Positive end-expiratory pressure in obese patients during general anaesthesia. The role of intra-abdominal pressure

Abstract

Editor—The application of PEEP after a recruitment manoeuvre (RM) can improve mechanical lung ventilation in obese patients undergoing surgery.1Aldenkortt M. Lysakowski C. Elia N. Brochard L. Tramèr M.R. Ventilation strategies in obese patients undergoing surgery: a quantitative systematic review and meta-analysis.Br J Anaesth. 2012; 109: 493-502Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar However, the benefit of higher PEEP values than those commonly used after an RM to improve compliance, lung volume, and intraoperative oxygenation in obese patients undergoing laparoscopic surgery is a recent finding.2Nestler C. Simon P. Petroff D. et al.Individualized positive end-expiratory pressure in obese patients during general anaesthesia: a randomized controlled clinical trial using electrical impedance tomography.Br J Anaesth. 2017; 119: 1194-1205Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar, 3Eichler L. Truskowska K. Dupree A. Busch P. Goetz A.E. Zöllner C. Intraoperative ventilation of morbidly obese patients guided by transpulmonary pressure.Obes Surg. 2018; 28: 122-129Crossref PubMed Scopus (31) Google Scholar Carbon dioxide pneumoperitoneum causes atelectasis, decreases end-expiratory lung volume, reduces respiratory compliance, and diminishes arterial oxygenation, increasing these effects common to general anaesthesia.1Aldenkortt M. Lysakowski C. Elia N. Brochard L. Tramèr M.R. Ventilation strategies in obese patients undergoing surgery: a quantitative systematic review and meta-analysis.Br J Anaesth. 2012; 109: 493-502Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar, 2Nestler C. Simon P. Petroff D. et al.Individualized positive end-expiratory pressure in obese patients during general anaesthesia: a randomized controlled clinical trial using electrical impedance tomography.Br J Anaesth. 2017; 119: 1194-1205Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar, 3Eichler L. Truskowska K. Dupree A. Busch P. Goetz A.E. Zöllner C. Intraoperative ventilation of morbidly obese patients guided by transpulmonary pressure.Obes Surg. 2018; 28: 122-129Crossref PubMed Scopus (31) Google Scholar, 4Valenza F. Vagginelli F. Tiby A. et al.Effects of the beach chair position, positive end-expiratory pressure, and pneumoperitoneum on respiratory function in morbidly obese patients during anesthesia and paralysis.Anesthesiology. 2007; 107: 725-732Crossref PubMed Scopus (97) Google Scholar, 5Carron M. Recruitment maneuvers and positive end-expiratory pressure titration in morbidly obese ICU patients: the role of positioning.Crit Care Med. 2016; 44 (e910)Crossref PubMed Scopus (2) Google Scholar The mechanism for these physiological changes is mainly related to increased intra-abdominal pressure that occurs with cephalad diaphragmatic shift.5Carron M. Recruitment maneuvers and positive end-expiratory pressure titration in morbidly obese ICU patients: the role of positioning.Crit Care Med. 2016; 44 (e910)Crossref PubMed Scopus (2) Google Scholar A combination of an RM and proper PEEP is therefore crucial to counteract these effects in high-risk patients such as those with obesity or morbid obesity.1Aldenkortt M. Lysakowski C. Elia N. Brochard L. Tramèr M.R. Ventilation strategies in obese patients undergoing surgery: a quantitative systematic review and meta-analysis.Br J Anaesth. 2012; 109: 493-502Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar, 2Nestler C. Simon P. Petroff D. et al.Individualized positive end-expiratory pressure in obese patients during general anaesthesia: a randomized controlled clinical trial using electrical impedance tomography.Br J Anaesth. 2017; 119: 1194-1205Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar, 3Eichler L. Truskowska K. Dupree A. Busch P. Goetz A.E. Zöllner C. Intraoperative ventilation of morbidly obese patients guided by transpulmonary pressure.Obes Surg. 2018; 28: 122-129Crossref PubMed Scopus (31) Google Scholar, 4Valenza F. Vagginelli F. Tiby A. et al.Effects of the beach chair position, positive end-expiratory pressure, and pneumoperitoneum on respiratory function in morbidly obese patients during anesthesia and paralysis.Anesthesiology. 2007; 107: 725-732Crossref PubMed Scopus (97) Google Scholar, 5Carron M. Recruitment maneuvers and positive end-expiratory pressure titration in morbidly obese ICU patients: the role of positioning.Crit Care Med. 2016; 44 (e910)Crossref PubMed Scopus (2) Google Scholar I read with great interest the manuscript by Nestler and colleagues evaluating the effect of individualized PEEP titrated with electrical impedance tomography in obese patients undergoing elective laparoscopic surgery.2Nestler C. Simon P. Petroff D. et al.Individualized positive end-expiratory pressure in obese patients during general anaesthesia: a randomized controlled clinical trial using electrical impedance tomography.Br J Anaesth. 2017; 119: 1194-1205Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar They showed how, in obese patients, an average PEEP of 18.5 (sd 5.6) cm H2O was necessary to restore end-expiratory lung volume, regional ventilation distribution, and oxygenation during pneumoperitoneum with an inflation pressure of 1.7 kPa.2Nestler C. Simon P. Petroff D. et al.Individualized positive end-expiratory pressure in obese patients during general anaesthesia: a randomized controlled clinical trial using electrical impedance tomography.Br J Anaesth. 2017; 119: 1194-1205Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar Eichler and colleagues recently reported the results of using oesophageal pressure measurement and electrical impedance tomography to individually adjust PEEP in mechanically ventilated, morbidly obese patients undergoing elective bariatric surgery.3Eichler L. Truskowska K. Dupree A. Busch P. Goetz A.E. Zöllner C. Intraoperative ventilation of morbidly obese patients guided by transpulmonary pressure.Obes Surg. 2018; 28: 122-129Crossref PubMed Scopus (31) Google Scholar Using linear regression they found that achieving a transpulmonary pressure of 0 cm H2O at end expiration required a PEEP of 23.8 cm H2O (95% confidence interval 19.6–40.4) during pneumoperitoneum with an inflation pressure of 1.6–1.8 kPa.3Eichler L. Truskowska K. Dupree A. Busch P. Goetz A.E. Zöllner C. Intraoperative ventilation of morbidly obese patients guided by transpulmonary pressure.Obes Surg. 2018; 28: 122-129Crossref PubMed Scopus (31) Google Scholar Individualized PEEP titration using electrical impedance tomography, associated or not with oesophageal pressure measurement, is not always feasible in routine clinical practice. Based on available data,2Nestler C. Simon P. Petroff D. et al.Individualized positive end-expiratory pressure in obese patients during general anaesthesia: a randomized controlled clinical trial using electrical impedance tomography.Br J Anaesth. 2017; 119: 1194-1205Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar, 3Eichler L. Truskowska K. Dupree A. Busch P. Goetz A.E. Zöllner C. Intraoperative ventilation of morbidly obese patients guided by transpulmonary pressure.Obes Surg. 2018; 28: 122-129Crossref PubMed Scopus (31) Google Scholar a PEEP at least equal to or, better, slightly higher than the inflation pressure used for pneumoperitoneum should be considered immediately after the RM and then titrated according to ventilation, oxygenation, and haemodynamic parameters in obese patients. Knowing the inflation pressure and the conversion factors (1 kPa = 10.19 cm H2O; 1 mm Hg = 1.36 cm H2O), it is easy to calculate the starting PEEP. Increasing PEEP above the inflation pressure should be carefully balanced with the risk of increased requirements for i.v. fluids and vasopressors.2Nestler C. Simon P. Petroff D. et al.Individualized positive end-expiratory pressure in obese patients during general anaesthesia: a randomized controlled clinical trial using electrical impedance tomography.Br J Anaesth. 2017; 119: 1194-1205Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar The required PEEP depends on different aspects including the patient's individual constitution, body mass index, and positioning.1Aldenkortt M. Lysakowski C. Elia N. Brochard L. Tramèr M.R. Ventilation strategies in obese patients undergoing surgery: a quantitative systematic review and meta-analysis.Br J Anaesth. 2012; 109: 493-502Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar, 3Eichler L. Truskowska K. Dupree A. Busch P. Goetz A.E. Zöllner C. Intraoperative ventilation of morbidly obese patients guided by transpulmonary pressure.Obes Surg. 2018; 28: 122-129Crossref PubMed Scopus (31) Google Scholar, 5Carron M. Recruitment maneuvers and positive end-expiratory pressure titration in morbidly obese ICU patients: the role of positioning.Crit Care Med. 2016; 44 (e910)Crossref PubMed Scopus (2) Google Scholar When electrical impedance tomography, eventually associated with oesophageal pressure measurement, is not available to provide individualized PEEP, I believe that the intra-abdominal pressure used for pneumoperitoneum should be carefully considered to guide application of PEEP after RM in morbidly obese patients undergoing laparoscopic surgery. None declared.