The effect of lung expansion and positive end-expiratory pressure on respiratory mechanics in anesthetized children.
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.
Kaditis
Athanasios G
AG
Department of Pediatrics, University of Pittsburgh School of Medicine and Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA.
Motoyama
Etsuro K
EK
Zin
Walter
W
Maekawa
Nobuhiro
N
Nishio
Isuta
I
Imai
Taiyo
T
Milic-Emili
Joseph
J
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