Incidence of and risk factors for pulmonary complications after nonthoracic surgery. Intraoperative Ventilatory Strategies for Prevention of Pulmonary Atelectasis in Obese Patients Undergoing Laparoscopic Bariatric Surgery Prevention of Atelectasis Formation During the Induction of General Anesthesia in Morbidly Obese Patients Positive end-expiratory pressure setting in adults with acute lung injury and acute respiratory distress syndrome: a randomized controlled trial. Mechanical Ventilation with Lower Tidal Volumes and Positive End-expiratory Pressure Prevents Pulmonary Inflammation in Patients without Preexisting Lung Injury Prevention of Atelectasis Formation During Induction of General Anesthesia Effects of Mechanical Ventilation on Release of Cytokines into Systemic Circulation in Patients with Normal Pulmonary Function Positive End-Expiratory Pressure During Induction of General Anesthesia Increases Duration of Nonhypoxic Apnea in Morbidly Obese Patients Clonidine produces a dose-dependent impairment of baroreflex-mediated thermoregulatory responses to positive end-expiratory pressure in anaesthetized humans. The Effects of Different Ventilatory Settings on Pulmonary and Systemic Inflammatory Responses During Major Surgery A high positive end-expiratory pressure, low tidal volume ventilatory strategy improves outcome in persistent acute respiratory distress syndrome: A randomized, controlled trial* Positive-end expiratory pressure reduces incidence of ventilator-associated pneumonia in nonhypoxemic patients* Effect of Pre-emptive Alveolar Recruitment Strategy before Pneumoperitoneum on Arterial Oxygenation during Laparoscopic Hysterectomy Monitoring dead space during recruitment and PEEP titration in an experimental model 'Alveolar recruitment strategy' improves arterial oxygenation during general anaesthesia. Airway pressure release ventilation. Effects of four intraoperative ventilatory strategies on respiratory compliance and gas exchange during laparoscopic gastric banding in obese patients. Tidal hyperinflation during low tidal volume ventilation in acute respiratory distress syndrome. Both lung recruitment maneuver and PEEP are needed to increase oxygenation and lung volume after cardiac surgery Higher versus lower positive end-expiratory pressures in patients with the acute respiratory distress syndrome. Alveolar recruitment improves ventilatory efficiency of the lungs during anesthesia Positive end‐expiratory pressure prevents atelectasisduring general anaesthesia even in the presence of a high inspired oxygen concentration Prevention of Atelectasis in Morbidly Obese Patients during General Anesthesia and Paralysis: A Computerized Tomography Study The Effect of Intraoperative Ventilation Strategies on Perioperative Atelectasis The Effect of an Alveolar Recruitment Strategy on Oxygenation during Laparascopic Cholecystectomy Positive end‐expiratory pressure improves arterial oxygenation during prolonged pneumoperitoneum Effects of lung recruitment maneuver and positiveend‐expiratory pressure on lung volume, respiratory mechanics and alveolar gas mixing in patients ventilated after cardiac surgery Optimizing peroperative compliance with PEEP during upper abdominal surgery: effects on perioperative oxygenation and complications in patients without preoperative cardiopulmonary dysfunction The Effects of Body Mass on Lung Volumes, Respiratory Mechanics, and Gas Exchange During General Anesthesia Beneficial effects of high positive end‐expiratory pressure in lung respiratory mechanics during laparoscopic surgery Mechanical Ventilation with Lower Tidal Volumes and Positive End-expiratory Pressure Prevents Alveolar Coagulation in Patients without Lung Injury Compliance and Dead Space Fraction Indicate an Optimal Level of Positive End-Expiratory Pressure After Recruitment in Anesthetized Patients
The prediction of postoperative pulmonary complications is an underinvestigated field . We conducted a prospect i ve cohort study ( with postoperative pulmonary complications ascertained by an investigator blinded to perioperative variables ) to determine the risk factors for pulmonary complications after elective nonthoracic surgery . Of 1,055 consecutive patients attending the Pre-Admission Clinic of a university hospital ( mean age 55 years , 50 % men , 15 % with history of obstructive airways disease ) , 28 ( 2.7 % ) suffered a postoperative pulmonary complication within 7 days of surgery : 13 patients developed respiratory failure requiring ventilatory support , 9 pneumonia , 5 atelectasis requiring bronchoscopic intervention , and 1 pneumothorax requiring intervention . Mean lengths of stay were substantially prolonged for those patients who developed pulmonary complications within 7 days of surgery : 27.9 days versus 4.5 days , p = 0.006 . Eight variables were statistically significantly associated with pulmonary complications on bivariate analyses . Multivariate analyses revealed that four were independently associated with increased risk of pulmonary complications : age ( odds ratio [ OR ] 5.9 for age > /= 65 years , p < 0.001 ) , positive cough test ( OR 3.8 , P = 0.01 ) , perioperative nasogastric tube ( OR 7.7 , p < 0.001 ) , and duration of anesthesia ( OR 3.3 for operations lasting at least 2.5 hours , p = 0.008 ) . Thus , several perioperative factors predict an increased risk for pulmonary complications after elective nonthoracic surgery BACKGROUND : Atelectasis occurs regularly after induction of general anesthesia , persists postoperatively , and may contribute to significant postoperative morbidity and additional health care costs . Laparoscopic surgery has been reported to be associated with an increased incidence of postoperative atelectasis . It has been shown that during general anesthesia , obese patients have a greater risk of atelectasis than nonobese patients . Preventing atelectasis is important for all patients but is especially important when caring for obese patients . METHODS : We r and omly allocated 66 adult obese patients with a body mass index between 30 and 50 kg/m2 scheduled to undergo laparoscopic bariatric surgery  into 3 groups . According to the recruitment maneuver used , the zero end-expiratory pressure ( ZEEP ) group ( n = 22 ) received the vital capacity maneuver ( VCM ) maintained for 7–8 s applied immediately after intubation plus ZEEP ; the positive end-expiratory pressure ( PEEP ) 5 group ( n = 22 ) received the VCM maintained for 7–8 s applied immediately after intubation plus 5 cm H2O of PEEP ; and the PEEP 10 group ( n = 22 ) received the VCM maintained for 7–8 s applied immediately after intubation plus 10 cm H2O of PEEP . All other variables ( e.g. , anesthetic and surgical techniques ) were the same for all patients . Heart rate , noninvasive mean arterial blood pressure , arterial oxygen saturation , and alveolar-arterial Pao2 gradient ( A-a Pao2 ) were measured intraoperatively and postoperatively in the postanesthesia care unit ( PACU ) . Length of stay in the PACU and the use of a nonrebreathing O2 mask ( 100 % Fio2 ) or reintubation were also recorded . A computed tomographic scan of the chest was performed preoperatively and postoperatively after discharge from the PACU to evaluate lung atelectasis . RESULTS : Patients in the PEEP 10 group had better oxygenation both intraoperatively and postoperatively in the PACU , lower atelectasis score on chest computed tomographic scan , and less postoperative pulmonary complications than the ZEEP and PEEP 5 groups . There was no evidence of barotrauma in any patient in the 3 study groups . CONCLUSIONS : Intraoperative alveolar recruitment with a VCM followed by PEEP 10 cm H2O is effective at preventing lung atelectasis and is associated with better oxygenation , shorter PACU stay , and fewer pulmonary complications in the postoperative period in obese patients undergoing laparoscopic bariatric surgery Atelectasis caused by general anesthesia is increased in morbidly obese patients . We have shown that application of positive end-expiratory pressure ( PEEP ) during the induction of anesthesia prevents atelectasis formation in nonobese patients . We therefore studied the efficacy of PEEP in morbidly obese patients to prevent atelectasis .  Twenty-three adult morbidly obese patients ( body mass index > 35 kg/m2 ) were r and omly assigned to one of two groups . In the PEEP group , patients breathed 100 % oxygen ( 5 min ) with a continuous positive airway pressure of 10 cm H2O and , after the induction , mechanical ventilation via a face mask with a PEEP of 10 cm H2O . In the control group , the same induction was applied but without continuous positive airway pressure or PEEP .  Atelectasis , determined by computed tomography , and blood gas analysis were measured twice : before the induction and directly after intubation . After endotracheal intubation , patients of the control group showed an increase in the amount of atelectasis , which was much larger than in the PEEP group ( 10.4 % ± 4.8 % in control group versus 1.7 % ± 1.3 % in PEEP group ; P<0.001 ) . After intubation with a fraction of inspired oxygen of 1.0 , Pao2 was significantly higher in the PEEP group compared with the control group ( 457 ± 130 mm Hg versus 315 ± 100 mm Hg , respectively ; P = 0.035 ) We conclude that in morbidly obese patients  , atelectasis formation is largely prevented by PEEP applied during the anesthetic induction and is associated with a better oxygenation CONTEXT The need for lung protection is universally accepted , but the optimal level of positive end-expiratory pressure ( PEEP ) in patients with acute lung injury ( ALI ) or acute respiratory distress syndrome remains debated . OBJECTIVE To compare the effect on outcome of a strategy for setting PEEP aim ed at increasing alveolar recruitment while limiting hyperinflation to one aim ed at minimizing alveolar distension in patients with ALI . DESIGN , SETTING , AND PATIENTS A multicenter r and omized controlled trial of 767 adults ( mean [ SD ] age , 59.9 [ 15.4 ] years ) with ALI conducted in 37 intensive care units in France from September 2002 to December 2005 . INTERVENTION Tidal volume was set at 6 mL/kg of predicted body weight in both strategies . Patients were r and omly assigned to a moderate PEEP strategy ( 5 - 9 cm H(2)O ) ( minimal distension strategy ; n = 382 ) or to a level of PEEP set to reach a plateau pressure of 28 to 30 cm H(2)O ( increased recruitment strategy ; n = 385 ) . MAIN OUTCOME MEASURES The primary end point was mortality at 28 days . Secondary end points were hospital mortality at 60 days , ventilator-free days , and organ failure-free days at 28 days . RESULTS The 28-day mortality rate in the minimal distension group was 31.2 % ( n = 119 ) vs 27.8 % ( n = 107 ) in the increased recruitment group ( relative risk , 1.12 [ 95 % confidence interval , 0.90 - 1.40 ] ; P = .31 ) . The hospital mortality rate in the minimal distension group was 39.0 % ( n = 149 ) vs 35.4 % ( n = 136 ) in the increased recruitment group ( relative risk , 1.10 [ 95 % confidence interval , 0.92 - 1.32 ] ; P = .30 ) . The increased recruitment group compared with the minimal distension group had a higher median number of ventilator-free days ( 7 [ interquartile range { IQR } , 0 - 19 ] vs 3 [ IQR , 0 - 17 ] ; P = .04 ) and organ failure-free days ( 6 [ IQR , 0 - 18 ] vs 2 [ IQR , 0 - 16 ] ; P = .04 ) . This strategy also was associated with higher compliance values , better oxygenation , less use of adjunctive therapies , and larger fluid requirements . CONCLUSIONS A strategy for setting PEEP aim ed at increasing alveolar recruitment while limiting hyperinflation did not significantly reduce mortality . However , it did improve lung function and reduced the duration of mechanical ventilation and the duration of organ failure . TRIAL REGISTRATION clinical trials.gov Identifier : NCT00188058 Background : Mechanical ventilation with high tidal volumes aggravates lung injury in patients with acute lung injury or acute respiratory distress syndrome . The authors sought to determine the effects of short-term mechanical ventilation on local inflammatory responses in patients without preexisting lung injury . Methods : Patients scheduled to undergo an elective surgical procedure ( lasting ≥5 h ) were r and omly assigned to mechanical ventilation with either higher tidal volumes of 12 ml/kg ideal body weight and no positive end-expiratory pressure ( PEEP ) or lower tidal volumes of 6 ml/kg and 10 cm H2O PEEP . After induction of anesthesia and 5 h thereafter , bronchoalveolar lavage fluid and /or blood was investigated for polymorphonuclear cell influx , changes in levels of inflammatory markers , and nucleosomes . Results : Mechanical ventilation with lower tidal volumes and PEEP ( n = 21 ) attenuated the increase of pulmonary levels of interleukin (IL)-8 , myeloperoxidase , and elastase as seen with higher tidal volumes and no PEEP ( n = 19 ) . Only for myeloperoxidase , a difference was found between the two ventilation strategies after 5 h of mechanical ventilation ( P < 0.01 ) . Levels of tumor necrosis factor α , IL-1α , IL-1β , IL-6 , macrophage inflammatory protein 1α , and macrophage inflammatory protein 1β in the bronchoalveolar lavage fluid were not affected by mechanical ventilation . Plasma levels of IL-6 and IL-8 increased with mechanical ventilation , but there were no differences between the two ventilation groups . Conclusion : The use of lower tidal volumes and PEEP may limit pulmonary inflammation in mechanically ventilated patients without preexisting lung injury . The specific contribution of both lower tidal volumes and PEEP on the protective effects of the lung should be further investigated General anesthesia promotes atelectasis formation , which is augmented by administration of large oxygen concentrations . We studied the efficacy of positive end-expiratory pressure ( PEEP ) application during the induction of general anesthesia ( fraction of inspired oxygen [ Fio2 ] 1.0 ) to prevent atelectasis . Sixteen adult patients were r and omly assigned to one of two groups . Both groups breathed 100 % O2 for 5 min and , after a general anesthesia induction , mechanical ventilation via a face mask with a Fio2 of 1.0 for another 5 min before endotracheal intubation . Patients in the first group ( PEEP group ) had continuous positive airway pressure ( CPAP ) ( 6 cm H2O ) and mechanical ventilation via a face mask with a PEEP of 6 cm H2O . No CPAP or PEEP was applied in the control group . Atelectasis , determined by computed radiograph tomography , and analysis of blood gases were measured twice : before the beginning of anesthesia and directly after the intubation . There was no difference between groups before the anesthesia induction . After endotracheal intubation , patients in the control group showed an increase of the mean area of atelectasis from 0.8 % ± 0.9 % to 4.1 % ± 2.0 % ( P = 0.0002 ) , whereas the patients of the PEEP group showed no change ( 0.5 % ± 0.6 % versus 0.4 % ± 0.7 % ) . After the intubation with a Fio2 of 1.0 , Pao2 was significantly higher in the PEEP group than in the control ( 591 ± 54 mm Hg versus 457 ± 99 mm Hg ; P = 0.005 ) . Atelectasis formation is prevented by application of PEEP during the anesthesia induction despite the use of large oxygen concentrations , result ing in improved oxygenation Background Mechanical ventilation with high tidal volumes ( VT ) in contrast to mechanical ventilation with low VT has been shown to increase plasma levels of proinflammatory and antiinflammatory mediators in patients with acute lung injury . The authors hypothesized that , in patients without previous lung injury , a conventional potentially injurious ventilatory strategy with high VT and zero end-expiratory pressure ( ZEEP ) will not cause a cytokine release into systemic circulation . Methods A total of 39 patients with American Society of Anesthesiologists physical status I – II and without signs of systemic infection scheduled for elective surgery with general anesthesia were r and omized to receive mechanical ventilation with either ( 1 ) VT = 15 ml/kg ideal body weight on ZEEP , ( 2 ) VT = 6 ml/kg ideal body weight on ZEEP , or ( 3 ) VT = 6 ml/kg ideal body weight on positive end-expiratory pressure of 10 cm H2O .  Plasma levels of proinflammatory and antiinflammatory mediators tumor necrosis factor , interleukin (IL)-6 , IL-10 , and IL-1 receptor antagonist were determined before and 1 h after the initiation of mechanical ventilation . Results Plasma levels of all cytokines remained low in all setting s. IL-6 , tumor necrosis factor , and IL-1 receptor antagonist did not change significantly after 1 h of mechanical ventilation . IL-10 was below the detection limit ( 10 pg/ml ) in 35 of 39 patients . There were no differences between groups . Conclusions Initiation of mechanical ventilation for 1 h in patients without previous lung injury caused no consistent changes in plasma levels of studied mediators . Mechanical ventilation with high VT on ZEEP did not result in higher cytokine levels compared with lung-protective ventilatory strategies . Previous lunge damage seems to be m and atory to cause an increase in plasma cytokines after 1 h of high VT mechanical ventilation Positive end-expiratory pressure ( PEEP ) applied during induction of anesthesia prevents atelectasis formation and increases the duration of nonhypoxic apnea in nonobese patients . PEEP also prevents atelectasis formation in morbidly obese patients . Because morbidly obese patients have difficult airway management more often and because arterial desaturation develops rapidly , we studied the clinical benefit of PEEP applied during anesthesia induction . Thirty morbidly obese patients were r and omly allocated to one of two groups . In the PEEP group , patients breathed 100 % O2 through a continuous positive airway pressure device ( 10 cm H2O ) for 5 min . After induction of anesthesia , they were mechanically ventilated with PEEP ( 10 cm H2O ) for another 5 min until tracheal intubation . In the control group , the sequence was the same but without any continuous positive airway pressure or PEEP . We measured apnea duration until Spo2 reached 90 % and we performed arterial blood gases analyses just before apnea and at 92 % Spo2 . Nonhypoxic apnea duration was longer in the PEEP group compared with the control group ( 188 ± 46 versus 127 ± 43 s ; P = 0.002 ) . Pao2 was higher before apnea in the PEEP group ( P = 0.038 ) . Application of positive airway pressure during induction of general anesthesia in morbidly obese patients  increases nonhypoxic apnea duration by 50 % BACKGROUND Perioperative hypothermia is common and results from anaesthesia-induced inhibition of thermoregulatory control . Hypothermia is blunted by baroreceptor unloading caused by positive end-expiratory pressure ( PEEP ) , and is mediated by an increase in the vasoconstriction threshold . Premedication with clonidine impairs normal thermoregulatory control . We therefore determined the effect of clonidine on PEEP-induced hypothermia protection . METHODS Core temperature was evaluated in patients undergoing combined general and epidural anaesthesia for lower abdominal surgery . They were assigned to an end-expiratory pressure of zero ( ZEEP ) or 10 cm H(2)O PEEP . The PEEP group was divided into three blinded subgroups that received placebo ( Cl-0 ) , clonidine 150 microg ( Cl-150 ) and clonidine 300 microg ( Cl-300 ) respectively . Placebo or clonidine was given orally 30 min before surgery . We evaluated core temperature and thermoregulatory vasoconstriction . We also determined plasma epinephrine , norepinephrine , angiotensin II concentrations and plasma renin activity . RESULTS Core temperature after 180 min of anaesthesia was 35.1 ( 0.4 ) degrees C in the ZEEP group . PEEP significantly increased final core temperature to 35.8 ( 0.5 ) degrees C ( Cl-0 group ) . Clonidine produced a linear , dose-dependent impairment of PEEP-induced hypothermia protection : final core temperatures were 35.4 ( 0.3 ) degrees C in the Cl-150 group and 35.0 ( 0.6 ) degrees C in the Cl-300 group . Similarly , clonidine produced a linear and dose-dependent reduction in vasoconstriction threshold : Cl-0 , 36.4 ( 0.3 ) degrees C ; Cl-150 , 35.8 ( 0.3 ) degrees C ; Cl-300 , 35.4 ( 0.6 ) degrees C. Plasma norepinephrine , angiotensin II concentrations and renin activity were consistent with the thermoregulatory responses . CONCLUSION Baroreceptor unloading by PEEP normally moderates perioperative hypothermia . However , clonidine premedication produces a linear , dose-dependent reduction in this benefit Mechanical ventilation with high tidal volumes ( VT ) and zero or low positive end-expiratory pressure increased mediator release to inflammatory stimuli or acute lung injury . We studied whether mechanical ventilation modifies the inflammatory responses during major thoracic or abdominal surgery . Sixty-four patients undergoing elective thoracotomy ( n = 34 ) or laparotomy ( n = 30 ) were r and omized to receive either mechanical ventilation with VT = 12 or 15 mL/kg ideal body weight , respectively , and zero end-expiratory pressure , or VT = 6 mL/kg ideal body weight with positive end-expiratory pressure of 10 cm H2O . In 62 patients who completed the study , arterial oxygena- tion was not different between groups . Tumor necrosis factor , interleukin (IL)-1 , IL-6 , IL-8 , IL-10 , and IL-12 were determined by cytometric bead array in plasma after 0 , 1 , 2 , and 3 h and in tracheal aspirates after 3 h of mechanical ventilation . Data were log-transformed and analyzed using parametric or nonparametric tests , as indicated . All plasma mediators increased more during abdominal than during thoracic surgery , although the differences were small . However , neither time course nor concentrations of pulmonary or systemic mediators differed between the two ventilatory setting s. Our data suggest that the ventilatory setting s we studied do not affect inflammatory reactions during major surgery within 3 Objective : It has been shown in a two-center study that high positive end-expiratory pressure ( PEEP ) and low tidal volume ( LTV ) improved outcome in ARDS . However , that study involved patients with underlying diseases unique to the study area , was conducted at only two centers , and enrolled a small number of patients . We similarly hypothesized that a ventilatory strategy based on PEEP above the lower inflection point of the pressure volume curve of the respiratory system ( Pflex ) set on day 1 with a low tidal volume would result in improved outcome in patients with severe and persistent acute respiratory distress syndrome ( ARDS ) . Design : R and omized , controlled clinical trial . Setting : Network of eight Spanish multidisciplinary intensive care units ( ICUs ) under the acronym of ARIES ( Acute Respiratory Insufficiency : España Study ) . Patients : All consecutive patients admitted into participating Spanish ICUs from March 1999 to March 2001 with a diagnosis of ARDS were considered for the study . If 24 hrs after meeting ARDS criteria , the Pao2/Fio2 remained ≤200 mm Hg on st and ard ventilator setting s , patients were r and omized into two groups : control and Pflex/LTV . Interventions : In the control group , tidal volume was 9–11 mL/kg of predicted body weight ( PBW ) and PEEP ≥5 cm H2O . In the Pflex/LTV group , tidal volume was 5–8 mL/kg PBW and PEEP was set on day 1 at Pflex + 2 cm H2O . In both groups , Fio2 was set to maintain arterial oxygen saturation > 90 % and Pao2 70–100 mm Hg , and respiratory rate was adjusted to maintain Paco2 between 35 and 50 mm Hg . Measurements and Main Results : The study was stopped early based on an efficacy stopping rule as described in the methods . Of 103 patients who were enrolled ( 50 control and 53 Pflex ) , eight patients ( five in control , three in Pflex ) were excluded from the final evaluation because the r and om group assignment was not performed in one center according to protocol . Main outcome measures were ICU and hospital mortality , ventilator-free days , and nonpulmonary organ dysfunction . ICU mortality ( 24 of 45 [ 53.3 % ] vs. 16 of 50 [ 32 % ] , p = .040 ) , hospital mortality ( 25 of 45 [ 55.5 % ] vs. 17 of 50 [ 34 % ] , p = .041 )  , and ventilator-free days at day 28 ( 6.02 ± 7.95 in control and 10.90 ± 9.45 in Pflex/LTV , p = .008 ) all favored Pflex/LTV . The mean difference in the number of additional organ failures postr and omization was higher in the control group ( p < .001 ) . Conclusions : A mechanical ventilation strategy with a PEEP level set on day 1 above Pflex and a low tidal volume compared with a strategy with a higher tidal volume and relatively low PEEP has a beneficial impact on outcome in patients with severe and persistent ARDS 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 In a r and omised , controlled , single-blind trial , we examined the effect of a pre-emptive alveolar recruitment strategy on arterial oxygenation during subsequent pneumoperitoneum . After intubation , 50 patients were r and omly allocated to receive either tidal volume 10 ml/kg with no positive end-expiratory pressure ( group C ) or alveolar recruitment strategy of 10 manual breaths with peak inspiratory pressure of 40 cmH2O plus positive end-expiratory pressure of 15 cmH2O before gas insufflation ( group P ) . During pneumoperitoneum , group P was ventilated with the same setting as group C ( FiO2=0.35 , tidal volume 10 ml/kg ) . PaO2 measured during peumoperitoneum was higher in group P than in group C ( 166∓32 mmHg vs 145∓34 mmHg at 15 minutes , P=0.028 , 155∓30 mmHg vs 136∓32 mmHg at 30 minutes , P=0.035 ) . Alveolar-arterial oxygen gradient in group P increased less after gas insufflation ( 13∓9 to 60∓34 mmHg vs 10∓9 to 37∓31 mmHg , P=0.013 ) . We conclude that the alveolar recruitment strategy we applied before insufflation of the peritoneal cavity may improve oxygenation during laparoscopic hysterectomy Objective To test the usefulness of dead space for determining open-lung PEEP , the lowest PEEP that prevents lung collapse after a lung recruitment maneuver . Design Prospect i ve animal study . Setting Department of Clinical Physiology , University of Uppsala , Sweden . SubjectsEight lung-lavaged pigs . Interventions Animals were ventilated using constant flow mode with VT of 6 ml/kg , respiratory rate of 30 bpm , inspiratory-to-expiratory ratio of 1 : 2 , and FiO2 of 1 . Baseline measurements were performed at 6 cmH2O of PEEP . PEEP was increased in steps of 6 cmH2O from 6 to 24 cmH2O . Recruitment maneuver was achieved within 2 min at pressure levels of 60/30 cmH2O for Peak/PEEP . PEEP was decreased from 24 to 6 cmH2O in steps of 2 cmH2O and then to 0 cmH2O . Each PEEP step was maintained for 10 min . Measurements and results Alveolar dead space ( VDalv ) , the ratio of alveolar dead space to alveolar tidal volume ( VDalv/VTalv ) , and the arterial to end-tidal PCO2 difference ( Pa-etCO2 ) showed a good correlation with PaO2 , normally aerated areas , and non-aerated CT areas in all animals ( minimum – maximum r2 = 0.83–0.99 ; p < 0.01 ) . Lung collapse ( non-aerated tissue > 5 % ) started at 12 cmH2O PEEP ; hence , open-lung PEEP was established at 14 cmH2O . The receiver operating characteristics curve demonstrated a high specificity and sensitivity of VDalv ( 0.89 and 0.90 ) , VDalv/VTalv ( 0.82 and 1.00 ) , and Pa − etCO2 ( 0.93 and 0.95 ) for detecting lung collapse . Conclusions Monitoring of dead space was useful for detecting lung collapse and for establishing open-lung PEEP after a recruitment maneuver Abnormalities in gas exchange during general anaesthesia are caused partly by atelectasis . Inspiratory pressures of approximately 40 cm H2O are required to fully re-exp and healthy but collapsed alveoli . However , without PEEP these re-exp and ed alveoli tend to collapse again . We hypothesized that an initial increase in pressure would open collapsed alveoli ; if this inspiratory recruitment is combined with sufficient end-expiratory pressure , alveoli will remain open during general anaesthesia . We tested the effect of an ' alveolar recruitment strategy ' on arterial oxygenation and lung mechanics in a prospect i ve , controlled study of 30 ASA II or III patients aged more than 60 yr allocated to one of three groups . Group  ZEEP received no PEEP . The second group received an initial control period without PEEP , and then PEEP 5 cm H2O was applied . The third group received an increase in PEEP and tidal volumes until a PEEP of 15 cm H2O and a tidal volume of 18 ml kg-1 or a peak inspiratory pressure of 40 cm H2O was reached . PEEP 5 cm H2O was then maintained . There was a significant increase in median PaO2 values obtained at baseline ( 20.4 kPa ) and those obtained after the recruitment manoeuvre ( 24.4 kPa ) at 40 min . This latter value was also significantly higher than PaO2 measured in the PEEP ( 16.2 kPa ) and ZEEP ( 18.7 kPa ) groups . Application of PEEP also had a significant effect on oxygenation ; no such intra-group difference was observed in the ZEEP group . No complications occurred . We conclude that during general anaesthesia , the alveolar recruitment strategy was an efficient way to improve arterial oxygenation Airway pressure release ventilation ( APRV ) delivers continuous positive airway pressure ( CPAP ) and may support ventilation simultaneously . This investigation tested whether , after acute lung injury ( ALI ) , APRV promotes alveolar ventilation and arterial oxygenation without increasing airway pressure ( Paw ) above the CPAP level and without depressing cardiac function .  Ten anesthetized dogs r and omly received either intermittent positive-pressure ventilation ( IPPV ) or APRV . APRV was delivered with a continuous-flow CPAP system . Expiration occurred when a switch in the expiratory limb opened and Paw decreased to near-ambient , which decreased lung volume . After baseline data collection , ALI was induced by infusing oleic acid iv . Two hours later , IPPV and APRV were administered r and omly , and data were collected . With normal lungs , APRV and IPPV achieved similar gas exchange and hemodynamic function . During ALI , arterial oxygenation was improved , and peak Paw which did not exceed the CPAP level , was lower during APRV . Similar minute ventilations were delivered by both modes but result ed in lower PaCO2 with APRV . Thus , APRV decreased physiologic deadspace ventilation . Hemodynamic status was similar during both modes . Therefore , APRV is an improved method of oxygenation and ventilatory support for patients with ALI that will allow unrestricted spontaneous ventilation and may decrease the incidence of barotrauma BACKGROUND Respiratory function is impaired in obese patients undergoing laparoscopic surgery . This study was performed to determine whether repeated lung recruitment combined with PEEP improves respiratory compliance and arterial partial pressure of oxygen ( Pa(O2 ) ) in obese patients undergoing laparoscopic gastric b and ing . METHODS Sixty patients with BMI > 30 kg m(-2 ) were r and omized , after induction of pneumoperitoneum  , to receive either PEEP of 10 cm H2O ( Group P ) , inspiratory pressure of 40 cm H2O for 15 s once ( Group R ) , Group R recruitment followed by PEEP 10 cm H2O ( Group RP ) , or Group RP recruitment but with the inspiratory manoeuvre repeated every 10 min ( Group RRP ) . Static respiratory compliance and Pa(O2 ) were determined after intubation , 10 min after pneumoperitoneum ( before lung recruitment ) , and every 10 min thereafter ( after recruitment ) . Results are presented as mean ( SD ) . RESULTS Pneumoperitoneum decreased respiratory compliance from 48 ( 3 ) to 30 ( 1 ) ml cm H2O(-1 ) and decreased Pa(O2 ) from 12.4 ( 0.3 ) to 8.8 ( 0.3 ) kPa in all groups ( P<0.01 ) . Immediately after recruitment , compliance was 32 ( 1 ) , 32 ( 2 ) , 40 ( 2 ) , and 40 ( 1 ) ml cm H2O(-1 ) and Pa(O2 ) was 9.1 ( 0.3 ) , 9.1 ( 0.1 ) , 11.9 ( 0.1 ) , and 11.9 ( 0.1 ) kPa in Groups P , R , RP , and RRP , respectively ( P<0.01 ) . Ten and 20 min later , Pa(O2 ) in Group R decreased to 9.2 ( 0.1 ) kPa and compliance in Group PR decreased to 33 ( 2 ) ml cm H2O(-1 ) , respectively ( P<0.01 ) . CONCLUSIONS Group RRP recruitment strategy was associated with the best intraoperative respiratory compliance and Pa(O2 ) in obese patients undergoing laparoscopic gastric b and ing RATIONALE Tidal volume and plateau pressure limitation decreases mortality in acute respiratory distress syndrome .  Computed tomography demonstrated a small , normally aerated compartment on the top of poorly aerated and nonaerated compartments that may be hyperinflated by tidal inflation . OBJECTIVES We hypothesized that despite tidal volume and plateau pressure limitation , patients with a larger nonaerated compartment are exposed to tidal hyperinflation of the normally aerated compartment . MEASUREMENTS AND MAIN RESULTS Pulmonary computed tomography  at end-expiration and end-inspiration was obtained in 30 patients ventilated with a low tidal volume ( 6 ml/kg predicted body weight ) . Cluster analysis identified 20 patients in whom tidal inflation occurred largely in the normally aerated compartment ( 69.9 + /- 6.9 % ; " more protected " ) , and 10 patients in whom tidal inflation occurred largely within the hyperinflated compartments ( 63.0 + /- 12.7 % ; " less protected " ) . The nonaerated compartment was smaller and the normally aerated compartment was larger in the more protected patients than in the less protected patients ( p = 0.01 ) . Pulmonary cytokines were lower in the more protected patients than in the less protected patients ( p < 0.05 ) . Ventilator-free days were 7 + /- 8 and 1 + /- 2 d in the more protected and less protected patients , respectively ( p = 0.01 ) . Plateau pressure ranged between 25 and 26 cm H(2)O in the more protected patients and between 28 and 30 cm H(2)O in the less protected patients ( p = 0.006 ) . CONCLUSIONS Limiting tidal volume to 6 ml/kg predicted body weight and plateau pressure to 30 cm H(2)O may not be sufficient in patients characterized by a larger nonaerated compartment Background : Patients ventilated after cardiac surgery commonly have impaired oxygenation , mainly due to lung collapse . We have previously found that PaO2 and end‐expiratory lung volume ( EELV ) were increased by a lung recruitment maneuver ( LRM ) followed by positive end‐expiratory pressure ( PEEP ) . The aim of this study was to evaluate whether only PEEP or only a LRM could give similar effects BACKGROUND Most patients requiring mechanical ventilation for acute lung injury and the acute respiratory distress syndrome ( ARDS ) receive positive end-expiratory pressure ( PEEP ) of 5 to 12 cm of water . Higher PEEP levels may improve oxygenation and reduce ventilator-induced lung injury but may also cause circulatory depression and lung injury from overdistention . We conducted this trial to compare the effects of higher and lower PEEP levels on clinical outcomes in these patients . METHODS We r and omly assigned 549 patients with acute lung injury and ARDS to receive mechanical ventilation with either lower or higher PEEP levels , which were set according to different tables of predetermined combinations of PEEP and fraction of inspired oxygen . RESULTS Mean ( + /-SD ) PEEP values on days 1 through 4 were 8.3+/-3.2 cm of water in the lower-PEEP group and 13.2+/-3.5 cm of water in the higher-PEEP group ( P<0.001 ) . The rates of death before hospital discharge were 24.9 percent and 27.5 percent , respectively ( P=0.48 ; 95 percent confidence interval for the difference between groups , -10.0 to 4.7 percent ) . From day 1 to day 28 , breathing was unassisted for a mean of 14.5+/-10.4 days in the lower-PEEP group and 13.8+/-10.6 days in the higher-PEEP group ( P=0.50 ) . CONCLUSIONS These results suggest that in patients with acute lung injury and ARDS who receive mechanical ventilation with a tidal-volume goal of 6 ml per kilogram of predicted body weight and an end-inspiratory plateau-pressure limit of 30 cm of water , clinical outcomes are similar whether lower or higher PEEP levels are used Purpose The goal of this study was to analyze the effect of positive end-expiratory pressure ( PEEP ) , with and without a lung recruitment maneuver , on dead space . Methods 16 anesthetized patients were sequentially studied in three steps : 1 ) without PEEP ( ZEEP ) , 2 ) with 5 cm H2O of PEEP and 3 ) with 5 cm H2O of PEEP after an alveolar recruitment strategy ( ARS ) . Ventilation was maintained constant . The single breath test of CO2 ( SBT-CO2 ) , arterial oxygenation , end-expiratory lung volume ( EELV ) and respiratory compliance were recorded every 30 min . Results Physiological dead space to tidal volume decreased after ARS ( 0.45 ±0.01 ) compared with ZEEP ( 0.50 ± 0.07 , P < 0.05 ) and PEEP ( 0.51 ± 0.06 , P < 0.05 ) . The elimination of CO2 per breath increased during PEEP ( 25 ± 3.3 mL · min−1 ) and ARS ( 27 ± 3.2 mL · min−1 ) compared to ZEEP ( 23 ± 2.6 mL · min−1 , P < 0.05 ) , although ARS showed larger values than PEEP(P < 0.05 ) . Pa-etCO2 difference was lower after recruitment ( 0.9 ± 0.5 kPa , P < 0.05 ) compared to ZEEP ( 1.1 ± 0.5 kPa ) and PEEP ( 1.2 ± 0.5 kPa ) . Slope II increased after ARS ( 63 ± 11%/L , P < 0.05 ) compared with ZEEP ( 46 ± 7.7%/L ) and PEEP ( 56 ± 10%/L ) . Slope III decreased significantly after recruitment ( 0.13 ± 0.07 1/L ) compared with ZEEP ( 0.21 ±0.1 1/L ) and PEEP ( 0.18 ± 0.10 1/L ) . The angle between slope II and III decreased only after ARS . After lung recruitment , PaO2 , EELV , and compliance increased significantly compared with ZEEP and PEEP Conclusion Lung recruitment improved the efficiency of ventilation in anesthetized patients .RésuméObjectifAnalyser l’effet de la pression télé-expiratoire positive ( PEEP ) sur l’espace mort , avec et sans recrutement pulmonaire . MéthodeNous avons réalisé une étude séquentielle en trois étapes auprès de 16 patients anesthésiés : 1 ) sans PEEP ( ZEEP ) , 2 ) avec 5 cm H2O de PEEP et 3 ) avec 5 cm H2O de PEEP  à la suite d’une stratégie de recrutement alvéolaire ( SRA ) . La ventilation a été maintenue constante . L’épreuve de l’apnée inspiratoire du CO2 , l’oxygénation artérielle , le volume pulmonaire télé-expiratoire ( VPTE ) et la compliance respiratoire ont été enregistrées toutes les 30 min . RésultatsLe rapport espace mort/volume courant a été réduit après la SRA ( 0,45 ±0,01 ) comparée à la ZEEP ( 0,50 ± 0,07 , P < 0,05 ) et à la PEEP ( 0,51 ± 0,06 , P < 0,05 ) . Lélimination du CO2 pour chaque respiration a augmenté pendant la PEEP ( 25 ± 3,3 mL · min−1 ) et la SRA ( 21 ± 3,2 mL · min−1 ) comparées à la ZEEP ( 23 ± 2,6 mL · min−1 , P < 0,05 ) , même si la SRA a présenté des valeurs plus élevées que la PEEP ( P < 0,05 ) . La différence Pa-etCO2 a été plus faible après le recrutement ( 0,9 ± 0,5 kPa , P < 0,05 ) comparé à la ZEEP ( 1,1 ± 0,5 kPa ) et à la PEEP ( 1,2 ± 0,5 kPa ) . La pente II s’est accentuée après la SRA ( 63 ± 11 % /L , P < 0,05 ) comparée à la ZEEP ( 46 ±7,7 % /L ) et à la PEEP ( 56 ± 10 % /L ) . La pente III s’est abaissée significativement après le recrutement ( 0,13 ± 0,01 1/L ) comparé à la ZEEP ( 0,21 ±0,11 1/L ) et à la PEEP ( 0,18 ± 0,10 1/L ) . Langle entre les pentes II et III a diminué seulement après la SRA . Après le recrutement alvéolaire , comparé à la ZEEP et à la PEEP , la PaO2 , le VPTE et la compliance ont augmenté significativement . Conclusion Le recrutement alvéolaire améliore l’efficacité de la ventilation chez les patients anesthésiés 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 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 Several methods of ventilation have previously been shown to reduce intraoperative atelectasis and alveolar to arterial oxygen gradient ( A-a DO2 ) in healthy patients . This study was design ed to show firstly the relative intra-operative benefit and secondly if any method had an effect on atelectasis postoperatively . Using a factorial design we r and omized 24 patients to each of the four ventilatory interventions ( manual inflations , large tidal volumes , PEEP , and pressure control inverse ratio ventilation ( IRV ) ) . The A-a DO2 was used as the measure of atelectasis and data collected intra- and postoperatively for 24 hours . The mean pre-induction A-a DO2 was 80 mmHg . This study demonstrated that PEEP and IRV were most effective in reducing intraoperative A-a DO2 ( P<0.05 ANCOVA ) . Using more than one intervention did not improve the A-a DO2 . No method had any effect on postoperative A-a DO2 This prospect i ve r and omized controlled trial examined the effect of an “ alveolar recruitment strategy ” ( ARS ) in healthy patients having laparoscopic cholecystectomy . Twenty-four consecutive ASA 1 or 2 patients were r and omly allocated to an ARS or control group . All patients were manually ventilated to a maximal airway pressure of 25 to 30 cmH 2 O or a tidal volume of 10 ml/kg during induction of general anaesthesia . After intubation , the control group was ventilated with st and ardized mechanical ventilation setting s. The ARS group was manually ventilated to an airway pressure of 40 cmH 2 O for 10 breaths over one minute , followed by mechanical ventilation with similar st and ardized setting s plus 5 cmH 2 0 positive end-expiratory pressure . Blood pressure , heart rate , arterial oxygen and carbon dioxide tension ( PaO 2 and PaCO 2 ) was measured pre-induction , 20 minutes post induction but before abdominal insufflation , 20 minutes after abdominal insufflation , and 20 minutes after arrival in the recovery room . Demographic and operation data were similar . The ARS group pre-insufflation PaO 2 [ 30.16 ( 9.43 ) ] was higher than the control group [ 22.19 ( 9.08 ) ] ( P=0.047 ) . There was a significant difference in PaO 2 between the ARS [ 23.94 ( 4.87 ) ] and control [ 17.26 ( 3.93 ) ] groups during the post-insufflation period ( P=0.001 ) . There were no significant differences in PaO 2 between the groups during baseline and recovery periods . No adverse effects were reported . ARS  improved arterial oxygenation intraoperatively in healthy patients having laparoscopic cholecystectomy , without clinical cardiovascular compromise or respiratory complication . We conclude that this alveolar recruitment strategy is a useful method of increasing arterial oxygenation Background : Laparoscopic surgery usually requires the use of a pneumoperitoneum by insufflating gas in the peritoneal space . The gas most commonly used for insufflation is carbon dioxide . Increased intra‐abdominal pressure causes cephalad displacement of the diaphragm result ing in compressed lung areas , which leads to formation of atelectasis , especially during mechanical ventilation . The aim of this prospect i ve study was to investigate the effect of prolonged intraperitoneal gas insufflation on arterial oxygenation and hemodynamics during mechanical ventilation with and without positive end‐expiratory pressure ( PEEP ) 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 ) Background and objective Late postoperative hypoxaemia after upper abdominal surgery is common even among cardiopulmonary healthy patients . Atelectasis may develop after intubation and persist into or reveal a disposition for atelectasis in the postoperative period . Positive end-expiratory pressure ( PEEP ) eliminates peroperative atelectasis but the effect on perioperative oxygenation is controversial . This study evaluated the effect of peroperative PEEP optimized pulmonary compliance on perioperative oxygenation and complications . Methods Forty patients assessed by electrocardiography , spirometry , functional residual capacity and diffusion capacity were r and omly assigned to receive positive end-expiratory pressure ( PEEP ) or zero end-expiratory pressure ( ZEEP ) during surgery . PaO2 , SPO2 and complications in the postoperative period were evaluated without knowledge of peroperative PEEP or ZEEP application . Results Peroperative arterial oxygenation improved for all patients receiving PEEP , mean 2.1 kPa ( 0.7–3.5 kPa ) . There was no difference in postoperative median PaO2 between the groups . The differences in the incidence of late prolonged postoperative hypoxaemia and complications were 25 % ( −5 % to 55 % ) and −1 % ( −31 % to 29 % ) between the ZEEP and the PEEP group , but were not statistically significant We investigated the effects of body mass index ( BMI ) on functional residual capacity ( FRC ) , respiratory mechanics ( compliance and resistance ) , gas exchange , and the inspiratory mechanical work done per liter of ventilation during general anesthesia . We used the esophageal balloon technique , together with rapid airway occlusion during constant inspiratory flow , to partition the mechanics of the respiratory system into its pulmonary and chest wall components . FRC was measured by using the helium dilution technique . We studied 24 consecutive and unselected patients during general anesthesia , before surgical intervention , in the supine position ( 8 normal subjects with a BMI < or = to25 kg/m2 , 8 moderately obese patients with a BMI > 25 kg/m2 and < 40 kg/m2 , and 8 morbidly obese patients with a BMI > or = to40 kg/m2 ) . We found that , with increasing BMI : 1.FRC decreased exponentially ( r = 0.86 ; P < 0.01 ) 2.the compliance of the total respiratory system and of the lung decreased exponentially ( r = 0.86 ; P < 0.01 and r = 0.81 ; P < 0.01 , respectively ) , whereas the compliance of the chest wall was only minimally affected ( r = 0.45 ; P < 0.05 ) 3.the resistance of the total respiratory system and of the lung increased ( r = 0.81 ; P < 0.01 and r = 0.84 ; P < 0.01 , respectively ) , whereas the chest wall resistance was unaffected ( r = 0.06 ; P = not significant ) 4.the oxygenation index ( PaO2/PAo2 ) decreased exponentially ( r = 0.81 ; P < 0.01 ) and was correlated with FRC ( r = 0.62 ; P < 0.01 ) , whereas PaCO2 was unaffected ( r = 0.06 ; P = not significant ) 5.the work of breathing of the total respiratory system increased , mainly due to the lung component ( r = 0.88 ; P < 0.01 and r = 0.81 ; P < 0.01 , respectively ) . In conclusion , BMI is an important determinant of lung volumes , respiratory mechanics , and oxygenation during general anesthesia with patients in the supine position . Implication s : The aim of this study was to investigate the influence of body mass on lung volumes , respiratory mechanics , and gas exchange during general anesthesia . ( Anesth Analg 1998;87:654 - 60 Background : The effect of neuromuscular blockade ( NMB ) and positive end‐expiratory pressure ( PEEP ) on the elastic properties of the respiratory system during  pneumoperitoneum ( PnP )  remains a controversial subject . The main objective of the present study was to evaluate the effects of NMB and PEEP on respiratory mechanics Background : Alveolar fibrin deposition is a hallmark of acute lung injury , result ing from activation of coagulation and inhibition of fibrinolysis . Previous studies have shown that mechanical ventilation with high tidal volumes may aggravate lung injury in patients with sepsis and acute lung injury . The authors sought to determine the effects of mechanical ventilation on the alveolar hemostatic balance in patients without preexistent lung injury . Methods : Patients scheduled for an elective surgical procedure ( lasting ≥ 5 h ) were r and omly assigned to mechanical ventilation with either higher tidal volumes of 12 ml/kg ideal body weight and no positive end-expiratory pressure ( PEEP ) or lower tidal volumes of 6 ml/kg and 10 cm H2O PEEP . After induction of anesthesia and 5 h later bronchoalveolar lavage fluid and blood sample s were obtained , and markers of coagulation and fibrinolysis were measured . Results : In contrast to mechanical ventilation with lower tidal volumes and PEEP ( n = 21 ) , the use of higher tidal volumes without PEEP ( n = 19 ) caused activation of bronchoalveolar coagulation , as reflected by a marked increase in thrombin – antithrombin complexes , soluble tissue factor , and factor VIIa after 5 h of mechanical ventilation . Mechanical ventilation with higher tidal volumes without PEEP caused an increase in soluble thrombomodulin in lavage fluids and lower levels of bronchoalveolar activated protein C in comparison with lower tidal volumes and PEEP . Bronchoalveolar fibrinolytic activity did not change by either ventilation strategy . Conclusions : Mechanical ventilation with higher tidal volumes and no PEEP promotes procoagulant changes , which are largely prevented by the use of lower tidal volumes and PEEP 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 General anaesthesia causes atelectasis which can lead to impaired respiratory function .
Positive end-expiratory pressure ( PEEP ) is a mechanical manoeuvre which increases functional residual capacity ( FRC ) and prevents collapse of the airways thereby reducing atelectasis .
It is not known whether intra-operative PEEP alters the risk of postoperative mortality and pulmonary complications .
OBJECTIVES To assess the benefits and harms of intraoperative PEEP , for all adult surgical patients , on postoperative mortality and pulmonary outcomes .