title: The impact of positive end-expiratory pressure on functional residual capacity and ventilation homogeneity impairment in anesthetized children exposed to high levels of inspired oxygen.
abstract: BACKGROUND
  High fractions of inspired oxygen (Fio2) result in resorption atelectasis shortly after their application. However, the impact of different levels of Fio2 and their interaction with positive end-expiratory pressure (PEEP) on functional residual capacity (FRC) and ventilation distribution is unknown in anesthetized children. We hypothesized that the use of a Fio2 of 1.0 results in a decrease of FRC and ventilation homogeneity compared with that of a Fio2 of 0.3, and that this decrease is prevented by PEEP of 6-cm H2O compared to a PEEP of 3-cm H2O.
  
  
  METHODS
  Forty-six children (3-6 yr) without cardiopulmonary disease were randomly allocated to receive PEEP of 6-cm H2O (PEEP 6 group) during the entire study period or PEEP of 3-cm H2O (PEEP 3 group). The order of the Fio2 (0.3 or 1.0) was also randomized. A defined recruitment maneuver was performed after tracheal intubation and 5 min later the first measurement. This procedure was then repeated with the second Fio2 level. FRC and lung clearance index (LCI) were calculated by a blinded observer.
  
  
  RESULTS
  While FRC (mean +/- sd) was similar at both levels of Fio2 (0.3: 25.6 +/- 2.9 mL/kg vs 1.0: 25.6 +/- 2.8 mL/kg, P = 0.189) in the PEEP 6 group, FRC decreased in the PEEP 3 group (0.3: 24.9 +/- 3.8 vs 1.0: 21.7 +/- 4.1, P < 0.0001). Furthermore, with continuous PEEP of 6-cm H2O a similar LCI was observed at both levels of Fio2 (0.3: 6.45 +/- 0.4 vs 6.43 +/- 0.4, P = 0.668) while LCI increased at the higher Fio2 in the PEEP 3 group (0.3: 6.5 +/- 0.5 vs 1.0: 7.7 +/- 1.2, P < 0.0001).
  
  
  CONCLUSIONS
  During the application of a very low PEEP of 3-cm H2O, FRC and ventilation distribution decreased significantly at an Fio2 of 1.0 compared with that at an Fio2 of 0.3. This decrease could be counterbalanced by the administration of PEEP of 6-cm H2O, indicating that a low level of PEEP is sufficient to maintain FRC and ventilation distribution regardless of the oxygen concentration.
authors.affiliation: Division of Anesthesia, University Children's Hospital, Basel, Switzerland. bvonungern@uhbs.ch
authors.forename: Britta S
authors.initials: BS
authors.lastname: von Ungern-Sternberg
authors.forename: Adrian
authors.initials: A
authors.lastname: Regli
authors.forename: Andreas
authors.initials: A
authors.lastname: Schibler
authors.forename: Jürg
authors.initials: J
authors.lastname: Hammer
authors.forename: Franz J
authors.initials: FJ
authors.lastname: Frei
authors.forename: Thomas O
authors.initials: TO
authors.lastname: Erb
mesh_terms: D000768:Anesthesia, General / Q000379:methods; D002648:Child; D002675:Child, Preschool; D005260:Female; D005652:Functional Residual Capacity / Q000187:drug effects / Q000502:physiology; D006801:Humans; D001239:Inhalation / Q000187:drug effects / Q000502:physiology*; D008297:Male; D010100:Oxygen / Q000008:administration & dosage*; D011175:Positive-Pressure Respiration / Q000379:methods; D012123:Pulmonary Ventilation / Q000187:drug effects / Q000502:physiology*; D012115:Residual Volume / Q000187:drug effects / Q000502:physiology; D014109:Total Lung Capacity / Q000502:physiology*
chemical_list: D010100:Oxygen