Protective positive end-expiratory pressure and tidal volume adapted to lung compliance determined by a rapid positive end-expiratory pressure-step procedure in the operating theatre: a post hoc analysis

Abstract

Editor—Postoperative pulmonary complications (PPCs) occur in up to 30% of patients undergoing major surgery.1Shander A. Fleisher L.A. Barie P.S. Bigatello L.M. Sladen R.N. Watson C.B. Clinical and economic burden of postoperative pulmonary complications: patient safety summit on definition, risk-reducing interventions, and preventive strategies.Crit Care Med. 2011; 39: 2163-2172Crossref PubMed Scopus (142) Google Scholar High airway driving pressure during surgery and changes in PEEP levels resulting in a higher airway driving pressure are associated with increased PPC.2Neto A.S. Hemmes S.N. Barbas C.S. et al.Association between driving pressure and development of postoperative pulmonary complications in patients undergoing mechanical ventilation for general anaesthesia: a meta-analysis of individual patient data.Lancet Respir Med. 2016; 4: 272-280Abstract Full Text Full Text PDF PubMed Scopus (302) Google Scholar Still, none of the predictive scores includes lung mechanical properties as a factor for PPC.3Miskovic A. Lumb A.B. Postoperative pulmonary complications.Br J Anaesth. 2017; 118: 317-334Abstract Full Text Full Text PDF PubMed Scopus (323) Google Scholar On an individual patient basis, airway driving pressure is not representative of the actual driving pressure distending the lung, the transpulmonary driving pressure.4Gattinoni L. Pelosi P. Suter P.M. Pedoto A. Vercesi P. Lissoni A. Acute respiratory distress syndrome caused by pulmonary and extrapulmonary disease. Different syndromes?.Am J Respir Crit Care Med. 1998; 158: 3-11Crossref PubMed Scopus (712) Google Scholar,5Chiumello D. Carlesso E. Brioni M. Cressoni M. Airway driving pressure and lung stress in ARDS patients.Crit Care. 2016; 20: 276Crossref PubMed Scopus (84) Google Scholar We have reported that by changing PEEP and determining the change in end-expiratory lung volume (ΔEELV) from ventilator spirometry,6Grivans C. Lundin S. Stenqvist O. Lindgren S. Positive end-expiratory pressure-induced changes in end-expiratory lung volume measured by spirometry and electric impedance tomography.Acta Anaesthesiol Scand. 2011; 55: 1068-1077Crossref PubMed Scopus (53) Google Scholar lung compliance can be calculated without using oesophageal pressure measurements.7Lundin S. Grivans C. Stenqvist O. Transpulmonary pressure and lung elastance can be estimated by a PEEP-step manoeuvre.Acta Anaesthesiol Scand. 2015; 59: 185-196Crossref PubMed Scopus (20) Google Scholar,8Persson P. Stenqvist O. Lundin S. Evaluation of lung and chest wall mechanics during anaesthesia using the PEEP-step method.Br J Anaesth. 2018; 120: 860-867Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar Here, we reanalysed post hoc our previous data8Persson P. Stenqvist O. Lundin S. Evaluation of lung and chest wall mechanics during anaesthesia using the PEEP-step method.Br J Anaesth. 2018; 120: 860-867Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar to see whether use of a two PEEP-step trial would provide a complete lung pressure/volume (P/V) curve from end-expiration at clinical PEEP to end-inspiration at the highest PEEP level, and if it could be used to determine the PEEP level with the lowest transpulmonary driving pressure (i.e. the optimal PEEP level).This is a post hoc analysis of raw data from the original validation study of the PEEP-step method,8Persson P. Stenqvist O. Lundin S. Evaluation of lung and chest wall mechanics during anaesthesia using the PEEP-step method.Br J Anaesth. 2018; 120: 860-867Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar in which 24 patients, age 55 (18) yr; BMI 24.9 (4.0) kg m−2; height 172 (8) cm; and scheduled for gynaecological, thyroid, or parathyroid surgery or thoracoscopy, were included.The study was approved by the Swedish Regional Research Ethics Committee and registered at ClinicalTrials.gov (NCT02830516). Informed consent was obtained from all patients.Measurements were performed before start of surgery in supine position during volume control ventilation with a tidal volume of 6 ml kg−1 ideal body weight. During PEEP steps of 5–9–5, 5–12–5, and 5–14–5 cm H2O, ΔEELV was determined as the cumulative difference in expiratory tidal volume before and during the first 15 breaths after changing PEEP.6Grivans C. Lundin S. Stenqvist O. Lindgren S. Positive end-expiratory pressure-induced changes in end-expiratory lung volume measured by spirometry and electric impedance tomography.Acta Anaesthesiol Scand. 2011; 55: 1068-1077Crossref PubMed Scopus (53) Google Scholar,8Persson P. Stenqvist O. Lundin S. Evaluation of lung and chest wall mechanics during anaesthesia using the PEEP-step method.Br J Anaesth. 2018; 120: 860-867Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar In the PEEP-step method, transpulmonary plateau pressure at the highest PEEP level (PLplat) must be estimated as airway plateau pressure minus tidal volume times chest wall elastance, the latter extrapolated from PEEP 5 and 9 cm H2O. This is a limitation of the PEEP-step method, but evaluation of this estimation shows that estimated PLplat only differed 0.1 (0.8) cm H2O from the corresponding PLplat calculated from conventional oesophageal measurements performed in the original study.The equation for the best-fit lung P/V curve was determined between end-expiration at baseline PEEP, ≈5 cm H2O, and end-inspiration at PEEP ≈14 cm H2O. The PEEP level where the transpulmonary driving pressure was lowest (i.e. optimal PEEP) was computed from the equation for the lung P/V curve. Overall lung compliance (CLtot) was calculated as the change in volume between end-expiration at 0 PEEP and end-inspiration at PEEP 14 cm H2O divided by the corresponding transpulmonary pressure.A lung P/V curve could be obtained by a two-PEEP-step procedure in all 24 patients. The mean CLtot was 97 (59–137) ml cm H2O−1 with an individual variation ranging from values indicative of moderate acute respiratory distress syndrome to emphysema in these patients undergoing elective surgery. In addition, patients with the same overall lung compliance showed completely opposite lung P/V curves with increasing or decreasing lung compliance when increasing PEEP (Fig. 1).At the PEEP level with the lowest transpulmonary driving pressure, or optimal PEEP, which was at 9.8 (5.0–15.0) cm H2O, the transpulmonary driving pressure was 3.8 (2.2–8.4) cm H2O (Fig. 1). The transpulmonary driving pressure at the clinically used PEEP level of 5 cm H2O was 4.9 (3.2–10.0) cm H2O, which was 22 (0–95)% higher than at the optimal PEEP level. The ratio of transpulmonary to airway driving pressure, ΔPL/ΔPAW, was 0.60 (0.13), ranging from 0.30 to 0.81, with only a very weak correlation between ΔPL and ΔPAW, R2=0.20 for the whole group. The change in ΔPL and ΔPAW when changing PEEP was not correlated in individual patients. Detailed methods, mathematical proof of concept of the PEEP-step method, measurement precision analysis of the PEEP-step method, and results with lung P/V curves and optimal PEEP for individual patients can be found in the Supplementary material.In patients undergoing elective surgery with a lung compliance of around 100 ml cm H2O−1, a tidal volume related to ideal body weight of 420 (299–547) ml resulted in a mean ΔPL of only 4.1 cm H2O. However, in two patients with very low lung compliance, ΔPL at baseline PEEP of 5 cm H2O was close or equal to the upper safety limit of 10 cm H2O (see Supplementary material for background of ΔPL limit). This indicates that a tidal volume of 6 ml kg−1 ideal body weight may not be protective in all patients. However, the PEEP-step method makes it possible to tailor tidal volume to lung compliance to reach a ΔPL that is within safe limits. Thus, in those two patients, a tidal volume adapted to lung compliance, around 300 ml, instead of 6 ml kg−1 ideal body weight, around 500 ml, resulted in a decrease in ΔPL from 8.4 and 7.4 cm H2O to 3.7 and 4.1 cm H2O, respectively.In nine of 10 patients, anaesthesia causes atelectasis with a decrease in EELV and compliance,9Hedenstierna G. Rothen H.U. Atelectasis formation during anesthesia: causes and measures to prevent it.J Clin Monit Comput. 2000; 16: 329-335Crossref PubMed Scopus (145) Google Scholar which remain postoperatively and are important sources of PPC. As the PEEP-step method offers quantification of ΔEELV and lung compliance, progress of atelectasis during major abdominal surgery, and need for a recruitment manoeuvre and possibly postoperative CPAP, can be identified by repeating the PEEP-step measurement before tracheal extubation.The great individual variation in lung compliance and PEEP response in patients scheduled for elective surgery implies a need for improved assessment of lung mechanics. We have shown that it is possible to determine lung compliance and the PEEP level, where transpulmonary driving pressure is lowest by implementing a rapid (≈3 min) two-PEEP step measurement procedure, instead of a conventional 10–30 min PEEP titration procedure to determine the PEEP level with highest respiratory system compliance and lowest airway driving pressure. Determination of overall lung compliance makes it possible to adapt tidal volume to the elastic properties of the individual patient's lungs instead of ideal body weight, minimising the risk of over-distension.10Young C.C. Harris E.M. Vacchiano C. et al.Lung-protective ventilation for the surgical patient: international expert panel-based consensus recommendations.Br J Anaesth. 2019; 123: 898-913Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar The need for individualised PEEP levels has also been highlighted in children, given their wide range in body weight.11Lee J.-H. Ji S.-H. Lee H.-C. et al.Evaluation of the intratidal compliance profile at different PEEP levels in children with healthy lungs: a prospective, crossover study.Br J Anaesth. 2020; 125: 818-825Abstract Full Text Full Text PDF PubMed Scopus (4) Google Scholar,12Lee J.-H. Kang P. Song I.S. et al.Determining optimal positive end-expiratory pressure and tidal volume in children by intratidal compliance: a prospective observational study.Br J Anaesth. 2021; 128: 214-221Abstract Full Text Full Text PDF PubMed Scopus (3) Google ScholarDeclarations of interestOS is a shareholder of Lung Barometry Sweden AB. PP has no conflict of interest to declare. Editor—Postoperative pulmonary complications (PPCs) occur in up to 30% of patients undergoing major surgery.1Shander A. Fleisher L.A. Barie P.S. Bigatello L.M. Sladen R.N. Watson C.B. Clinical and economic burden of postoperative pulmonary complications: patient safety summit on definition, risk-reducing interventions, and preventive strategies.Crit Care Med. 2011; 39: 2163-2172Crossref PubMed Scopus (142) Google Scholar High airway driving pressure during surgery and changes in PEEP levels resulting in a higher airway driving pressure are associated with increased PPC.2Neto A.S. Hemmes S.N. Barbas C.S. et al.Association between driving pressure and development of postoperative pulmonary complications in patients undergoing mechanical ventilation for general anaesthesia: a meta-analysis of individual patient data.Lancet Respir Med. 2016; 4: 272-280Abstract Full Text Full Text PDF PubMed Scopus (302) Google Scholar Still, none of the predictive scores includes lung mechanical properties as a factor for PPC.3Miskovic A. Lumb A.B. Postoperative pulmonary complications.Br J Anaesth. 2017; 118: 317-334Abstract Full Text Full Text PDF PubMed Scopus (323) Google Scholar On an individual patient basis, airway driving pressure is not representative of the actual driving pressure distending the lung, the transpulmonary driving pressure.4Gattinoni L. Pelosi P. Suter P.M. Pedoto A. Vercesi P. Lissoni A. Acute respiratory distress syndrome caused by pulmonary and extrapulmonary disease. Different syndromes?.Am J Respir Crit Care Med. 1998; 158: 3-11Crossref PubMed Scopus (712) Google Scholar,5Chiumello D. Carlesso E. Brioni M. Cressoni M. Airway driving pressure and lung stress in ARDS patients.Crit Care. 2016; 20: 276Crossref PubMed Scopus (84) Google Scholar We have reported that by changing PEEP and determining the change in end-expiratory lung volume (ΔEELV) from ventilator spirometry,6Grivans C. Lundin S. Stenqvist O. Lindgren S. Positive end-expiratory pressure-induced changes in end-expiratory lung volume measured by spirometry and electric impedance tomography.Acta Anaesthesiol Scand. 2011; 55: 1068-1077Crossref PubMed Scopus (53) Google Scholar lung compliance can be calculated without using oesophageal pressure measurements.7Lundin S. Grivans C. Stenqvist O. Transpulmonary pressure and lung elastance can be estimated by a PEEP-step manoeuvre.Acta Anaesthesiol Scand. 2015; 59: 185-196Crossref PubMed Scopus (20) Google Scholar,8Persson P. Stenqvist O. Lundin S. Evaluation of lung and chest wall mechanics during anaesthesia using the PEEP-step method.Br J Anaesth. 2018; 120: 860-867Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar Here, we reanalysed post hoc our previous data8Persson P. Stenqvist O. Lundin S. Evaluation of lung and chest wall mechanics during anaesthesia using the PEEP-step method.Br J Anaesth. 2018; 120: 860-867Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar to see whether use of a two PEEP-step trial would provide a complete lung pressure/volume (P/V) curve from end-expiration at clinical PEEP to end-inspiration at the highest PEEP level, and if it could be used to determine the PEEP level with the lowest transpulmonary driving pressure (i.e. the optimal PEEP level). This is a post hoc analysis of raw data from the original validation study of the PEEP-step method,8Persson P. Stenqvist O. Lundin S. Evaluation of lung and chest wall mechanics during anaesthesia using the PEEP-step method.Br J Anaesth. 2018; 120: 860-867Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar in which 24 patients, age 55 (18) yr; BMI 24.9 (4.0) kg m−2; height 172 (8) cm; and scheduled for gynaecological, thyroid, or parathyroid surgery or thoracoscopy, were included. The study was approved by the Swedish Regional Research Ethics Committee and registered at ClinicalTrials.gov (NCT02830516). Informed consent was obtained from all patients. Measurements were performed before start of surgery in supine position during volume control ventilation with a tidal volume of 6 ml kg−1 ideal body weight. During PEEP steps of 5–9–5, 5–12–5, and 5–14–5 cm H2O, ΔEELV was determined as the cumulative difference in expiratory tidal volume before and during the first 15 breaths after changing PEEP.6Grivans C. Lundin S. Stenqvist O. Lindgren S. Positive end-expiratory pressure-induced changes in end-expiratory lung volume measured by spirometry and electric impedance tomography.Acta Anaesthesiol Scand. 2011; 55: 1068-1077Crossref PubMed Scopus (53) Google Scholar,8Persson P. Stenqvist O. Lundin S. Evaluation of lung and chest wall mechanics during anaesthesia using the PEEP-step method.Br J Anaesth. 2018; 120: 860-867Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar In the PEEP-step method, transpulmonary plateau pressure at the highest PEEP level (PLplat) must be estimated as airway plateau pressure minus tidal volume times chest wall elastance, the latter extrapolated from PEEP 5 and 9 cm H2O. This is a limitation of the PEEP-step method, but evaluation of this estimation shows that estimated PLplat only differed 0.1 (0.8) cm H2O from the corresponding PLplat calculated from conventional oesophageal measurements performed in the original study. The equation for the best-fit lung P/V curve was determined between end-expiration at baseline PEEP, ≈5 cm H2O, and end-inspiration at PEEP ≈14 cm H2O. The PEEP level where the transpulmonary driving pressure was lowest (i.e. optimal PEEP) was computed from the equation for the lung P/V curve. Overall lung compliance (CLtot) was calculated as the change in volume between end-expiration at 0 PEEP and end-inspiration at PEEP 14 cm H2O divided by the corresponding transpulmonary pressure. A lung P/V curve could be obtained by a two-PEEP-step procedure in all 24 patients. The mean CLtot was 97 (59–137) ml cm H2O−1 with an individual variation ranging from values indicative of moderate acute respiratory distress syndrome to emphysema in these patients undergoing elective surgery. In addition, patients with the same overall lung compliance showed completely opposite lung P/V curves with increasing or decreasing lung compliance when increasing PEEP (Fig. 1). At the PEEP level with the lowest transpulmonary driving pressure, or optimal PEEP, which was at 9.8 (5.0–15.0) cm H2O, the transpulmonary driving pressure was 3.8 (2.2–8.4) cm H2O (Fig. 1). The transpulmonary driving pressure at the clinically used PEEP level of 5 cm H2O was 4.9 (3.2–10.0) cm H2O, which was 22 (0–95)% higher than at the optimal PEEP level. The ratio of transpulmonary to airway driving pressure, ΔPL/ΔPAW, was 0.60 (0.13), ranging from 0.30 to 0.81, with only a very weak correlation between ΔPL and ΔPAW, R2=0.20 for the whole group. The change in ΔPL and ΔPAW when changing PEEP was not correlated in individual patients. Detailed methods, mathematical proof of concept of the PEEP-step method, measurement precision analysis of the PEEP-step method, and results with lung P/V curves and optimal PEEP for individual patients can be found in the Supplementary material. In patients undergoing elective surgery with a lung compliance of around 100 ml cm H2O−1, a tidal volume related to ideal body weight of 420 (299–547) ml resulted in a mean ΔPL of only 4.1 cm H2O. However, in two patients with very low lung compliance, ΔPL at baseline PEEP of 5 cm H2O was close or equal to the upper safety limit of 10 cm H2O (see Supplementary material for background of ΔPL limit). This indicates that a tidal volume of 6 ml kg−1 ideal body weight may not be protective in all patients. However, the PEEP-step method makes it possible to tailor tidal volume to lung compliance to reach a ΔPL that is within safe limits. Thus, in those two patients, a tidal volume adapted to lung compliance, around 300 ml, instead of 6 ml kg−1 ideal body weight, around 500 ml, resulted in a decrease in ΔPL from 8.4 and 7.4 cm H2O to 3.7 and 4.1 cm H2O, respectively. In nine of 10 patients, anaesthesia causes atelectasis with a decrease in EELV and compliance,9Hedenstierna G. Rothen H.U. Atelectasis formation during anesthesia: causes and measures to prevent it.J Clin Monit Comput. 2000; 16: 329-335Crossref PubMed Scopus (145) Google Scholar which remain postoperatively and are important sources of PPC. As the PEEP-step method offers quantification of ΔEELV and lung compliance, progress of atelectasis during major abdominal surgery, and need for a recruitment manoeuvre and possibly postoperative CPAP, can be identified by repeating the PEEP-step measurement before tracheal extubation. The great individual variation in lung compliance and PEEP response in patients scheduled for elective surgery implies a need for improved assessment of lung mechanics. We have shown that it is possible to determine lung compliance and the PEEP level, where transpulmonary driving pressure is lowest by implementing a rapid (≈3 min) two-PEEP step measurement procedure, instead of a conventional 10–30 min PEEP titration procedure to determine the PEEP level with highest respiratory system compliance and lowest airway driving pressure. Determination of overall lung compliance makes it possible to adapt tidal volume to the elastic properties of the individual patient's lungs instead of ideal body weight, minimising the risk of over-distension.10Young C.C. Harris E.M. Vacchiano C. et al.Lung-protective ventilation for the surgical patient: international expert panel-based consensus recommendations.Br J Anaesth. 2019; 123: 898-913Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar The need for individualised PEEP levels has also been highlighted in children, given their wide range in body weight.11Lee J.-H. Ji S.-H. Lee H.-C. et al.Evaluation of the intratidal compliance profile at different PEEP levels in children with healthy lungs: a prospective, crossover study.Br J Anaesth. 2020; 125: 818-825Abstract Full Text Full Text PDF PubMed Scopus (4) Google Scholar,12Lee J.-H. Kang P. Song I.S. et al.Determining optimal positive end-expiratory pressure and tidal volume in children by intratidal compliance: a prospective observational study.Br J Anaesth. 2021; 128: 214-221Abstract Full Text Full Text PDF PubMed Scopus (3) Google Scholar Declarations of interestOS is a shareholder of Lung Barometry Sweden AB. PP has no conflict of interest to declare. OS is a shareholder of Lung Barometry Sweden AB. PP has no conflict of interest to declare. Appendix A. Supplementary dataThe following is the Supplementary data to this article: Download .pdf (1.59 MB) Help with pdf files Multimedia component 1 The following is the Supplementary data to this article: Download .pdf (1.59 MB) Help with pdf files Multimedia component 1

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