human
***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND Cardiac surgery-related pulmonary complications include alterations in lung mechanics and anomalies in gas exchange . Higher levels of positive end-expiratory pressure ( PEEP ) have been suggested to benefit cardiac surgical patients . We compared respiratory compliance , arterial oxygenation and time till tracheal extubation in 2 cohorts of patients weaned from mechanical ventilation with different levels of PEEP after elective and uncomplicated coronary artery bypass grafting ( CABG ) . We hypothesized that higher PEEP levels improve pulmonary compliance and gas exchange in the first hours of weaning from mechanical ventilation , but not to shorten time till tracheal extubation . METHODS Secondary retrospective analysis of 2 r and omized controlled trials : in the first trial patients were weaned with PEEP levels of 10 cmH2O for the first 4 hours followed by PEEP levels of 5 cmH2O until tracheal extubation ( high PEEP , HP ) ; and the second trial patients were weaned with PEEP levels of 5 cmH2O during the entire weaning phase ( low PEEP , LP ) . The primary endpoint was pulmonary compliance . Secondary endpoints included arterial oxygenation , duration of mechanical ventilation and postoperative pulmonary complications . RESULTS The analysis included 121 patients ; 60 HP patients and 61 LP patients . Baseline characteristics were similar . Compared to LP patients , HP patients had a better pulmonary compliance , 47.2±14.1 versus 42.7±10.2 ml/cmH2O ( P<0.05 ) , and higher levels of PaO2 , 18.5±6.6 ( 138.75±49.5 ) versus 16.7±5.4 ( 125.25±40.5 ) kPa ( mmHg ) ( P<0.05 ) . Patients in the HP group were less frequent in need of supplementary oxygen after ICU discharge . These differences remained present during the entire weaning phase , even after reduction of PEEP . However , HP patients had a longer time till tracheal extubation , 16.9±6.1 versus 10.5±5.0 hours ( P<0.001 ) . HP patients had longer duration s of postoperative infusion of propofol , 4.9 ( 2.6 - 7.4 ) versus 3.5 ( 1.8 - 5.8 ) hours ( P<0.05 ) . There were no differences in use of inotropes . Cumulative fluid balances were slightly higher in HP patients . CONCLUSION Use of higher PEEP levels after elective uncomplicated CABG improves pulmonary compliance and oxygenation but seems to be associated with a delay in tracheal extubation BACKGROUND Survival of patients with acute lung injury or the acute respiratory distress syndrome ( ARDS ) has been improved by ventilation with small tidal volumes and the use of positive end-expiratory pressure ( PEEP ) ; however , the optimal level of PEEP has been difficult to determine . In this pilot study , we estimated transpulmonary pressure with the use of esophageal balloon catheters . We reasoned that the use of pleural-pressure measurements , despite the technical limitations to the accuracy of such measurements , would enable us to find a PEEP value that could maintain oxygenation while preventing lung injury due to repeated alveolar collapse or overdistention . METHODS We r and omly assigned patients with acute lung injury or ARDS to undergo mechanical ventilation with PEEP adjusted according to measurements of esophageal pressure ( the esophageal-pressure-guided group ) or according to the Acute Respiratory Distress Syndrome Network st and ard-of-care recommendations ( the control group ) . The primary end point was improvement in oxygenation . The secondary end points included respiratory-system compliance and patient outcomes . RESULTS The study reached its stopping criterion and was terminated after 61 patients had been enrolled . The ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen at 72 hours was 88 mm Hg higher in the esophageal-pressure-guided group than in the control group ( 95 % confidence interval , 78.1 to 98.3 ; P=0.002 ) . This effect was persistent over the entire follow-up time ( at 24 , 48 , and 72 hours ; P=0.001 by repeated- measures analysis of variance ) . Respiratory-system compliance was also significantly better at 24 , 48 , and 72 hours in the esophageal-pressure-guided group ( P=0.01 by repeated- measures analysis of variance ) . CONCLUSIONS As compared with the current st and ard of care , a ventilator strategy using esophageal pressures to estimate the transpulmonary pressure significantly improves oxygenation and compliance . Multicenter clinical trials are needed to determine whether this approach should be widely adopted . ( Clinical Trials.gov number , NCT00127491 . OBJECTIVE To compare the effects of different levels of positive end-expiratory pressure on respiratory mechanics and oxygenation indexes in the immediate postoperative period of coronary artery bypass grafting . METHODS R and omized clinical trial in which 136 patients underwent coronary artery bypass grafting between January 2011 and March 2012 were divided into three groups and admitted to mechanical ventilation with different positive end-expiratory pressure levels : Group A , 5 cmH2O ( n=44 ) , Group B , 8 cmH2O ( n=47 ) and Group C , 10 cmH2O ( n=45 ) . Data about respiratory mechanics were obtained from mechanical ventilator monitor and oxygenation indexes from arterial blood gas sample s , collected twenty minutes after intensive care unit admission . Patients with chronic obstructive pulmonary disease and patients su bmi tted to off-pump , emergency or combined operations were not included . For statistical analysis , we used Kruskal-Wallis , G and Chi-square tests , considering results significant when P<0.05 . RESULTS Groups were homogeneous in terms of demographic , clinical and surgical variables . Patients ventilated with positive end-expiratory pressure of 10 cmH2O ( Group C ) had best compliance ( P=0.04 ) and airway resistance values , this , however , without statistical significance . They also had best oxygenation indexes , with statistical difference in all analyzed variables , and lower frequency of hypoxemia ( P=0.03 ) . CONCLUSION Higher levels of positive end-expiratory pressure in immediate postoperative period of coronary artery bypass grafting improved pulmonary compliance values and increased oxygenation indexes , result ing in lower frequency of hypoxemia The role of positive end-expiratory pressure ( PEEP ) in the postoperative course of cardiac surgery patients remains question able . In this prospect i ve study , we examined the effect of different levels of PEEP on arterial oxygenation , SvO2 and PvO2 values , and on haemodynamic indices , during the early postoperative period in cardiac surgery patients . Upon transfer to the ICU , 67 adult patients with normal preoperative respiratory status were r and omly assigned to receive zero PEEP ( Group A ) , 5 cmH2O ( Group B ) , or 10 cmH2O PEEP ( Group C ) during mechanical ventilatory support .  PaO2/FIO2 ratio , mixed venous PvO2 and SvO2 , and cardiac index , were measured 30 min , 4 h and 8 h after application of mechanical ventilation in the ICU , just prior to extubation , half an hour after extubation , and 4 h post-extubation . We found no statistically significant differences ( P = n.s . ) in arterial oxygenation expressed by PaO2/FIO2 ratio , SvO2 and PvO2 values , and in cardiac index among the three groups at any study interval . We conclude that low levels of PEEP have no advantage over zero PEEP in improving gas exchange in the early postoperative course of patients following open heart surgery Background : The impact of intraoperative ventilation on postoperative pulmonary complications is not defined . The authors aim ed at determining the effectiveness of protective mechanical ventilation during open abdominal surgery on a modified Clinical Pulmonary Infection Score as primary outcome and postoperative pulmonary function . Methods : Prospect i ve r and omized , open-label , clinical trial performed in 56 patients scheduled to undergo elective open abdominal surgery lasting more than 2 h. Patients were assigned by envelopes to mechanical ventilation with tidal volume of 9 ml/kg ideal body weight and zero-positive end-expiratory pressure ( st and ard ventilation strategy ) or tidal volumes of 7 ml/kg ideal body weight , 10 cm H2O positive end-expiratory pressure , and recruitment maneuvers ( protective ventilation strategy ) . Modified Clinical Pulmonary Infection Score , gas exchange , and pulmonary functional tests were measured preoperatively , as well as at days 1 , 3 , and 5 after surgery . Results : Patients ventilated protectively showed better pulmonary functional tests up to day 5 , fewer alterations on chest x-ray up to day 3 and higher arterial oxygenation in air at days 1 , 3 , and 5 ( mmHg ; mean ± SD ) : 77.1 ± 13.0 versus 64.9 ± 11.3 ( P = 0.0006 ) , 80.5 ± 10.1 versus 69.7 ± 9.3 ( P = 0.0002 ) , and 82.1 ± 10.7 versus 78.5 ± 21.7 ( P = 0.44 ) respectively . The modified Clinical Pulmonary Infection Score was lower in the protective ventilation strategy at days 1 and 3 . The percentage of patients in hospital at day 28 after surgery was not different between groups ( 7 vs. 15 % respectively , P = 0.42 ) . Conclusion : A protective ventilation strategy during abdominal surgery lasting more than 2 h improved respiratory function and reduced the modified Clinical Pulmonary Infection Score without affecting length of hospital stay This prospect i ve study was design ed to determine the effect of positive end-expiratory pressure ( PEEP ) instituted early in the course of adult respiratory distress syndrome ( ARDS ) . Seventy-nine ( 7 % ) of 1,200 patients admitted to the surgical intensive care unit were selected because of a high probability that ARDS would develop , and were r and omized into two treatment groups . Of the 79 patients , 45 were immediately treated with 5 cm H2O of end-expiratory pressure ( early PEEP group ) , and 34 received PEEP only when severe hypoxemia developed ( late PEEP group ) . The incidence of ARDS was significantly lower in the early PEEP group than in the late PEEP group ( 20 % vs 53 % ; P less than .002 ) . Fewer pulmonary deaths occurred in this group ( 11 % vs 29 % ; P = .02 ) , and there was less pulmonary morbidity . This study supports the efficacy of early low-level PEEP in the treatment of patients for whom there is a high probability that ARDS will develop BACKGROUND Mechanical-ventilation strategies that use lower end-inspiratory ( plateau ) airway pressures , lower tidal volumes ( VT ) , and higher positive end-expiratory pressures ( PEEPs ) can improve survival in patients with the acute respiratory distress syndrome ( ARDS ) , but the relative importance of each of these components is uncertain . Because respiratory-system compliance ( CRS ) is strongly related to the volume of aerated remaining functional lung during disease ( termed functional lung size ) , we hypothesized that driving pressure ( ΔP = VT/CRS ) , in which VT is intrinsically normalized to functional lung size ( instead of predicted lung size in healthy persons ) , would be an index more strongly associated with survival than VT or PEEP in patients who are not actively breathing . METHODS Using a statistical tool known as multilevel mediation analysis to analyze individual data from 3562 patients with ARDS enrolled in nine previously reported r and omized trials , we examined ΔP as an independent variable associated with survival . In the mediation analysis , we estimated the isolated effects of changes in ΔP result ing from r and omized ventilator setting s while minimizing confounding due to the baseline severity of lung disease . RESULTS Among ventilation variables , ΔP was most strongly associated with survival . A 1-SD increment in ΔP ( approximately 7 cm of water ) was associated with increased mortality ( relative risk , 1.41 ; 95 % confidence interval [ CI ] , 1.31 to 1.51 ; P<0.001 ) , even in patients receiving " protective " plateau pressures and VT ( relative risk , 1.36 ; 95 % CI , 1.17 to 1.58 ; P<0.001 ) . Individual changes in VT or PEEP after r and omization were not independently associated with survival ; they were associated only if they were among the changes that led to reductions in ΔP ( mediation effects of ΔP , P=0.004 and P=0.001 , respectively ) . CONCLUSIONS We found that ΔP was the ventilation variable that best stratified risk . Decreases in ΔP owing to changes in ventilator setting s were strongly associated with increased survival . ( Funded by Fundação de Amparo e Pesquisa do Estado de São Paulo and others . ) Introduction There is an increasing interest in biphasic positive airway pressure with spontaneous breathing ( BIPAP+SBmean ) , which is a combination of time-cycled controlled breaths at two levels of continuous positive airway pressure ( BIPAP+SBcontrolled ) and non-assisted spontaneous breathing ( BIPAP+SBspont ) 
    Output:
    
agent
***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND Cardiac surgery-related pulmonary complications include alterations in lung mechanics and anomalies in gas exchange . Higher levels of positive end-expiratory pressure ( PEEP ) have been suggested to benefit cardiac surgical patients . We compared respiratory compliance , arterial oxygenation and time till tracheal extubation in 2 cohorts of patients weaned from mechanical ventilation with different levels of PEEP after elective and uncomplicated coronary artery bypass grafting ( CABG ) . We hypothesized that higher PEEP levels improve pulmonary compliance and gas exchange in the first hours of weaning from mechanical ventilation , but not to shorten time till tracheal extubation . METHODS Secondary retrospective analysis of 2 r and omized controlled trials : in the first trial patients were weaned with PEEP levels of 10 cmH2O for the first 4 hours followed by PEEP levels of 5 cmH2O until tracheal extubation ( high PEEP , HP ) ; and the second trial patients were weaned with PEEP levels of 5 cmH2O during the entire weaning phase ( low PEEP , LP ) . The primary endpoint was pulmonary compliance . Secondary endpoints included arterial oxygenation , duration of mechanical ventilation and postoperative pulmonary complications . RESULTS The analysis included 121 patients ; 60 HP patients and 61 LP patients . Baseline characteristics were similar . Compared to LP patients , HP patients had a better pulmonary compliance , 47.2±14.1 versus 42.7±10.2 ml/cmH2O ( P<0.05 ) , and higher levels of PaO2 , 18.5±6.6 ( 138.75±49.5 ) versus 16.7±5.4 ( 125.25±40.5 ) kPa ( mmHg ) ( P<0.05 ) . Patients in the HP group were less frequent in need of supplementary oxygen after ICU discharge . These differences remained present during the entire weaning phase , even after reduction of PEEP . However , HP patients had a longer time till tracheal extubation , 16.9±6.1 versus 10.5±5.0 hours ( P<0.001 ) . HP patients had longer duration s of postoperative infusion of propofol , 4.9 ( 2.6 - 7.4 ) versus 3.5 ( 1.8 - 5.8 ) hours ( P<0.05 ) . There were no differences in use of inotropes . Cumulative fluid balances were slightly higher in HP patients . CONCLUSION Use of higher PEEP levels after elective uncomplicated CABG improves pulmonary compliance and oxygenation but seems to be associated with a delay in tracheal extubation BACKGROUND Survival of patients with acute lung injury or the acute respiratory distress syndrome ( ARDS ) has been improved by ventilation with small tidal volumes and the use of positive end-expiratory pressure ( PEEP ) ; however , the optimal level of PEEP has been difficult to determine . In this pilot study , we estimated transpulmonary pressure with the use of esophageal balloon catheters . We reasoned that the use of pleural-pressure measurements , despite the technical limitations to the accuracy of such measurements , would enable us to find a PEEP value that could maintain oxygenation while preventing lung injury due to repeated alveolar collapse or overdistention . METHODS We r and omly assigned patients with acute lung injury or ARDS to undergo mechanical ventilation with PEEP adjusted according to measurements of esophageal pressure ( the esophageal-pressure-guided group ) or according to the Acute Respiratory Distress Syndrome Network st and ard-of-care recommendations ( the control group ) . The primary end point was improvement in oxygenation . The secondary end points included respiratory-system compliance and patient outcomes . RESULTS The study reached its stopping criterion and was terminated after 61 patients had been enrolled . The ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen at 72 hours was 88 mm Hg higher in the esophageal-pressure-guided group than in the control group ( 95 % confidence interval , 78.1 to 98.3 ; P=0.002 ) . This effect was persistent over the entire follow-up time ( at 24 , 48 , and 72 hours ; P=0.001 by repeated- measures analysis of variance ) . Respiratory-system compliance was also significantly better at 24 , 48 , and 72 hours in the esophageal-pressure-guided group ( P=0.01 by repeated- measures analysis of variance ) . CONCLUSIONS As compared with the current st and ard of care , a ventilator strategy using esophageal pressures to estimate the transpulmonary pressure significantly improves oxygenation and compliance . Multicenter clinical trials are needed to determine whether this approach should be widely adopted . ( Clinical Trials.gov number , NCT00127491 . OBJECTIVE To compare the effects of different levels of positive end-expiratory pressure on respiratory mechanics and oxygenation indexes in the immediate postoperative period of coronary artery bypass grafting . METHODS R and omized clinical trial in which 136 patients underwent coronary artery bypass grafting between January 2011 and March 2012 were divided into three groups and admitted to mechanical ventilation with different positive end-expiratory pressure levels : Group A , 5 cmH2O ( n=44 ) , Group B , 8 cmH2O ( n=47 ) and Group C , 10 cmH2O ( n=45 ) . Data about respiratory mechanics were obtained from mechanical ventilator monitor and oxygenation indexes from arterial blood gas sample s , collected twenty minutes after intensive care unit admission . Patients with chronic obstructive pulmonary disease and patients su bmi tted to off-pump , emergency or combined operations were not included . For statistical analysis , we used Kruskal-Wallis , G and Chi-square tests , considering results significant when P<0.05 . RESULTS Groups were homogeneous in terms of demographic , clinical and surgical variables . Patients ventilated with positive end-expiratory pressure of 10 cmH2O ( Group C ) had best compliance ( P=0.04 ) and airway resistance values , this , however , without statistical significance . They also had best oxygenation indexes , with statistical difference in all analyzed variables , and lower frequency of hypoxemia ( P=0.03 ) . CONCLUSION Higher levels of positive end-expiratory pressure in immediate postoperative period of coronary artery bypass grafting improved pulmonary compliance values and increased oxygenation indexes , result ing in lower frequency of hypoxemia The role of positive end-expiratory pressure ( PEEP ) in the postoperative course of cardiac surgery patients remains question able . In this prospect i ve study , we examined the effect of different levels of PEEP on arterial oxygenation , SvO2 and PvO2 values , and on haemodynamic indices , during the early postoperative period in cardiac surgery patients . Upon transfer to the ICU , 67 adult patients with normal preoperative respiratory status were r and omly assigned to receive zero PEEP ( Group A ) , 5 cmH2O ( Group B ) , or 10 cmH2O PEEP ( Group C ) during mechanical ventilatory support .  PaO2/FIO2 ratio , mixed venous PvO2 and SvO2 , and cardiac index , were measured 30 min , 4 h and 8 h after application of mechanical ventilation in the ICU , just prior to extubation , half an hour after extubation , and 4 h post-extubation . We found no statistically significant differences ( P = n.s . ) in arterial oxygenation expressed by PaO2/FIO2 ratio , SvO2 and PvO2 values , and in cardiac index among the three groups at any study interval . We conclude that low levels of PEEP have no advantage over zero PEEP in improving gas exchange in the early postoperative course of patients following open heart surgery Background : The impact of intraoperative ventilation on postoperative pulmonary complications is not defined . The authors aim ed at determining the effectiveness of protective mechanical ventilation during open abdominal surgery on a modified Clinical Pulmonary Infection Score as primary outcome and postoperative pulmonary function . Methods : Prospect i ve r and omized , open-label , clinical trial performed in 56 patients scheduled to undergo elective open abdominal surgery lasting more than 2 h. Patients were assigned by envelopes to mechanical ventilation with tidal volume of 9 ml/kg ideal body weight and zero-positive end-expiratory pressure ( st and ard ventilation strategy ) or tidal volumes of 7 ml/kg ideal body weight , 10 cm H2O positive end-expiratory pressure , and recruitment maneuvers ( protective ventilation strategy ) . Modified Clinical Pulmonary Infection Score , gas exchange , and pulmonary functional tests were measured preoperatively , as well as at days 1 , 3 , and 5 after surgery . Results : Patients ventilated protectively showed better pulmonary functional tests up to day 5 , fewer alterations on chest x-ray up to day 3 and higher arterial oxygenation in air at days 1 , 3 , and 5 ( mmHg ; mean ± SD ) : 77.1 ± 13.0 versus 64.9 ± 11.3 ( P = 0.0006 ) , 80.5 ± 10.1 versus 69.7 ± 9.3 ( P = 0.0002 ) , and 82.1 ± 10.7 versus 78.5 ± 21.7 ( P = 0.44 ) respectively . The modified Clinical Pulmonary Infection Score was lower in the protective ventilation strategy at days 1 and 3 . The percentage of patients in hospital at day 28 after surgery was not different between groups ( 7 vs. 15 % respectively , P = 0.42 ) . Conclusion : A protective ventilation strategy during abdominal surgery lasting more than 2 h improved respiratory function and reduced the modified Clinical Pulmonary Infection Score without affecting length of hospital stay This prospect i ve study was design ed to determine the effect of positive end-expiratory pressure ( PEEP ) instituted early in the course of adult respiratory distress syndrome ( ARDS ) . Seventy-nine ( 7 % ) of 1,200 patients admitted to the surgical intensive care unit were selected because of a high probability that ARDS would develop , and were r and omized into two treatment groups . Of the 79 patients , 45 were immediately treated with 5 cm H2O of end-expiratory pressure ( early PEEP group ) , and 34 received PEEP only when severe hypoxemia developed ( late PEEP group ) . The incidence of ARDS was significantly lower in the early PEEP group than in the late PEEP group ( 20 % vs 53 % ; P less than .002 ) . Fewer pulmonary deaths occurred in this group ( 11 % vs 29 % ; P = .02 ) , and there was less pulmonary morbidity . This study supports the efficacy of early low-level PEEP in the treatment of patients for whom there is a high probability that ARDS will develop BACKGROUND Mechanical-ventilation strategies that use lower end-inspiratory ( plateau ) airway pressures , lower tidal volumes ( VT ) , and higher positive end-expiratory pressures ( PEEPs ) can improve survival in patients with the acute respiratory distress syndrome ( ARDS ) , but the relative importance of each of these components is uncertain . Because respiratory-system compliance ( CRS ) is strongly related to the volume of aerated remaining functional lung during disease ( termed functional lung size ) , we hypothesized that driving pressure ( ΔP = VT/CRS ) , in which VT is intrinsically normalized to functional lung size ( instead of predicted lung size in healthy persons ) , would be an index more strongly associated with survival than VT or PEEP in patients who are not actively breathing . METHODS Using a statistical tool known as multilevel mediation analysis to analyze individual data from 3562 patients with ARDS enrolled in nine previously reported r and omized trials , we examined ΔP as an independent variable associated with survival . In the mediation analysis , we estimated the isolated effects of changes in ΔP result ing from r and omized ventilator setting s while minimizing confounding due to the baseline severity of lung disease . RESULTS Among ventilation variables , ΔP was most strongly associated with survival . A 1-SD increment in ΔP ( approximately 7 cm of water ) was associated with increased mortality ( relative risk , 1.41 ; 95 % confidence interval [ CI ] , 1.31 to 1.51 ; P<0.001 ) , even in patients receiving " protective " plateau pressures and VT ( relative risk , 1.36 ; 95 % CI , 1.17 to 1.58 ; P<0.001 ) . Individual changes in VT or PEEP after r and omization were not independently associated with survival ; they were associated only if they were among the changes that led to reductions in ΔP ( mediation effects of ΔP , P=0.004 and P=0.001 , respectively ) . CONCLUSIONS We found that ΔP was the ventilation variable that best stratified risk . Decreases in ΔP owing to changes in ventilator setting s were strongly associated with increased survival . ( Funded by Fundação de Amparo e Pesquisa do Estado de São Paulo and others . ) Introduction There is an increasing interest in biphasic positive airway pressure with spontaneous breathing ( BIPAP+SBmean ) , which is a combination of time-cycled controlled breaths at two levels of continuous positive airway pressure ( BIPAP+SBcontrolled ) and non-assisted spontaneous breathing ( BIPAP+SBspont ) 
    Output:
    