***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
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    ***EXAMPLES*** 
    Input: 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 Background : Obese patients are at a high risk of postoperative complication , including surgical site infection ( SSI ) . Our aim was to evaluate the effect of a high inspiratory oxygen fraction ( 80 % ) on SSI and pulmonary complications in obese patients undergoing laparotomy . Methods : This study was a planned analysis of the obese patients ( body mass index ≥ 30 kg/m2 ) recruited in the Danish multicenter , patient- and observer-blinded , PROXI Trial of 1,400 patients undergoing acute or elective laparotomy .  Patients were r and omized to receive either 80 % or 30 % oxygen during and for 2 h after surgery . The primary outcome was SSI within 14 days . Secondary outcomes were atelectasis , pneumonia , and respiratory failure . Results : Two hundred thirteen patients had a body mass index ≥ 30 kg/m2 . The median ( 5–95 % range ) body mass index was 34 kg/m2 ( 30–44 ) and 33 kg/m2 ( 30–41 ) in patients allocated to the 80 % and 30 % oxygen group . SSI occurred in 32 of 102 ( 31 % ) versus 29 of 111 ( 26 % ) patients given 80 % and 30 % oxygen , respectively ( odds ratio , 1.29 ; 95 % CI , 0.71–2.34 ; P = 0.40 ) . In addition , the incidence of pulmonary complications was not significantly different , with atelectasis occurring in 9 % versus 6 % , pneumonia in 6 % versus 5 % , and respiratory failure in 8 % versus 5 % in patients given 80 % and 30 % oxygen , respectively . Conclusion : Administration of 80 % oxygen , compared with 30 % oxygen , did not reduce the frequency of SSI in obese patients . Moreover , no significant association was found between oxygen fraction and the risk of pulmonary complications A major cause of impaired gas exchange during general anaesthesia is atelectasis , causing pulmonary shunt . A ' vital capacity ' ( VC ) manoeuvre ( i.e. inflation of the lungs up to 40 cm H2O , maintained for 15 s ) may re-exp and atelectasis and improve oxygenation . However , such a manoeuvre may cause adverse cardiovascular effects . Reducing the time of maximal inflation may improve the margin of safety . The aim of this study was to analyse the change over time in the amount of atelectasis during a VC manoeuvre in 12 anaesthetized adults with healthy lungs .  I.v . anaesthesia with controlled mechanical ventilation ( VT 9 ( SD 1 ) ml kg-1 ) was used . For the VC manoeuvre , the lungs were inflated up to an airway pressure ( Paw ) of 40 cm H2O . This pressure was maintained for 26 s. Atelectasis was assessed by analysis of computed x-ray tomography . The amount of atelectasis , measured at the base of the lungs , was 4.0 ( SD 2.7 ) cm2 after induction of anaesthesia . The decrease in the amount of atelectasis over time during the VC manoeuvre was described by a negative exponential function with a time constant of 2.6 s. At an inspired oxygen concentration of 40 % , PaO2 increased from 17.2 ( 4.0 ) kPa before to 22.2 ( 6.0 ) kPa ( P = 0.013 ) after the VC manoeuvre . Thus in anaesthetized adults undergoing mechanical ventilation with healthy lungs , inflation of the lungs to a Paw of 40 cm H2O , maintained for 7 - 8 s only , may re-exp and all previously collapsed lung tissue , as detected by lung computed tomography , and improve oxygenation . We conclude that the previously proposed time for a VC manoeuvre may be halved in such subjects BACKGROUND This study was conducted to determine whether an alveolar recruitment strategy ( ARS ) applied during two-lung ventilation ( TLV ) just before starting one-lung ventilation ( OLV ) improves ventilatory efficiency . METHODS Subjects were r and omly allocated to two groups : ( i ) control group : ventilation with tidal volume ( VT ) of 8 or 6 ml kg(-1 ) for TLV and OLV , respectively , and ( ii )  ARS group : same ventilatory pattern with ARS consisting of 10 consecutive breaths at a plateau pressure of 40 and 20 cm H(2)O PEEP applied immediately before and after OLV . Volumetric capnography and arterial blood sample s  were recorded 5 min ( baseline ) and 20 min into TLV , at 20 and 40 min during OLV , and finally 10 min after re-establishing TLV . RESULTS Twenty subjects were included in each group . In all subjects , the airway component of dead space remained constant during the study . Compared with baseline , the alveolar dead space ratio ( VD(alv)/VT(alv ) ) increased throughout the protocol in the control but decreased in the ARS group . Differences in VD(alv)/VT(alv ) between groups were significant ( P<0.001 ) . Except for baseline , all values in kPa ( sd ) were higher in the ARS than in the control group ( P<0.001 ) , respectively [ 70 ( 7 ) and 55 ( 9 ) ; 33 ( 9 ) and 24 ( 10 ) ; 33 ( 8) and 22 ( 10 ) ; 70 ( 7 ) and 55 ( 10 ) ] . CONCLUSIONS Recruitment of both lungs before instituting OLV not only decreased alveolar dead space but also improved arterial oxygenation and the efficiency of ventilation Pulmonary collapse is a common problem after coronary artery bypass graft surgery ( CABG ) . If absorption atelectasis during anaesthesia is an important mechanism in the genesis of pulmonary collapse after CABG , the addition of nitrogen to the inspired gas during anaesthesia should reduce the amount of postoperative collapse . We studied 30 patients who were allocated r and omly and prospect ively to receive either 100 % oxygen or an oxygen-air mixture as the inspired gas during anaesthesia for CABG .  Lung volumes , PaO2 , and an x-ray atelectasis score were measured before and after surgery to assess the degree of atelectasis . There were no significant differences between the two treatment groups in any of these measurements BACKGROUND : Collapse of the ipsilateral lung facilitates surgical exposure during thoracic procedures . The use of different gas mixtures during two-lung ventilation ( 2LV ) may improve or impede surgical conditions during subsequent one-lung ventilation ( OLV ) by increasing or delaying lung collapse . We investigated the effects of three different gas mixtures during 2LV on lung collapse and oxygenation during subsequent OLV : Air/Oxygen ( fraction of inspired oxygen [ Fio2 ] = 0.4 ) , Nitrous Oxide/Oxygen ( “ N2O , ” Fio2 = 0.4 ) and Oxygen ( “ O2 , ” Fio2 = 1.0 ) . METHODS : Subjects were r and omized into three groups : Air/Oxygen ( n = 33 ) , N2O ( n = 34 ) or O2 ( n = 33 ) and received the design ated gas mixture during induction and until the start of OLV . Subjects ’ lungs in all groups were then ventilated with Fio2 = 1.0 during OLV . The surgeons , who were blinded to the r and omization , evaluated the lung deflation using a verbal rating scale at 10 and 20 min after the start of OLV . Serial arterial blood gases were performed before anesthesia induction , during 2LV , and every 5 min , for 30 min , after initiation of OLV . RESULTS : The use of air in the inspired gas mixture during 2LV led to delayed lung deflation during OLV , whereas N2O improved lung collapse . Arterial oxygenation was significantly improved in the O2 group only for the first 10 min of OLV , after which there were no differences in mean Pao2 values among groups . CONCLUSIONS : De-nitrogenation of the lung during 2LV is a useful strategy to improve surgical conditions during OLV . The use of Fio2 1.0 or N2O/O2 ( Fio2 0.4 ) during 2LV did not have an adverse effect on subsequent oxygenation during OLV Purpose One hundred percent O2 is used routinely for preoxy-genation and induction of anesthesia . The higher the O2 concentration the faster is the development of atelectasis , an important cause of impaired pulmonary gas exchange during general anesthesia ( GA ) . We evaluated the effect of ventilation with 0.4FiO2 in air , 0.4FiO2 in N2O and 100 % O2 following intubation on the development of impaired gas exchange . Methods Twenty-seven patients aged 18–40 yr , undergoing elective laparoscopic cholecystectomy were administered 100 % O2 for preoxygenation ( three minutes ) and ventilation by mask ( two minutes ) . Following intubation these patients were r and omly divided 
    Output:
    
Positive end-expiratory pressure following a vital capacity recruitment maneuver can virtually eliminate atelectasis formation even in the presence of a high inspired oxygen content .