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: Athanasios G Kaditis, Etsuro K Motoyama, Walter Zin, Nobuhiro Maekawa, Isuta Nishio, Taiyo Imai, Joseph Milic-Emili
• Journal: Anesthesia and analgesia (Anesth Analg) Vol. 106 Issue 3 Pg. 775-85, table of contents (Mar 2008) ISSN: 1526-7598 [Electronic] United States
• PMID: 18292419 (Publication Type: Clinical Trial, Journal Article, Research Support, Non-U.S. Gov't)

Topics

• Airway Resistance
• Anesthesia, General (adverse effects)
• Child
• Child, Preschool
• Elasticity
• Female
• Humans
• Lung (physiopathology)
• Lung Compliance
• Male
• Models, Biological
• Positive-Pressure Respiration
• Pulmonary Atelectasis (etiology, physiopathology, prevention & control)
• Respiratory Function Tests
• Respiratory Mechanics
• Total Lung Capacity