根据压力-容积曲线选择理想潮气量对呼吸机护理的指导

目的探讨使用呼吸机时,不同的潮气量对急性肺损伤患者血流动力学、肺通气和肺机械力学的影响及护理要点。方法对ICU急性肺损伤16例患者采取自身对照的方法,利用压力-容积（P．v）曲线下曲点＋0．196kPa确定呼气末正压（PEEP）后,再根据P—V曲线的上拐点（VUIP）,分别取上拐点对应的潮气量100％Vt、85％Vt和70％Vt分为3组,以相同的分钟通气量和吸入氧浓度分别给予定容机械通气,监测肺机械力学、血流动力学、血气改变及P—V曲线的变化。结果85％Vt组在心率、中心静脉压、动脉血氧分压、气道峰值压、气道平均压及系统静态顺应性等对患者的综合影响优于100％Vt组和70％Vt组。结论以呼吸系统P-V曲线的下曲点（Pinf）确定PEEP值,以上拐点压力对应的潮气量的85％调节潮气量符合个体化保护性通气策略,对改善肺的顺应性、降低肺病理性损伤效果最好。护理时应注重P—V曲线的变化。     

压力-容积曲线指导个体化保护性单肺通气在开胸术中的应用

目的:应用动态压力-容积曲线设定全身麻醉单肺通气时个体化的潮气量和呼气末正压(PEEP)。方法:42例ASAⅠ～Ⅱ级择期行肺叶切除术患者,常规双肺通气30min后(T0)行单肺通气,按照患者单肺通气即刻动态压力-容积曲线低位拐点对应的压力(PLIP)+0.196kPa设定PEEP值,依次按照100%、80%、60%高位拐点对应的容量(VUIP)设定潮气量,分别通气30min(T1、T2、T3)。记录各时点血流动力学和呼吸力学参数,并采集动脉和混合静脉血行血气分析,根据公式计算肺内分流率。结果:T1、T2、T3的PEEP值均为(0.64±0.13)kPa,潮气量分别为(10.1±1.2)mL/kg、(7.2±1.1)mL/kg、(5.6±0.7)mL/kg,与T1相比,T2的气道峰压、气道阻力、分流率降低;动脉氧分压、胸肺顺应性增加;T3的平均动脉压、动脉二氧化碳分压增高,差异有统计学意义(P<0.05)。结论:根据动态压力-容积曲线,80%VUIP联合PLIP+0.196kPa水平的PEEP有助于改善单肺通气氧合,降低分流,对血流动力学影响轻微。     

利用压力-容积曲线呼气支最大曲率拐点选择PEEP对ARDS患者氧合及血流动力学的影响

目的 探讨利用压力-容积(P-V)曲线呼气支最大曲率拐点选择呼气末正压(PEEP)对急性呼吸窘迫综合征(ARDS)患者氧合及血流动力学影响.方法 选取25例ARDS患者,采用肺保护性通气,肺复张(RM)后随机分为两组:利用P-V曲线呼气支最大曲率拐点设置PEEP组(PPMC)和以P-V曲线低位拐点设置PEEP组(PLIP),观察并比较RM前后两组患者PaO2/FiO2、呼吸系统动态顺应性(Cdyn)、心率(HR)、平均动脉压(MAP)、中心静脉压(CVP)等指标的变化.结果 RM后两组患者短时间内PaO2/FiO2和Cdyn均明显增加,PPMC组PaO2/FiO2在RM后1、2、4 h较PLIP组升高(P<0.05).PLIP组Cdyn在RM后很快降至RM前水平,PPMC组Cdyn在RM后1、2 h高于PLIP组(P<0.05).两组RM时均有MAP、CVP下降,HR升高(P<0.01);HR、MAP在RM后很快恢复,PPMC组CVP持续升高至RM后2 h(P<0.05).结论 RM后利用P-V曲线呼气支最大曲率拐点选择PEEP可以使氧合及呼吸系统顺应性改善更为明显,对血流动力学无严重的不良影响.     

肺保护性通气对犬海水淹溺型肺水肿的治疗作用

目的 观察肺保护性通气对海水淹溺型肺水肿(PE-SWD)犬肺内气体交换、气道力学、血流动力学及外周血炎性介质的影响,并与常规机械通气进行比较.方法健康成年杂种犬15只,经气管插管灌人海水形成PE-SWD模型后,随机分为3组(n=5):阳性对照组(Ⅰ组),常规机械通气治疗组(Ⅱ组),肺保护性通气治疗组(Ⅲ组)(VT 8 mL/kg+PEEP 8 cm H2O).治疗180 min,分别观察各组治疗前后不同时间点动脉血气、呼吸力学、血流动力学以及外周血炎性介质的变化.结果肺保护性通气治疗后海水淹溺型肺水肿犬动脉血气、呼吸力学、血流动力学以及炎性介质指标均较Ⅰ、Ⅱ组明显改善(P<0.05).结论肺保护性通气可明显改善PE-SWD犬动脉血气,并能提高肺顺应性、降低气道峰压、降低肺动脉压、减少肺组织损伤.肺保护性通气模式可能是治疗PE-SWD的有效方法,值得临床实践应用.     

肺复张策略抢救急性呼吸窘迫综合征患者的最佳PEEP设置

目的探讨肺复张(RM)策略抢救急性呼吸窘迫综合征(ARDS)患者的最佳PEEP设置。方法将37例ARDS患者采用压力控制法肺复张后随机分为治疗组(n=19)和对照组(n=18),分别以P-V曲线呼气支拐点和吸气支低拐点+2cmH2O设置PEEP。比较2组患者RM前、后(15 min,1、2 h)氧合和呼吸系统动态顺应性、血流动力学等指标的变化。结果 2组RM后(15 min,1、2 h)的PaO2/FiO2较RM前均明显增高(P<0.01),治疗组RM后(1、2 h)的PaO2/FiO2明显高于对照组(P<0.05或P<0.01);2组RM后的Cdyn短时间内(15 min)较RM前明显增高(P<0.01),治疗组RM后(15 min,1、2h)均明显高于对照组(P<0.05);RM后2组平均气道压、气道峰压均明显高于同组RM前(P<0.01),2组组间比较无显著差异(P>0.05);2组RM前后PaCO2比较无明显差异(P>0.05);2组RM后短时间内(15 min)均有HR、CVP增高,MAP下降(P<0.01)。结论肺复张策略能改善ARDS患者的氧合和呼吸系统顺应性,RM后以P-V曲线呼气支拐点设置PEEP更佳。     

压力-容积曲线指导下个体化保护性双肺通气在食管癌手术肺复张后的应用

目的观察食管癌根治术中单肺通气结束肺复张后,动态压力-容积(pressure-volume,P-V)曲线指导下行个体化保护性双肺通气对患者肺功能及肺毛细血管内皮功能的影响。方法食管中上段癌择期行经右胸三切口根治术患者30例,随机分为常规双肺通气组(I组)和个体化保护性双肺通气组(P组)各15例;单肺通气结束后,I组恢复双肺间歇正压通气,P组在I组基础上应用动态P-V曲线低位拐点对应的压力+0.196kPa设定呼气末正压,根据动态P-V曲线高位拐点对应容量的80%设定潮气量,行个体化保护性双肺通气;分别于诱导后切皮前(T1)、单肺通气结束时(T2)、手术结束时(T3)测定肺顺应性和pa(O2),同时采集血液标本检测血浆血管性假血友病因子水平。结果与T1比较,2组T2时肺顺应性及pa(O2)明显下降(P<0.05),I组T3点肺顺应性仍明显低于T1(P<0.05);2组血浆血管性假血友病因子水平T2较T1明显升高(P<0.05),T3较T2明显升高(P<0.05);与I组比较,P组肺顺应性T3时明显升高(P<0.05),P组血浆血管性假血友病因子水平T3时明显降低(P<0.01)。结论食管癌根治术中肺复张后应用动态P-V曲线指导个体化保护性双肺通气对患者肺功能及肺毛细血管内皮功能有一定保护作用。     

小潮气量通气联合肺表面活性物质在新生儿肺外源性急性肺损伤的临床应用

目的探讨小潮气量通气(Low Tidal Volume Ventilation,LTVV)联合肺表面活性物质(pulmonary surfactant,PS)在新生儿肺外源性急性肺损伤的临床价值。方法选取本院2013年10月至2016年10月诊治的新生儿肺外源性急性肺损伤患者88例,采用随机数字表法分为两组各44例,对照组采用LTVV治疗,观察组采用LTVV联合PS治疗,于治疗前后行临床指标检测,比较两组患儿的住院情况、治疗效果。结果治疗后两组患儿血氧饱和度(SaO_2)、血氧分压(PaO_2)、氧合指数(OI)、呼吸功、潮气量增加,血二氧化碳分压(PaCO_2)、肺动态顺应性、呼吸频率(RR)、呼气末压力(PEEP)、平均气道压(MAP)、气道峰压(PIP)、吸入氧体积分数(FiO_2)降低(P0.05);观察组患儿SaO_2、PaO_2、OI、呼吸功、潮气量、撤机成功率高于对照组,PaCO_2、肺动态顺应性、RR、PEEP、MAP、PIP、FiO_2、并发症发生率低于对照组,机械通气时间、吸氧时间、住院时间少于对照组(P0.05)。结论小潮气量通气联合肺表面活性物质治疗新生儿肺外源性急性肺损伤的效果显著,可缩短治疗时间并改善肺功能,具有高安全性,值得临床推广。     

肺复张法对机械通气相关肺不张的影响

[目的]评价肺复张法(RM)对机械通气相关肺不张的影响.[方法]对21例机械通气相关肺不张病人行RM治疗2周,观察RM前后病人血流动力学、动脉血气、呼吸力学各参数指标的变化.[结果]RM前后病人血流动力学指标无显著性变化(均P>0.05),动脉血气、呼吸力学各参数变化显著(均P<0.05),CT和胸部X线片证实肺复张.[结论]RM使潮气量增加,肺顺应性改善,脉搏血氧饱和度、动脉血氧分压、动脉血氧饱和度明显上升,气道峰压、平台压、气道阻力下降,呼吸做功减少,促进肺复张,且血流动力学未受到明显影响,对预防和治疗肺不张具有积极意义.     

急性呼吸窘迫综合征患者血清Clara细胞蛋白16表达及与肺顺应性关系

目的探讨行有创机械通气治疗急性呼吸窘迫综合征(acute respiratory distress syndrome,ARDS)患者血清Clara细胞蛋白16(Clara cell protein 16,Cc16)表达及与肺顺应性的关系。方法行有创机械通气治疗ARDS患者69例(观察组),同期行有创机械通气治疗非ARDS患者51例(对照组),采用ELISA法检测2组有创机械通气治疗3h内血清Cc16水平,并记录肺顺应性、呼吸频率、气道平均压、气道峰压、潮气量及呼气末正压(positive end expiratory pressure,PEEP),Pearson相关法分析血清Cc16水平与肺顺应性等指标的相关性。结果观察组有创机械通气治疗3h内血清Cc16[(59.25±17.62)ng/L]、气道峰压[(21.50±5.73)mm Hg]、气道平均压[(11.64±3.43)mm Hg]、PEEP[(4.42±1.67)cm H_2O]]、呼吸频率[(22.05±6.37)次/min]均高于对照组[(31.47±20.49)ng/L、(17.29±4.26)mm Hg、(8.67±1.74)mm Hg、(3.67±0.80)cm H_2O]、(18.54±5.63)次/min](P0.05),肺顺应性[(37.74±13.59)mL/cm H_2O]]低于对照组[(50.64±24.99)mL/cm H_2O]](P0.05),潮气量[(466.44±110.93)mL]与对照组[(445.17±105.50)mL]比较差异无统计学意义(P0.05);Pearson相关分析结果显示,观察组有创机械通气治疗3h内血清Cc16水平与肺顺应性呈负相关(r=-0.252,P=0.036),与呼吸频率、潮气量、气道峰压、气道平均压及PEEP无线性相关(r=-0.015,P=0.835;r=-0.171,P=0.902;r=-0.007,P=0.816;r=-0.026,P=0.865;r=0.068,P=0.783);对照组有创机械通气治疗3h内血清Cc16水平与PEEP呈正相关(r=0.281,P=0.046),与肺顺应性、潮气量、呼吸频率、气道峰压及气道平均压无线性相关(r=-0.018,P=0.612;r=-0.148,P=0.536;r=-0.109,P=0.928;r=0.019,P=0.653;r=0.077,P=0.537)。结论 ARDS患者肺顺应性降低,且与血清Cc16水平呈负相关。     

静态肺压力-容积曲线确定最佳呼气末正压的比较性试验研究

目的　通过静态肺压力 -容积曲线 (P -Vcurve)法和最大氧分压 (PEEPtrail)法确定不同PEEP对急性肺损伤家兔模型肺机械力学、氧代谢、血流动力学及病理学方面的影响 ,探讨最佳PEEP(BestPEEP)的确定方法。方法　采用内毒素诱导的家兔急性肺损伤 (ALI)模型 ,根据P -V曲线低位转折点 (Pinf)和PEEPtrail法确定PEEP水平 :Pinf- 2cmH2 O、Pinf、Pinf+2cmH2 O以及Ptrail,观察不同水平PEEP对ALI家兔肺机械力学、氧代谢、血流动力学及病理学的影响。结果　Ptrail和Pinf分别为 (15 8± 2 5 )cmH2 O和 (10 2± 2 1)cmH2 O差异显著 (P >0 0 5 )。虽然Ptrail组PaO2 显著高于Pinf组和Pinf+2cmH2 O组 ,但是Ptrail组心脏指数及氧输送指数均显著低于Pinf组和Pinf+2cmH2 O组 (P <0 0 5 )。Pinf组及Pinf+2cmH2 O组肺静态顺应性显著高于Ptrail组和Pinf- 2cmH2 O组 ,且Pinf组及Pinf+2cmH2 O组肺损伤指数显著低于Ptrail组和Pinf - 2cmH2 O组 (P <0 0 1)。结论　根据P -V曲线法确定PEEP是选择最佳PEEP的理想方法。Pinf或Pinf+2cmH2 O为最佳PEEP ,可获得最大肺顺应性和最大氧输送 ,而肺损伤最小。     

Positive end-expiratory pressure modulates local and systemic inflammatory responses in a sepsis-induced lung injury model

OBJECTIVE: Previous animal studies have shown that certain modes of mechanical ventilation (MV) can injure the lungs. Most of those studies were performed with models that differ from clinical causes of respiratory failure. We examined the effects of positive end-expiratory pressure (PEEP) in the setting of a clinically relevant, in vivo animal model of sepsis-induced acute lung injury ventilated with low or injurious tidal volume. METHODS: Septic male Sprague-Dawley rats were anesthetized and randomized to spontaneous breathing or four different strategies of MV for 3 h at low (6 ml/kg) or high (20 ml/kg) tidal volume (V(T)) with zero PEEP or PEEP above inflection point in the pressure-volume curve. Sepsis was induced by cecal ligation and perforation. Mortality rates, pathological evaluation, lung tissue cytokine gene expression, and plasma cytokine concentrations were analyzed in all experimental groups. RESULTS: Lung damage, cytokine synthesis and release, and mortality rates were significantly affected by the method of MV in the presence of sepsis. PEEP above the inflection point significantly attenuated lung damage and decreased mortality during 3 h of ventilation with low V(T) (25% vs. 0%) and increased lung damage and mortality in the high V(T) group (19% vs. 50%). PEEP attenuated lung cytokine gene expression and plasma concentrations during mechanical ventilation with low V(T). CONCLUSIONS: The use of a PEEP level above the inflection point in a sepsis-induced acute lung injury animal model modulates the pulmonary and systemic inflammatory responses associated with sepsis and decreases mortality during 3 h of MV.     

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.     

压力调节容量控制通气对急性肺损伤血流呼吸动力学和氧代谢的影响

目的研究压力调节容量控制通气(PRVC)和间歇正压通气(IPPV)对急性肺损伤(ALI)患者血流动力学、呼吸动力学和氧代谢的影响.方法对30例ALI患者分别进行呼吸末正压(PEEP)0、5、10 cmH2O水平下的PRVC和IPPV通气,测定其血流动力学、呼吸力学和氧代谢参数.结果比较PRVC和IPPV二种通气模式,同一水平PEEP其血流动力学无明显差异(P＞0.05),但吸气峰压(PIP)、肺动态顺应性(Cst)、动脉氧分压(PaO2)和氧供(DO2)均有明显差异(P＜0.05).结论PRVC与IPPV相比能明显降低PIP,增加Cst,增加DO2.     

The open lung during small tidal volume ventilation: concepts of recruitment and "optimal" positive end-expiratory pressure.

OBJECTIVES: To test the hypotheses that during small tidal volume ventilation (5 mL/kg) deliberate volume recruitment maneuvers allow expansion of atelectatic lung units and that a high positive end-expiratory pressure (PEEP) above the lower inflection point of the pressure/volume (PV) curve is not necessarily required to maintain recruited lung volume in acute lung injury. DESIGN: Prospective, randomized, controlled animal study. SETTING: An animal laboratory in a university setting. SUBJECTS: Adult New-Zealand rabbits. INTERVENTIONS: We studied a) the relationship of dynamic loops during intermittent positive pressure ventilation to the quasi-static PV curve, and b) the effect of lung recruitment on oxygenation, end-expiratory lung volume (EELV), and dynamic compliance in two groups (n = 4 per group) of lung-injured animals (lung lavage model): 1) the sustained inflation group, which received ventilation after a recruitment maneuver (sustained inflation); and 2) the control group, which received ventilation without any lung recruitment. MEASUREMENTS AND MAIN RESULTS: In the presence of PV hysteresis, a single sustained inflation to 30 cm H2O boosted the ventilatory cycle onto the deflation limb of the PV curve. This resulted in a significant increase in EELV, oxygenation, and dynamic compliance despite equal PEEP levels used before and after the recruitment maneuver. Furthermore, after a single sustained inflation, oxygenation remained high over 4 hrs of ventilation when a PEEP above the critical closing pressure of the lungs, defined as "optimal" PEEP, was used and was significantly higher compared with that in the control group ventilated at equal PEEP without preceding lung recruitment. CONCLUSIONS: The observation that ventilation occurs on the deflation limb of the tidal cycle-specific PV curve allows placement of the ventilatory cycle, by means of a recruitment maneuver, onto the deflation limb of the PV envelope of the optimally recruited lung. This strategy ensures sufficient lung volume recruitment to maintain the lungs during the tidal cycle while using relatively low airway pressures.     

Static and dynamic pressure-volume curves reflect different aspects of respiratory system mechanics in experimental acute respiratory distress syndrome.

INTRODUCTION: A lower inflection point, an upper inflection (or deflection) point, and respiratory system compliance can be estimated from an inspiratory static pressure-volume (SPV) curve of the respiratory system. Such data are often used to guide selection of positive end-expiratory pressure (PEEP)/tidal volume combinations. Dynamic pressure-volume (DPV) curves obtained during tidal ventilation are effortlessly displayed on modern mechanical ventilator monitors and bear a theoretical but unproven relationship to the more labor-intensive SPV curves. OBJECTIVE: Attempting to relate the SPV and DPV curves, we assessed both curves under a range of conditions in a canine oleic acid lung injury model. METHODS: Five mongrel dogs were anesthetized, paralyzed, and monitored to assure a stable preparation. Acute lung injury was induced by infusing oleic acid. SPV curves were constructed by the super-syringe method. DPV curves were constructed for a range of PEEP and inspiratory constant flow settings while ventilating at a frequency of 15 breaths/min and tidal volume of 350 mL. Functional residual capacity at PEEP = 0 cm H2O was measured by helium dilution. The change in lung volume by PEEP at 8, 16, and 24 cm H2O was measured by respiratory inductance plethysmography. RESULTS: The slope of the second portion of the DPV curve did not parallel the corresponding slope of the SPV curve. The mean lower inflection point of the SPV curve was 13.2 cm H2O, whereas the lower inflection point of the DPV curve was related to the prevailing flow and PEEP settings. The absolute lung volume during the DPV recordings exceeded (p < 0.05) that anticipated from the SPV curves by (values are mean +/- SEM) 267 +/- 86 mL, 425 +/- 129 mL, and 494 +/- 129 mL at end expiration for PEEP = 8, 16, and 24 cm H2O, respectively. CONCLUSIONS: The contours of the SPV curve are not reflected by those of the DPV curve in this model of acute lung injury. Therefore, this study indicates that DPV curve should not be used to guide the selection of PEEP/tidal volume combinations. Furthermore, an increase in end-expiratory lung volume occurs during tidal ventilation that is not reflected by the classical SPV curve, suggesting a stable component of lung volume recruitment attributable to tidal ventilation, independent of 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.     

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.