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Anatomic dead space in infants and children
1Division of Pediatric Critical Care, Children's Hospital Los Angeles, University of Southern California 90027, USA.
Summary
Pediatric anatomic dead space is significantly larger in infants compared to adults, decreasing with age. This study quantifies this age-dependent relationship in children.
Area of Science:
- Pediatric physiology
- Respiratory mechanics
Background:
- Adult anatomic dead space is approximately 2.2 ml/kg.
- Infants and children have a proportionally larger head size, suggesting greater extrathoracic dead space.
Purpose of the Study:
- To investigate the hypothesis that pediatric subjects have relatively larger extrathoracic and total dead space compared to adults.
- To quantify the age-dependent relationship of anatomic dead space in pediatric patients.
Main Methods:
- Extrathoracic dead space was measured using a water displacement technique in 40 intubated pediatric patients (7 days to 14.2 years).
- Intrathoracic dead space was measured via continuous analysis of PCO2 and ventilation in 10 pediatric patients (18 days to 14.7 years).
Main Results:
- Extrathoracic dead space per kilogram decreased exponentially with age, from 2.3 ml/kg in infancy to 0.8 ml/kg in children over 6 years.
- Mean intrathoracic dead space was 1.03 ml/kg and showed no age dependency.
- A derived formula showed total anatomic dead space (ml/kg) = 3.28 - 0.56 [ln(1 + Age)], with high correlation (r=0.95, P=0.0001).
Conclusions:
- Anatomic dead space in pediatric patients is age-dependent.
- Total anatomic dead space is greater than 3 ml/kg in early infancy.