title: The effect of lung expansion and positive end-expiratory pressure on respiratory mechanics in anesthetized children.
abstract: BACKGROUND
  Imaging studies have shown that general anesthesia in children results in atelectasis. Lung recruitment total lung capacity (TLC) maneuvers plus positive end-expiratory pressure (PEEP) are effective in preventing atelectasis. However, physiological changes in children during general anesthesia have not been elucidated.
  
  
  METHODS
  In eight anesthetized and mechanically ventilated children (median age: 3.5 years; range: 2.3-6.5), we measured static respiratory system elastance (E(st)), flow resistance (R(int)), and elastance and resistance components resulting from tissue viscoelasticity (deltaE and deltaR, respectively) using the constant inflow, end-inspiratory occlusion method preceded by TLC maneuvers, both with zero PEEP (ZEEP) and PEEP (5 cm H2O) for comparison.
  
  
  RESULTS
  With constant inspiratory flow V(I) and ZEEP, increases in end-inspiratory lung volume above relaxation volume (tidal volume, V(T)) from 8 to 20 mL x kg(-1) resulted in decreases in E(st) from 1.06 to 0.82 cm H2O x mL(-1) x kg, deltaE from 0.16 to 0.09, and R(int) from 0.13 to 0.11 cm H2O x mL(-1) x s x kg, whereas deltaR increased from 0.08 to 0.12 (P < 0.05). Similar relationships were found with PEEP. Increases in V(I) (8 to 26 mL x s(-1) x kg) with constant V(T) and ZEEP resulted in decreases in E(st) from 1.09 to 0.9 and deltaR from 0.17 to 0.06 (P < 0.01), whereas deltaE and R(int) did not change. There was a similar flow and volume dependence of elastance and resistance with PEEP.
  
  
  CONCLUSIONS
  The observed steady decreases in E(st) with increasing V(T) (up to 16 mL/kg with PEEP) indicate marked reductions in end-expiratory relaxation volume (functional residual capacity) even with PEEP. Similarity in results with ZEEP and PEEP suggests that TLC-maneuvers and O2-N2 ventilation prevented airway closure throughout the study.
authors.affiliation: Department of Pediatrics, University of Pittsburgh School of Medicine and Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Athanasios G
authors.initials: AG
authors.lastname: Kaditis
authors.forename: Etsuro K
authors.initials: EK
authors.lastname: Motoyama
authors.forename: Walter
authors.initials: W
authors.lastname: Zin
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Maekawa
authors.forename: Isuta
authors.initials: I
authors.lastname: Nishio
authors.forename: Taiyo
authors.initials: T
authors.lastname: Imai
authors.forename: Joseph
authors.initials: J
authors.lastname: Milic-Emili
mesh_terms: D000403:Airway Resistance; D000768:Anesthesia, General / Q000009:adverse effects*; D002648:Child; D002675:Child, Preschool; D004548:Elasticity; D005260:Female; D006801:Humans; D008168:Lung / Q000503:physiopathology*; D008170:Lung Compliance; D008297:Male; D008954:Models, Biological; D011175:Positive-Pressure Respiration; D001261:Pulmonary Atelectasis / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D012129:Respiratory Function Tests; D015656:Respiratory Mechanics; D014109:Total Lung Capacity