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Intraoperative Lung-Protective Ventilation Trends and Practice Patterns

A Report from the Multicenter Perioperative Outcomes Group

Bender, S. Patrick MD*; Paganelli, William C. MD, PhD*; Gerety, Lyle P. MD*; Tharp, William G. MD, PhD*; Shanks, Amy M. PhD; Housey, Michelle MPH; Blank, Randal S. MD, PhD; Colquhoun, Douglas A. MBChB, MSc, MPH; Fernandez-Bustamante, Ana MD, PhD§; Jameson, Leslie C. MD§; Kheterpal, Sachin MD, MBA

doi: 10.1213/ANE.0000000000000940
Patient Safety: Research Report
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BACKGROUND: The use of an intraoperative lung-protective ventilation strategy through tidal volume (TV) size reduction and positive end-expiratory pressure (PEEP) has been increasingly investigated. In this article, we describe the current intraoperative lung-protective ventilation practice patterns and trends.

METHODS: By using the Multicenter Perioperative Outcomes Group database, we identified all general endotracheal anesthetics from January 2008 through December 2013 at 10 institutions. The following data were calculated: (1) percentage of patients receiving TV > 10 mL/kg predicted body weight (PBW); (2) median initial and overall TV in mL/kg PBW and; (3) percentage of patients receiving PEEP ≥ 5 cm H2O. The data were analyzed at 3-month intervals. Interinstitutional variability was assessed.

RESULTS: A total of 330,823 patients met our inclusion criteria for this study. During the study period, the percentage of patients receiving TV > 10 mL/kg PBW was reduced for all patients (26% to 14%) and in the subpopulations of obese (41% to 25%), short stature (52% to 36%), and females (39% to 24%; all P values <0.001). There was a significant reduction in TV size (8.90–8.20 mL/kg PBW, P < 0.001). There was also a statistically significant but clinically irrelevant difference between initial and overall TV size (8.65 vs 8.63 mL/kg PBW, P < 0.001). Use of PEEP ≥ 5 cm H2O increased during the study period (25%–45%, P < 0.001). TV usage showed significant interinstitutional variability (P < 0.001).

CONCLUSIONS: Although decreasing, a significant percentage of patients are ventilated with TV > 10 mL/kg PBW, especially if they are female, obese, or of short stature. The use of PEEP ≥ 5 cm H2O has increased significantly. Creating awareness of contemporary practice patterns and demonstrating the efficacy of lung-protective ventilation are still needed to optimize intraoperative ventilation.

Published ahead of print September 1, 2015

From the *Department of Anesthesiology, University of Vermont College of Medicine, Burlington, Vermont; Department of Anesthesiology, University of Michigan Medical School, Ann Arbor, Michigan; Department of Anesthesiology, University of Virginia School of Medicine, Charlottesville, Virginia; and §Department of Anesthesiology, University of Colorado School of Medicine, Aurora, Colorado.

Lyle P. Gerety, MD, is currently affiliated with Stanford University, Stanford, California.

Accepted for publication July 7, 2015.

Published ahead of print September 1, 2015

Funding: All work and partial funding attributed to the Department of Anesthesiology, University of Vermont College of Medicine, Burlington, VT; Department of Anesthesiology, University of Virginia School of Medicine, Charlottesville, VA; Department of Anesthesiology, University of Colorado, Aurora, CO; and Department of Anesthesiology, University of Michigan Medical School, Ann Arbor, MI.

Conflict of Interest: See Disclosures at the end of the article.

This report was previously presented, in part, at the 2014 ASA Journal Symposium, New Orleans, LA.

LMA is a registered trade mark of The Laryngeal Mask Company Limited, an affiliate of Teleflex Incorporated.

Reprints will not be available from the authors.

Address correspondence to S. Patrick Bender, MD, University of Vermont, College of Medicine, 111 Colchester Ave., ACC-WP2, Burlington, VT 05401. Address e-mail to stephen.bender@uvmhealth.org.

Initial experimentation with lower tidal volumes (TVs) was shown to be a safe approach for intensive care unit (ICU) patients.1 Further data have demonstrated that lung-protective ventilation (LPV) with low TVs of 6 mL/kg predicted body weight (PBW) results in reduced mortality in patients with acute lung injury (ALI) and acute respiratory distress syndrome.2,3 In addition, there is evidence for an association between high initial TV at mechanical ventilation onset and the eventual development of lung inflammation and injury in ventilated patients without preexisting ALI.4–8 The use of LPV in ICU patients at risk for ALI or acute respiratory distress syndrome is now widely accepted.

The notion that intraoperative LPV strategies may be beneficial for surgical patients is appealing and is mostly supported by recently emerging data.9 Specifically, intraoperative LPV has shown benefits for patients undergoing pneumonectomy,10 cardiac surgery,11–13 esophagectomy,14 or abdominal surgery.15 In 2007, Schultz et al.16 published recommendations regarding intraoperative TV size. They recommend patients with abnormal lungs and/or risk factors for ALI to receive TV ≤ 6 mL/kg PBW and those with normal lungs and no ALI risk factors to receive TV of ≤ 10 mL/kg PBW. Despite these recommendations, a single-center study reported that ventilation with a TV of >10 mL/kg PBW continued to be performed at a frequent rate. This rate was more likely to occur in the subpopulations of obese patients, patients of short stature, and female patients, suggesting ventilation with TV > 10 mL/kg PBW may be unintentional.17 Likewise, clinicians do not seem to adjust their ventilation strategies routinely based on a diagnosis of ALI.18

Another possibly beneficial component of intraoperative LPV is the routine use of positive end-expiratory pressure (PEEP). Schultz et al.16 also recommended PEEP ≥ 5 cm H2O for all patients. However, more recent data regarding intraoperative PEEP for LPV have conflicting results. The PROVHILO study demonstrated no difference in postoperative pulmonary complications between high and low PEEP,19 whereas the IMPROVE study demonstrated more postoperative pulmonary complications in the low-PEEP, high-TV group.15

What remains controversial is whether the control group protocols in the highly discussed IMPROVE (10–12 mL/kg PBW, no PEEP) and PROVHILO (8 mL/kg PBW, PEEP ≤ 2 cm H2O) studies accurately reflect modern clinical practice,15 and there has been a call for a more accurate demonstration of contemporary practice patterns.20 Recently, it has been reported that intraoperative ventilation habits in Australia (mean TV, 9.7 mL/kg PBW and frequent use of PEEP) and Europe (mean TV, 8.8 mL/kg IBW and infrequent use of PEEP) vary compared with each other and are not completely consistent with the control groups of these previously described IMPROVE or PROVHILO trials.21,22

We sought to contribute to a better understanding of true contemporary practice by using the Multicenter Perioperative Outcomes Group (MPOG) database for the assessment of intraoperative TV and PEEP habits and temporal trends. We hypothesized that (1) many patients continue to receive TV > 10 mL/kg PBW, especially obese, short, and female patients; (2) initial TV may differ from overall TV because of an adjustment delay in the default ventilator settings (the preset values that exist when a ventilator is activated from power off to power on); (3) many patients receive PEEP < 5 cm H2O and; (4) TV habits may vary by institution.

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METHODS

University of Michigan IRB approval (Ann Arbor, MI) was obtained for this retrospective observational study. Each participating institution that contributed data also received IRB approval to submit a limited dataset without direct patient identifiers into the centralized data repository (MPOG). Because no patient care interventions were needed, signed informed patient consent was waived by each participating IRB.

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Patient Population

The following MPOG participating institutions contributed data for this study: Columbia University Medical Center (New York, NY), Oregon Health and Science University (Portland, OR), University Medical Center—Utrecht (Netherlands), University of Colorado (Aurora, CO), University of Michigan Health System (Ann Arbor, MI), University of Oklahoma Health Sciences Center (Oklahoma City, OK), University of Tennessee Medical Center (Knoxville, TN), University of Vermont Medical Center (Burlington, VT), University of Virginia Health System (Charlottesville, VA), and Washington University School of Medicine (St. Louis, MO).

All adult (18 years or older) patients undergoing an operative procedure involving anesthesiology care at the participating institutions between 2008 and 2013 with a valid height of 48 to 84 inches (121.92–213.36 cm) and a valid median overall TV (100–2000 mL) were included in the analysis. The following exclusion criteria were then applied: nongeneral anesthetic procedures defined as the absence of documented intubation or administration of neuromuscular blockade, procedures involving use of a laryngeal mask airway, total anesthesia time from anesthesia start to end of <45 minutes, ASA physical status VI, 1-lung ventilation cases, or <30 valid TV measurements during the procedure.

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Data Collection

Research data were extracted from the MPOG centralized repository. The detailed methodology of the MPOG has been discussed elsewhere,23–25 and the components related to this study are discussed here. All consecutive intraoperative anesthesia records that are documented within each institution’s electronic health record (EHR) were electronically extracted and stored within the MPOG database. Automated, validated interfaces at each site record physiologic measurements from the ventilator, gas analyzer, and physiologic monitor every 60 seconds. All manual documentation of preoperative history and physical, intraoperative interventions, medications, and observations also are included in the MPOG database.

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TV Measurements

A variety of modern anesthesia machines from several vendors were in use during the study period. We extracted intraoperative TV data from anesthesia start to anesthesia end. All centers contributing data to this project recorded intraoperative TV every 60 seconds using an automated interface. For each procedure, the expired TV, as measured and reported by the ventilator, was used. If expired TV was not recorded for a specific procedure, the TV set (for volume control modes) was used. TV measurements were converted from liters to milliliters, as appropriate. All measurements <100 mL or >2000 mL were excluded as artifact or outlier data. This wide range of valid TVs (100–2000 mL) was chosen to ensure capture of true ventilation onset and end, because small or large TV may occur at the beginning or end of a case, respectively.

The median overall TV was defined as the median of all valid TVs from anesthesia start to anesthesia end. The total number of TV measurements included in this median calculation also was recorded for each operation. To assess the impact of ventilator default settings, the median initial TV was then calculated for each operation. The initial period was identified using 2 mechanisms. First, for centers that contributed automated ventilator mode data every 60 seconds, the initial period was defined as the period from 0 to 10 minutes after controlled ventilation was initiated. For centers without automated data capture of ventilator mode, the initial period was defined as the period from 10 to 20 minutes after a peak inspiratory pressure of 5 cm H2O was observed to accommodate the period of mask ventilation (if any) and airway instrumentation before controlled ventilation. Patient PBW was calculated for both males and females: males = 50 kg + 2.3 kg (height [in] − 60) and females = 45.5 kg + 2.3 kg (height [in] − 60).a Obesity was defined using the World Health Organization Classification of body mass index ≥ 30 mg/kg2. Short stature was defined as a height < 165 cm, consistent with the previously mentioned single-center study.17

In addition to TV data, measured PEEP data were collected every 60 seconds from anesthesia start to anesthesia end. A median was calculated for each procedure. All institutions except 1 contributed PEEP data.

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Outcomes

The primary outcome was large overall median TV defined as >10 mL/kg PBW (yes/no). Secondary outcomes included large initial TV (>10 mL/kg PBW), median TV as a continuous measure (mL/kg PBW), and median overall PEEP of ≥5 cm H2O. The incidence of large overall and initial TV administration was evaluated for the overall study population and for the subpopulations of obese patients, patients with short stature, and females. To identify practice change over time, procedures were grouped into consecutive 3-month periods (quarters) from 2008 to 2013. In addition, we investigated the percentage of large TVs across the institutions for each of the aforementioned groups. Finally, the incidence of median overall PEEP ≥ 5 cm H2O was calculated over time and across institutions.

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Statistical Analysis

All data processing and statistical analysis were performed using SPSS®, version 21 (IBM Corporation, Yonkers, NY) and StataSE®, version 13 (College Station, TX). All figures were prepared using Sigma Plot® (San Jose, CA). The primary outcome was defined as an overall median TV > 10 mL/kg PBW (yes/no). It was registered with the MPOG publications committee on December 9, 2013, and approved on January 6, 2014. Per MPOG bylaws, the study protocol must be approved before any data extraction or analysis. To investigate variance in overall and initial TVs across institutions, a random-effects population–averaged linear model was developed. The panel variable was the institution, and the time variable was the period. To assess significant changes in overall and initial TVs across the periods, the coefficient and P value were examined. The variance in overall and initial TVs attributed to institutions was evaluated and denoted by ρ (intraclass correlation). The same modeling techniques were used to assess the subpopulations (obesity, short stature, female) as well as the median overall PEEP ≥ 5 cm H2O. We also analyzed for a statistical difference within institutions and across all institutions between the initial and overall median TV using a Wilcoxon signed rank test. To determine the variance across institutions in patients receiving overall median TVs >10 mL/kg PBW, a mixed-effects logistic regression model was developed controlling for the fixed effects of age, male gender, body mass index, short stature, ASA physical status, emergent case, year of operation, and the interaction effect of year and institution. The random effect in this model was institution. A P of <0.05 was considered statistically significant throughout.

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RESULTS

Table 1

Table 1

Table 2

Table 2

Table 3

Table 3

Figure 1

Figure 1

Figure 2

Figure 2

Figure 3

Figure 3

Figure 4

Figure 4

Figure 5

Figure 5

A total of 330,823 cases met our inclusion criteria for this study (Fig. 1). The percentage of patients who have received TVs > 10 mL/kg PBW has significantly decreased for the overall TV of the case (26% to 14%), for the initial TV of the case (32% to 16%), and in the subpopulations of obesity (41% to 25%), short stature (52% to 36%), and females (39% to 24%), and all demonstrated large institution variance (Fig. 2; Table 1; Appendix 1, all P values <0.001). The trend in the median TV has also significantly decreased for the overall TVs (8.90 mL/kg PBW interquartile range [IQR], 7.88–10.04 to 8.20 mL/kg PBW IQR, 7.34–9.28), for initial TVs (9.07 mL/kg PBW IQR, 7.89–10.39 to 8.08 mL/kg PBW IQR 7.05–9.34), and in the subpopulations of obesity (9.59 mL/kg PBW IQR, 8.53–10.87 to 8.80 mL/kg PBW IQR 7.78–9.98), short stature (10.10 mL/kg PBW IQR, 8.88–11.24 to 9.44 mL/kg PBW IQR, 8.44–10.56), and females (9.56 mL/kg PBW IQR, 8.47–10.68 to 8.86 mL/kg PBW IQR, 7.89–9.94; Fig. 3), and all demonstrated large institution variance (Fig. 4; Table 2, all P values <0.001). When comparing the initial median TV in milliliter per kilogram of PBW with the overall median TV across all institutions, we found statistically significant differences, but not clinically relevant differences (8.65 mL/kg PBW IQR, 7.53–9.95 and 8.63 mL/kg PBW IQR, 7.66–9.76, P < 0.001; Table 3). There was also a significant increase during the study period in the percentage of patients receiving PEEP ≥ 5 cm H2O (25% to 45%; coefficient, 0.74; P < 0.001) as well as large institution variance (ρ, 85%; Fig. 5). The mixed-effects logistic regression model confirmed significant variation across institutions in the percentage of patients receiving TVs > 10 mL/kg PBW and demonstrated an 18% (95% confidence interval, 7.4%–42.8%) variance.

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DISCUSSION

This study demonstrates that (1) a significant percentage of patients continue to be mechanically ventilated at TVs > 10 mL/kg PBW; (2) median intraoperative TV size has decreased in the past 6 years; (3) short-stature, obese, or female patients generally have their lungs ventilated with larger TVs per PBW than the general population; (4) the percentage of patients receiving PEEP ≥ 5 cm H2O is increasing; and (5) there is a significant variability among institutions in the percentage of patients who receive TVs > 10 mL/kg PBW.

Many of the intraoperative studies showing benefit of LPV have focused on TV size reduction, leading some to caution against the premature translation of standard ICU ventilation strategies to the operating room, reminding us that atelectasis prevention is another important part of LPV. This is usually accomplished in the ICU by the administration of PEEP and, occasionally, recruitment maneuvers.26 The IMPROVE15 study of low intraoperative TVs in abdominal surgery used PEEP and recruitment maneuvers in the low TV group and no PEEP or recruitment maneuvers in the high TV group, showing fewer pulmonary complications in the former group. It is possible that the decrease in postoperative pulmonary complications is attributable to the use of PEEP and recruitment maneuvers, leading to the prevention of atelectasis and atelectrauma, and not from the use of low TVs. This is contradicted by the results of the PROVHILO study, which showed no difference in postoperative pulmonary complications between the low and high PEEP groups.19 Some of the contradictory results between the IMPROVE and PROVIHLO trials could be attributable to varying TV in the control groups (10–12 mL/kg PBW vs 8 mL/kg PBW), varying PEEP levels in the study groups (6–8 cm H2O vs 12 cm H2O), or slightly different study populations (IMPROVE included laparoscopic cases). Our data demonstrate that there has been a progressive increase in the use of PEEP by anesthesiologists in the intraoperative period to accompany the decrease in TV size. Because PEEP use is becoming more widespread, recent control groups using no PEEP in the IMPROVE study or PEEP ≤ 2 in the PROVHILO study may be inappropriate because they may not reflect current practice. Because the application of recruitment maneuvers is not documented consistently within and across EHRs or centers, we could not describe current practice patterns in this area of LPV.

Because of the inherent need to know height to calculate milliliter per kilogram of PBW, we were only able to include patients with documented height in the database. We hypothesize that a significant obstacle preventing consistent appropriate TV selection is the availability of patient height documentation and anesthesiology provider awareness of its clinical impact. In care systems without enterprise EHRs, this presents significant care process challenges. Communication across providers must improve, or patient height must be measured or inquired about before arrival to the operating room. In addition, ventilators on modern anesthesia machines do not commonly require gender or height data when setting a TV. This is a likely reason why short-stature, obese, and/or female patients are more frequently have their lungs ventilated at inappropriately high TVs. It would be ideal for a ventilator to require gender, height, and desired milliliter per kilogram before initiation of mechanical ventilation. Although actual body weight is well documented by anesthesiologists and incorporated into care processes during medication dosing, patient’s height lacks this clinical primacy in the typical operating room.

Our hypothesis that initial TVs would differ from overall TVs was statistically confirmed. Because of the large number of patients included in this study, even the small difference between initial and overall TVs was statistically significant. However, we do not feel this small difference between initial and overall TV is clinically relevant, because it does not meet our predetermined clinical significance threshold of >1 mL/kg PBW difference.

Each of the overall, obese, short stature, and female subgroup analyses showed marked variation across institutions. Our data suggest that 18% of the variation in TV is attributable to institutional bias alone with controlling for age, gender, obesity, short stature, ASA, emergency status, and the interaction effect of year and institution. One possible explanation of this variability is the potential of diverse default ventilator settings at different institutions and/or different anesthetizing locations within the same institution. In addition, the use of cognitive aids to alert providers that a patient has ALI risk factors has been shown to reduce TV size.27 Certainly, this type of cognitive aid use may vary across institutions, contributing to interinstitutional variability of TV size. Also, different educational programs, degree of LPV literature familiarity, and areas of scholastic interest may all differ among the varied institutions.

Another obstacle to consistent implementation of this careful approach to selection of intraoperative LPV settings may be the same obstacle seen in many, if not all, areas of medical research; a lag from publication to wide implementation. There are many things that influence the duration of this usual lag; skepticism, the need for a article to be cited frequently enough to create awareness, and importance of the clinical problem.26,28 Our data do demonstrate a gradual reduction over time in the percentage of patients ventilated at >10 mL/kg PBW and the percentage of patients receiving PEEP < 5 cm H2O. Also, the data period for this study ended in December 2013. The IMPROVE study was published in 2013 and PROVHILO in 2014. Certainly, our data cannot currently demonstrate the full impact these studies have had on the TV size and PEEP usage.

This study has several other limitations. First, there are no data in this study that demonstrate patients receiving large TVs or low PEEP had worse outcomes. This is a descriptive study using TVs from a heterogeneous population that generated a single-target median TV without delineating between patients who should have received LPV and those who were appropriate for higher TVs. Ideally, the next step would be to link these data with outcome data to identify a relationship in real-world practice. Analyzing these data according to ASA physical status would certainly help to distinguish more ill patients, but would not necessarily discriminate between those with and without ALI risk factors and thus was not performed in this study.

Next, this is an analysis using data from institutions with varied EHRs, and these data are then merged into a single database. This may have resulted in data inconsistency issues. Although distinct EHRs may store similar clinical concepts with distinct terminologies, the MPOG methodology involves detailed mapping by clinicians of each data element. Objective concepts such as height, weight, gender, TVs, and PEEP are mapped to MPOG standardized terminology, and units of measures are synchronized. Hundreds of hours are spent at each MPOG site performing detailed content mapping, schema transformation, data diagnostics, and data validation to minimize or eliminate the variation in data used for analyses. Despite this, there remains the potential for data errors.

Despite these limitations, this study has shown that, although decreasing, a significant percentage of patients receive PEEP < 5 cm H2O and TV > 10 mL/kg PBW intraoperatively. We believe that this highlights the need for continued investigation and education regarding the potential benefits of intraoperative LPV. Particular areas of focus should include (1) broad clinical investigations regarding the clinical impact of integrating PEEP use and reduced TVs for the prevention of perioperative complications; (2) improvement of height documentation; (3) departmental thoughtfulness of default ventilator settings; and (4) mindfulness of targeted intraoperative TV selection based on the patient lung injury risk factors, gender, and height.

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Appendix 1. Percentage of Cases Receiving TV > 10 mL/kg PBW per Institution by Subgroup Population

Table

Table

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APPENDIX 2

Members of the MPOG Perioperative Clinical Research Committee

  • Ana Fernandez-Bustamante, MD, PhD, Associate Professor, Department of Anesthesiology, University of Colorado, Aurora, CO.
  • Leslie C. Jameson, MD, Associate Professor and Vice Chair, Department of Anesthesiology, University of Colorado, Aurora, CO.
  • Daniel A. Biggs, MD, Associate Professor, Department of Anesthesiology, University of Oklahoma Health Sciences Center, Oklahoma City, OK.
  • Jonathan Wanderer, MD, PhD, Assistant Professor, Department of Anesthesiology, Vanderbilt University Medical Center, Nashville, TN.
  • Jerry L. Epps, MD, Associate Professor and Chair, Department of Anesthesiology, University of Tennessee Graduate School of Medicine, Knoxville, TN.
  • Robert M. Craft, MD, Professor, Department of Anesthesiology, University of Tennessee Graduate School of Medicine, Knoxville, TN.
  • Michael F. Aziz, MD, Associate Professor, Department of Anesthesiology, Oregon Health and Science University, Portland, OR.
  • Mitchell F. Berman, MD, Professor, Department of Anesthesiology, Columbia University Medical Center, New York, NY.
  • Kevin L. Wethington, MD, Associate Professor, Department of Anesthesiology, University of Utah, Salt Lake City, UT.
  • Nathan L. Pace, MD, MStat, Professor, Department of Anesthesiology, University of Utah, Salt Lake City, UT.
  • William C. Paganelli, MD, PhD, Associate Professor, Department of Anesthesiology, University of Vermont College of Medicine, Burlington, VT.
  • Wilton Van Klei, MD, PhD, Professor, Department of Anesthesiology, University Medical Center, Utrecht, Netherlands.
  • Peter Fleischut, MD, Associate Professor, Department of Anesthesiology, Weill Cornell Medical College, New York, NY.
  • Timothy Morey, MD, Professor, Department of Anesthesiology, University of Florida Medical School, Gainesville, FL.
  • Marcel Durieux, MD, PhD, Professor, Department of Anesthesiology, University of Virginia School of Medicine, Charlottesville, VA.
  • Bhiken Naik, MBBCh, Assistant Professor, Department of Anesthesiology, University of Virginia School of Medicine, Charlottesville, VA.
  • Bala Nair, PhD, Assistant Professor, Department of Anesthesiology, University of Washington Medical School, Seattle, WA.
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DISCLOSURES

Name: S. Patrick Bender, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: S. Patrick Bender has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Conflicts of Interest: S. Patrick Bender has no conflicts of interest to declare.

Name: William C. Paganelli, MD, PhD.

Contribution: This author helped design the study, conduct the study, and analyze the data.

Attestation: William C. Paganelli has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: William C. Paganelli has no conflicts of interest to declare.

Name: Lyle P. Gerety, MD.

Contribution: This author helped design the study, conduct the study, and analyze the data.

Attestation: Lyle P. Gerety has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Lyle P. Gerety declares no conflicts of interest.

Name: William G. Tharp, MD, PhD.

Contribution: This author helped design the study, analyze the data, and write the manuscript.

Attestation: William G. Tharp has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: William G. Tharp declares no conflicts of interest.

Name: Amy M. Shanks, PhD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Amy M. Shanks has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Amy M. Shanks declares no conflicts of interest.

Name: Michelle Housey, MPH.

Contribution: This author helped analyze the data and write the manuscript.

Attestation: Michelle Housey has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Michelle Housey declares no conflicts of interest.

Name: Randal S. Blank, MD, PhD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Randal S. Blank has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Randal S. Blank declares no conflicts of interest.

Name: Douglas A. Colquhoun, MBChB, MSc, MPH.

Contribution: This author helped design the study, analyze the data, and write the manuscript.

Attestation: Douglas A. Colquhoun has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Douglas A. Colquhoun declares no conflicts of interest.

Name: Ana Fernandez-Bustamante, MD, PhD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Ana Fernandez-Bustamante has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Ana Fernandez-Bustamante declares no conflicts of interest.

Name: Leslie C. Jameson, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Leslie C. Jameson has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Leslie C. Jameson served on a GE International Advisory Board last year, but has since termed out. GE makes anesthesia workstations. Dr. Jameson has also served on a Masimo Advisory Board, which is held at ASA every year, but did not attend this year.

Name: Sachin Kheterpal, MD, MBA.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Sachin Kheterpal has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Sachin Kheterpal declares no conflicts of interest.

This manuscript was handled by: Sorin J. Brull, MD.

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ACKNOWLEDGMENTS

The authors thank the MPOG Perioperative Clinical Research Committee for their contributions to the development and management of the MPOG database (Appendix 2).

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FOOTNOTE

a NHLBI ARDS Network predicted body weight calculator. Available at: http://www.ardsnet.org/tools.shtml. Accessed August 13, 2015.
Cited Here...

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