Intraoperative Ventilatory Strategies for Prevention of Pulmonary Atelectasis in Obese Patients Undergoing Laparoscopic Bariatric Surgery Positive end-expiratory pressure improves end-expiratory lung volume but not oxygenation after induction of anaesthesia Lung recruitment maneuver depresses central hemodynamics in patients following cardiac surgery Dynamics of re-expansion of atelectasis during general anaesthesia. Effects of the Beach Chair Position, Positive End-expiratory Pressure, and Pneumoperitoneum on Respiratory Function in Morbidly Obese Patients during Anesthesia and Paralysis Respiratory effects of different recruitment maneuvers in acute respiratory distress syndrome Analysis of the effects of the alveolar recruitment maneuver on blood oxygenation during bariatric surgery. Safety and efficacy of a sustained inflation for alveolar recruitment in adults with respiratory failure Ventilation strategy using low tidal volumes, recruitment maneuvers, and high positive end-expiratory pressure for acute lung injury and acute respiratory distress syndrome: a randomized controlled trial. Effects of short-term pressure-controlled ventilation on gas exchange, airway pressures, and gas distribution in patients with acute lung injury/ARDS: comparison with volume-controlled ventilation. Transient hemodynamic effects of recruitment maneuvers in three experimental models of acute lung injury* Optimal duration of a sustained inflation recruitment maneuver in ARDS patients Comparison of Volume-controlled and Pressure-controlled Ventilation during Laparoscopic Gastric Banding in Morbidly Obese Patients [Effectiveness of a recruitment manoeuvre and positive end-expiratory pressure on respiratory mechanics during laparoscopic bariatric surgery]. Noninvasive Ventilation and Alveolar Recruitment Maneuver Improve Respiratory Function during and after Intubation of Morbidly Obese Patients: A Randomized Controlled Study Effect of vital capacity manoeuvres on arterial oxygenation in morbidly obese patients undergoing open bariatric surgery Effects of four intraoperative ventilatory strategies on respiratory compliance and gas exchange during laparoscopic gastric banding in obese patients. Effect of intra‐operative pressure support vs pressure controlled ventilation on oxygenation and lung function in moderately obese adults* Effects of recruitment maneuvers in patients with acute lung injury and acute respiratory distress syndrome ventilated with high positive end-expiratory pressure* Both lung recruitment maneuver and PEEP are needed to increase oxygenation and lung volume after cardiac surgery Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome. Mechanistic scheme and effect of “extended sigh” as a recruitment maneuver in patients with acute respiratory distress syndrome: A preliminary study Pressure-controlled ventilation improves oxygenation during laparoscopic obesity surgery compared with volume-controlled ventilation. Prevention of Atelectasis in Morbidly Obese Patients during General Anesthesia and Paralysis: A Computerized Tomography Study Effects of lung recruitment maneuver and positiveend‐expiratory pressure on lung volume, respiratory mechanics and alveolar gas mixing in patients ventilated after cardiac surgery The Effects of Body Mass on Lung Volumes, Respiratory Mechanics, and Gas Exchange During General Anesthesia Pressure-controlled Ventilation Does Not Improve Gas Exchange in Morbidly Obese Patients Undergoing Abdominal 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 Background and objective Induction of anaesthesia promotes collapse of dependent lung regions in both obese and nonobese patients . We hypothesized that end-expiratory lung volume ( EELV ) may be more sensitive than oxygenation to evaluate the effects of positive end-expiratory pressure ( PEEP ) after anaesthesia induction . Methods Forty patients ( 20 nonobese patients and 20 obese patients ) were prospect ively studied .  After anaesthesia induction , PEEP was adjusted in a stepwise fashion [ zero end-expiratory pressure ( ZEEP ) , PEEP 5 cmH2O and PEEP 10 cmH2O ] . At each step , we measured EELV , static elastance , gas exchange and dead space . Other than changing PEEP , respiratory setting s were kept constant throughout . Results Anaesthesia induction and ZEEP both lowered EELV by 39 % in nonobese patients and 59 % in obese patients ( both P < 0.05 ) , as well as oxygenation ( P < 0.05 ) . Compared with ZEEP , in nonobese patients , PEEP 5 cmH2O and PEEP 10 cmH2O improved EELV ( + 15 and + 40 % , respectively , P < 0.01 ) and elastance but not oxygenation . In obese patients , PEEP 10 cmH2O also improved EELV ( 49 % vs. ZEEP and 30 % vs. PEEP 5 cmH2O , P < 0.01 ) , elastance and dead-space fraction , with no effect on oxygenation . PEEP-induced changes of EELV correlated with changes of elastance ( r2 = 0.46 , P = 0.003 ) , but not with oxygenation . Conclusion After induction of anaesthesia , mechanical ventilation with ZEEP is associated with a profound reduction in EELV . PEEP improves efficiently EELV and respiratory mechanics , with no major effect on oxygenation . EELV may be a useful indicator to guide PEEP setting in the operating room Objective To assess the impact of the lung recruitment maneuver on circulation following cardiac surgery . Design and setting Prospect i ve r and omized cross-over study at the Departments of Anesthesia and Thoracic Surgery , Copenhagen University Hospital . Patients Ten adult undergoing coronary artery bypass surgery . Interventions Patients were r and omized to two duration s of lung recruitment maneuvers ( 40 cmH2O airway pressure for 10 s and 20 s or vice versa after 5 min ) administered immediately after surgery . Measurements and results Transesophageal echocardiography ( left ventricular short axis view ) , pulse contour cardiac output , and arterial blood pressure were monitored continuously . Systemic and pulmonary arterial blood gases were sample d before and after each lung recruitment maneuver to calculate the intrapulmonary shunt . Left ventricular end-diastolic areas decreased significantly during both the 10-s and the 20-s lung recruitment maneuvers . Cardiac output was 5.6±0.8 l/min at baseline , decreasing by 3.0±1.1 l/min and 3.6±1.2 l/min during lung recruitment maneuvers of 10 and 20 s , respectively . Shunt decreased from 20±5 % to 15±6 % after the first lung recruitment maneuver and from 15±6 % to 12±5 % after the second . Conclusions Lung recruitment maneuvers markedly reduced cardiac output and left ventricular end-diastolic areas in hemodynamically stable patients following cardiac surgery 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 : The authors studied the effects of the beach chair ( BC ) position , 10 cm H2O positive end-expiratory pressure ( PEEP ) , and pneumoperitoneum on respiratory function in morbidly obese patients undergoing laparoscopic gastric b and ing . Methods : The authors studied 20 patients ( body mass index 42 ± 5 kg/m2 ) during the supine and BC positions , before and after pneumoperitoneum was instituted ( 13.6 ± 1.2 mmHg ) .  PEEP was applied during each combination of position and pneumoperitoneum . The authors measured elastance ( E , rs ) of the respiratory system , end-expiratory lung volume ( helium technique ) , and arterial oxygen tension . Pressure – volume curves were also taken ( occlusion technique ) . Patients were paralyzed  during total intravenous anesthesia . Tidal volume ( 10.5 ± 1 ml/kg ideal body weight ) and respiratory rate ( 11 ± 1 breaths/min ) were kept constant throughout . Results : In the supine position , respiratory function was abnormal : E , rs was 21.71 ± 5.26 cm H2O/l , and end-expiratory lung volume was 0.46 ± 0.1 l. Both the BC position and PEEP improved E , rs ( P < 0.01 ) . End-expiratory lung volume almost doubled ( 0.83 ± 0.3 and 0.85 ± 0.3 l , BC and PEEP , respectively ; P < 0.01 vs. supine zero end-expiratory pressure ) , with no evidence of lung recruitment ( 0.04 ± 0.1 l in the supine and 0.07 ± 0.2 in the BC position ) . PEEP was associated with higher airway pressures than the BC position ( 22.1 ± 2.01 vs. 13.8 ± 1.8 cm H2O ; P < 0.01 ) . Pneumoperitoneum further worsened E , rs ( 31.59 ± 6.73 ; P < 0.01 ) and end-expiratory lung volume ( 0.35 ± 0.1 l ; P < 0.01 ) . Changes of lung volume correlated with changes of oxygenation ( linear regression , R2 = 0.524 , P < 0.001 ) so that during pneumoperitoneum , only the combination of the BC position and PEEP improved oxygenation . Conclusions : The BC position and PEEP counteracted the major derangements of respiratory function produced by anesthesia and paralysis . During pneumoperitoneum , only the combination of the two maneuvers improved oxygenation Introduction Alveolar derecruitment may occur during low tidal volume ventilation and may be prevented by recruitment maneuvers ( RMs ) . The aim of this study was to compare two RMs in acute respiratory distress syndrome ( ARDS ) patients . Methods Nineteen patients with ARDS and protective ventilation were included in a r and omized crossover study . Both RMs were applied in each patient , beginning with either continuous positive airway pressure ( CPAP ) with 40 cm H2O for 40 seconds or extended sigh ( eSigh ) consisting of a positive end-expiratory pressure maintained at 10 cm H2O above the lower inflection point of the pressure-volume curve for 15 minutes . Recruited volume , arterial partial pressure of oxygen/fraction of inspired oxygen ( PaO2/FiO2 ) , and hemodynamic parameters were recorded before ( baseline ) and 5 and 60 minutes after RM . All patients had a lung computed tomography ( CT ) scan before study inclusion . Results Before RM , PaO2/FiO2 was 151 ± 61 mm Hg . Both RMs increased oxygenation , but the increase in PaO2/FiO2 was significantly higher with eSigh than CPAP at 5 minutes ( 73 % ± 25 % versus 44 % ± 28 % ; P < 0.001 ) and 60 minutes ( 68 % ± 23 % versus 35 % ± 22 % ; P < 0.001 ) . Only eSigh significantly increased recruited volume at 5 and 60 minutes ( 21 % ± 22 % and 21 % ± 25 % ; P = 0.0003 and P = 0.001 , respectively ) . The only difference between responders and non-responders was CT lung morphology . Eleven patients were considered as recruiters with eSigh ( 10 with diffuse loss of aeration ) and 6 with CPAP ( 5 with diffuse loss of aeration ) . During CPAP , 2 patients needed interruption of RM due to a drop in systolic arterial pressure . Conclusion Both RMs effectively increase oxygenation , but CPAP failed to increase recruited volume . When the lung is recruited with an eSigh adapted for each patient , alveolar recruitment and oxygenation are superior to those observed with CPAP UNLABELLED BACKGROUND AND METHDS : Alveolar recruitment maneuver ( ARM ) is indicated in the treatment of intraoperative atelectasis . The objective of the present study was to compare two techniques of ARM using the response of the PaO2/FiO2 ratio and [ PaO2 + PaCO2 ] in patients with grade III obesity . METHODS This was an open prospect i ve study with adult patients with grade III obesity who underwent bariatric surgery under volume-controlled mechanical ventilation with positive end-expiratory pressure ( PEEP ) of 5 cmH2O , divided in three groups : G CONT : PEEP of 5 cmH2O ; G ARM10/15/20 after suture of the aponeurosis : progressive increase in PEEP to 10 , 15 , and 20 cmH2O with a 40-second pause and maintaining each level of PEEP for 2 minutes ; and G ARM30 after suture of the aponeurosis : sudden increase in PEEP to 30 cmH2O with a 40-second pause and maintaining a PEEP of 30 for 2 minutes . Heart rate , mean arterial pressure , systolic and diastolic blood pressure , mean ( P AW ) and plateau ( P PLAT ) airways pressure , partial pressure of oxygen ( PaO2 ) , partial pressure of carbon dioxide ( PaCO2 ) , PaO2/FiO2 ratio ( inspired fraction of oxygen ) , and [ PaO2 + PaCO2 ] were analyzed . RESULTS The following parameters showed statistically significant differences among the study groups : P PLAT , P AW , PaO2 , PaO2/FiO2 ratio , and [ PaO2 + PaCO2 ] ( p < 0.0001 ) . Comparing the groups two by two , the following parameters showed statistically significant differences : for P PLAT and P AW : G CONT x G2ARM10/15/20 and G CONT x G ARM30 ; and for PaO2/FiO2 ratio and [ PaO2 + PaCO2 ] : G CONT x G ARM30 . CONCLUSIONS Alveolar recruitment maneuver with sudden increase of PEEP to 30 cmH2O showed a better response of the PaO2/FiO2 ratio Objective : To assess the safety and efficacy of a sustained inflation , used as a lung volume recruitment maneuver in ventilated patients with hypoxemic respiratory failure.¶ Design : Prospect i ve data collection as part of a quality assurance program following introduction of a lung volume recruitment guideline in the intensive care unit.¶ Setting : Academic medical-surgical critical care unit.¶ Patients : Hypoxemic patients with bilateral pulmonary infiltrates . Patients with chronic obstructive pulmonary disease , pulmonary barotrauma and hemodynamic instability were excluded.¶ Interventions : A sustained inflation using a pressure of 30 to 45 cmH2O was applied for 20 s. The pressure was determined as the lesser of 45 cmH2O or the peak pressure while ventilated at a tidal volume of 12 ml/kg . Intra-arterial blood pressure and pulse oximetry were monitored continuously.¶ Measurements and results : Significant improvement in oxygenation occurred in the majority of patients within 10 min . The mean oxygen saturation improved from 86.9 ± 5.5 to 94.3 ± 2.3 % ( p < 0.01 ) . No significant adverse effects were noted : hypotension and mild oxygen desaturation occurred in some patients during the 20-s inflation , reversing rapidly after inflation was terminated . No barotrauma occurred.¶ Conclusions : A sustained inflation is a safe , clinical ly applicable method of lung volume recruitment which improves oxygenation in selected patients and may have a role in ventilatory management CONTEXT Low-tidal-volume ventilation reduces mortality in critically ill patients with acute lung injury and acute respiratory distress syndrome . Instituting additional strategies to open collapsed lung tissue may further reduce mortality . OBJECTIVE To compare an established low-tidal-volume ventilation strategy with an experimental strategy based on the original " open-lung approach , " combining low tidal volume , lung recruitment maneuvers , and high positive-end-expiratory pressure . DESIGN AND SETTING R and omized controlled trial with concealed allocation and blinded data analysis conducted between August 2000 and March 2006 in 30 intensive care units in Canada , Australia , and Saudi Arabia . PATIENTS Nine hundred eighty-three consecutive patients with acute lung injury and a ratio of arterial oxygen tension to inspired oxygen fraction not exceeding 250 . INTERVENTIONS The control strategy included target tidal volumes of 6 mL/kg of predicted body weight , plateau airway pressures not exceeding 30 cm H2O , and conventional levels of positive end-expiratory pressure ( n = 508 ) . The experimental strategy included target tidal volumes of 6 mL/kg of predicted body weight , plateau pressures not exceeding 40 cm H2O , recruitment maneuvers , and higher positive end-expiratory pressures ( n = 475 ) . MAIN OUTCOME MEASURE All-cause hospital mortality . RESULTS Eighty-five percent of the 983 study patients met criteria for acute respiratory distress syndrome at enrollment . Tidal volumes remained similar in the 2 groups , and mean positive end-expiratory pressures were 14.6 ( SD , 3.4 ) cm H2O in the experimental group vs 9.8 ( SD , 2.7 ) cm H2O among controls during the first 72 hours ( P < .001 ) . All-cause hospital mortality rates were 36.4 % and 40.4 % , respectively ( relative risk [ RR ] , 0.90 ; 95 % confidence interval [ CI ] , 0.77 - 1.05 ; P = .19 ) . Barotrauma rates were 11.2 % and 9.1 % ( RR , 1.21 ; 95 % CI , 0.83 - 1.75 ; P = .33 ) . The experimental group had lower rates of refractory hypoxemia ( 4.6 % vs 10.2 % ; RR , 0.54 ; 95 % CI , 0.34 - 0.86 ; P = .01 ) , death with refractory hypoxemia ( 4.2 % vs 8.9 % ; RR , 0.56 ; 95 % CI , 0.34 - 0.93 ; P = .03 ) , and previously defined eligible use of rescue therapies ( 5.1 % vs 9.3 % ; RR , 0.61 ; 95 % CI , 0.38 - 0.99 ; P = .045 ) . CONCLUSIONS For patients with acute lung injury and acute respiratory distress syndrome , a multifaceted protocol ized ventilation strategy design ed to recruit and open the lung result ed in no significant difference in all-cause hospital mortality or barotrauma compared with an established low-tidal-volume protocol ized ventilation strategy . This " open-lung " strategy did appear to improve secondary end points related to hypoxemia and use of rescue therapies . TRIAL REGISTRATION clinical trials.gov Identifier : NCT00182195 STUDY OBJECTIVES The potential clinical benefits of pressure-controlled ventilation ( PCV ) over volume-controlled ventilation ( VCV ) in patients with acute lung injury ( ALI ) or ARDS still remain debated . We compared PCV with VCV in patients with ALI/ARDS with respect to the following physiologic end points : ( 1 ) gas exchange and airway pressures , and ( 2 ) CT scan intrapulmonary gas distribution at end-expiration . DESIGN Prospect i ve , observational study . SETTING A multidisciplinary ICU in a nonuniversity , acute-care hospital . PATIENTS Ten patients with ALI or ARDS ( 9 men and 1 woman ; age range , 17 to 80 years ) . INTERVENTIONS Sequential ventilation in PCV and VCV with a constant inspiratory/expiratory ratio , tidal volume , respiratory rate , and total positive end-expiratory pressure ; measurement of gas exchange and airway pressures ; and achievement of CT sections at lung base , hilum , and apex for the quantitative analysis of lung densities and of aerated vs nonaerated zones . RESULTS PaO(2 ) , PaCO(2 ) , and PaO(2)/fraction of inspired oxygen ratio levels did not differ between PCV and VCV .  Peak airway pressure ( Ppeak ) was significantly lower in PCV compared with VCV ( 26 + /- 2 cm H(2)O vs 31 + /- 2 cm H(2)O ; p < 0.001 ; mean + /- SEM ) . The surface areas of the nonaerated zones as well as the total areas at each section level were unchanged in PCV compared with VCV , except at the apex level , where there was a significantly greater nonaerated area in VCV ( 11 + /- 2 cm(2 ) vs 9 + /- 2 cm(2 ) ; p < 0.05 ) . The total mean CT number of each lung ( 20 lungs from 10 patients ) was similar in the two modes , as were the density values at the basal and apical levels ; the hilum mean CT number was - 442 + /- 28 Hounsfield units ( HU ) in VCV and - 430 + /- 26 HU in PCV ( p < 0.005 ) . CONCLUSIONS These data show that PCV allows the generation of lower Ppeaks through the precise titration of the lung distending pressure , and might be applied to avoid regional overdistension by means of a more homogeneous gas distribution Elevated lung volumes and increased pleural pressures associated with recruitment maneuvers ( RM ) may adversely affect pulmonary vascular resistance and cardiac filling or performance . We investigated the hemodynamic consequences of three RM techniques after inducing acute lung injury . Design : Prospect i ve , r and omized , controlled experimental study . Setting : Hospital research laboratory . Subjects : Thirteen anesthetized , mechanically ventilated pigs . Interventions : We induced three types of acute lung injury : oleic acid injury ( n = 4 ) ; ventilator-induced lung injury ( n = 4 ) ; and pneumonia ( n = 5 ) . All three models were design ed to initiate a similar severity of oxygenation impairment . RM methods tested were sustained inflation , incremental positive end-expiratory pressure ( PEEP ) with a limited peak pressure , and pressure-controlled ventilation with increased PEEP and a fixed driving pressure . From a baseline PEEP of 8 cm H2O , all interventions were tested using post-RM PEEP levels of 8 , 12 , and 16 cm H2O . Cardiac output by thermodilution and systemic and pulmonary artery pressures were measured frequently during the RM and for 15 mins after its completion . Measurements and Main Results : During the RM , cardiac output decreased to a greater extent in the pneumonia model ( 0.49 of baseline cardiac output ) than in the oleic acid injury ( 0.67 of baseline ) or ventilator-induced lung injury ( 0.79 of baseline ) models . Cardiac output recovered to the baseline value by 5 mins post-RM in oleic acid injury and ventilator-induced lung injury models . However , cardiac output remained decreased 15 mins post-RM in the pneumonia model . There were no differences in hemodynamic parameters among RM methods in oleic acid injury and ventilator-induced lung injury models . In the pneumonia model , however , cardiac output decreased to a greater extent during the RM with sustained inflation ( to 0.33 of baseline cardiac output ) compared with pressure-controlled ventilation ( to 0.68 of baseline ) . Conclusions : We conclude that RM transiently but profoundly depressed cardiac output in three models of acute lung injury . The results imply that a lung recruiting maneuver should be used with caution , especially when using sustained inflation in the setting of pneumonia Purpose To measure the dynamics of recruitment and the hemodynamic status during a sustained inflation recruitment maneuver ( RM ) in order to determine the optimal duration of RM in acute respiratory distress syndrome ( ARDS ) patients . Methods This prospect i ve study was conducted in a 12-bed intensive care unit ( ICU ) in a general hospital . A 40 cmH2O sustained inflation RM maintained for 30 s was performed in 50 se date d ventilated patients within the first 24 h of meeting ARDS criteria .  Invasive arterial pressures , heart rate , and SpO2  were measured at 10-s intervals during the RM . The volume increase during the RM was measured by integration of the flow required to maintain the pressure at 40 cmH2O , which provides an estimation of the volume recruited during the RM . Raw data were corrected for gas consumption and fitted with an exponential curve in order to determine an individual time constant for the volume increase . Results The average volume increase and time constant were 210 ± 198 mL and 2.3 ± 1.3 s , respectively . Heart rate , diastolic arterial pressure , and SpO2 did not change during or after the RM . Systolic and mean arterial pressures were maintained at 10 s , decreased significantly at 20 and 30 s during the RM , and recovered to the pre-RM value 30 s after the end of the RM ( ANOVA , p < 0.01 ) . Conclusions In early-onset ARDS patients , most of the recruitment occurs during the first 10 s of a sustained inflation RM . However , hemodynamic impairment is significant after the tenth second of RM Background There are no guidelines on ventilation modes in morbidly obese patients . We investigated the effects of volume-controlled ( VCV ) and pressure-controlled ventilation ( PCV ) on gas exchange , respiratory mechanics , and cardiovascular responses in laparoscopic gastric b and ing procedures . Methods After Institutional Review Board approval , 24 adult consenting patients scheduled for laparoscopic gastric b and ing were studied . Anesthesia was st and ardized using remifentanil , propofol , rocuronium , and sevoflurane . All patients started with VCV with a tidal volume of 10 ml kg−1 ideal body weight , respiratory rate adjusted to obtain an end-tidal carbon dioxide of 35–40 mmHg , positive end-expiratory pressure of 5 cmH2O , an inspiratory pause of 10 % and an inspiratory/expiratory ratio of 1:2 . Fifteen minutes after pneumoperitoneum , the patients were r and omly allocated to two groups . In Group VCV ( n = 12 ) , ventilation was with the same parameters . In Group PCV ( n = 12 ) , the airway pressure was set to provide a tidal volume of 10 ml kg−1 ideal body weight without exceeding 35 cm H2O . Respiratory rate was adjusted to keep an end-tidal carbon dioxide of 35–40 mmHg . Arterial blood sample s were drawn after surgical positioning and 15 min after allocation . Analysis of variance ( ANOVA ) was used for statistical analysis . Results With constant minute ventilation , VCV generates equal airway pressures and cardiovascular effects with a lower PaCO2 as compared to PCV ( 42.5 ( 5.2 ) mmHg versus 48.9 ( 4.3 ) mmHg , p < 0.01 ANOVA ) . Arterial oxygenation remained unchanged . Conclusions VCV and PCV appear to be an equally suited ventilatory technique for laparoscopic procedures in morbidly obese patients .  Carbon dioxide elimination is more efficient when using VCV OBJECTIVE To evaluate recruitment manoeuvre ( RM ) efficiency associated with a 10 cmH(2)O positive end expiratory pressure ( PEEP ) on respiratory mechanic estimated by lung compliance ( Ctp ) and PEEP to ZEEP expiratory volume delta ( Delta VTE ) during laparoscopic bariatric surgery in patients with morbid obesity . STUDY DESIGN Prospect i ve r and omized study . METHODS Twenty-six obese patients ( BMI > 40 kg/m(2 ) ) undergoing laparoscopic bariatric surgery .  The recruitment group received an RM followed by a 10 cmH(2)O PEP versus only 10 cmH(2)O PEP in the control group . Ctp was measured during the intervention and functional residual capacity ( FRC ) was estimated measuring Delta VTE during a PEP to ZEP manoeuvre . Mann and Whitney tests as well as a t-test were used ( significance p<0.05 ) . RESULTS In the RM group , a significant improvement of 52+/-14 ml/cmH(2)O was noted versus a 36+/-10 ml/cmH(2)O in the PEP group ( p=0,004 ) . This improvement was transitory and no statistically significant Delta VTE difference was noted between the groups at the end of the intervention ( 360 [90 - 770]ml [ MRA ] and 310 [190 - 450]ml [ PEP ] ) . CONCLUSION In patients with morbid obesity undergoing laparoscopic bariatric surgery , an RM conducted prior the pneumoperitoneum temporarily improves lung mechanics but without any change of the end expiratory lung volume at the end of the surgery in comparison with PEP alone . The RM was well tolerated Background : Morbid obesity predisposes patients to lung collapse and hypoxemia during induction of anesthesia . The aim of this prospect i ve study was to determine whether noninvasive positive pressure ventilation ( NPPV )  improves arterial oxygenation and end-expiratory lung volume ( EELV ) compared with conventional preoxygenation , and whether NPPV followed by early recruitment maneuver ( RM ) after endotracheal intubation ( ETI ) further improves oxygenation and respiratory function compared with NPPV alone . Methods : Sixty-six consecutive patients ( body mass index , 46 ± 6 kg/m2 ) were r and omized to receive 5 min of either conventional preoxygenation with spontaneous breathing of 100 % O2 ( CON ) , NPPV ( pressure support and positive end-expiratory pressure ) , or NPPV followed by RM ( NPPV+RM ) . Gas exchange was measured in awake patients , at the end of preoxygenation , immediately after ETI , and 5 min after the onset of mechanical ventilation . EELV was measured immediately after ETI and 5 min after mechanical ventilation . The primary endpoint was arterial oxygenation 5 min after the onset of mechanical ventilation . Results are presented as mean ± SD . Results : At the end of preoxygenation , Pao2 was higher in the NPPV and NPPV+RM groups ( 382 ± 87 mmHg and 375 ± 82 mmHg , respectively ; both P < 0.001 ) compared with the CON group ( 306 ± 51 mmHg ) and remained higher after ETI ( 225 ± 104 mmHg and 221 ± 110 mmHg , in the NPPV and NPPV+RM groups , respectively ; both P < 0.01 compared with the CON group [ 150 ± 50 mmHg ] ) . After the onset of mechanical ventilation , Pao2 was 93 ± 25 mmHg in the CON group , 128 ± 54 mmHg in the NPPV group ( P = 0.035 vs. CON group ) , and 234 ± 73 mmHg in the NPPV+RM group ( P < 0.0001 vs. NPPV group ) . After ETI , EELV was higher in the NPPV group compared with the CON group ( P < 0.001 ) . Compared with NPPV alone , RM further improved gas exchange and EELV ( all P < 0.05 ) . A significant correlation was found between Pao2 obtained 5 min after mechanical ventilation and EELV ( R2 = 0.41 , P < 0.001 ) . Conclusion : NPPV improves oxygenation and EELV in morbidly obese patients compared with conventional preoxygenation . NPPV combined with early RM is more effective than NPPV alone at improving respiratory function after ETI Background : Arterial oxygenation may be compromised in morbidly obese patients undergoing bariatric surgery . The aim of this study was to evaluate the effect of a vital capacity manoeuvre ( VCM ) , followed by ventilation with positive end‐expiratory pressure ( PEEP ) , on arterial oxygenation in morbidly obese patients undergoing open bariatric surgery . Methods : Fifty‐two morbidly obese patients ( body mass index > 40 kg m−2 ) undergoing open bariatric surgery were enrolled in this prospect i ve and r and omized study . Anaesthesia and surgical techniques were st and ardized . Patients were ventilated with a tidal volume of 10 mL kg−1 of ideal body weight , a mixture of oxygen and nitrous oxide ( FiO2 = 40 % ) and respiratory rate was adjusted to maintain end‐tidal carbon dioxide at a level of 30–35 mmHg . After abdominal opening , patients in Group 1 had a PEEP of 8 cm H2O applied and patients in Group 2 had a VCM followed by PEEP of 8 cm H2O . This manoeuvre was defined as lung inflation by a positive inspiratory pressure of 40 cm H2O maintained for 15 s. PEEP was maintained until extubation in the two groups . Haemodynamics , ventilatory and arterial oxygenation parameters were measured at the following times : T0 = before application of VCM and /or PEEP , T1 = 5 min after VCM and /or PEEP and T2 = before abdominal closure . Results : Patients in the two groups were comparable regarding patient characteristics , surgical , haemodynamic and ventilatory parameters . In Group 1 , arterial oxygen partial pressure ( PaO2 ) and arterial haemoglobin oxygen saturation ( SaO2 ) were significantly increased and alveolar‐arterial oxygen pressure gradient ( A‐aDO2 ) decreased at T2 when compared with T0 and T1 . In Group 2 , PaO2 and SaO2 were significantly increased and A‐aDO2 decreased at T1 and T2 when compared with T0 . Arterial oxygenation parameters at T1 and T2 were significantly improved in Group 2 when compared with Group 1 . Conclusion : The addition of VCM to PEEP improves intraoperative arterial oxygenation in morbidly obese patients undergoing open bariatric surgery 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 Obesity impairs peri‐operative lung function . To evaluate the impact of pressure support ventilation vs pressure controlled ventilation in moderately obese adults upon early postoperative lung function , we r and omly assigned 68 moderately obese patients ( body mass index 25–35 kg.m−2 ) undergoing minor surgery  to receive intra‐operative ventilation either with pressure support or pressure controlled ventilation . We performed intra‐operative blood gas analysis and measured pulse oximetry saturation , spirometry values at pre‐operative assessment ( baseline ) and at 10 min , 30 min , 2 h and 24 h after extubation . The intra‐operative oxygenation index ( arterial partial pressure of oxygen/fraction of inspired oxygen ) in the pressure support ventilation group was significantly improved over time ( p < 0.0001 ) . Postoperatively , the pressure support ventilation group also had better lung function and oxygenation values than did the pressure controlled ventilation group ( p < 0.005 ) . We conclude that pressure support ventilation better maintains lung function than pressure controlled ventilation in moderately overweight patients scheduled for minor surgery Objective Positive end-expiratory pressure ( PEEP ) and recruitment maneuvers ( RMs ) may partially reverse atelectasis and reduce ventilation-associated lung injury . The purpose s of this study were to assess a ) magnitude and duration of RM effects on arterial oxygenation and on requirements for oxygenation support ( Fio2/PEEP ) in patients with acute lung injury and acute respiratory distress syndrome ( ALI/ARDS ) receiving ventilation with low tidal volumes and high levels of PEEP ; and b ) frequency of adverse respiratory and circulatory events attributable to RMs . Design Prospect i ve , r and omized , crossover study . Setting Thirty-four intensive care units at 19 hospitals . Patients Seventy-two patients with early ALI/ARDS . Baseline PEEP and Fio2 were 13.8 ± 3.0 cm H2O and 0.39 ± 0.10 , respectively ( mean ± sd ) . Interventions We conducted RMs by applying continuous positive airway pressure of 35–40 cm H2O for 30 secs. We conducted sham RMs on alternate days . We monitored oxyhemoglobin saturation by pulse oximetry ( SpO2 ) , Fio2/PEEP , blood pressure , and heart rate for 8 hrs after RMs and sham RMs . We examined chest radiographs for barotrauma . Measurements and Main Results Responses to RMs were variable . Greatest increments from baseline SpO2 within 10 mins after RMs were larger than after sham RMs ( 1.7 ± 0.2 vs. 0.6 ± 0.3 % , mean ± sem , p < .01 ) . Systolic blood pressure decreased more within 10 mins after RMs ( 9.4 ± 1.1 vs. 3.1 ± 1.1 mm Hg , p < .01 ) . Changes in Fio2/PEEP requirements were not significantly different at any time after RMs vs. sham RMs . Barotrauma was apparent on first radiographs after one RM and one sham RM . Conclusions In ALI/ARDS patients receiving mechanical ventilation with low tidal volumes and high PEEP , short-term effects of RMs as conducted in this study are variable . Beneficial effects on gas exchange in responders appear to be of brief duration . More information is needed to determine the role of recruitment maneuvers in the management of ALI/ARDS 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 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 devise a new form of sigh ( “ extended sigh ” ) capable of providing a sufficient recruiting pressure × time , and to test it as a recruitment maneuver in patients with acute respiratory distress syndrome . Design Prospect i ve uncontrolled clinical trial . Setting Medical intensive care unit of a university-affiliated hospital . Patients Twenty consecutive patients diagnosed with acute respiratory distress syndrome ( 18 men , 2 women , age 59 ± 10 yrs ) . Interventions From baseline setting s of tidal volume ( Vt ) 8 mL/kg and positive end-expiratory pressure ( PEEP ) 10 cm H2O on volume control mode with the high pressure limit at 40 cm H2O , the Vt-PEEP values were changed to 6–15 , 4–20 , and 2–25 , each step being 30 secs ( inflation phase ) . After Vt-PEEP 2–25 , the mode was switched to continuous positive airway pressure of 30 cm H2O for a duration of 30 secs ( pause ) , after which the baseline setting was resumed following the reverse sequence of inflation ( deflation phase ) . This extended sigh was performed twice with 1 min of baseline ventilation between . Measurements and Results Airway pressures and hemodynamic parameters were traced at each step during the extended sigh . Arterial blood gases and physiologic parameters were determined before the extended sigh ( pre-extended sigh ) , at 5 mins after two extended sighs ( post-extended sigh ) , and then every 15 mins for 1 hr . In our average patient , the recruiting pressure × time of the inflation phase was estimated to be 32.8–35.4 cm H2O × 90 secs. Compared with the inflation phase , inspiratory pause pressure of the deflation phase was lower at Vt-PEEP 6–15 ( 28.9 ± 2.7 cm H2O vs. 27.3 ± 2.8 cm H2O ) and 4–20 ( 31.8 ± 2.9 cm H2O vs. 31.1 ± 2.9 cm H2O ; both p < .05 ) . Compared with pre-extended sigh , Pao2 ( 81.5 ± 15.3 mm Hg vs. 104.8 ± 25.0 mm Hg;p < .001 ) and static respiratory compliance both increased post-extended sigh ( 27.9 ± 7.9 mL/cm H2O vs. 30.2 ± 9.7 mL/cm H2O;p = .009 ) . Improvement in these parameters was sustained above pre-extended sigh for the duration of the study . Major hemodynamic or respiratory complications were not noted during the study . Conclusion We present a new form of sigh ( i.e. , extended sigh ) capable of achieving an augmented recruiting pressure × time through a prolonged inflation on a gradually increased end-expiratory pressure . In view of the sustained effect and absence of major complications in our patients , extended sigh could be a useful recruitment maneuver in acute respiratory distress syndrome BACKGROUND We compared pressure and volume-controlled ventilation ( PCV and VCV ) in morbidly obese patients undergoing laparoscopic gastric b and ing surgery . METHODS Thirty-six patients , BMI > 35 kg m(-2 ) , no major obstructive or restrictive respiratory disorder , and Pa(CO(2))<6.0 kPa , were r and omized to receive either VCV or PCV during the surgery . Ventilation setting s followed two distinct algorithms aim ing to maintain end-tidal CO(2 ) ( E'(CO(2 ) ) ) between 4.40 and 4.66 kPa and plateau pressure ( P(plateau ) ) as low as possible . Primary outcome variable was peroperative P(plateau ) . Secondary outcomes were Pa(O(2 ) ) ( Fi(O(2 ) ) at 0.6 in each group ) and Pa(CO(2 ) ) during surgery and 2 h after extubation . Pressure , flow , and volume time curves were recorded . RESULTS There were no significant differences in patient characteristics and co-morbidity in the two groups . Mean pH , Pa(O(2 ) ) , Sa(O(2 ) ) , and the Pa(O(2))/Fi(O(2 ) ) ratio were higher in the PCV group , whereas Pa(CO(2 ) ) and the E'(CO(2))-Pa(CO(2 ) ) gradient were lower ( all P<0.05 ) . Ventilation variables , including plateau and mean airway pressures , anaesthesia-related variables , and postoperative cardiovascular variables , blood gases , and morphine requirements after the operation were similar . CONCLUSIONS The changes in oxygenation can only be explained by an improvement in the lungs ventilation/perfusion ratio . The decelerating inspiratory flow used in PCV generates higher instantaneous flow peaks and may allow a better alveolar recruitment . PCV improves oxygenation without any side-effects 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 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 ) 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 Abstract Background Morbid obesity results in marked respiratory pathophysiologic changes that may lead to impaired intraoperative gas exchange . The decelerating inspiratory flow and constant inspiratory airway pressure result ing from pressure-controlled ventilation ( PCV ) may be more adapted to these changes and improve gas exchanges compared with volume-controlled ventilation ( VCV ) . Methods Forty morbidly obese patients scheduled for gastric bypass were included in this study . Total intravenous anesthesia was given using the target-controlled infusion technique . During the first intraoperative hour , VCV was used and the tidal volume was adjusted to keep end-tidal PCO2 around 35 mmHg . After 1 h , patients were r and omly allocated to 30-min VCV followed by 30-min PCV or the opposite sequence using a Siemens ® Servo 300 . FiO2 was 0.6 . During PCV  , airway pressure was adjusted to provide the same tidal volume as during VCV  . Arterial blood was sample d for gas analysis every 15 min . Ventilatory parameters were also recorded . Results Peak inspiratory airway pressures were significantly lower during PCV than during VCV ( P < 0.0001 ) . The other ventilatory parameters were similar during the two periods of ventilation . PaO2 and PaCO2 were not significantly different during PCV and VCV . Conclusion PCV does not improve gas exchange in morbidly obese patients undergoing gastric bypass compared to VCV
BACKGROUND Pathophysiological changes due to obesity may complicate mechanical ventilation during general anaesthesia .
The ideal ventilation strategy is expected to optimize gas exchange and pulmonary mechanics and to reduce the risk of respiratory complications .