Positive end-expiratory pressure following coronary artery bypass grafting. Mechanical ventilation guided by esophageal pressure in acute lung injury. Effects of different PEEP levels on respiratory mechanics and oxygenation after coronary artery bypass grafting. Effects of positive end-expiratory pressure (PEEP) in cardiac surgery patients. Protective Mechanical Ventilation during General Anesthesia for Open Abdominal Surgery Improves Postoperative Pulmonary Function Early positive end-expiratory pressure in the adult respiratory distress syndrome. Driving pressure and survival in the acute respiratory distress syndrome. Regional lung aeration and ventilation during pressure support and biphasic positive airway pressure ventilation in experimental lung injury Fluid resuscitation in septic shock: A positive fluid balance and elevated central venous pressure are associated with increased mortality* Positive End-expiratory Pressure Titration after Alveolar Recruitment Directed by Electrical Impedance Tomography High versus low positive end-expiratory pressure during general anaesthesia for open abdominal surgery (PROVHILO trial): a multicentre randomised controlled trial. Positive-end expiratory pressure reduces incidence of ventilator-associated pneumonia in nonhypoxemic patients* The Pulmonary and Hemodynamic Effects of Two Different Recruitment Maneuvers After Cardiac Surgery The effects of positive end-expiratory pressure of intrapulmonary shunt and ventilatory deadspace in nonhypoxic trauma patients. A trial of intraoperative low-tidal-volume ventilation in abdominal surgery. A universal definition of ARDS: the PaO2/FiO2 ratio under a standard ventilatory setting—a prospective, multicenter validation study Titrating positive end‐expiratory pressure therapy in patients with early, moderate arterial hypoxemia Minimal positive end-expiratory pressure (PEEP) may be "best PEEP". Effects of positive end-expiratory pressure on mechanical ventilation duration after coronary artery bypass grafting: a randomized clinical trial. Prophylactic positive end-expiratory pressure and postintubation hemodynamics: an interventional, randomized study. Positive end-expiratory pressure in pressure-controlled ventilation improves ventilatory and oxygenation parameters during laparoscopic cholecystectomy Spontaneous breathing during ventilatory support improves ventilation-perfusion distributions in patients with acute respiratory distress syndrome. Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome. [Effect of high positive end-expiratory pressure for mechanical ventilation in the treatment of neurological pulmonary edema]. Positive end‐expiratory pressure prevents atelectasisduring general anaesthesia even in the presence of a high inspired oxygen concentration The routine use of positive end-expiratory pressure after open heart surgery. Biological Impact of Transpulmonary Driving Pressure in Experimental Acute Respiratory Distress Syndrome Prevention of Atelectasis in Morbidly Obese Patients during General Anesthesia and Paralysis: A Computerized Tomography Study [Effect of lung protection mechanical ventilation on respiratory function in the elderly undergoing spinal fusion]. Positive End-Expiratory Pressure Increases the Right-to-Left Shunt in Mechanically Ventilated Patients with Patent Foramen Ovale Effects of lung recruitment maneuver and positiveend‐expiratory pressure on lung volume, respiratory mechanics and alveolar gas mixing in patients ventilated after cardiac surgery Early application of positive end-expiratory pressure in patients at risk for the adult respiratory-distress syndrome. Positive end‐expiratory pressure does not affect indocyanine green plasma disappearance rate or gastric mucosal perfusion after cardiac surgery* Failure of positive end-expiratory pressure to decrease postoperative bleeding after cardiac surgery. Effect of positive end-expiratory pressure on excessive mediastinal bleeding after cardiac operations. A controlled study. Compliance and Dead Space Fraction Indicate an Optimal Level of Positive End-Expiratory Pressure After Recruitment in Anesthetized Patients
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 ) , in the early phase of acute lung injury ( ALI ) . However , pressure support ventilation ( PSV ) remains the most commonly used mode of assisted ventilation . To date , the effects of BIPAP+SBmean and PSV on regional lung aeration and ventilation during ALI are only poorly defined . Methods In 10 anesthetized juvenile pigs , ALI was induced by surfactant depletion . BIPAP+SBmean and PSV were performed in a r and om sequence ( 1 h each ) at comparable mean airway pressures and minute volumes . Gas exchange , hemodynamics , and inspiratory effort were determined and dynamic computed tomography scans obtained . Aeration and ventilation were calculated in four zones along the ventral-dorsal axis at lung apex , hilum and base . Results Compared to PSV , BIPAP+SBmean result ed in : 1 ) lower mean tidal volume , comparable oxygenation and hemodynamics , and increased PaCO2 and inspiratory effort ; 2 ) less nonaerated areas at end-expiration ; 3 ) decreased tidal hyperaeration and re-aeration ; 4 ) similar distributions of ventilation . During BIPAP+SBmean : i ) BIPAP+SBspont had lower tidal volumes and higher rates than BIPAP+SBcontrolled ; ii ) BIPAP+SBspont and BIPAP+SBcontrolled had similar distributions of ventilation and aeration ; iii ) BIPAP+SBcontrolled result ed in increased tidal re-aeration and hyperareation , compared to PSV . BIPAP+SBspont showed an opposite pattern . Conclusions In this model of ALI , the reduction of tidal re-aeration and hyperaeration during BIPAP+SBmean compared to PSV is not due to decreased nonaerated areas at end-expiration or different distribution of ventilation , but to lower tidal volumes during BIPAP+SBspont . The ratio between spontaneous to controlled breaths seems to play a pivotal role in reducing tidal re-aeration and hyperaeration during BIPAP+SBmean Objective : To determine whether central venous pressure and fluid balance after resuscitation for septic shock are associated with mortality . Design : We conducted a retrospective review of the use of intravenous fluids during the first 4 days of care . Setting : Multicenter r and omized controlled trial . Patients : The Vasopressin in Septic Shock Trial ( VASST ) study enrolled 778 patients who had septic shock and who were receiving a minimum of 5 & mgr;g of norepinephrine per minute .  Interventions : None . Measurements and Main Results : Based on net fluid balance , we determined whether one 's fluid balance quartile was correlated with 28-day mortality . We also analyzed whether fluid balance was predictive of central venous pressure and furthermore whether a guideline -recommended central venous pressure of 8–12 mm Hg yielded a mortality advantage . At enrollment , which occurred on average 12 hrs after presentation , the average fluid balance was + 4.2 L. By day 4 , the cumulative average fluid balance was + 11 L. After correcting for age and Acute Physiology and Chronic Health Evaluation II score , a more positive fluid balance at both at 12 hrs and day 4 correlated significantly with increased mortality . Central venous pressure was correlated with fluid balance at 12 hrs , whereas on days 1–4 , there was no significant correlation . At 12 hrs , patients with central venous pressure < 8 mm Hg had the lowest mortality rate followed by those with central venous pressure 8–12 mm Hg . The highest mortality rate was observed in those with central venous pressure > 12 mm Hg . Contrary to the overall effect , patients whose central venous pressure was < 8 mm Hg had improved survival with a more positive fluid balance . Conclusions : A more positive fluid balance both early in resuscitation and cumulatively over 4 days is associated with an increased risk of mortality in septic shock . Central venous pressure may be used to gauge fluid balance ≤12 hrs into septic shock but becomes an unreliable marker of fluid balance thereafter . Optimal survival in the VASST study occurred with a positive fluid balance of approximately 3 L at 12 hrs Background : Electrical impedance tomography ( EIT ) is a real-time bedside monitoring tool , which can reflect dynamic regional lung ventilation . The aim of the present study was to monitor regional gas distribution in patients with acute respiratory distress syndrome ( ARDS ) during positive-end-expiratory pressure ( PEEP ) titration using EIT . Methods : Eighteen ARDS patients under mechanical ventilation in Department of Critical Care Medicine of Peking Union Medical College Hospital from January to April in 2014 were included in this prospect i ve observational study . After recruitment maneuvers ( RMs ) , decremental PEEP titration was performed from 20 cmH2O to 5 cmH2O in steps of 3 cmH2O every 5–10 min . Regional over-distension and recruitment were monitored with EIT . Results : After RMs , patient with arterial blood oxygen partial pressure ( PaO2 ) + carbon dioxide partial pressure ( PaCO2 ) > 400 mmHg with 100 % of fractional inspired oxygen concentration were defined as RM responders . Thirteen ARDS patients was diagnosed as responders whose PaO2 + PaCO2 were higher than nonresponders ( 419 ± 44 mmHg vs. 170 ± 73 mmHg , P < 0.0001 ) . In responders , PEEP mainly increased recruited pixels in dependent regions and over-distended pixels in nondependent regions . PEEP alleviated global inhomogeneity of tidal volume and end-expiratory lung volume . PEEP levels without significant alveolar derecruitment and over-distension were identified individually . Conclusions : After RMs , PEEP titration significantly affected regional gas distribution in lung , which could be monitored with EIT . EIT has the potential to optimize PEEP titration BACKGROUND The role of positive end-expiratory pressure in mechanical ventilation during general anaesthesia for surgery remains uncertain . Levels of pressure higher than 0 cm H2O might protect against postoperative pulmonary complications but could also cause intraoperative circulatory depression and lung injury from overdistension . We tested the hypothesis that a high level of positive end-expiratory pressure with recruitment manoeuvres protects against postoperative pulmonary complications in patients at risk of complications who are receiving mechanical ventilation with low tidal volumes during general anaesthesia for open abdominal surgery . METHODS In this r and omised controlled trial at 30 centres in Europe and North and South America , we recruited 900 patients at risk for postoperative pulmonary complications who were planned for open abdominal surgery under general anaesthesia and ventilation at tidal volumes of 8 mL/kg . We r and omly allocated patients to either a high level of positive end-expiratory pressure ( 12 cm H2O ) with recruitment manoeuvres ( higher PEEP group ) or a low level of pressure ( ≤2 cm H2O ) without recruitment manoeuvres ( lower PEEP group ) . We used a central ised computer-generated r and omisation system . Patients and outcome assessors were masked to the intervention . Primary endpoint was a composite of postoperative pulmonary complications by postoperative day 5 . Analysis was by intention-to-treat . The study is registered at Controlled-Trials.com , number IS RCT N70332574 . FINDINGS From February , 2011 , to January , 2013 , 447 patients were r and omly allocated to the higher PEEP group and 453 to the lower PEEP group . Six patients were excluded from the analysis , four because they withdrew consent and two for violation of inclusion criteria . Median levels of positive end-expiratory pressure were 12 cm H2O ( IQR 12 - 12 ) in the higher PEEP group and 2 cm H2O ( 0 - 2 ) in the lower PEEP group . Postoperative pulmonary complications were reported in 174 ( 40 % ) of 445 patients in the higher PEEP group versus 172 ( 39 % ) of 449 patients in the lower PEEP group ( relative risk 1·01 ; 95 % CI 0·86 - 1·20 ; p=0·86 ) . Compared with patients in the lower PEEP group , those in the higher PEEP group developed intraoperative hypotension and needed more vasoactive drugs . INTERPRETATION A strategy with a high level of positive end-expiratory pressure and recruitment manoeuvres during open abdominal surgery does not protect against postoperative pulmonary complications . An intraoperative protective ventilation strategy should include a low tidal volume and low positive end-expiratory pressure , without recruitment manoeuvres . FUNDING Academic Medical Center ( Amsterdam , Netherl and s ) , European Society of Anaesthesiology Objective : To analyze the effect on clinical outcomes of prophylactic positive end expiratory pressure in nonhypoxemic ventilated patients . Design : Multicenter r and omized controlled clinical trial . Setting : One trauma and two general intensive care units in two university hospitals . Patients : One hundred thirty-one mechanically ventilated patients with normal chest radiograph and Pao2/Fio2 above 250 . Interventions : Patients were r and omly allocated to receive mechanical ventilation with 5–8 cm H2O of positive end-expiratory pressure ( PEEP ) ( PEEP group , n = 66 ) or no-PEEP ( control group , n = 65 ) . Measurements and Main Results : Primary end-point variable was hospital mortality . Secondary outcomes included microbiologically confirmed ventilator-associated pneumonia , acute respiratory distress syndrome , barotrauma , atelectasis , and hypoxemia ( Pao2/Fio2 < 175 ) . Both groups were similar at r and omization in demographic characteristics , intensive care unit admission diagnoses , severity of illness , and risk factors for ventilator-associated pneumonia . Hospital mortality rate was similar ( p = 0.58 ) between PEEP ( 29.7 % ) and control ( 25.4 % ) groups . Ventilator-associated pneumonia was detected in 16 ( 25.4 % ) patients in the control group and 6 ( 9.4 % ) in the PEEP group ( relative risk , 0.37 ; 95 % confidence interval = 0.15–0.84 ; p = 0.017 ) . The number of patients who developed hypoxemia was significantly higher in the control group ( 34 of 63 patients , 54 % ) than in the PEEP group ( 12 of 64 , 19 % ) ( p < 0.001 ) , and the hypoxemia developed after a shorter period ( median [ interquartile range ] ) in the control group than in the PEEP group ( 38 [ 20–70 ] hrs vs. 77 [ 32–164 ] hrs , p < 0.001 ) . Groups did not significantly differ in incidence of acute respiratory distress syndrome ( 14 % in controls vs. 5 % in the PEEP group , p = 0.08 ) , barotrauma ( 8 % vs. 2 % , respectively , p = 0.12 ) , or atelectasis ( 27 % vs. 19 % , respectively , p = 0.26 ) . Conclusions : These findings indicate that application of prophylactic PEEP in nonhypoxemic ventilated patients reduces the number of hypoxemia episodes and the incidence of ventilator-associated pneumonia BACKGROUND : The aim of our study was to evaluate the pulmonary and hemodynamic effects of two different recruitment maneuvers after open heart surgery . METHODS : Sixty patients undergoing coronary artery bypass surgery  were r and omized into three groups after operation : recruitment maneuver with continuous positive airway pressure ( CPAP ) ( CPAP-40 group , n = 20 ) , recruitment by positive end-expiratory pressure ( PEEP ) ( PEEP-20 group , n = 20 ) , and 5 cm H2O PEEP ( PEEP-5 group , n = 20 ) . In the CPAP-40 group , 40 cm H2O peak inspiratory pressure was applied for 30 s , then PEEP was reduced to 20 cm H2O and ventilation was continued with baseline variables with PEEP decreased until the best Pao2 was achieved . In the PEEP-20 group , 20 cm H2O PEEP was set for 2 min , tidal volume was adjusted to achieve a peak inspiratory airway pressure of 40 cm H2O during the maneuver , then PEEP was decreased until the best Pao2 had been achieved . In the PEEP-5 group , 5 cm H2O PEEP was applied postoperatively . RESULTS : The mean arterial blood pressure of the CPAP-40 group was lower than that of the PEEP-20 ( P < 0.01 ) and PEEP-5 groups ( P < 0.01 ) during the interventions . Oxygenation was higher in both recruitment groups than in the PEEP-5 group during the mechanical ventilation period . There was no significant difference among the groups beyond that period . The atelectasis score of the PEEP-5 group ( 1.3 ± 0.9 ) on postoperative day 1 was higher than that of the CPAP-40 ( 0.65 ± 0.6 ; P = 0.01 ) and PEEP-20 ( 0.65 ± 0.5 ; P = 0.01 ) groups . CONCLUSIONS : The recruitment techniques with postmaneuver PEEP increased oxygenation and decreased atelectasis equally , whereas PEEP-20 provided more stable hemodynamic conditions than the CPAP maneuver Controversy exists regarding the routine use of positive end-expiratory pressure ( PEEP ) in mechanically ventilated patients . We hypothesized that nonhypoxic patients receiving 5-cm H2O PEEP would have improved shunt and PaO2/F10(2 ) ratios ( P/F ) , without an increased dead space to tidal volume ratio ( VD/VT ) versus patients receiving no PEEP . Forty-four trauma patients were r and omized to receive 5-cm H2O PEEP ( PEEP ) or 0-cm H2O PEEP ( ZEEP ) . Shunt VD/VT and P/F were measured at 0 , 12 , 24 , 36 , and 48 hours after intubation and after extubation . PEEP and ZEEP comparisons used Student 's t test and the General Linear Models procedure . Shunt was significantly increased at t = 0 and at extubation in the PEEP group . At extubation , the PEEP group demonstrated significantly higher VD/VT and poorer P/F ratios . After correction for baseline values , no statistically significant differences were noted in spite of a trend toward worsening pulmonary function in all measured parameters . These results suggest that routine use of 5-cm H2O PEEP in mechanical ventilated trauma patients is not necessary BACKGROUND Lung-protective ventilation with the use of low tidal volumes and positive end-expiratory pressure is considered best practice in the care of many critically ill patients . However , its role in anesthetized patients undergoing major surgery is not known . METHODS In this multicenter , double-blind , parallel-group trial , we r and omly assigned 400 adults at intermediate to high risk of pulmonary complications after major abdominal surgery to either nonprotective mechanical ventilation or a strategy of lung-protective ventilation . The primary outcome was a composite of major pulmonary and extrapulmonary complications occurring within the first 7 days after surgery . RESULTS The two intervention groups had similar characteristics at baseline . In the intention-to-treat analysis , the primary outcome occurred in 21 of 200 patients ( 10.5 % ) assigned to lung-protective ventilation , as compared with 55 of 200 ( 27.5 % ) assigned to nonprotective ventilation ( relative risk , 0.40 ; 95 % confidence interval [ CI ] , 0.24 to 0.68 ; P=0.001 ) . Over the 7-day postoperative period , 10 patients ( 5.0 % ) assigned to lung-protective ventilation required noninvasive ventilation or intubation for acute respiratory failure , as compared with 34 ( 17.0 % ) assigned to nonprotective ventilation ( relative risk , 0.29 ; 95 % CI , 0.14 to 0.61 ; P=0.001 ) . The length of the hospital stay was shorter among patients receiving lung-protective ventilation than among those receiving nonprotective ventilation ( mean difference , -2.45 days ; 95 % CI , -4.17 to -0.72 ; P=0.006 ) . CONCLUSIONS As compared with a practice of nonprotective mechanical ventilation , the use of a lung-protective ventilation strategy in intermediate-risk and high-risk patients undergoing major abdominal surgery was associated with improved clinical outcomes and reduced health care utilization . ( IMPROVE Clinical Trials.gov number , NCT01282996 . ) Purpose The PaO2/FiO2 is an integral part of the assessment of patients with acute respiratory distress syndrome ( ARDS ) . The American-European Consensus Conference definition does not m and ate any st and ardization procedure . We hypothesized that the use of PaO2/FiO2 calculated under a st and ard ventilatory setting within 24 h of ARDS diagnosis allows a more clinical ly relevant ARDS classification . Methods We studied 452 ARDS patients enrolled prospect ively in two independent , multicenter cohorts treated with protective mechanical ventilation .  At the time of ARDS diagnosis , patients had a PaO2/FiO2 ≤ 200 . In the derivation cohort ( n = 170 ) , we measured PaO2/FiO2 with two levels of positive end-expiratory pressure ( PEEP ) ( ≥5 and ≥10 cmH2O ) and two levels of FiO2 ( ≥0.5 and 1.0 ) at ARDS onset and 24 h later . Dependent upon PaO2 response , patients were reclassified into three groups : mild ( PaO2/FiO2 > 200 ) , moderate ( PaO2/FiO2 101–200 ) , and severe ( PaO2/FiO2 ≤ 100 ) ARDS . The primary outcome measure was ICU mortality . The st and ard ventilatory setting that reached the highest significance difference in mortality among these categories was tested in a separate cohort ( n = 282 ) . Results The only st and ard ventilatory setting that identified the three PaO2/FiO2 risk categories in the derivation cohort was PEEP ≥ 10 cmH2O and FiO2 ≥ 0.5 at 24 h after ARDS onset ( p = 0.0001 ) . Using this ventilatory setting , patients in the validation cohort were reclassified as having mild ARDS ( n = 47 , mortality 17 % ) , moderate ARDS ( n = 149 , mortality 40.9 % ) , and severe ARDS ( n = 86 , mortality 58.1 % ) ( p = 0.00001 ) . Conclusions Our method for assessing PaO2/FiO2 greatly improved risk stratification of ARDS and could be used for enrolling appropriate ARDS patients into therapeutic clinical trials A prospect i ve r and omized study to compare two physiologic end-points for titrating positive end-expiratory pressure ( PEEP ) was performed in patients with early , moderate arterial hypoxemia after surgery or trauma . All patients initially received 5 cm H2O of PEEP . In group 1 patients , PEEP was increased only if Pao2 decreased below 65 torr on an inspired oxygen fraction ( FIO2 ) of 0.45 . PEEP was then added in 2− to 3-cm H2O increments until Pao2 again was above 65 torr . Group 2 patients were treated with incremental PEEP until the Pao2/Fio2 ratio was greater than 300 or physiologic shunt ( Qsp/Qt ) was less than 0.20 . All therapy other than PEEP was similar in the two groups . There were no statistically significant differences in entry Pao2 ( mean 85 ± 11 [ SD ] and 87 ± 11 torr in groups 1 and 2 , respectively ) , and Qsp/Qt was 0.22 in each group . Five ( 28 % ) of 18 patients in group 1 and 19 ( 95 % ) of 20 patients in group 2 received more than 5 cm H2O of PEEP . Between groups 1 and 2 there were no statistically significant differences in days intubated ( 3.4 ± 3 vs. 5.3 ± 5 , respectively ) , ICU days ( 5.3 ± 3 vs. 6.6 ± 5 ) , hospitalization days ( 26 ± 24 vs. 28 ± 24 ) , incidence of pulmonary barotrauma ( 0/18 vs. 1/20 ) , ICU mortality ( 22 % vs. 20 % ) , or overall mortality ( 33 % vs. 25 % ) . The number of blood gas analyses and cardiac output measurements , and the total hospital charges were also similar in both groups . Thus , titrating PEEP therapy to a prescribed Qsp/ Qt of less than 0.20 did not improve patient outcome or decrease re source utilization . Instead , group 2 patients were subjected to more frequent manipulation of PEEP levels than group 1 patients , who received PEEP therapy titrated to saturate hemoglobin at a nontoxic Fio2 In the absence of clinical trials , positive end-expired pressure ( PEEP ) has been accepted as efficacious for treatment of postoperative decreases in arterial oxygen tension ( PaO2 ) from a variety of causes including adult respiratory distress syndrome ( ARDS ) . PEEP is thought to increase PaO2 by alveolar recruitment , which in turn , has been hypothesized to play a decisive role in pulmonary recovery . One hundred and eighteen patients were followed prospect ively , and after development of decreased PaO2 , r and omized to receive recruitive PEEP  ( determined by blood gas criteria )  or supportive PEEP ( the minimal PEEP required to maintain PaO2 above 60 mm Hg on .5 inspired O2 fraction ( FIO2 ) . No prognostic factors were significantly different between the two groups . Recruitive PEEP application in 22 patients yielded a significantly increased incidence of hypotension ( 55 percent ) , pneumothorax ( 20 percent ) , and death during treatment ( 27 percent ) when compared to the 28 supportive PEEP  patients who had no hypotension or pneumothorax and only one death during treatment ( 4 percent ) . After PEEP treatment , deaths in each group were similar ( 19 percent and 15 percent , respectively ) . We find no evidence that PEEP treatment promotes beneficial outcomes and conclude that recruitment attempts may be harmful Patients undergoing cardiac surgery remain on mechanical ventilation postoperatively until they regain consciousness . Positive end-expiratory pressure ( PEEP ) may influence the duration of mechanical ventilation after coronary artery bypass grafting ( CABG ) . The aim of this study was to compare the effects of different levels of PEEP on the duration of  mechanical ventilation after coronary artery bypass grafting . This was a r and omized clinical trial with 136 patients undergoing CABG between January 2011 and March 2012 . We divided the patients into three groups with different levels of PEEP at the onset of mechanical ventilation : Group A , PEEP=5 cmH2O ( n=44 ) ; Group B , PEEP=8 cmH2O ( n=47 ) and Group C , PEEP=10 cmH2O ( n=45 ) .  Mechanical ventilation time was obtained from a Physical Therapy Evaluation Form . We excluded patients with chronic obstructive pulmonary disease and those requiring concomitant , emergency or off-pump surgeries . For statistical analysis , we used the Kruskal-Wallis , G and Chi-square tests , with p<0.05 considered significant . From the point of weaning from mechanical ventilation until 12 hours after intensive care unit ( ICU ) admission , we saw a statistically different duration of mechanical ventilation between groups ( p=0.029 ) . In Group A , the average mechanical ventilation time was 6.7±3.2 hours ; it was 6.8±3.3 hours in Group B and 5.1±2.9 hours in Group C. The use of higher levels of PEEP was associated with shorter duration of mechanical ventilation in postoperative CABG patients OBJECTIVE To investigate the hemodynamic and outcome effects of implementing prophylactic positive end-expiratory pressure ( PEEP ) versus zero end-expiratory pressure ( ZEEP ) in patients during the postintubation period in the emergency setting . METHODS The present study was a prospect i ve , single-centre , interventional , single-blinded r and omized trial performed in a 16-bed medical intensive care unit . The study cohort consisted of consecutive patients who urgently required intubation . During the postintubation period , patients received either 5 cmH2O PEEP or ZEEP . The primary aim was to assess the variation in mean arterial pressure ( MAP ) from baseline up to 90 min postintubation . The secondary aim was to determine the mean duration of intubation , level of MAP support after intubation and 28-day mortality . RESULTS Seventy-five consecutive patients with similar mean ( + /- SD ) baseline characteristics and preintubation MAP ( 76+/-18 mmHg in the ZEEP group and 78.5+/-23 mmHg in the PEEP group , P = Not significant [ NS ] ) were studied . The final analysis was performed in 33 patients in the ZEEP group and 30 patients in the PEEP group . Regarding outcome measures following intubation , delta MAP ( ie , the difference between the lowest MAP values from baseline ) was not differentially affected in either group ( P = NS ) ; the mean duration s of intubation were similar ( ZEEP 9.2+/-8.5 days versus PEEP 9.2+/-8.8 days , P = NS ) ; 28-day mortality was not discriminative ( ZEEP 14 of 33 , PEEP nine of 30 ; P = NS ) ; and levels of MAP support after intubation were comparable between the two groups . CONCLUSION In the present trial , there was no evidence that implementing a prophylactic PEEP of 5 cmH2O adversely affects short-term hemodynamics or outcome in medical intensive care patients during the postintubation period Background During laparoscopy , pneumoperitoneum may result in intraoperative atelectasis , which impairs normal gas exchange . This study investigated whether positive end-expiratory pressure ( PEEP ) of 5 cmH2O in pressure-controlled ventilation ( PCV ) mode can improve ventilatory and oxygenation parameters during pneumoperitoneum . Methods Thirty patients , aged 18–65 years , undergoing laparoscopic cholecystectomy were r and omly allocated to the ZEEP ( PEEP = 0 cmH2O ) or PEEP ( PEEP = 5 cmH2O ) group . PCV was started after induction of anesthesia . Apart from PEEP level , all other ventilator setting s were identical for both groups . Peak airway pressure was set at induction and reset after pneumoperitoneum to deliver tidal volume of 8 ml/kg in both groups . Hemodynamic , ventilatory , and oxygenation parameters were measured after induction of anesthesia ( T1 ) and 30 min after pneumoperitoneum ( T2 ) . Results Oxygenation index ( PaO2/FiO2 ) was significantly higher in the PEEP group than in the ZEEP group at T2 ( P = 0.031 ) . In both groups , dynamic compliance significantly decreased over 40 min from T1 to T2 . There were no significant differences in hemodynamics between the two groups during the study period . Conclusion Application of PEEP of 5 cmH2O should be considered in PCV during laparoscopic surgeries to decrease intraoperative atelectasis caused by pneumoperitoneum to improve gas exchange and oxygenation Ventilation-perfusion ( V A/Q ) distributions were evaluated in 24 patients with acute respiratory distress syndrome ( ARDS ) , during airway pressure release ventilation ( APRV ) with and without spontaneous breathing , or during pressure support ventilation ( PSV ) .  Whereas PSV provides mechanical assistance of each inspiration , APRV allows unrestricted spontaneous breathing throughout the mechanical ventilation . Patients were r and omly assigned to receive APRV and PSV with equal airway pressure limits ( Paw ) ( n = 12 ) or minute ventilation ( V E ) ( n = 12 ) . In both groups spontaneous breathing during APRV was associated with increases ( p < 0.05 ) in right ventricular end-diastolic volume , stroke volume , cardiac index ( CI ) , PaO2 , oxygen delivery , and mixed venous oxygen tension ( PvO2 ) and with reductions ( p < 0.05 ) in pulmonary vascular resistance and oxygen extraction .  PSV did not consistently improve CI and PaO2 when compared with APRV without spontaneous breathing . Improved V A/Q matching during spontaneous breathing with APRV was evidence d by decreases in intrapulmonary shunt ( equal Paw : 33 + /- 4 to 24 + /- 4 % ; equal V E : 32 + /- 4 to 25 + /- 2 % ) ( p < 0.05 ) , dead space ( equal Paw : 44 + /- 9 to 38 + /- 6 % ; equal V E : 44 + /- 9 to 38 + /- 6 % ) ( p < 0.05 ) , and the dispersions of ventilation ( equal Paw : 0.96 + /- 0.23 to 0.78 + /- 0.22 ; equal V E : 0.92 + /- 0.23 to 0.79 + /- 0.22 ) ( p < 0.05 ) , and pulmonary blood flow distribution ( equal Paw : 0.89 + /- 0.12 to 0.72 + /- 0.10 ; equal V E : 0.94 + /- 0.19 to 0.78 + /- 0.22 ) ( p < 0.05 ) . PSV did not improve V A/Q distributions when compared with APRV without spontaneous breathing . These findings indicate that uncoupling of spontaneous and mechanical ventilation during APRV improves V A/Q matching in ARDS presumably by recruiting nonventilated lung units . Apparently , mechanical assistance of each inspiration during PSV is not sufficient to counteract the V A/Q maldistribution caused by alveolar collapse in patients with ARDS 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 OBJECTIVE To explore the effect of high positive end-expiratory pressure ( PEEP ) for the treatment of neurological pulmonary edema ( NPE ) in patients undergoing mechanical ventilation  , and to look for the best mechanical ventilation strategy to improve the prognosis . METHODS A prospect i ve study was conducted , and 120 patients with NEP admitted to Department of Critical Care Medicine of the First Affiliated Hospital of Guangxi Traditional Chinese Medical University from January 2010 to August 2013 were enrolled and divided into two groups according to r and om number table ( n=60 in each group ) . The patients in two groups were given empiric treatment for the disease , and they underwent mechanical ventilation . In the normal PEEP group PEEP was 3 - 10 cmH2O ( 1 cmH2O=0.098 kPa ) , and in the high PEEP group PEEP was 11 - 30 cmH2O , and all the rest parameters were the same . Clinical indices before and 7 days after treatment , and 28-day morality rate were compared between two groups . RESULTS The 28-day morality rate in high PEEP group was obviously lower than that in the normal PEEP group [ 25.0 % ( 15/60 ) vs. 65.0 % ( 39/60 ) , χ(2)=6.465 , P=0.011 ] . The clinical signs in both groups were improved after treatment . Compared with the normal PEEP group , the clinical indices in high PEEP group were more significantly improved . There were significant differences in body temperature ( 37.4±0.5 centi grade vs. 38.5±0.6 centi grade ) , respiratory rate ( 18.3±3.1 times/min vs. 23.3±3.5 times/min ) , heart rate ( 94.7±8.5 beats/min vs. 113.5±8.0 beats/min ) , white blood cell count ( WBC : 12.5±2.1 ×10(9)/L vs. 17.1±1.7 ×10(9)/L ) , acute physiology and chronic health evaluation II ( APACHEII ) score ( 15.6±3.2 vs. 19.8±3.7 ) , Glasgow coma score ( GCS : 12.5±2.1 vs. 8.5±2.9 ) , gastrointestinal dysfunction score ( 3.9±3.0 vs. 3.6±2.4 ) , oxygenation index ( PaO2/FiO2 : 196.5±45.1 mmHg vs. 134.1±22.3 mmHg ) , serum creatinine ( SCr : 86.5±35.6 μmol/L vs. 98.5±37.7 μmol/L ) , total bilirubin ( TBil : 39.7±23.5 μmol/L vs. 41.5±16.2 μmol/L ) , C-reacting protein ( CRP : 53.7±21.4 mmol/L vs. 108.4±26.3 mmol/L ) , prothrombin time ( PT : 15.0±2.1 s vs. 20.4±2.2 s ) , activated partial thromboplastin time ( APTT : 37.3±4.9 s vs. 56.7±13.6 s ) , international normalized ratio ( INR : 2.52±0.64 vs. 4.01±0.77 ) , extra vascular lung water index ( EVLWI : 7.53±1.21 mL/kg vs. 15.85±3.41 mL/kg ) , pulmonary vascular permeability index ( PVPI : 6.07±0.89 vs. 9.47±1.26 ) , mean arterial pressure ( MAP : 87.3±10.9 mmHg vs. 98.7±13.6 mmHg ) , cardiac output ( CO : 7.15±1.42 L/min vs. 5.65±1.82 L/min ) , systemic vascular resistance index ( SVRI : 112.4±9.5 KP vs. 136.5±11.9 KP ) , and blood lactate ( 2.53±1.23 mmol/L vs. 5.81±2.17 mmol/L ) between high PEEP group and normal PEEP group ( P<0.05 or P<0.01 ) . CONCLUSIONS Prognosis can be improved in NPE patients with the use of high PEEP in mechanical ventilation Background : General anaesthesia impairs the gas exchange in the lungs , and moderate desaturation ( SaO2 86–90 % ) occurred in 50 % of anaesthetised patients in a blinded pulse oximetry study . A high FiO2 might reduce the risk of hypoxaemia , but can also promote atelectasis . We hypothesised that a moderate positive end‐expiratory pressure ( PEEP ) level of 10 cmH2O can prevent atelectasis during ventilation with an FiO2=1.0 Because atelectasis of the left lower lobe is a frequent complication of open heart surgery , we evaluated the efficacy of routine therapy with positive end-expiratory pressure ( PEEP ) to prevent this complication . Twenty-four patients were r and omly assigned to either a group receiving therapy with PEEP ( ten patients ) or to a group with no PEEP ( 14 patients ) . The two groups could not be distinguished by age , weight , the forced expiratory volume in one second ( FEV1 ) , the ratio of FEV1 over the forced vital capacity , the time on the pump , the units of blood transfused , the tidal volume , or the hours of mechanical ventilation . There was no significant roentgenographic difference between the two groups in either the degree or frequency of left lower lobe atelectasis . While the arterial-alveolar ratios tended to improve over time in those patients receiving therapy with PEEP , this improvement was not clinical ly significant . No complications were encountered with the use of PEEP . We conclude that the routine use of PEEP following open heart surgery is safe but offers no advantage over st and ard ventilatory techniques Background : Ventilator-induced lung injury has been attributed to the interaction of several factors : tidal volume ( VT ) , positive end-expiratory pressure ( PEEP ) , transpulmonary driving pressure ( difference between transpulmonary pressure at end-inspiration and end-expiration , & Dgr;P , L ) , and respiratory system plateau pressure ( Pplat , rs ) . Methods : Forty-eight Wistar rats received Escherichia coli lipopolysaccharide  intratracheally . After 24 h , animals were r and omized into combinations of VT and PEEP , yielding three different & Dgr;P , L levels : & Dgr;P , LLOW ( VT = 6 ml/kg , PEEP = 3 cm H2O ) ; & Dgr;P , LMEAN ( VT = 13 ml/kg , PEEP = 3 cm H2O or VT = 6 ml/kg , PEEP = 9.5 cm H2O ) ; and & Dgr;P , LHIGH ( VT = 22 ml/kg , PEEP = 3 cm H2O or VT = 6 ml/kg , PEEP = 11 cm H2O ) . In other groups , at low VT , PEEP was adjusted to obtain a Pplat , rs similar to that achieved with & Dgr;P , LMEAN and & Dgr;P , LHIGH at high VT . Results : At & Dgr;P , LLOW , expressions of interleukin (IL)-6 , receptor for advanced glycation end products ( RAGE ) , and amphiregulin were reduced , despite morphometric evidence of alveolar collapse . At & Dgr;P , LHIGH ( VT = 6 ml/kg and PEEP = 11 cm H2O ) , lungs were fully open and IL-6 and RAGE were reduced compared with & Dgr;P , LMEAN ( 27.4 ± 12.9 vs. 41.6 ± 14.1 and 0.6 ± 0.2 vs. 1.4 ± 0.3 , respectively ) , despite increased hyperinflation and amphiregulin expression . At & Dgr;P , LMEAN ( VT = 6 ml/kg and PEEP = 9.5 cm H2O ) , when PEEP was not high enough to keep lungs open , IL-6 , RAGE , and amphiregulin expression increased compared with & Dgr;P , LLOW ( 41.6 ± 14.1 vs. 9.0 ± 9.8 , 1.4 ± 0.3 vs. 0.6 ± 0.2 , and 6.7 ± 0.8 vs. 2.2 ± 1.0 , respectively ) . At Pplat , rs similar to that achieved with & Dgr;P , LMEAN and & Dgr;P , LHIGH , higher VT and lower PEEP reduced IL-6 and RAGE expression . Conclusion : In the acute respiratory distress syndrome model used in this experiment , two strategies minimized ventilator-induced lung injury : ( 1 ) low VT and PEEP , yielding low & Dgr;P , L and Pplat , rs ; and ( 2 ) low VT associated with a PEEP level sufficient to keep the lungs open Background : Morbidly obese patients show impaired pulmonary function during anesthesia and paralysis , partly due to formation of atelectasis . This study analyzed the effect of general anesthesia and three different ventilatory strategies to reduce the amount of atelectasis and improve respiratory function . Methods : Thirty patients ( body mass index 45 ± 4 kg/m2 ) scheduled for gastric bypass surgery  were prospect ively r and omized into three groups : ( 1 ) positive end-expiratory pressure of 10 cm H2O ( PEEP ) , ( 2 ) a recruitment maneuver with 55 cm H2O for 10 s followed by zero end-expiratory pressure , ( 3 ) a recruitment maneuver followed by PEEP . Transverse lung computerized tomography scans and blood gas analysis were recorded : awake , 5 min after induction of anesthesia and paralysis at zero end-expiratory pressure , and 5 min and 20 min after intervention . In addition , spiral computerized tomography scans were performed at two occasions in 23 of the patients . Results : After induction of anesthesia , atelectasis increased from 1 ± 0.5 % to 11 ± 6 % of total lung volume ( P < 0.0001 ) . End-expiratory lung volume decreased from 1,387 ± 581 ml to 697 ± 157 ml ( P = 0.0014 ) . A recruitment maneuver + PEEP reduced atelectasis to 3 ± 4 % ( P = 0.0002 ) , increased end-expiratory lung volume and increased Pao2/Fio2 from 266 ± 70 mmHg to 412 ± 99 mmHg ( P < 0.0001 ) . PEEP alone did not reduce the amount of atelectasis or improve oxygenation . A recruitment maneuver + zero end-expiratory pressure had a transient positive effect on respiratory function . All values are presented as mean ± SD . Conclusions : A recruitment maneuver followed by PEEP reduced atelectasis and improved oxygenation in morbidly obese patients , whereas PEEP or a recruitment maneuver alone did not OBJECTIVE To determine the effect of lung protection mechanical ventilation on respiratory function in the elderly undergoing spinal fusion . METHODS Sixty 70 - 85 year old patients , ASA class II or III , undergoing spinal fusion were r and omly assigned into 2 groups ( 30 in each group ) : a protection mechanical ventilation group ( group P ) and a conventional mechanical ventilation group ( group C ) . Low VT and low level positive end expiratory pressure ( PEEP ) mechanical ventilation were applied in group P ( VT=6mL/kg , RR=12 - 18 b/min , I : E=1:2 , PEEP=10 cmH2O , alveolar recruitment performed once every 15 min ) , while traditional ventilation was used in group C ( VT=10 - 12 mL/kg , RR=12 b/min , I : E=1:2 ) . Arterial blood sample s were taken and pH , PaO2 , PaCO2 , PaO2/FiO2 , A-aDO2 , HR , SBP , DBP and CVP were recorded before the operation ( T0 ) , 1 h after tracheal intubation ( T1 ) , tracheal extubation immediately ( T2 ) , 1 h after tracheal extubation ( T3 ) , 1 d , 2 d , and 3 d after the operation ( T4 , T5 , and T6 ) . The pulmonary complication was also examined 1 d after the operation . RESULTS At T1 , T2 , T3 , T4 and T5 , PaO2 and PaO2/FiO2 in group P were higher than those in group C , but A-aDO2 in group P was lower than that in group C. Five patients had bronchitis , 5 had hyoxemia , and 3 had atelectasis in group C , but 2 bronchitis in group P. The incidence of pulmonary complication was 43.3 % in group C and 6.6 % in group P. There was no significant difference in HR , SBP , DBP and CVP between the 2 groups . CONCLUSION Lung protection mechanical ventilation improves the arterial oxygenation and accelerates the recovery of respiratory functions in elderly patients after spinal fusion operation , with no influence on hemodynamics Ventilation-perfusion mismatch and intrapulmonary shunting are common causes of hypoxemia in respiratory failure . Less commonly , intracardiac shunting of blood from a right-to-left heart chamber may also cause hypoxemia . Several case reports [ 1 - 8 ] have described worsening of hypoxemia in critically ill patients with intracardiac shunts from the right atrium to the left atrium through a patent foramen ovale . A patent foramen ovale may be present at autopsy in 20 % to 34 % of the general population [ 9 ] , but shunting of blood from the right-to-left atrium through the patent foramen ovale is detected in only 6 % to 18 % of an otherwise healthy population [ 10 - 12 ] . Pathologic conditions that reverse the normal pressure gradient from the left to right atrium predispose persons to a right-to-left shunt through a patent foramen ovale [ 13 ] . Thus , in the setting of an increased right atrial pressure , the systemic hypoxemia of patients with acute respiratory failure may be due to intrapulmonary shunting in combination with an intracardiac shunt . Moreover , supportive therapy using intermittent positive pressure ventilation or the addition of positive end-expiratory pressure ( PEEP ) may further increase right atrial pressure [ 14 , 15 ] and actually worsen the systemic hypoxemia [ 2 , 3 ] by increasing the intracardiac right-to-left shunt . In this study , we tested patients with acute respiratory failure for the presence of a patent foramen ovale using saline contrast transesophageal echocardiography .  All patients were receiving mechanical ventilation , and we compared systemic oxygenation and right-to-left shunt fraction in each patient with and without PEEP . Because PEEP may worsen systemic oxygenation through depression of cardiac output [ 16 , 17 ] , we concurrently measured mixed venous oxygen saturation levels and obtained estimated cardiac output [ 18 ] . We report the effects of PEEP in mechanically ventilated patients with a patent foramen ovale and compare them with similar patients without a patent foramen ovale . Methods Patients The study was approved by the University of Saskatchewan Ethics Committee on Human Experimentation . Informed consent from the patient or family was obtained . Hemodynamically stable patients in acute respiratory failure who required mechanical ventilation with an inspired oxygen concentration of 50 % or more and a PEEP of 5 cm of H2O or more were considered eligible for the study . Between October 1991 and September 1992 , 46 patients were entered into the study ; they were selected from 940 of the total admissions to a combined medical-surgical intensive care unit of a university teaching hospital . Specific causes of respiratory failure and clinical ly significant chest radiographic findings are listed in Table 1 . We collected demographic data that included age , sex , weight , medical diagnosis , and Apache II score [ 19 ] . Table 1 . Characteristics of Patients with and without Patent Foramen Ovale Baseline Hemodynamics and Gas Exchange Patients were hemodynamically stable for at least 1 hour before starting the study . We then obtained baseline measurements of central venous pressure and mean systemic arterial pressure in all patients and , in the 23 patients with a pulmonary artery catheter ( Model 93A-1317F ; Baxter-Edwards , Santa Ana , California ) , we also measured pulmonary artery systolic pressure , pulmonary artery diastolic pressure , pulmonary capillary wedge pressure , and cardiac output in triplicate using thermodilution ( Merlin Monitor , model 565 ; Hewlett Packard , Boston , Massachusetts ) . Arterial and mixed venous blood sample s were collected , and we measured the respective blood gas tensions ( corrected for temperature ) [ 20 ] using appropriately calibrated electrodes ( Nova Biomedical # 75SP1070 , Waltham , Massachusetts ) as well as the respective oxyhemoglobin saturation levels using co-oximetry ( OSM-2 Co-oximeter ; Radiograph , Copenhagen , Denmark ) . Experimental Protocol A transesophageal ultrasound transducer ( biplane 5 mHz phased-array transducer ; Aloka 870 , Tokyo , Japan ) was inserted into the esophagus after premedication ( if necessary ) using 2 to 5 mg of midazolam ( Hoffman-LaRoche , Mississauga , Ontario ) intravenously and 2 % lidocaine topical spray . The inspired oxygen concentration was increased to 100 % and the level of the PEEP was r and omized to 0 cm of H2O or 10 cm of H2O . After waiting 15 minutes , all baseline measurements were repeated . St and ard transesophageal images were obtained [ 21 ] . Left ventricular internal dimensions and area during systole and diastole were obtained from the transgastric short-axis view [ 22 ] . The right ventricular internal dimension was measured during diastole from the four-chamber view at the tricuspid chordal level . Atrial septal motion was assessed in the four-chamber view . Loss of phasic motion with sustained convexity toward the left atrium or the right atrium was described as deviation into the left atrium or the right atrium , respectively [ 23 ] . Regurgitation of the tricuspid , mitral , and aortic valves was assessed using color flow imaging . Agitated saline contrast [ 13 ] was injected rapidly into the right atrium through the central line or proximal port of the pulmonary artery catheter for detection of patent foramen ovale . Transesophageal images were obtained in either the four-chamber view or the long-axis ascending aorta-atrial septal view [ 21 ] during the injection of saline contrast . Each saline injection was repeated no less than three times and was determined to be adequate if the right atrium was entirely opacified with microbubbles . A patent foramen ovale was diagnosed if , on any injection , three or more bubbles were visualized in the left atrium within three cardiac cycles from the time of complete opacification of the right atrium [ 13 , 23 , 24 ] . Semiquantification of the right-to-left intracardiac shunt was done using the following criteria : 1 ) a small shunt was less than 5 microbubbles in the left atrium on any frozen frame ; 2 ) a moderate shunt was 5 to 20 microbubbles in the left atrium on any frozen frame ; 3 ) a severe shunt was more than 20 microbubbles or more than 50 % of the left atrium was opacified on any frozen frame . All agitated saline injections were assessed by two experienced observers , and injections were repeated until agreement was reached on the interpretation of the study . After these measurements , the alternate level of PEEP was set , and all hemodynamic , blood gas , and echocardiographic measurements were repeated ( for example , those patients initially studied using a PEEP of 10 cm of H2O were switched to 0 cm of H2O and those studied using a PEEP of 0 cm of H2O were switched to 10 cm of H2O ) . Calculations The total right-to-left shunt fraction ( Qs/Qt ) was calculated using the shunt equation Qs/Qt = ( CcO 2 CaO 2)/ ( CcO 2 CvO 2 ) where CaO2 ( arterial oxygen content ) and CvO2 ( mixed venous oxygen content ) were calculated from the directly measured hemoglobin and blood oxyhemoglobin saturation levels [ 25 ] . The end-capillary oxygen content ( CcO2 ) and the alveolar-to-arterial difference for oxygen were calculated using the alveolar gas equation . The left ventricular fractional area change was defined as the left ventricular area during diastole minus the left ventricular area during systole divided by the left ventricular area during diastole [ 22 ] . The stroke volume was calculated using left ventricular volumes obtained by the Teichholz method [ 18 , 26 ] as follows : stroke volume = ( 7/[2.4 + diastolic dimension ] x diastolic dimension3 ) minus ( 7/[2.4 + systolic dimension ] x systolic dimension3 ) . The cardiac index was then calculated by multiplying the stroke volume by the heart rate and dividing by the body surface area . Statistics Hemodynamic , gas exchange , and echocardiographic data between patients were compared by paired t-tests . These data were also compared between groups by unpaired t-tests . Percentages in different groups were compared using a chi-square test with Yates correction or the Fisher exact test . Linear regression was calculated using the method of least squares . Statistical significance was defined as P < 0.05 [ 27 ] . Measurements are expressed as mean st and ard deviation . Results Demographic and Baseline Characteristics Forty-six patients were recruited and 7 ( 15 % ) were found to have a patent foramen ovale by saline contrast transesophageal echocardiography .  No statistical differences were noted between the 39 patients without a patent foramen ovale and the 7 patients with a patent foramen ovale in terms of age ( 58 19 years compared with 65 11 years ) , sex ( 12 women ; 27 men compared with 3 women ; 4 men ) , days to study after onset of respiratory failure ( 2.3 2.9 days compared with 1.6 1.1 days ) , and Apache II score ( 20 5 compared with 20 7 ) . Before insertion of the ultrasound transducer , no differences were noted between patients without or with a patent foramen ovale in terms of inspired oxygen concentration ( 61 % 11 % compared with 60 % 10 % ) , PEEP ( 7.1 2.8 cm of H2O compared with 6.8 2.4 cm H2O ) , pH ( 7.42 0.07 compared with 7.40 0.07 ) , Pco 2 ( 24 7 mm Hg compared with 36 7 mm Hg ) , Po 2 ( 86 25 mm Hg compared with 74 16 mm Hg ) , the alveolar-to-arterial difference for oxygen ( 275 81 mm Hg compared with 281 66 mm Hg ) , the mean systemic blood pressure ( 81 13 mm Hg compared with 74 16 mm Hg ) , central venous pressure ( 12 6 mm Hg compared with 9 6 mm Hg ) , and diffuse chest radiographic findings ( 31 of 39 compared with 5 of 7 patients , P > 0.2 ) or regional chest radiographic findings ( 8 of 39 compared with 2 of 7 patients , P > 0.2 ) . Other Cardiac Diseases Left ventricular systolic function was assessed by a visual estimate of the left ventricular ejection fraction ( LVEF ) . Of the 7 patients with patent foramen ovale , 5 ( 71 % ) patients had normal left ventricular systolic function ( LVEF > 60 % ) , 1 ( 14 % ) patient had mild systolic dysfunction ( LVEF between 40 % and 60 % ) , and 1 ( 14 % ) patient had moderate-severe left ventricular dysfunction ( LVEF < 40 % ) . No patient Background : It is unclear whether positive end‐expiratory pressure ( PEEP ) is needed to maintain the improved oxygenation and lung volume achieved after a lung recruitment maneuver in patients ventilated after cardiac surgery performed in the cardiopulmonary bypass ( CPB ) Previous studies have suggested that the early application of positive end-expiratory pressure ( PEEP ) reduces the incidence of the adult respiratory-distress syndrome . We r and omly assigned 92 patients with a known risk for this syndrome to receive mechanical ventilation either without PEEP ( control ) or with early PEEP at 8 cm H2O . These therapies continued for 72 hours unless respiratory distress developed or arterial oxygen tension was above 140 ( fractional inspired oxygen concentration , 0.5 ) at 24 hours or later and remained at that level after removal of PEEP . The study was design ed to have an 80 per cent probability of detecting a 60 per cent reduction in the incidence of the syndrome . The treatment groups were comparable in age , severity of injury , number and type of risk factors for adult respiratory-distress syndrome , and initial oxygenation . The syndrome developed in 11 of 44 patients given early PEEP  ( 25 per cent ) and in 13 of 48 control patients ( 27 per cent ) . The incidence of atelectasis , pneumonia , and barotrauma was the same in both groups , as was mortality . We found that the early application of PEEP at 8 cm H2O in high-risk patients had no effect on the incidence of the adult respiratory-distress syndrome or other , associated complications Background and objective : Positive end‐expiratory pressure ( PEEP ) may affect hepato‐splanchnic blood flow . We studied whether a PEEP of 10 mbar may negatively influence flow‐dependent liver function ( indocyanine green plasma disappearance rate , ICG‐PDR ) and splanchnic microcirculation as estimated by gastric mucosal PCO2 ( PRCO2 ) . Methods : In a r and omized , controlled clinical study , we enrolled 28 patients after elective cardiac surgery using cardiopulmonary bypass .  In 14 patients ( 13 male , 1 female ; age 48–74 , mean 63 ± 7 yr ) we assessed ICG‐PDR and PRCO2 on intensive care unit admission with PEEP 5 mbar , after 2 h with PEEP of 10 mbar and again after 2 h at PEEP 5 mbar . Inspiratory peak pressure was adjusted to maintain normocapnia . Fourteen other patients ( 8 male , 6 female ; age 46–86 , mean 68 ± 11 yr ) in whom PEEP was 5 mbar throughout served as controls . All patients underwent haemodynamic monitoring by measurement of central venous pressure , left atrial pressure and cardiac index using pulmonary artery thermodilution . Results : While doses of vasoactive drugs and cardiac filling pressures did not change significantly , cardiac index slightly increased in both groups . ICG‐PDR remained unchanged either within or between both groups ( PEEP10 group : 24.0 ± 6.9 , 22.0 ± 7.9 and 25.5 ± 7.7 % min−1 vs. controls : 22.0 ± 7.5 , 23.8 ± 8.4 and 21.4 ± 6.5 % min−1 ) ( P = 0.05 ) . The difference between PRCO2 and end‐tidal PCO2 ( PCO2‐gap ) did not change significantly ( PEEP10 group : 1.1 ± 0.9 , 1.3 ± 0.7 and 1.3 ± 0.9 kPa vs. controls : 0.8 ± 0.5 , 0.9 ± 0.5 and 0.9 ± 0.5 kPa ) . Conclusion : A PEEP of 10 mbar for 2 h does not compromise liver function and gastric mucosal perfusion in patients after cardiac surgery with maintained cardiac output To determine whether the application of positive end-expiratory pressure ( PEEP ) in the postoperative period after cardiac operation would reduce postoperative blood loss , the number of transfusions required , or the rate of reoperation for bleeding , we conducted a prospect i ve study of 83 patients who underwent elective coronary revascularization . These patients were r and omly assigned to receive either PEEP ( 10 cm H2O ) or no PEEP ( zero end-expiratory pressure ) . All other aspects of their care were identical . There was no statistically significant reduction in the amount of bleeding in patients treated with PEEP at 8 or 24 hours postoperatively . There was no significant difference in hematocrit between the groups preoperatively or postoperatively . There was no statistically significant difference in the number of reexplorations for bleeding . Finally , there was no significant difference between the groups in the amount of blood administered . On the basis of our results , we conclude that the application of PEEP in the postoperative period of cardiac operation did not reduce the amount of blood loss , the need for reexploration for bleeding , or the blood requirements in this group of patients The efficacy of mechanical ventilation with positive end-expiratory pressure ( PEEP ) in the therapy of excessive mediastinal hemorrhage following cardiac operations remains unproved . One hundred thirty-nine patients undergoing elective myocardial revascularization were divided into two groups on the basis of preoperative hematologic evaluation : Group I , 94 patients with no history of hematologic abnormalities and a normal coagulation profile ; Group II , 45 patients with a recent use of antiplatelet medications and /or a prolonged template bleeding time . Both groups were r and omized to receive mechanical ventilation with 10 cm H2O of PEEP or no PEEP beginning 1 hour after operation and continuing for an 8 hour study period . Mean blood loss at 8 hours ( BVt ) was not significantly different between PEEP and control patients in either group . Fifty-seven patients in Groups I and II had mediastinal bleeding in excess of 180 ml/hr at the initiation of the study period . There was no significant difference in mean BVt or mean hourly chest tube output with or without PEEP in either group of this subset . In view of the lack of demonstrable efficacy in decreasing mediastinal hemorrhage and the potential of adverse hemodynamic effects , PEEP should no longer be used for therapy of excessive bleeding after cardiac operation , especially in patients with reduced cardiac reserve BACKGROUND : “ Optimal ” positive end-expiratory pressure ( PEEP ) can be defined as the PEEP that prevents recollapse after a recruitment maneuver , avoids over-distension , and , consequently , leads to optimal lung mechanics at minimal dead space ventilation . In this study , we analyzed the effects of PEEP and recruitment on functional residual capacity ( FRC ) , compliance , arterial oxygen partial pressure ( Pao2 ) and dead space fraction , and we determined the most suitable variables indicating optimal PEEP . METHODS : We studied 20 anesthetized patients with healthy lungs undergoing faciomaxillary surgery .  After a stepwise increase of PEEP/inspiratory pressures ( 0/10 , 5/15 , 10/20 , 15/25 cm H2O , each level lasting for 20 min ) using a pressure-controlled ventilation mode , a recruitment maneuver ( at 20/45 cm H2O for a maximum of 20 min ) was performed , followed by a stepwise pressure reduction ( 15/25 , 10/20 , 5/15 , 0/10 cm H2O , with 20 min at each level ) . At each pressure level , FRC , compliance , Pao2 , and dead space fraction were measured . RESULTS : When comparing the values before and after recruitment at identical PEEP levels , all variables showed significant changes at 10/20 cm H2O ; compliance was also significantly higher at the pressure step 15/25 cm H2O . In addition , FRC values showed significant differences at 5/15 cm H2O and 15/25 cm H2O . CONCLUSIONS : All variables showed the positive effects of PEEP in conjunction with a recruitment maneuver . Optimal PEEP was 10 cm H2O because at this pressure level the highest compliance value in conjunction with the lowest dead space fraction indicated a maximum amount of effectively exp and ed alveoli . FRC and Pao2 were insensitive to alveolar over-distension
Background The aim of this investigation was to compare ventilation at different levels of positive end-expiratory pressure ( PEEP ) with regard to clinical important outcomes of intensive care unit ( ICU ) patients without acute respiratory distress syndrome ( ARDS ) at onset of ventilation .