title: Increasing positive end-expiratory pressure (re-)improves intraoperative respiratory mechanics and lung ventilation after prone positioning.
abstract: BACKGROUND
  Turning a patient prone, changes the respiratory mechanics and potentially the level of positive end-expiratory pressure (PEEP) that is necessary to prevent alveolar collapse. In this prospective clinical study we examined the impact of PEEP on the intratidal respiratory mechanics and regional lung aeration in the prone position. We hypothesized that a higher PEEP is required to maintain compliance and regional ventilation in the prone position.
  
  
  METHODS
  After ethical approval, 45 patients with healthy lungs undergoing lumbar spine surgery were examined in the supine position at PEEP 6 cm H2O and in the prone position at PEEP (6, 9 and 12 cm H2O). Dynamic compliance (CRS) and intratidal compliance-volume curves were determined and regional ventilation was measured using electrical impedance tomography. The compliance-volume curves were classified to indicate intratidal derecruitment, overdistension, or neither.
  
  
  RESULTS
  CRS did not differ between postures and PEEP levels (P>0.28). At a PEEP of 6 cm H2O a compliance-volume profile indicating neither derecruitment nor overdistension was observed in 38 supine, but only in 20 prone positioned patients (P<0.001). The latter increased to 33 and 37 (both P<0.001) when increasing PEEP to 9 and 12 cm H2O, respectively. Increasing PEEP from 6 to 9 cm H2O in the prone position increased peripheral ventilation significantly.
  
  
  CONCLUSIONS
  Respiratory system mechanics change substantially between supine and prone posture, which is not demonstrated in routine measurements. The intratidal compliance analysis suggests that in most patients a PEEP above commonly used settings is necessary to avoid alveolar collapse in the prone position.
  
  
  BACKGROUND
  DRKS 00005692.
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Medical Center Freiburg, Hugstetter Str. 55, Freiburg, Germany johannes.spaeth@uniklinik-freiburg.de.
authors.forename: J
authors.initials: J
authors.lastname: Spaeth
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Medical Center Freiburg, Hugstetter Str. 55, Freiburg, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Daume
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Medical Center Freiburg, Hugstetter Str. 55, Freiburg, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Goebel
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Medical Center Freiburg, Hugstetter Str. 55, Freiburg, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Wirth
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Medical Center Freiburg, Hugstetter Str. 55, Freiburg, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Schumann
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018592:Cross-Over Studies; D017097:Electric Impedance; D005260:Female; D006439:Hemodynamics; D006801:Humans; D007430:Intraoperative Care / Q000379:methods*; D008161:Lumbosacral Region / Q000601:surgery; D008168:Lung / Q000000981:diagnostic imaging; D008170:Lung Compliance; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D016684:Prone Position; D011446:Prospective Studies; D012123:Pulmonary Ventilation; D015656:Respiratory Mechanics; D013131:Spine / Q000601:surgery; D016683:Supine Position; D014054:Tomography
keywords: circulatory and respiratory physiological phenomena; lung; lung-compliance; positive-pressure respiration; posture; prone position; respiration; respiration, artificial; respiratory mechanics