Open Lung Approach for the Acute Respiratory Distress Syndrome: A Pilot, Randomized Controlled Trial* Regional distribution of gas and tissue in acute respiratory distress syndrome. III. Consequences for the effects of positive end-expiratory pressure AMSTAR is a reliable and valid measurement tool to assess the methodological quality of systematic reviews. Efficacy of positive end-expiratory pressure titration after the alveolar recruitment manoeuvre in patients with acute respiratory distress syndrome A randomised controlled trial of an open lung strategy with staircase recruitment, titrated PEEP and targeted low airway pressures in patients with acute respiratory distress syndrome Lung recruitment in patients with the acute respiratory distress syndrome. Complications From Recruitment Maneuvers in Patients With Acute Lung Injury: Secondary Analysis From the Lung Open Ventilation Study Ventilation strategy using low tidal volumes, recruitment maneuvers, and high positive end-expiratory pressure for acute lung injury and acute respiratory distress syndrome: a randomized controlled trial. Bedside Estimation of Nonaerated Lung Tissue Using Blood Gas Analysis* Recruitment maneuver in experimental acute lung injury: The role of alveolar collapse and edema Clinical efficacy and safety of recruitment maneuver in patients with acute respiratory distress syndrome using low tidal volume ventilation: a multicenter randomized controlled clinical trial. Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome. PEEP-induced changes in lung volume in acute respiratory distress syndrome. Two methods to estimate alveolar recruitment Recruitment and derecruitment during acute respiratory failure: a clinical study. Oxygenation response to positive end-expiratory pressure predicts mortality in acute respiratory distress syndrome. A secondary analysis of the LOVS and ExPress trials.
Objective : The open lung approach is a mechanical ventilation strategy involving lung recruitment and a decremental positive end-expiratory pressure trial . We compared the Acute Respiratory Distress Syndrome network protocol using low levels of positive end-expiratory pressure with open lung approach result ing in moderate to high levels of positive end-expiratory pressure for the management of established moderate/severe acute respiratory distress syndrome . Design : A prospect i ve , multicenter , pilot , r and omized controlled trial . Setting : A network of 20 multidisciplinary ICUs . Patients : Patients meeting the American-European Consensus Conference definition for acute respiratory distress syndrome were considered for the study . Interventions : At 12 - 36 hours after acute respiratory distress syndrome onset , patients were  assessed under st and ardized ventilator setting s ( FIO2≥0.5 , positive end-expiratory pressure ≥10 cm H2O ) . If Pao2/FIO2 ratio remained less than or equal to 200 mm Hg , patients were r and omized to open lung approach or Acute Respiratory Distress Syndrome network protocol . All patients were ventilated with a tidal volume of 4 to 8 ml/kg predicted body weight . Measurements and Main Results : From 1,874 screened patients with acute respiratory distress syndrome , 200 were r and omized : 99 to open lung approach and 101 to Acute Respiratory Distress Syndrome network protocol . Main outcome measures were 60-day and ICU mortalities , and ventilator-free days . Mortality at day-60 ( 29 % open lung approach vs. 33 % Acute Respiratory Distress Syndrome Network protocol , p = 0.18 , log rank test ) , ICU mortality ( 25 % open lung approach vs. 30 % Acute Respiratory Distress Syndrome network protocol , p = 0.53 Fisher ’s exact test ) , and ventilator-free days ( 8 [ 0 - 20 ] open lung approach vs. 7 [ 0 - 20 ] d Acute Respiratory Distress Syndrome network protocol , p = 0.53 Wilcoxon rank test ) were not significantly different . Airway driving pressure ( plateau pressure - positive end-expiratory pressure ) and PaO2/FIO2 improved significantly at 24 , 48 and 72 hours in patients in open lung approach compared with patients in Acute Respiratory Distress Syndrome network protocol . Barotrauma rate was similar in both groups . Conclusions : In patients with established acute respiratory distress syndrome , open lung approach improved oxygenation and driving pressure , without detrimental effects on mortality , ventilator-free days , or barotrauma . This pilot study supports the need for a large , multicenter trial using recruitment maneuvers and a decremental positive end-expiratory pressure trial in persistent acute respiratory distress syndrome Objective : To determine whether differences in lung morphology assessed by computed tomography ( CT ) affect the response to positive end-expiratory pressure (PEEP).¶ Design : Prospect i ve study over a 53-month period.¶ Setting : Fourteen-bed surgical intensive care unit of a university hospital.¶ Patients and participants : Seventy-one consecutive patients with early adult respiratory distress syndrome (ARDS).¶ Measurements and results : Fast spiral thoracic CT was performed at zero end-expiratory pressure ( ZEEP ) and after implementation of PEEP 10 cmH2O . Hemodynamic and respiratory parameters were measured in both conditions . PEEP-induced overdistension and alveolar recruitment were quantified by specifically design ed software ( Lungview ) . Overdistension occurred only in the upper lobes and was significantly correlated with the volume of lung , characterized by a CT attenuation ranging between –900 and –800 HU in ZEEP conditions . Cardiorespiratory effects of PEEP were similar in patients with primary and secondary ARDS . PEEP-induced alveolar recruitment of the lower lobes was significantly correlated with their lung volume ( gas + tissue ) at functional residual capacity . PEEP-induced alveolar recruitment was greater in the lower lobes with “ inflammatory atelectasis ” than in the lower lobes with “ mechanical atelectasis . ” Lung morphology as assessed by CT markedly influenced the effects of PEEP : in patients with diffuse CT attenuations PEEP induced a marked alveolar recruitment without overdistension , whereas in patients with lobar CT attenuations PEEP induced a mild alveolar recruitment associated with overdistension of previously aerated lung areas . These results can be explained by the uneven distribution of regional compliance characterizing patients with lobar CT attenuations ( compliant upper lobes and stiff lower lobes ) contrasting with a more even distribution of regional compliances observed in patients with diffuse CT attenuations.¶ Conclusions : In patients with ARDS , the cardiorespiratory effects of PEEP are affected by lung morphology rather than by the cause of the lung injury ( primary versus secondary ARDS ) . The regional distribution of the loss of aeration and the type of atelectasis –“mechanical ” with a massive loss of lung volume , or “ inflammatory ” with a preservation of lung volume – characterizing the lower lobes are the main determinants of the cardiorespiratory effects of PEEP OBJECTIVE Our purpose was to measure the agreement , reliability , construct validity , and feasibility of a measurement tool to assess  systematic review s ( AMSTAR ) . STUDY DESIGN AND SETTING We r and omly selected 30 systematic review s from a data base . Each was assessed by two review ers using : ( 1 ) the enhanced quality assessment question naire ( Overview of Quality Assessment Question naire [ OQAQ ] ) ; ( 2 ) Sacks ' instrument ; and ( 3 ) our newly developed measurement tool ( AMSTAR ) . We report on reliability ( interobserver kappas of the 11 AMSTAR items ) , intraclass correlation coefficients ( ICCs ) of the sum scores , construct validity ( ICCs of the sum scores of AMSTAR compared with those of other instruments ) , and completion times . RESULTS The interrater agreement of the individual items of AMSTAR was substantial with a mean kappa of 0.70 ( 95 % confidence interval [ CI ] : 0.57 , 0.83 ) ( range : 0.38 - 1.0 ) . Kappas recorded for the other instruments were 0.63 ( 95 % CI : 0.38 , 0.78 ) for enhanced OQAQ and 0.40 ( 95 % CI : 0.29 , 0.50 ) for the Sacks ' instrument . The ICC of the total score for AMSTAR was 0.84 ( 95 % CI : 0.65 , 0.92 ) compared with 0.91 ( 95 % CI : 0.82 , 0.96 ) for OQAQ and 0.86 ( 95 % CI : 0.71 , 0.94 ) for the Sacks ' instrument . AMSTAR proved easy to apply , each review taking about 15 minutes to complete . CONCLUSIONS AMSTAR has good agreement , reliability , construct validity , and feasibility . These findings need confirmation by a broader range of assessors and a more diverse range of review Introduction In acute respiratory distress syndrome ( ARDS ) , adequate positive end-expiratory pressure ( PEEP ) may decrease ventilator-induced lung injury by minimising overinflation and cyclic recruitment-derecruitment of the lung . We evaluated whether setting the PEEP using decremental PEEP titration after an alveolar recruitment manoeuvre ( ARM ) affects the clinical outcome in patients with ARDS . Methods Fifty-seven patients with early ARDS were r and omly assigned to a group given decremental PEEP titration following ARM or a table-based PEEP ( control ) group . PEEP  and  inspired fraction of oxygen ( FiO2 )  in the control group were set according to the table-based combinations of FiO2 and PEEP of the ARDS network , by which we aim ed to achieve a PEEP level compatible with an oxygenation target . In the decremental PEEP titration group , the oxygen saturation and static compliance were monitored as the patients performed the ARM along with the extended sigh method , which is design ed to gradually apply and withdraw a high distending pressure over a prolonged period , and the decremental titration of PEEP . Results The baseline characteristics did not differ significantly between the control and decremental PEEP titration groups . Initial oxygenation improved more in the decremental PEEP titration group than in the control group . However , dynamic compliance , tidal volume and PEEP were similar in the two groups during the first week . The duration of use of paralysing or sedative agents , mechanical ventilation , stay in the intensive care unit and mortality at 28 days did not differ significantly between the decremental PEEP titration and control groups . Conclusions The daily decremental PEEP titration after ARM showed only initial oxygenation improvement compared with the table-based PEEP method . Respiratory mechanics and patient outcomes did not differ between the decremental PEEP titration and control groups . Trial registration Clinical Trials.gov identifier : IS RCT N79027921 Introduction Tidal volume and plateau pressure minimisation are the st and ard components of a protective lung ventilation strategy for patients with acute respiratory distress syndrome ( ARDS ) . Open lung strategies , including higher positive end-expiratory pressure ( PEEP ) and recruitment manoeuvres to date have not proven efficacious . This study examines the effectiveness and safety of a novel open lung strategy , which includes permissive hypercapnia , staircase recruitment manoeuvres ( SRM ) and low airway pressure with PEEP titration . Method Twenty ARDS patients were r and omised to treatment or ARDSnet control ventilation strategies . The treatment group received SRM with decremental PEEP titration and targeted plateau pressure < 30 cm H2O . Gas exchange and lung compliance were measured daily for 7 days and plasma cytokines in the first 24 hours and on days 1 , 3 , 5 and 7 ( mean ± SE ) . Duration of ventilation , ICU stay and hospital stay ( median and interquartile range ) and hospital survival were determined . Results There were significant overall differences between groups when considering plasma IL-8 and TNF-α . For plasma IL-8 , the control group was 41 % higher than the treatment group over the seven-day period ( ratio 1.41 ( 1.11 to 1.79 ) , P = 0.01 ) , while for TNF-α the control group was 20 % higher over the seven-day period ( ratio 1.20 ( 1.01 to 1.42 ) P = 0.05 ) . PaO2/FIO2 ( 204 ± 9 versus 165 ± 9 mmHg , P = 0.005 ) and static lung compliance ( 49.1 ± 2.9 versus 33.7 ± 2.7 mls/cm H2O , P < 0.001 ) were higher in the treatment group than the control group over seven days . There was no difference in duration of ventilation ( 180 ( 87 to 298 ) versus 341 ( 131 to 351 ) hrs , P = 0.13 ) , duration of ICU stay ( 9.9 ( 5.6 to 14.8 ) versus 16.0 ( 8.1 to 19.3 ) days , P = 0.19 ) and duration of hospital stay ( 17.9 ( 13.7 to 34.5 ) versus 24.7 ( 20.5 to 39.8 ) days , P = 0.16 ) between the treatment and control groups . Conclusions This open lung strategy was associated with greater amelioration in some systemic cytokines , improved oxygenation and lung compliance over seven days . A larger trial powered to examine clinical ly-meaningful outcomes is warranted . Trial registration BACKGROUND In the acute respiratory distress syndrome ( ARDS ) , positive end-expiratory pressure ( PEEP ) may decrease ventilator-induced lung injury by keeping lung regions open that otherwise would be collapsed . Since the effects of PEEP probably depend on the recruitability of lung tissue , we conducted a study to examine the relationship between the percentage of potentially recruitable lung , as indicated by computed tomography ( CT ) , and the clinical and physiological effects of PEEP . METHODS Sixty-eight patients with acute lung injury or ARDS underwent whole-lung CT during breath-holding sessions at airway pressures of 5 , 15 , and 45 cm of water . The percentage of potentially recruitable lung was defined as the proportion of lung tissue in which aeration was restored at airway pressures between 5 and 45 cm of water . RESULTS The percentage of potentially recruitable lung varied widely in the population , accounting for a mean ( + /-SD ) of 13+/-11 percent of the lung weight , and was highly correlated with the percentage of lung tissue in which aeration was maintained after the application of PEEP ( r2=0.72 , P<0.001 ) . On average , 24 percent of the lung could not be recruited . Patients with a higher percentage of potentially recruitable lung ( greater than the median value of 9 percent ) had greater total lung weights ( P<0.001 ) , poorer oxygenation ( defined as a ratio of partial pressure of arterial oxygen to fraction of inspired oxygen ) ( P<0.001 ) and respiratory-system compliance ( P=0.002 ) , higher levels of dead space ( P=0.002 ) , and higher rates of death ( P=0.02 ) than patients with a lower percentage of potentially recruitable lung . The combined physiological variables predicted , with a sensitivity of 71 percent and a specificity of 59 percent , whether a patient 's proportion of potentially recruitable lung was higher or lower than the median . CONCLUSIONS In ARDS , the percentage of potentially recruitable lung is extremely variable and is strongly associated with the response to PEEP BACKGROUND : There are limited data on the safety and efficacy of recruitment maneuvers ( RMs ) in acute lung injury ( ALI ) patients . OBJECTIVE : To evaluate the frequency , timing , and risk factors for complications from RMs in adult ALI patients . METHODS : Secondary analysis of data from a r and omized controlled trial of a lung open ventilation strategy that included sustained inflation RMs . RESULTS : Respiratory ( eg , desaturation ) and cardiovascular ( eg , hypotension ) complications from recruitment maneuvers were common ( 22 % of all patients receiving RMs ) , and the majority occurred within 7 days of enrollment . New air leak through an existing chest tube was uncommon ( < 5 % ) . As compared to patients receiving 1 or fewer RMs , the number of RMs received was associated with increased risk in both younger ( age ≤ 56 y ) and older patients ( age > 56 y ) : 2 RMs odds ratio [ OR ] 6.92 ( 95 % CI 1.70–28.2 ) , ≥ 3 RMs OR 15.4 ( 95 % CI 4.77–49.6 ) , and 2 RMs OR 5.43 ( 95 % CI 1.76–16.8 ) , ≥ 3 RMs OR 4.93 ( 95 % CI 1.78–13.7 ) , respectively . Patients with extrapulmonary ALI had decreased odds of developing complications ( OR 0.42 , 95 % CI 0.22–0.80 ) . CONCLUSIONS : Complications in adult ALI patients receiving RMs were common , but serious complications ( eg , new air leak through an existing chest tube ) were infrequent . There is a significant association between the number of RMs received and complications , even after controlling for illness severity and duration . Given their uncertain benefit in ALI patients , and the potential for complications with repeated application , the routine use of sustained inflation RMs is not justified CONTEXT Low-tidal-volume ventilation reduces mortality in critically ill patients with acute lung injury and acute respiratory distress syndrome . Instituting additional strategies to open collapsed lung tissue may further reduce mortality . OBJECTIVE To compare an established low-tidal-volume ventilation strategy with an experimental strategy based on the original " open-lung approach , " combining low tidal volume , lung recruitment maneuvers , and high positive-end-expiratory pressure . DESIGN AND SETTING R and omized controlled trial with concealed allocation and blinded data analysis conducted between August 2000 and March 2006 in 30 intensive care units in Canada , Australia , and Saudi Arabia . PATIENTS Nine hundred eighty-three consecutive patients with acute lung injury and a ratio of arterial oxygen tension to inspired oxygen fraction not exceeding 250 . INTERVENTIONS The control strategy included target tidal volumes of 6 mL/kg of predicted body weight , plateau airway pressures not exceeding 30 cm H2O , and conventional levels of positive end-expiratory pressure ( n = 508 ) . The experimental strategy included target tidal volumes of 6 mL/kg of predicted body weight , plateau pressures not exceeding 40 cm H2O , recruitment maneuvers , and higher positive end-expiratory pressures ( n = 475 ) . MAIN OUTCOME MEASURE All-cause hospital mortality . RESULTS Eighty-five percent of the 983 study patients met criteria for acute respiratory distress syndrome at enrollment . Tidal volumes remained similar in the 2 groups , and mean positive end-expiratory pressures were 14.6 ( SD , 3.4 ) cm H2O in the experimental group vs 9.8 ( SD , 2.7 ) cm H2O among controls during the first 72 hours ( P < .001 ) . All-cause hospital mortality rates were 36.4 % and 40.4 % , respectively ( relative risk [ RR ] , 0.90 ; 95 % confidence interval [ CI ] , 0.77 - 1.05 ; P = .19 ) . Barotrauma rates were 11.2 % and 9.1 % ( RR , 1.21 ; 95 % CI , 0.83 - 1.75 ; P = .33 ) . The experimental group had lower rates of refractory hypoxemia ( 4.6 % vs 10.2 % ; RR , 0.54 ; 95 % CI , 0.34 - 0.86 ; P = .01 ) , death with refractory hypoxemia ( 4.2 % vs 8.9 % ; RR , 0.56 ; 95 % CI , 0.34 - 0.93 ; P = .03 ) , and previously defined eligible use of rescue therapies ( 5.1 % vs 9.3 % ; RR , 0.61 ; 95 % CI , 0.38 - 0.99 ; P = .045 ) . CONCLUSIONS For patients with acute lung injury and acute respiratory distress syndrome , a multifaceted protocol ized ventilation strategy design ed to recruit and open the lung result ed in no significant difference in all-cause hospital mortality or barotrauma compared with an established low-tidal-volume protocol ized ventilation strategy . This " open-lung " strategy did appear to improve secondary end points related to hypoxemia and use of rescue therapies . TRIAL REGISTRATION clinical trials.gov Identifier : NCT00182195 Objectives : Studies correlating the arterial partial pressure of oxygen to the fraction of nonaerated lung assessed by CT shunt yielded inconsistent results . We systematic ally analyzed this relationship and scrutinized key method ological factors that may compromise it . We hypothesized that both physiological shunt and the ratio between PaO2 and the fraction of inspired oxygen enable estimation of CT shunt at the bedside . Design : Prospect i ve observational clinical and laboratory animal investigations . Setting : ICUs ( University Hospital Leipzig , Germany ) and Experimental Pulmonology Laboratory ( University of São Paulo , Brazil ) . Patients , Subjects and Interventions : Whole-lung CT and arterial blood gases  were acquired simultaneously in 77 patients mechanically ventilated with pure oxygen . A subgroup of 28 patients was su bmi tted to different Fio2 . We also studied 19 patients who underwent repeat CT .  Furthermore we studied ten pigs with acute lung injury at multiple airway pressures , as well as a theoretical model relating PaO2 and physiological shunt . We logarithmically transformed the PaO2/Fio2 to change this nonlinear relationship into a linear regression problem . Measurements and Main Results : We observed strong linear correlations between Riley ’s approximation of physiological shunt and CT shunt ( R2 = 0.84 ) and between logarithmically transformed PaO2/Fio2 and CT shunt ( R2 = 0.86 ) , allowing us to construct a look-up table with prediction intervals . Strong linear correlations were also demonstrated within- patients ( R2 = 0.95 ) . Correlations were significantly improved by the following method ological issues : measurement of PaO2/Fio2 during pure oxygen ventilation , use of logarithmically transformed PaO2/Fio2 instead of the “ raw ” PaO2/Fio2 , quantification of nonaerated lung as percentage of total lung mass and definition of nonaerated lung by the [ –200 to + 100 ] Hounsfield Units interval , which includes shunting units within less opacified lung regions . Conclusion : During pure oxygen ventilation , logarithmically transformed PaO2/Fio2 allows estimation of CT shunt and its changes in patients during systemic inflammation . Relevant intrapulmonary shunting seems to occur in lung regions with CT numbers between [ –200 and + 100 ] Hounsfield Units Objective : In acute lung injury , recruitment maneuvers have been used to open collapsed lungs and set positive end-expiratory pressure , but their effectiveness may depend on the degree of lung injury . This study uses a single experimental model with different degrees of lung injury and tests the hypothesis that recruitment maneuvers may have beneficial or deleterious effects depending on the severity of acute lung injury . We speculated that recruitment maneuvers may worsen lung mechanical stress in the presence of alveolar edema . Design : Prospect i ve , r and omized , controlled experimental study . Setting : University research laboratory . Subjects : Thirty-six Wistar rats r and omly divided into three groups ( n = 12 per group ) . Interventions : In the control group , saline was intraperitoneally injected , whereas moderate and severe acute lung injury animals received paraquat intraperitoneally ( 20 mg/kg [ moderate acute lung injury ] and 25 mg/kg [ severe acute lung injury ] ) . After 24 hrs , animals were further r and omized into subgroups ( n = 6/each ) to be recruited ( recruitment maneuvers : 40 cm H2O continuous positive airway pressure for 40 secs ) or not , followed by 1 hr of protective mechanical ventilation ( tidal volume , 6 mL/kg ; positive end-expiratory pressure , 5 cm H2O ) . Measurements and Main Results : Only severe acute lung injury caused alveolar edema . The amounts of alveolar collapse were similar in the acute lung injury groups . Static lung elastance , viscoelastic pressure , hyperinflation , lung , liver , and kidney cell apoptosis , and type 3 procollagen and interleukin-6 mRNA expressions in lung tissue were more elevated in severe acute lung injury than in moderate acute lung injury . After recruitment maneuvers , static lung elastance , viscoelastic pressure , and alveolar collapse were lower in moderate acute lung injury than in severe acute lung injury . Recruitment maneuvers reduced interleukin-6 expression with a minor detachment of the alveolar capillary membrane in moderate acute lung injury . In severe acute lung injury , recruitment maneuvers were associated with hyperinflation , increased apoptosis of lung and kidney , expression of type 3 procollagen , and worsened alveolar capillary injury . Conclusions : In the presence of alveolar edema , regional mechanical heterogeneities , and hyperinflation , recruitment maneuvers promoted a modest but consistent increase in inflammatory and fibrogenic response , which may have worsened lung function and potentiated alveolar and renal epithelial injury BACKGROUND The recruitment maneuver ( RM ) has been shown to improve oxygenation in some patients with acute respiratory distress syndrome . But there is a lack of st and ardization and lack of clinical studies to prove the improvement on clinical outcome . We conducted this study to evaluate the clinical efficacy and safety of the RM in patients with acute respiratory distress syndrome ( ARDS ) using low tidal volume ventilation . METHODS We r and omly assigned 110 patients with ARDS from 14 Chinese intensive care units ( ICUs ) at the tertiary teaching hospitals . Patients with PaO2 ≤ 200 mmHg at FiO2 1.0 and PEEP ≥ 10 cmH2O were included in the study . Patients were r and omized into two groups : control group and RM group . The tidal volume was set to 6 - 8 ml per kilogram of predicted body weight ( PBW ) in both groups . RM was performed by continuous positive airway pressure ( CPAP ) of 40 cmH2O maintained for 40 seconds . RMs was conducted every eight hours for the first five days , or stopped within five days if the patient reached the weaning st and ard . RESULTS One hundred and ten patients had completed the requirements for the primary study goals , 55 from the RM group and 55 control patients . Baseline characteristics remained similar in the two groups . In the RM group the PaO2/FiO2 was significantly increased compared to baseline at 120 minutes after RM on day one and day two ( P = 0.007 and P = 0.001 ) . There were no significant differences between the RM and control group in hospital mortality ( 41.8 % vs. 56.4 % , P = 0.13 ) , 28-day mortality ( 29.1 % vs. 43.6 % , P = 0.11 ) and ventilator-free days at day 28 ( 10.8 ± 10.1 vs. 7.4 ± 10.0 , P = 0.08 ) . ICU mortality ( 32.7 % vs. 52.7 % , P = 0.03 ) , the rate of survival with unassisted breathing for at least 48 consecutive hours at day 28 ( 58.2 % vs. 36.2 % , P = 0.02 ) , and nonpulmonary organ failure-free days at day 28 ( 17.4 ± 11.1 vs. 13.0 ± 12.0 , P = 0.03 ) favored the RM group . There was no significant difference in mean blood pressure and heart rate before RM and at 30 , 60 , 120 minutes after RM . There was no incidence of barotraumas . CONCLUSIONS RM was safe and useful for improving oxygenation in patients with ARDS who were ventilated with a low tidal volume , with a beneficial impact on their clinical outcome BACKGROUND In patients with the acute respiratory distress syndrome , massive alveolar collapse and cyclic lung reopening and overdistention during mechanical ventilation may perpetuate alveolar injury . We determined whether a ventilatory strategy design ed to minimize such lung injuries could reduce not only pulmonary complications but also mortality at 28 days in patients with the acute respiratory distress syndrome . METHODS We r and omly assigned 53 patients with early acute respiratory distress syndrome ( including 28 described previously ) , all of whom were receiving identical hemodynamic and general support , to conventional or protective mechanical ventilation . Conventional ventilation was based on the strategy of maintaining the lowest positive end-expiratory pressure ( PEEP ) for acceptable oxygenation , with a tidal volume of 12 ml per kilogram of body weight and normal arterial carbon dioxide levels ( 35 to 38 mm Hg ) . Protective ventilation involved end-expiratory pressures above the lower inflection point on the static pressure-volume curve , a tidal volume of less than 6 ml per kilogram , driving pressures of less than 20 cm of water above the PEEP value , permissive hypercapnia , and preferential use of pressure-limited ventilatory modes . RESULTS After 28 days , 11 of 29 patients ( 38 percent ) in the protective-ventilation group had died , as compared with 17 of 24 ( 71 percent ) in the conventional-ventilation group ( P<0.001 ) . The rates of weaning from mechanical ventilation were 66 percent in the protective-ventilation group and 29 percent in the conventional-ventilation group ( P=0.005 ) : the rates of clinical barotrauma were 7 percent and 42 percent , respectively ( P=0.02 ) , despite the use of higher PEEP and mean airway pressures in the protective-ventilation group . The difference in survival to hospital discharge was not significant ; 13 of 29 patients ( 45 percent ) in the protective-ventilation group died in the hospital , as compared with 17 of 24 in the conventional-ventilation group ( 71 percent , P=0.37 ) . CONCLUSIONS As compared with conventional ventilation , the protective strategy was associated with improved survival at 28 days , a higher rate of weaning from mechanical ventilation , and a lower rate of barotrauma in patients with the acute respiratory distress syndrome .  Protective ventilation was not associated with a higher rate of survival to hospital discharge Purpose Lung volumes , especially functional residual capacity ( FRC ) , are decreased in acute respiratory distress syndrome ( ARDS ) .  Positive end-expiratory pressure ( PEEP ) contributes to increased end-expiratory lung volume ( EELV ) and to improved oxygenation , but differentiating recruitment of previously nonaerated lung units from distension of previously open lung units remains difficult . This study evaluated simple methods derived from bedside EELV measurements to assess PEEP-induced lung recruitment while monitoring strain . Methods Prospect i ve multicenter study in 30 mechanically ventilated patients with ARDS in five university hospital ICUs . Two PEEP levels were studied , each for 45 min , and  EELV ( nitrogen washout/washin technique )  was measured at both levels , with the difference ( Δ ) reflecting PEEP-induced lung volume changes . Alveolar recruitment was measured using pressure-volume ( PV ) curves . High and low recruiters were separated based on median recruitment at high PEEP . Minimum predicted increase in lung volume computed as the product of ΔPEEP by static compliance was subtracted from ΔEELV as an independent estimate of recruitment . Estimated and measured recruitments were compared . Strain induced by PEEP was also calculated from the same measurements . Results FRC was 31 ± 11 % of predicted . Median [ 25th–75th percentiles ] PEEP-induced recruitment was 272 [ 187–355 ] mL. Estimated recruitment correlated with recruited volume measured on PV curves ( ρ = 0.68 ) , with a slope close to identity . The ΔEELV/FRC ratio differentiated high from low recruiters ( 110 [ 76–135 ] vs. 55 [23–70]% , p = 0.001 ) . Strain increase due to PEEP was larger in high recruiters ( p = 0.002 ) . Conclusion PEEP-induced recruitment and strain can be assessed at the bedside using EELV measurement . We describe two bedside methods for predicting low or high alveolar recruitment during ARDS In a model of acute lung injury , we showed that positive end-expiratory pressure ( PEEP ) and tidal volume ( VT ) are interactive variables that determine the extent of lung recruitment , that recruitment occurs across the entire range of total lung capacity , and that superimposed pressure is a key determinant of lung collapse . Aim ing to verify if the same rules apply in a clinical setting , we r and omly ventilated five ALI/ARDS patients with 10 , 15 , 20 , 30 , 35 , and 45 cm H2O plateau pressure and 5 , 10 , 15 , and 20 cm H2O of PEEP .  For each PEEP-VT condition , we obtained computed tomography at end inspiration and end expiration . We found that recruitment occurred along the entire volume-pressure curve , independent of lower and upper inflection points , and that estimated threshold opening pressures were normally distributed ( mode = 20 cm H2O ) . Recruitment occurred progressively from nondependent to dependent lung regions . Overstretching was not associated with hyperinflation . Derecruitment did not parallel deflation , and estimated threshold closing pressures were normally distributed ( mode = 5 cm H2O ) . End-inspiratory and end-expiratory collapse were correlated , suggesting a plateau-PEEP interaction . When superimposed gravitational pressure exceeded PEEP , end-expiratory collapse increased . We concluded that the rules governing recruitment and derecruitment equally apply in an oleic acid model and in human ALI/ARDS RATIONALE Previous trials of higher positive end-expiratory pressure ( PEEP ) for acute respiratory distress syndrome ( ARDS ) failed to demonstrate mortality benefit , possibly because of differences in lung recruitability among patients with ARDS . OBJECTIVES To determine whether the physiological response to increased PEEP is associated with mortality . METHODS In a secondary analysis of the Lung Open Ventilation Study ( LOVS , n = 983 ) , we examined the relationship between the initial response to changes in PEEP after r and omization and mortality . We sought to corroborate our findings using data from a different trial of higher PEEP ( ExPress , n = 749 ) . MEASUREMENTS AND MAIN RESULTS The oxygenation response ( change in ratio of arterial partial pressure of oxygen to fraction of inspired oxygen : P/F ) after the initial change in PEEP after r and omization varied widely ( median , 9.5 mm Hg ; interquartile range , -16 to 47 ) and was only weakly related to baseline P/F or the magnitude of PEEP change . Among patients in whom  PEEP  was increased after r and omization , an increase in P/F was associated with reduced mortality ( multivariable logistic regression ; adjusted odds ratio , 0.80 [ 95 % confidence interval , 0.72 - 0.89 ] per 25-mm Hg increase in P/F ) , particularly in patients with severe disease ( baseline P/F [ less-than-or-equal-to ] 150 mm Hg ) . Changes in compliance and dead space were not associated with mortality . These findings were confirmed by a similar analysis of data from the ExPress trial . CONCLUSIONS Patients with ARDS who respond to increased PEEP by improved oxygenation have a lower risk of death . The oxygenation response to PEEP might be used to predict whether patients will benefit from higher versus lower PEEP
Rationale : In patients with acute respiratory distress syndrome ( ARDS ) , lung recruitment maneuvers ( LRMs ) may prevent ventilator‐induced lung injury and improve survival .
Objectives : To summarize the current evidence in support of the use of LRMs in adult patients with ARDS and to inform the recently published American Thoracic Society/European Society of Intensive Care Medicine/Society of Critical Care Medicine clinical practice guideline on mechanical ventilation in ARDS .