title: The sixth vital sign: prehospital end-tidal carbon dioxide predicts in-hospital mortality and metabolic disturbances.
abstract: OBJECTIVE
  To determine the ability of prehospital end-tidal carbon dioxide (ETCO₂) to predict in-hospital mortality compared to conventional vital signs.
  
  
  METHODS
  We conducted a retrospective cohort study among patients transported by emergency medical services during a 29-month period. Included patients had ETCO₂ recorded in addition to initial vital signs. The main outcome was death at any point during hospitalization. Secondary outcomes included laboratory results and admitting diagnosis.
  
  
  RESULTS
  Of 1328 records reviewed, hospital discharge data, ETCO₂, and all 6 prehospital vital signs were available in 1088 patients. Low ETCO₂ levels were the strongest predictor of mortality in the overall group (area under the receiver operating characteristic curve (AUC of 0.76, 95% confidence interval [CI] 0.66-0.85), as well as subgroup analysis excluding prehospital cardiac arrest (AUC of 0.77, 95% CI 0.67-0.87). The sensitivity of abnormal ETCO₂ for predicting mortality was 93% (95% CI 79%-98%), the specificity was 44% (95% CI 41%-48%), and the negative predictive value was 99% (95% CI 92%-100%). There were significant associations between ETCO₂ and serum bicarbonate levels (r = 0.429, P < .001), anion gap (r = -0.216, P < .001), and lactate (r = -0.376, P < .001).
  
  
  CONCLUSIONS
  Of all prehospital vital signs, ETCO₂ was the most predictive and consistent for mortality, which may be related to an association with metabolic acidosis.
authors: Department of Emergency Medicine, Orlando Regional Medical Center, Orlando, FL, USA; University of Central Florida College of Medicine, Orlando, FL, USA. Electronic address: christopher.hunter@ocfl.net.
authors: Christopher L
authors: CL
authors: Hunter
authors: Department of Emergency Medicine, Orlando Regional Medical Center, Orlando, FL, USA; University of Central Florida College of Medicine, Orlando, FL, USA.
authors: Salvatore
authors: S
authors: Silvestri
authors: Department of Emergency Medicine, Orlando Regional Medical Center, Orlando, FL, USA; University of Central Florida College of Medicine, Orlando, FL, USA.
authors: George
authors: G
authors: Ralls
authors: University of Central Florida College of Medicine, Orlando, FL, USA.
authors: Steven
authors: S
authors: Bright
authors: Department of Emergency Medicine, Orlando Regional Medical Center, Orlando, FL, USA.
authors: Linda
authors: L
authors: Papa
mesh_terms: D000138:Acidosis / Q000097:blood*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002245:Carbon Dioxide / Q000097:blood*; D004632:Emergency Medical Services / Q000706:statistics & numerical data; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D008297:Male; D008875:Middle Aged; D058687:Out-of-Hospital Cardiac Arrest / Q000097:blood / Q000401:mortality; D011237:Predictive Value of Tests; D012372:ROC Curve; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055986:Vital Signs; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide