title: Prediction equation to estimate dead space to tidal volume fraction correlates with mortality in critically ill patients.
abstract: OBJECTIVE
  The measurement of dead space to tidal volume fraction (Vd/Vt) using various methodologies has been shown to be a reliable predictor of mortality in critically ill patients. In this study, we evaluated the correlation of a validated equation using clinically available information to predict calculation of Vd/Vt with clinically relevant outcome parameters in patients requiring mechanical ventilation.
  
  
  METHODS
  Calculations of Vd/Vt were obtained based upon a previously published prediction equation for dead space ventilation fraction: Vd/Vt = 0.320 + 0.0106 (Paco2--end-tidal carbon dioxide measurement) + 0.003 (respiratory rate per minute) + 0.0015 (age in years) on study days 1, 3 to 4, 6 to 9, and 14 after initiation of mechanical ventilation in adult patients who satisfied 1 of the 3 study defined diseases: (1) acute bacterial pneumonia, (2) acute respiratory distress syndrome, or (3) cystic fibrosis.
  
  
  RESULTS
  Using the final/last available time point calculation of Vd/Vt, a significant difference was observed between survivors and nonsurvivors both in relation to mean and median values (56.5% vs 71.2% and 56.0% vs 65.0%, respectively). In addition, sequential analyses of Vd/Vt calculations over time also demonstrated a statistically significant difference between survivors and nonsurvivors for days 6 to 9.
  
  
  CONCLUSIONS
  In this study-specific population of critically ill patients, the prediction equation of Vd/Vt using clinically available parameters correlates with mortality. In addition, we provide a simple method to estimate Vd/Vt that can be potentially applicable to all critically ill intensive care unit patients.
authors.affiliation: Department of Medicine, Division of Pulmonary, Allergy, and Critical Care Medicine, Penn State Milton S. Hershey Medical Center, Hershey, PA. Electronic address: rvender@psu.edu.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Vender
authors.affiliation: Department of Medicine, Division of Pulmonary, Allergy, and Critical Care Medicine, Penn State Milton S. Hershey Medical Center, Hershey, PA.
authors.forename: Manuel F
authors.initials: MF
authors.lastname: Betancourt
authors.affiliation: Department of Public Health Sciences, Penn State College of Medicine, Hershey, PA.
authors.forename: Erik B
authors.initials: EB
authors.lastname: Lehman
authors.affiliation: Department of Respiratory Therapy, Penn State Milton S. Hershey Medical Center, Hershey, PA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Harrell
authors.affiliation: Department of Surgery, Division of Trauma, Acute Surgery and Critical Care Surgery, Penn State Milton S. Hershey Medical Center, Hershey, PA.
authors.forename: Dan
authors.initials: D
authors.lastname: Galvan
authors.affiliation: Department of Clinical Nutrition, Penn State Milton S. Hershey Medical Center, Hershey, PA.
authors.forename: David C
authors.initials: DC
authors.lastname: Frankenfield
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D002245:Carbon Dioxide / Q000032:analysis; D016638:Critical Illness / Q000401:mortality*; D003550:Cystic Fibrosis / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018410:Pneumonia, Bacterial / Q000503:physiopathology; D012121:Respiration, Artificial; D012126:Respiratory Dead Space / Q000502:physiology*; D012128:Respiratory Distress Syndrome / Q000503:physiopathology; D013990:Tidal Volume / Q000502:physiology*; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide
keywords: Critical care; Mortality; Respiratory dead space; Ventilation