O) were effective; (3) Cst,rs, Vrec, and delta EELV were higher during stepwise PEEP decrease; (4) after the first and second stepwise PEEP increase-decrease run, there was a small persistent increase in EELV and Cst,rs at ZEEP. No further changes were found after the third run. We conclude that after open heart surgery, PEEP less than 10 cm H2O is not effective to reopen atelectatic lung units.     

部分液体通气治疗急性肺损伤家兔

目的 观察部分液体通气（ＰＬＶ）对急性肺损伤（ＡＬＩ）家兔肺内气体交换、肺顺应性、体循环功能的影响。方法 健康雄性新西兰兔２４只,用油酸制备成急性肺损伤模型后随机分为３组,每组８只。各组采用不同方法治疗：呼气末正压（ＰＥＥＰ）组,常规机构通气（ＣＭＶ）＋ＰＥＥＰ治疗;生理盐水（ＮＳ）组,肺内注入ＮＳ同时＋ＣＭＶ＋ＰＥＥＰ;ＰＤＣ组,肺内注入全氟碳化合物－全氟萘烷（ＦＤＣ）同时＋ＣＭＶ＋ＰＥＥＰ。分     

Pressure controlled inverse ratio ventilation in severe adult respiratory failure

Thirty-one patients with severe respiratory failure who were failing volume controlled conventional ratio ventilation were placed on pressure controlled inverse ratio ventilation (PC-IRV) for a total of 4,426 patient-hours. The PC-IRV resulted in a reduction of minute ventilation from 22 +/- 1.0 L/min (mean +/- SEM) to 15 +/- 0.7 L/min. Peak inspiratory pressure (PIP) was reduced from 66 +/- 2.3 cm H2O to 46 +/- 1.6 cm H2O and positive end expiratory pressures (PEEP) from 15 +/- 1.0 cm H2O to 2.5 +/- 0.5 cm H2O. Mean airway pressure increased from 30 +/- 1.7 cm H2O to 35 +/- 1.7 cm H2O. Oxygenation (PaO2) improved from 69 +/- 4.0 mm Hg to 80 +/- 4.5 mm Hg. The PaCO2 and arterial pH were not significantly changed. There were no significant changes in mean hemodynamic pressures. A lung compromise index (FIO2.PIP.10/PaO2) retrospectively distinguished between successful and unsuccessful PC-IRV episodes. These data suggest that PC-IRV can be successfully and safely implemented in critically ill patients with severe respiratory failure over prolonged periods of time resulting in significant improvement in oxygenation at lower minute volume, peak airway pressure and PEEP requirements.     

肺泡复张后不同呼气末正压和潮气量调节策略对防止肺泡再萎陷效果的实验研究

目的探讨肺泡复张(RM)后再萎陷的机制以及呼气末正压(PEEP)和潮气量(VT)的调节策略。方法健康杂种犬18只,建立油酸所致急性呼吸窘迫综合征(ARDS),行容量控制通气(VCV)、PEEP 16 cm H2O、VT10 m l/kg、通气频率(RR)30次/m in,稳定后作为基础状态(0 m in)。以压力控制通气[气道峰压(PIP)50 cm H2O,PEEP 35 cm H2O,持续60 s]行RM,然后随机分为小VT中等PEEP组(LVMP组,VT10 m l/kg、PEEP 16 cm H2O、RR 30次/m in),小VT低PEEP组(LVLP组,VT10 m l/kg、PEEP 10 cm H2O、RR 30次/m in)和中等VT低PEEP组(MVLP组,VT15 m l/kg、PEEP 10cm H2O、RR 20次/m in)。观察4 h后处死动物,行支气管肺泡灌冼。监测氧合、呼吸力学、血流动力学及肺损伤指标。结果(1)LVMP、LVLP、MVLP组低位拐点(LIP)分别为(16.0±1.3)、(15.8±3.0)、(16.3±1.9)cm H2O。(2)在RM后30、60 m in,LVMP组动脉血氧分压(PaO2)[(371±64)、(365±51)mm Hg]显著高于LVLP组[(243±112)、(240±108)mm Hg]及MVLP组[(242±97)、(232±87)mm Hg,P均<0.05],但直至RM后4 h 3组比较差异无统计学意义;LVLP与MVLP组在RM后各个时间点的PaO2与基础状态比较差异均无统计学意义;MVLP组的通气功能较其他两组显著改善。(3)与基础状态比较,RM后LVMP组平均动脉压(mABP)显著降低,平均肺动脉压(mPAP)显著增加,而其他两组mABP保持稳定,mPAP降低。(4)与基础状态比较,3组PIP和气道平台压(Pp lat)在RM后均显著降低,呼吸系统静态顺应性(Cst)显著改善。在RM后同一时间点比较,MVLP组PIP、Pp lat和Cst均显著好于LVMP组。MVLP组与LVLP组相比,Cst有增加趋势。(5)在相同部位的支气管肺泡灌冼液中,肺损伤指标在各组之间无显著差异。结论与LIP相近的高PEEP有助于防止复张肺泡的再萎陷,但对血流动力学和呼吸力学产生不利影响;早期应用RM能有效“节约”PEEP,并为上调VT提供了较肺泡复张之前更大的空间。     

低流速法测定急性呼吸窘迫综合征静态肺压力-容积曲线的比较性实验研究

目的 探讨低流速法代替气道闭合法测定急性呼吸窘迫综合征(ARDS)静态肺压力-容积曲线的可行性.方法 采用内毒素(LPS)诱导的绵羊ARDS模型,利用低流速法和气道闭合法测定肺压力-容积曲线,并用双向直线回归法确定相应曲线低位转折点压力(Pinf), 低流速法和气道闭合法测定的Pinf分别表示为Pinfd和Pinfb.结果 Pinfd与Pinfb分别为(8.91±0.82) cm H2O与(8.59±0.78) cm H2O ,两者比较差异无显著性,具有显著相关性(r=0.93, P<0.05).相同潮气量情况下,两种方法 测定的相应气道压力呈正相关(r=0.99, P<0.005).低流速法和气道闭合法测定的肺顺应性分别为(19±7) L/cm H2O和(20±7) L/cm H2O,差异无显著性(P>0.05).低流速法测定肺压力-容积曲线的时间需3～4 min,气道闭合法需30～35 min.结论 低流速法测定肺压力-容积曲线准确安全,简便省时,可代替气道闭合法.     

急性呼吸窘迫综合征犬肺牵张指数与肺复张及氧合的关系

目的探讨以不同肺牵张指数(lung stress index)选择的呼气末正压(PEEP)与急性呼吸窘迫综合征(ARDS)肺复张容积与氧合的关系。方法油酸静脉注射复制犬ARDS模型,容量控制通气,流速恒定的压力-时间(P-t)曲线吸气支,回归法计算得方程P=a×timeb+c,b为肺牵张指数。调整PEEP水平使b=1。采用控制性肺膨胀实施肺复张手法,复张后再次调整PEEP水平分别达到b=1、0．60．05)。在呼吸力学方面,与复张后b=1相比, 1．1相似文献   

The relationship between gas delivery patterns and the lower inflection point of the pressure-volume curve during partial liquid ventilation

STUDY QUESTION: To determine whether a positive end-expiratory pressure (PEEP) level equivalent to the lower inflection point (LIP) could be identified by evaluation of the airway pressure, flow (f1. gif" BORDER="0">), and volume vs time waveforms during partial liquid ventilation (PLV). DESIGN: Prospective application of PEEP during PLV in a healthy animal model. SETTING: University hospital animal laboratory. PARTICIPANTS: Five healthy sheep weighing 30 kg each. INTERVENTIONS: The sequential application of 0 to 20 cm H(2)O PEEP in 2.5-cm H(2)O steps during PLV with both pressure and volume ventilation. MEASUREMENTS: Analysis of the pressure, volume, and f1. gif" BORDER="0"> waveforms as PEEP is sequentially increased. RESULTS: At 0 cm H(2)O PEEP, VT was markedly reduced compared with PEEP VT at > or = 7.5 cm H(2)O (p < 0.05) in pressure control ventilation (PCV), and peak inspiratory pressure minus PEEP was markedly increased compared with PEEP at > or = 5.0 cm H(2)O (p < 0.05) in volume control ventilation. At 10 cm H(2)O PEEP, all waveforms began to stabilize, and no significant differences in any variable assessed were measured at > 12.5 cm H(2)O PEEP. CONCLUSIONS: The application of PEEP during PLV markedly alters airway waveforms. Low PEEP decreases VT in PCV and increases airway pressure in VCV. The PEEP level equal to the LIP during PLV can be grossly estimated from airway waveforms. PEEP at > or = 10 cm H(2)O is needed to normalize gas delivery to functional residual capacity in the uninjured lung that is partially filled with perfluorocarbon.     

Airway pressure release ventilation in severe acute respiratory failure

Airway pressure release ventilation (APRV), a new ventilatory support technique, was compared with conventional intermittent positive-pressure ventilation plus PEEP (CPPV) in 18 patients with severe acute respiratory failure. Patients were initially stabilized on CPPV and then switched to APRV. The APRV provided effective ventilatory support in 17 of 18 patients; APRV achieved similar levels of alveolar ventilation as CPPV (for APRV, mean PaCO2 = 45.0 +/- 6.2 mm Hg; vs for CPPV, mean PaCO2 = 43.3 +/- 5.7 mm Hg), with significantly lower mean maximum airway pressures (38.9 +/- 10.1 cm H2O vs 64.6 +/- 15.4 cm H2O; p = 0.0001) and mean VT (0.79 +/- 0.11 L vs 1.05 +/- 0.15 L; p = 0.0002). No significant differences in mean airway pressure, end-expiratory pressure, FIO2, ventilator rate, arterial blood gas levels, and hemodynamic function were noted between APRV and CPPV.     

Hypothermia with and without end-expiratory pressure in canine oleic acid pulmonary edema

An important goal in managing patients with respiratory failure using mechanical ventilatory support and positive end-expiratory pressure (PEEP) is to optimize tissue oxygen delivery relative to oxygen consumption. To this end, systemic hypothermia has been reported to reduce oxygen consumption. Cooling, however, may antagonize hypoxic pulmonary vasoconstriction and depress cardiac output. To determine whether these potentially adverse effects of cooling on tissue oxygen delivery would outweigh any potential benefits, we studied the effects of systemic hypothermia and end-expiratory pressure on venous admixture, intrapulmonary blood distribution, and oxygenation variables in 40 dogs with oleic acid-induced pulmonary edema of the right lung. The dogs were randomly assigned to four treatment groups of 10 dogs each: normothermia and zero end-expiratory pressure (ZEEP); normothermia and 10 cm H2O PEEP; hypothermia and ZEEP; hypothermia and PEEP. Hypothermia to 31.9 +/- 0.1 degree C (mean +/- SEM) caused no adverse effects on intrapulmonary blood flow distribution (measured by radioactive microspheres) or on venous admixture. Tissue oxygen delivery and arterial oxygenation did not improve with hypothermia, the latter being 109 +/- 13 mm Hg and 70 +/- 8 mm Hg with PEEP and ZEEP, respectively. However, hypothermia significantly reduced oxygen consumption, so that the coefficient of oxygen delivery (i.e., the ratio of oxygen supply to consumption) increased from 2.5 +/- 0.1 to 3.2 +/- 0.2 (p less than 0.01) with ZEEP and from 2.0 +/- 0.1 to 2.6 +/- 0.3 with PEEP (p = 0.016). Thus, although systemic hypothermia failed to improve arterial oxygenation and tissue oxygen delivery, it decreased systemic oxygen demands, thereby improving the oxygen supply-demand balance.