Airway closure in anesthetized infants and children: influence of inspiratory pressures and volumes.
BACKGROUND
Cyclic opening and closing of lung units during tidal breathing may be an important cause of iatrogenic lung injury. We hypothesized that airway closure is uncommon in children with healthy lungs when inspiratory pressures are kept low, but paradoxically may occur when inspiratory pressures are increased.


METHODS
Elastic equilibrium volume (EEV) and closing capacity (CC) were measured with a tracer gas (SF(6)) technique in 11 anesthetized, muscle-relaxed, endotracheally intubated and artificially ventilated healthy children, aged 0.6-13 years. Airway closing was studied in a randomized order at two inflation pressures, +20 or +30 cmH(2)O, and CC and CC/EEV were calculated from the plots obtained when the lungs were exsufflated to -20 cmH(2)O. (CC/EEV >1 indicates that airway closure might occur during tidal breathing). Furthermore, a measure of uneven ventilation, multiple breath alveolar mixing efficiency (MBAME), was obtained.


RESULTS
Airway closure within the tidal volume (CC/EEV >1) was observed in four and eight children (not significant, NS) after 20 and 30 cmH(2)O inflation, respectively. However, CC(30)/EEV was >CC(20)/EEV in all children (P< or = 0.001). The MBAME was 75+/-7% (normal) and did not correlate with CC/EEV.


CONCLUSIONS
Airway closure within tidal volumes may occur in artificially ventilated healthy children during ventilation with low inspiratory pressure. However, the risk of airway closure and thus opening within the tidal volume increases when the inspiratory pressures are increased.
Thorsteinsson
A
A
Department of Anesthesia and Intensive Care, Landspitalinn University Hospital, Hringbraut, Iceland. adalbjn@landspitali.is
Werner
O
O
Jonmarker
C
C
Larsson
A
A
D000293:Adolescent; D000399:Air Pressure; D000402:Airway Obstruction / Q000209:etiology*; D002138:Calibration; D002648:Child; D002675:Child, Preschool; D004548:Elasticity; D005260:Female; D005652:Functional Residual Capacity; D006801:Humans; D007223:Infant; D007431:Intraoperative Complications / Q000503:physiopathology*; D008176:Lung Volume Measurements; D008297:Male; D012121:Respiration, Artificial; D013459:Sulfur Hexafluoride
D013459:Sulfur Hexafluoride