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From the *Department of Pediatrics, University of Pittsburgh School of Medicine and Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania; Department of Pediatrics, University of Thessaly School of Medicine, Larissa, Greece; Department of Anesthesiology University of Pittsburgh School of Medicine and Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania; Carlos Chagas Filho Institute of Biophysics, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; ||Department of Anesthesiology, Kobe University School of Medicine, Kobe, Japan; ¶Department of Anesthesiology, University of WA, Seattle, Washington; #Meakins-Christie Laboratories, Department of Physiology, McGill University Faculty of Medicine, Montreal, Quebec, Canada.
Address correspondence and reprint requests to Etsuro K. Motoyama, MD, Children's Hospital of Pittsburgh, Department of Anesthesiology, 3705 Fifth Ave., Pittsburgh, PA 15213. Address e-mail to motoyamaek{at}anes.upmc.edu.
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 (Est), flow resistance (Rint), and elastance and resistance components resulting from tissue viscoelasticity (
E and R, 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 (
I) and ZEEP, increases in end-inspiratory lung volume above relaxation volume (tidal volume, VT) from 8 to 20 mL · kg–1 resulted in decreases in Est from 1.06 to 0.82 cm H2O · mL–1 · kg, E from 0.16 to 0.09, and Rint from 0.13 to 0.11 cm H2O · mL–1 · s · kg, whereas R increased from 0.08 to 0.12 (P < 0.05). Similar relationships were found with PEEP. Increases in I (8 to 26 mL · s–1 · kg) with constant VT and ZEEP resulted in decreases in Est from 1.09 to 0.9 and R from 0.17 to 0.06 (P < 0.01), whereas E and Rint did not change. There was a similar flow and volume dependence of elastance and resistance with PEEP.
CONCLUSIONS: The observed steady decreases in Est with increasing VT (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.
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