PT  - JOURNAL ARTICLE
AU  - Bhalla, Anoopindar K
AU  - Rubin, Sarah
AU  - Newth, Christopher JL
AU  - Ross, Patrick
AU  - Morzov, Rica
AU  - Soto-Campos, Gerardo
AU  - Khemani, Robinder
TI  - Monitoring Dead Space in Mechanically Ventilated Children: Volumetric Capnography Versus Time-Based Capnography
AID  - 10.4187/respcare.03892
DP  - 2015 Jul 21
TA  - Respiratory Care
PG  - respcare.03892
4099  - http://rc.rcjournal.com/content/early/2015/07/21/respcare.03892.short
4100  - http://rc.rcjournal.com/content/early/2015/07/21/respcare.03892.full
AB  - BACKGROUND: Volumetric capnography dead-space measurements (physiologic dead-space-to-tidal-volume ratio [VD/VT] and alveolar VD/VT) are considered more accurate than the more readily available time-based capnography dead-space measurement (end-tidal alveolar dead-space fraction [AVDSF]). We sought to investigate the correlation between volumetric capnography and time-based capnography dead-space measurements.METHODS: This was a single-center prospective cohort study of 65 mechanically ventilated children with arterial lines. Physiologic VD/VT, alveolar VD/VT, and AVDSF were calculated with each arterial blood gas using capnography data.RESULTS: We analyzed 534 arterial blood gases from 65 children (median age 4.9 y, interquartile range 1.7–12.8). The correlation between physiologic VD/VT and AVDSF (r = 0.66, 95% CI 0.59–0.72) was weaker than the correlation between alveolar VD/VT and AVDSF (r = 0.8, 95% CI 0.76–0.85). The correlation between physiologic VD/VT and AVDSF was weaker in children with low PaO2/FIO2 (<200 mm Hg), low exhaled VT (<100 mL), a pulmonary reason for mechanical ventilation, or large airway VD (>3 mL/kg). All 3 dead-space measurements were highly correlated (r > 0.7) in children without hypoxemia (PaO2/FIO2 >300 mm Hg), mechanically ventilated for a neurologic or cardiac reason, or on significant inotropes or vasopressors.CONCLUSIONS: In mechanically ventilated children without significant hypoxemia or with cardiac output-related dead-space changes, physiologic VD/VT was highly correlated with AVDSF and alveolar VD/VT. In children with significant hypoxemia, physiologic VD/VT was poorly correlated with AVDSF. Alveolar VD/VT and AVDSF correlated well in most tested circumstances. Therefore, AVDSF may be useful in most children for alveolar dead-space monitoring.