title: Monitoring Dead Space in Mechanically Ventilated Children: Volumetric Capnography Versus Time-Based Capnography.
abstract: 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.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Children's Hospital Los Angeles, Los Angeles, California. Keck School of Medicine, University of Southern California, Los Angeles, California. abhalla@chla.usc.edu.
authors.forename: Anoopindar K
authors.initials: AK
authors.lastname: Bhalla
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Children's Hospital Los Angeles, Los Angeles, California. Keck School of Medicine, University of Southern California, Los Angeles, California.
authors.forename: Sarah
authors.initials: S
authors.lastname: Rubin
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Children's Hospital Los Angeles, Los Angeles, California. Keck School of Medicine, University of Southern California, Los Angeles, California.
authors.forename: Christopher J L
authors.initials: CJ
authors.lastname: Newth
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Children's Hospital Los Angeles, Los Angeles, California. Keck School of Medicine, University of Southern California, Los Angeles, California.
authors.forename: Patrick
authors.initials: P
authors.lastname: Ross
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Children's Hospital Los Angeles, Los Angeles, California.
authors.forename: Rica
authors.initials: R
authors.lastname: Morzov
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Children's Hospital Los Angeles, Los Angeles, California.
authors.forename: Gerardo
authors.initials: G
authors.lastname: Soto-Campos
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Children's Hospital Los Angeles, Los Angeles, California. Keck School of Medicine, University of Southern California, Los Angeles, California.
authors.forename: Robinder
authors.initials: R
authors.lastname: Khemani
mesh_terms: D001784:Blood Gas Analysis; D019296:Capnography / Q000379:methods*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006331:Heart Diseases / Q000503:physiopathology / Q000628:therapy; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology; D007223:Infant; D008171:Lung Diseases / Q000503:physiopathology / Q000628:therapy; D008297:Male; D008991:Monitoring, Physiologic / Q000379:methods*; D009422:Nervous System Diseases / Q000503:physiopathology / Q000628:therapy; D011446:Prospective Studies; D011650:Pulmonary Alveoli / Q000503:physiopathology; D012121:Respiration, Artificial; D012126:Respiratory Dead Space / Q000502:physiology*; D013990:Tidal Volume
keywords: acute lung injury; capnography; mechanical ventilation; pediatrics; respiratory dead space; respiratory failure