Eur J Anaesthesiol 2017; 34:534–543 ORIGINAL ARTICLE Ventilation with high versus low peep levels during general anaesthesia for open abdominal surgery does not affect postoperative spirometry A randomised clinical trial Tanja A Treschan, Maximilian Schaefer, Johann Kemper, Bea Bastin, Peter Kienbaum, Benedikt Pannen, Sabrine N Hemmes, Marcelo G de Abreu, Paolo Pelosi and Marcus J Schultz, for the PROVEM Network Investigators BACKGROUND Invasive mechanical ventilation during general anaesthesia for surgery typically causes atelectasis and impairs postoperative lung function OBJECTIVE We investigated the effect of intraoperative ventilation with high positive end-expiratory pressure (PEEP) and recruitment manoeuvres (RMs) on postoperative spirometry DESIGN This was a preplanned, single-centre substudy of an international multicentre randomised controlled trial, the PROVHILO trial SETTING University hospital from November 2011 to January 2013 PATIENTS Nonobese patients scheduled for major abdominal surgery at a high risk of postoperative pulmonary complications (PPCs) INTERVENTION Intraoperative low tidal volume ventilation with PEEP levels of 12 cmH2O and RM (the high PEEP group) or with PEEP levels of cmH2O or less without RM (the low PEEP group) MAIN OUTCOME MEASURES Time-weighted averages (TWAs) of the forced expiratory volume in s (FEV1) and the forced vital capacity (FVC) up to postoperative day five RESULTS Thirty-one patients were allocated to the high PEEP group and 32 to the low PEEP group No postoperative spirometry test results were available for patients In both groups, TWA of FEV1 and FVC until postoperative day five were lower than preoperative values Postoperative spirometry test results were not different between the high and low PEEP group; Data are median [interquartile range], TWA FVC 1.8 [1.6 to 2.4] versus 1.7 [1.2 to 2.4] l (P ¼ NS) and TWA FEV1 1.2 [1.1 to 2.5] versus 1.2 [0.9 to 1.9] l (P ¼ NS) Patients who developed PPCs had lower FEV1 and FVC on postoperative day five; 1.1 [0.9 to 1.6] versus 1.6 [1.4 to 1.9] l (P ¼ 0.001) and 1.6 [1.2 to 2.6] versus 2.3 [1.7 to 2.6] l (P ¼ 0.036), respectively CONCLUSION Postoperative spirometry is not affected by PEEP and RM during intraoperative ventilation for open abdominal surgery in nonobese patients at a high risk of PPCs, but rather is associated with the development of PPCs TRIAL REGISTRATION ClinicalTrials.gov NCT01441791 Published online 16 March 2017 From the Department of Anesthesiology, Duăsseldorf University Hospital, Medical Faculty of Heinrich-Heine University, Duăsseldorf, Germany (TAT, MS, JK, BB, PK, BP), The Department of Anesthesiology, The Academic Medical Center, Amsterdam, The Netherlands (SNH), The Department of Anesthesiology and Intensive Care, University Hospital Carl Gustav Carus, Dresden, Germany (MGA), The Department of Surgical Sciences and Integrated Diagnostics, IRCCS San Martino IST, University of Genoa, Genoa, Italy (PP) and the Laboratory of Experimental Intensive Care and Anesthesiology (LÁEÁIÁCÁA), and the Department of Intensive Care, The Academic Medical Center, Amsterdam, The Netherlands (MJS) for the PROVE Network Investigators Correspondence to Tanja A Treschan, MD, CLiPS – Clinical Trials – Patient–centred Studies, Department of Anesthesiology, Duăsseldorf University Hospital, Moorenstrasse 5, 40225 Duăsseldorf, Germany E-mail: tanja.treschan@med.uni-duesseldorf.de *PROVE network = the PROtective VEntilation Network (www.provenet.eu) 0265-0215 Copyright ß 2017 European Society of Anaesthesiology All rights reserved DOI:10.1097/EJA.0000000000000626 Copyright © European Society of Anaesthesiology Unauthorized reproduction of this article is prohibited PROVHILO spirometry 535 Introduction Invasive mechanical ventilation during general anaesthesia for surgery typically results in atelectasis as well as reduced lung volume due to a cephalad shift of the diaphragm and a decreased muscle tone after induction of anesthesia.1 In particular, in patients undergoing abdominal surgery, the risk of atelectasis increases the closer the incision is to the diaphragm.2,3 Although intraoperative atelectasis impairs intraoperative oxygenation,4 more importantly, atelectasis often continues into the postoperative period, changing the mechanics of regional lung aeration and impairing the postoperative recovery of pulmonary function.5 Accordingly, atelectasis could predispose to the development of postoperative pulmonary complications (PPCs), including hypoxemia and pneumonia,2 with an increased risk of postoperative morbidity and mortality.6 Postoperative regeneration of pulmonary function could depend, at least in part, on the intraoperative ventilation strategy Indeed, a significantly greater reduction in perioperative and postoperative lung volumes is seen with general anaesthesia as compared with spinal anesthesia,7 and with controlled rather than with assisted modes of ventilation.8 Furthermore, so-called ‘protective intraoperative ventilation’ that uses a combination of low tidal volumes and positive end-expiratory pressure (PEEP) and recruitment manoeuvres (RMs) could prevent the development of PPCs.9–12 However, the protective role of PEEP in preventing PPCs was challenged recently.13,14 Despite protective intraoperative ventilation, PPCs occur in up to 39% of patients.9,10,13 Risk scores, using preoperative characteristics, for the development of PPCs and early recognition of patients who develop PPCs could contribute to an improved patient outcome.15,16 As with preoperative spirometry to predict PPCs,17,18 postoperative spirometry could be a useful tool to monitor postoperative recovery of lung function.7,9 Therefore, in this substudy of the international multicentre, randomised controlled ‘PROtective Ventilation using HIgh versus LOw PEEP’ (PROVHILO) trial,13,19 in which intraoperative ventilation with a high level of PEEP (12 cmH2O) and RMs was compared with a low level of PEEP ( cmH2O) without RMs during general anaesthesia for planned open abdominal surgery in nonobese patients at risk of PPCs, we tested the hypothesis that postoperative spirometry results would be modified by the intraoperative level of PEEP In addition, we compared postoperative spirometry test results in patients who did and who did not develop PPCs Materials and methods Ethical approval and informed consent This was a preplanned substudy of the recently published PROVHILO trial.13,19 This single-centre substudy was performed at the Duăsseldorf University Hospital, Duăsseldorf, Germany Patients at our institution were included from November 2011 until January 2013 The original trial was approved by the Institutional Review Boards of the Academic Medical Center (AMC), Amsterdam, The Netherlands, and on July 2011 by the Medizinischen Fakultaăt der HeinrichHeine Universitaăt Duăsseldorf, Duăsseldorf, Germany (Study number 3664, chairperson Prof Kroăncke), and registered at ClinicalTrials.gov NCT01441791 The latter additionally approved this substudy as an amendment Participants had to give written informed consent prior to participation for any procedure related to the original trial and this substudy Design of the original trial In the PROVHILO trial, nonobese patients with an intermediate or high risk of PPCs according to the Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score15,16 and who were scheduled for open abdominal surgery under general anaesthesia were randomly assigned to intraoperative ventilation with high levels of PEEP and RMs (12 cmH2O; the ‘high PEEP group’) or ventilation with lower levels of PEEP without RMs (44) – % (n/N) Smoking status – n/N Never Former Current Alcohol status (past weeks) – % (n/N) None to units of alcohol >2 units of alcohol ASA physical status classification system – % (n/N) New York Heart Association Classification – % (n/N) I II III IV Functional status – % (n/N) Nondependent Partially dependent Totally dependent History of active cancer – n/N History of chronic renal failure – % (n/N) COPD – % (n/N) With inhalation therapy With systemic steroids Diabetes mellitus – % (n/N) With oral medication With insulin therapy Use of systemic steroids – % (n/N) Use of statins – % (n/N) Preoperative transfusion – % (n/N) Preoperative tests Haemoglobin (g lÀ1) Creatinine (mmol/l) median [IQR] Urea, mmol/l, median [IQR] White blood cells (Â 109 lÀ1) median [IQR] Preoperative SpO2 – %, median [IQR] Abnormalities on chest radiograph – % (n/N) Peri-operative variables Duration of surgerya (min), mean (SD) Surgical procedure – % (n/N) Gastric Pancreatic biliary Liver Colonic Rectal Bladder Kidney Vascular Other Antibiotic prophylaxis – % (n/N) Type of anaesthesia – % (n/N) Total intravenous Mixed (volatile and intravenous) Epidural – % (n/N) thoracic lumbar All patients N U 57 30 (53%) 57 [44 to 69] 27 Æ 77 Æ 17 41 [38 to 50] 39/57 (68%) 18/57 (32%) Higher PEEP N U 27 Group Lower PEEP N U 30 Group P 13 (48%) 55 [44 to 68] 26 Ỉ 77 Ỉ 16 41 [38 to 51] 19/27 (70%) 8/27 (30%) 17 (56%) 59 [44 to 69] 25 Ỉ 75 Ỉ 18 41 [34 to 50] 20/30 (67%) 10/30 (33%) 0.600 0.876 0.510 0.850 0.462 26/57 (46%) 11/57 (19%) 20/57 (35%) 13 (48%) (19%) (33%) 13 (43%) (20%) 11 (37%) 0.935 39/57 (69%) 15/57 (26%) 3/57 (5%) 17 (63%) (33%) (4%) 22 (73%) (20%) (7%) 0.492 10/56 26/56 19/56 1/56 (18%) (46%) (34%) (2%) 5/27 (19%) 12/27 (44%) 10/27 (37%) 0/27 5/29 14/29 9/29 1/29 (17%) (48%) (31%) (4%) 0.768 46/50 (92%) 4/50 (8%) 0/50 0/50 21/23 (91%) 2/23 (9%) 0/23 0/23 25/27 (93%) 2/27 (7%) 0/27 0/27 0.632 54/57 (95%) 3/57 (5%9 0/57 31/52 (60%) 2/57 (4%) 1/57 (2%) 1/56 (2%) 1/56 (2%) 6/57 (11%) 1/4 (25%) 3/4 (75%) 5/56 (9%) 3/57 (5%) 0/57 25/27 (93%) 2/27 (7%) 0/28 12/23 (52%) 1/27 (4%) 0/27 0/27 1/27 (4%) 4/27 (15%) 1/3 (33%) 2/3 (67%) 3/27 (11%) 2/27 (7%) 0/27 29/30 (97%) 1/30 (3%) 0/30 19/29 (56%) 1/30 (3%) 1/30 (3%) 1/29 (3%) 0/29 2/30 (7%) 0/1 1/1 (100%) 2/29 (7%) 1/30 (3%) 0/30 0.599 129 (22) 61 [46 to 61] 4.3 [2.6 to 5.6] 7.2 [5.6 to 9.6] 97 [96 to 98.5] 1/36 (3%) 128 (23) 61 [46 to 61] 4.3 [3.6 to 5.7] 7.6 [6.2 to 10.2] 97 [96 to 99] 1/17 (5%) 0.400 1.0 1.0 1.0 0.482 0.408 0.664 0.599 1.0 131 (21) 51 [46 to 61] 4.5 [3.8 to 5.2] 7.0 [5.5 to 8.5] 96 [96 to 98] 0/19 0.620 0.952 0.527 0.275 0.145 0.563 309 (161) 326 (132) 295 (184) 0.473 5/57 10/57 2/57 12/57 15/57 4/57 0/57 1/57 2/57 6/57 57/57 (100%) 1/27 5/27 1/27 4/27 7/27 3/27 0/27 1/27 1/27 4/27 27/27 (100%) 4/30 5/30 1/30 8/30 8/30 1/30 0/30 0/30 1/30 2/30 30/30 (100%) 0.678 3/57 54/57 42/57 42/42 (100%) 1/27 26/27 19/27 19/19 (100%) 2/30 28/30 23/30 23/23 (100%) 1.0 1.0 0.764 Eur J Anaesthesiol 2017; 34:534–543 Copyright © European Society of Anaesthesiology Unauthorized reproduction of this article is prohibited PROVHILO spirometry 539 Table (continued ) Variable All patients N U 57 Preoperative spirometry- median [IQR] FVC (l) FEV1 (l) FEV1/FVC (%) Higher PEEP N U 27 Group 3.7 (2.9 to 4.5) 2.7 (2.1 to 3.3) 73 (69 to 80) Lower PEEP N U 30 Group 3.6 (2.7 to 4.6) 2.6 (2.0 to 3.0) 73 (68 to 80) 3.7 (3.1 to 4.5) 2.8 (2.3 to 3.6) 77 (72 to 79) P 0.587 0.274 0.243 Data are presented as means (SD) Median [IQR] or n/N and proportion %; Calculated as weight (kg)/ height (m)2 ¼ kg/m2 ASA, American Society of Anesthesiology; COPD, chronic obstructive pulmonary disease; FVC, forced vital capacity, FEV1, forced expiratory volume in s; Inhalation therapy for COPD, inhaled bronchodilators and/or steroids’ SpO2, oxyhaemoglobin saturation measured by pulse oximeter; kg, kilogram; m, meters; n, number of patients; N, total patients a Duration of surgery is the time between skin incision and closure of the incision FVC ¼ 1.8 (1.6 to 2.4) versus 1.7 (1.2 – 2.4) l (P ¼ 0.792) and TWA FEV1 ¼ 1.2 (1.1 to 2.5) versus 1.2 (0.9 to 1.9)] l (P ¼ 0.497) There were also no differences in FVC or FEV1 between randomisation groups on individual postoperative days (Fig 2) (supplement Table 7, http://links.lww.com/EJA/A115), but more frequently received intraoperative ventilation with high PEEP (supplement Table 8, http://links.lww com/EJA/A115), but incidence of PPCs was not different (supplement Table 9, http://links.lww.com/EJA/A115) Association between the occurrence of postoperative pulmonary complication and spirometry results Association between location of incision and spirometry results In patients who developed PPCs, FEV1 and FVC values on postoperative day were about 30% lower than patients who did not develop PPCs (Fig 3) Compared with patients who did not develop PPCs, patients who developed PPCs had longer surgery (supplement Table 5, http://links.lww.com/EJA/A115), received higher tidal volumes, higher minute ventilation volumes and more intravenous fluids during surgery (supplement Table 6, http://links.lww.com/EJA/A115) Patients who had upper abdominal surgery were current smokers more frequently and had a longer duration of surgery than patients who had lower abdominal surgery (supplement Table 10, http://links.lww.com/EJA/A115) and received more fluids and transfusions (supplement Table 11, http://links.lww.com/EJA/A115) The incidence of PPCs, however, was not different (supplement Table 12, http://links.lww.com/EJA/A115) Postoperative spirometry showed no differences between the high and low PEEP groups, neither in patients who had upper abdominal surgery nor in patients who had lower abdominal surgery (Fig 4c, d) Posthoc analyses Association between intraoperative pulmonary compliance and spirometry results On the first postoperative day, spirometry results were about 40% higher in patients with high pulmonary compliance, but unaffected by PEEP and RM (Fig 4a, b) Patients with high intraoperative pulmonary compliance were not different from those with a low compliance Discussion The results of this substudy of a larger randomised controlled trial comparing high with low PEEP during intraoperative ventilation in nonobese patients at risk of PPCs and scheduled for open abdominal surgery can be Fig FVC litres (a) (b) litres 6.0 6.0 4.0 4.0 2.0 2.0 0.0 0.0 PRE DAY DAY DAY FEV1 PRE DAY DAY DAY Results of spirometry for patients ventilated with high or low PEEP (a) Forced vital capacity (FVC), and (b) Forced expiratory volume in s (FEV1) in patients ventilated with high (black bars) and low PEEP (grey bars) during intraoperative ventilation On postoperative day 1, spirometric results were significantly lower than preoperative values (P < 0.001 in both groups) Compared with day 3, spirometric values increased significantly by day (P ¼ 0.001 for FVC and P ¼ 0.005 for FEV in both groups) Differences between PEEP groups are nonsignificant Data are presented as median (thick line across box), interquartile ranges (ends of boxes), 90% range (whiskers) and outliers (standalone data points) Eur J Anaesthesiol 2017; 34:534–543 Copyright © European Society of Anaesthesiology Unauthorized reproduction of this article is prohibited 540 Treschan et al Fig FVC (a) FEV1 (b) litres litres 6.0 6.0 P < 0.05 4.0 4.0 2.0 2.0 0.0 P < 0.05 0.0 PRE DAY DAY DAY PRE DAY DAY DAY Results of spirometry of patients with or without postoperative pulmonary complications (a) Forced vital capacity (FVC), and (b) Forced expiratory volume in s (FEV1) in patients with (grey bars) or without (black bars) postoperative pulmonary complications On postoperative day 5, spirometric results were significantly lower in patients who developed postoperative pulmonary complications Data are presented as median (thick line across box), interquartile ranges (ends of boxes), 90% range (whiskers) and outliers (standalone data points) summarised as follows: In patients ventilated with a tidal volume of ml kgÀ1 PBW, postoperative spirometry results are no different between patients receiving ventilation with high PEEP and RM and patients receiving ventilation with low PEEP without RM: postoperative spirometry results are abnormal up to postoperative day 5: occurrence of PPCs seems to be associated with a change in postoperative spirometry results on postoperative day To our knowledge, this is one of the largest prospective randomised controlled studies investigating the association between postoperative spirometry changes in patients undergoing major abdominal surgery and at risk of developing PPCs This substudy stopped when the PROVHILO trial completed recruitment, so we did not recruit the total number of patients required according to the sample size calculation, and we had less than 80% power to show a 20% statistically significant difference between the two groups A comparison of the median TWAs of the two treatment groups, high PEEP with RM versus low PEEP without RM, suggests no difference between FEV1 and a difference of only 6% in FVC The latter would not be considered to be of clinical relevance We calculated a potential effect size based on the means and standard deviation of each treatment group FVC TWA in the high PEEP group was 1.89 Ỉ 0.99 versus 1.95 Ỉ 0.68 in the low PEEP group FEV1 TWA in the high PEEP groups was 1.46 Ỉ 0.8 versus 1.29 Ỉ 0.5 I in the low PEEP group Thus, dCohen effect size for FVC TWA would be 0.07 [95% confidence interval, 95% CI -0.4 to 0.59] and 0.24 [95% CI -0.7 to 0.27] Our initial hypothesis and sample size calculation was built on a much stronger effect size of 0.5, which we consider to be clinically relevant However, we detected significant differences in spirometric test results between patients who developed PPCs and those who did not Although this might not seem to be a surprising result, to our knowledge, postoperative spirometry is not used commonly as a tool to detect or predict PPC It is important to note that our study was not designed to show a direct or timely correlation between spirometric results and the development of PPCs Further studies are needed to determine, whether spirometric results could predict or indicate the development of PPCs at an early stage such that this would allow the initiation of preventive or early therapeutic measures Postoperative spirometry per se might be a useful as a tool to detect PPCs However, technical and practical reasons limit its utility as a postoperative monitor For instance, pain needs to be adequately controlled and patients need to be fully awake and compliant In this substudy and preplanned analysis, we had a unique opportunity to determine the effect of two different levels of PEEP and RM during intraoperative ventilation on postoperative lung function test results Its prospective design, the completeness of follow-up and the fact that occurrence of PPCs was scored by assessors who were blind to the intraoperative ventilation strategy helped reduce bias In addition, the definition of PPCs was defined a priori and the patients were similar with regard to their clinical characteristics and type of surgery Lastly, all patients were ventilated with tidal volumes of ml kgÀ1 PBW; thus, we were able to assess the effect of PEEP and RMs on postoperative lung function FVC and FEV1 decreased by more than 50% compared with preoperative values in both randomisation groups This restrictive ventilatory pattern has long been recognised after upper abdominal surgery and results from Eur J Anaesthesiol 2017; 34:534–543 Copyright © European Society of Anaesthesiology Unauthorized reproduction of this article is prohibited PROVHILO spirometry 541 Fig FVC (a) litres 6.0 6.0 4.0 4.0 2.0 2.0 0.0 Low High PRE Low High DAY Low High DAY Low High 0.0 litres 6.0 6.0 4.0 4.0 2.0 2.0 UpperLower PRE UpperLower DAY UpperLower DAY UpperLower DAY 0.0 Low High DAY Low High DAY Low High DAY FEV1 (d) litres 0.0 Low High PRE DAY FVC (c) FEV1 (b) litres UpperLower PRE UpperLower DAY UpperLower DAY UpperLower DAY Results of spirometry in patients with high or low pulmonary compliance and upper or lower abdominal surgery, ventilated with high or low PEEP (a) Forced vital capacity (FVC), and (b) Forced expiratory volume in s (FEV1) for patients with high or low pulmonary compliance ventilated with high or low PEEP Patients with low ( 50 ml cmÀ1 H2O) or high (>50 ml cmÀ1 H2O) dynamic pulmonary compliance (as indicated by the brackets labelled ‘high’ or ‘low’ in the figures) were ventilated with high PEEP (black bars) or low PEEP (grey bars) On postoperative day 1, patients with high intraoperative pulmonary compliance had higher FVC (P ¼ 0.021) and FEV1 (P ¼ 0.016) than patients with low intraoperative pulmonary compliance Time-weighted average of FVC and FEV1 did not differ between patients with high or low intraoperative pulmonary compliance Data are presented as median (thick line across box), interquartile ranges (ends of boxes), 90% range (whiskers) and outliers (standalone data points) (c) Forced vital capacity (FVC), and (d) Forced expiratory volume in s (FEV1) for patients with upper or lower abdominal surgery ventilated with high or low PEEP Patients undergoing upper or lower abdominal surgery (indicated by brackets labelled ‘upper’ or ‘lower’ in the figures) were ventilated with high PEEP (black bars) or low PEEP (grey bars) On postoperative day 1, patients with lower abdominal surgery had higher FVC (P ¼ 0.011) and FEV1 (P ¼ 0.018) than patients with upper abdominal surgery Time-weighted average of FVC and FEV1 did not differ between patients with upper or lower abdominal surgery Data are presented as median (thick line across box), interquartile ranges (ends of boxes), 90% range (whiskers) and outliers (standalone data points) reduced ventilatory muscle activity, diaphragmatic dysfunction and decreased lung compliance and is also influenced by pain levels.21 Although we found intraoperative dynamic lung compliance to be significantly higher in the high PEEP group, this did not protect against a decline in postoperative lung function These findings are consistent with the overall results of the PROVHILO trial, in which the occurrence of PPCs was high, but not different between patients who received high PEEP or low PEEP during intraoperative ventilation.13 The results of the present study support the information that came from two preceding trials of intraoperative ventilation.9,22 In an Italian single-centre, randomised controlled trial of patients scheduled for open abdominal surgery lasting more than h, the FVC and FEV1 on postoperative day were also approximately 50% lower than preoperative values.9 However, in that trial, recovery of lung function was better in patients ventilated with a lung-protective ventilation strategy (a PEEP of 10 cmH2O, a low tidal volume of ml kgÀ1 PBW and RM) compared with patients ventilated with a Eur J Anaesthesiol 2017; 34:534–543 Copyright © European Society of Anaesthesiology Unauthorized reproduction of this article is prohibited 542 Treschan et al conventional ventilation strategy (no PEEP, a tidal volume of ml kgÀ1 PBW, without RM).9 In a German single-centre, randomised controlled trial of patients undergoing upper abdominal surgery, in which all patients received a similar level of PEEP and the same RM, postoperative changes in spirometry results were not different in patients ventilated with ml kgÀ1 PBW versus 12 ml kgÀ1 PBW.22 On the basis of the results of these two preceding trials and the results from the present study, we suggest that postoperative spirometry changes, specifically in the time course of lung function recovery, might be affected by a combination of the two parameters ‘size of intraoperative tidal volume’ along with ‘PEEP’ and ‘RM’, but not solely by changes either in ‘tidal volume’ or ‘PEEP’ alone Since publication of the Italian trial mentioned above, two other randomised trials of intraoperative ventilation have been published.10,11 In both trials, patients were randomly assigned to lung-protective ventilation with low tidal volumes and high PEEP or conventional ventilation with high tidal volume and no PEEP Both trials found fewer pulmonary complications with lung-protective ventilation The results from the original trial of this substudy, the PROVHILO trial,13 suggest that high levels of PEEP with RM not protect against development of PPCs in patients ventilated with low tidal volumes Accordingly, a differentiated algorithm for protective intraoperative mechanical ventilation has recently been proposed.23 In nonobese patients without acute respiratory distress syndrome undergoing open abdominal surgery, mechanical ventilation should be performed with tidal volumes of to ml kgÀ1 PBW combined with a low PEEP of cmH2O or less If hypoxemia develops and hypotension, hypoventilation or other causes have been excluded, inspiratory oxygen fraction should be increased first, followed by increase of PEEP and recruitment manoeuvers.23 Of note, high PEEP with RM failed to affect postoperative spirometry results in two subgroups of patients in which more benefit of high PEEP could be expected, that is in patients with a lower pulmonary compliance during intraoperative ventilation and patients who underwent upper abdominal surgery Our study was restricted to patients at risk of PPCs who were scheduled to undergo open abdominal surgery The majority of patients in our substudy received thoracic epidural anaesthesia both intraoperatively and postoperatively Therefore, the results could be different in other patient groups We detected differences in spirometric test results between patients who developed PPCs and those who did not However, our study was not designed to show a direct or timely correlation between spirometric results and the development of PPCs Further studies are needed to determine whether spirometric results could predict or indicate the development of PPCs at an early stage, and whether this would allow preventive or early therapeutic measures to be initiated However, even though postoperative spirometry per se might prove to be useful as a tool to detect PPCs, technical and practical reasons could limit its utility: postoperative pain needs to be adequately controlled, and patients need to be fully awake and compliant Another limitation of our study relates to intra-abdominal pressure Intra-abdominal pressure in the postoperative period could interfere with lung function and hence spirometry results We did not measure intra-abdominal pressure, and thus cannot evaluate, whether this influenced our results With the knowledge of our results, the question may arise as to whether patient management during the emergence phase of anaesthesia could influence lung function to such an extent that the consequences of several hours of intraoperative ventilation become negligible We not know whether extending the application of PEEP into the postoperative period, or prohibiting use of 100% oxygen during extubation would have changed our results Other trials suggest that if there is an effect due to how the emergence phase of anaesthesia is managed, this would only have minor consequences.24,25 Interestingly, as part of a protective ventilation strategy, the beneficial effect of RMs might also be questioned.26 The focus of our study was to compare the effects of several hours of ventilation using high levels of PEEP along with RMs with similar periods of ventilation without PEEP and RMs In conclusion, postoperative spirometry test results are not affected by the PEEP level during intraoperative ventilation during anaesthesia for open abdominal surgery in patients at high risk of PPC Spirometry test results on postoperative day five are associated with the development of PPCs during this time period Acknowledgements relating to this article Assistance with the study: we thank Renate Babian for her assistance with the study Financial support and sponsorship: this work was supported by the Department of Anesthesiology, Duăsseldorf University Hospital, Duăsseldorf, Germany Conflicts of interest: none Presentation: none References Tiefenthaler W, Pehboeck D, Hammerle E, et al Lung function after total 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104:643–647 Defresne AA, Hans GA, Goffin PJ, et al Recruitment of lung volume during surgery neither affects the postoperative spirometry nor the risk of hypoxaemia after laparoscopic gastric bypass in morbidly obese patients: a randomized controlled study Br J Anaesth 2014; 113:501–507 Eur J Anaesthesiol 2017; 34:534–543 Copyright © European Society of Anaesthesiology Unauthorized reproduction of this article is prohibited ... tone after induction of anesthesia. 1 In particular, in patients undergoing abdominal surgery, the risk of atelectasis increases the closer the incision is to the diaphragm.2,3 Although intraoperative... results of patients who had the incision closer to the diaphragm (i.e upper abdominal surgery) with those with the incision at a distance from the diaphragm (i.e lower abdominal surgery) and also... characteristics of patients enrolled in the original trial and patients in the substudy is provided in the online supplement (Supplement Table S2, http:// links.lww.com/EJA/A115) Among patients participating