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(Chest. 2003;123:2050-2056.)
© 2003 American College of Chest Physicians

Dead Space Ventilation in Critically Ill Children With Lung Injury*

Jorge A. Coss-Bu, MD; David L. Walding, BSBE; Yadin B. David, PhD and Larry S. Jefferson, MD

* From the Section of Critical Care Medicine, Department of Pediatrics, Baylor College of Medicine, Houston, TX.

Correspondence to: Jorge A. Coss-Bu, MD, Critical Care Section, Texas Children’s Hospital, 6621 Fannin St, Suite 440, MC 2-3450, Houston, TX 77030-2399; e-mail: jorgec{at}bcm.tmc.edu

Study objective: In children with acute lung injury, there is an increase in minute ventilation (E) and inefficient gas exchange due to a high level of physiologic dead space ventilation (VD/VT). Mechanical ventilation with positive end-expiratory pressure, when used in critically ill patients to correct hypoxemia, may contribute to increased VD/VT. The purpose of this study was to measure metabolic parameters and VD/VT in critically ill children.

Design: A cross-sectional study.

Setting: Pediatric ICU of a university hospital.

Patients: A total of 45 mechanically intubated children (mean age, 5.5 years).

Interventions: Indirect calorimetry was used to measure metabolic parameters. VD/VT parameters were calculated using the modified Bohr-Enghoff equation. ARDS was defined based on criteria by The American-European Consensus Conference.

Measurements and results: The group mean (± SD) ventilatory equivalent for oxygen (VeqO2) and ventilatory equivalent for carbon dioxide (VeqCO2) were 2.9 ± 1 and 3.3 ± 1 L per 100 mL, respectively. The group mean VD/VT was 0.48 ± 0.2. When compared to non-ARDS patients (33 patients), the patients with ARDS (12 patients) had a significantly higher VeqO2 (3.3 ± 1 vs 2.8 ± 1 L per 100 mL, respectively; p < 0.05), a significantly higher VeqCO2 (3.7 ± 1 L/100 vs 3.1 ± 1 L per 100 mL, respectively; p < 0.05), and a significantly higher VD/VT (0.62 ± 0.14 vs 0.43 ± 0.15, respectively; p < 0.0005).

Conclusions: Critically ill children with ARDS have increased VD/VT. Increased VD/VT was the main cause of the excess of E demand in these patients. Increased metabolic demands, as shown by the VeqO2, VeqCO2, and ventilatory support, are the major determinants of E requirements in children with ARDS.

Key Words: acute lung injury • critical care • indirect calorimetry • mechanical ventilation • pediatrics • respiratory dead space






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