title: The utility of early end-tidal capnography in monitoring ventilation status after severe injury.
abstract: BACKGROUND
  An arterial CO2 (Paco2) of 30 mm Hg to 39 mm Hg has been shown to be the ideal target range for early ventilation in trauma patients; however, this requires serial arterial blood gases. The use of end-tidal capnography (EtCO2) has been recommended as a surrogate measure of ventilation in the prehospital arena. This is based on the observation of close EtCO2 Pa(CO2) correlation in healthy patients, yet trauma patients frequently suffer from impaired pulmonary ventilation/perfusion. Thus, we hypothesize that EtCO2 will demonstrate a poor reflection of actual ventilation status after severe injury.
  
  
  METHODS
  Prospective observational study on consecutive intubated trauma patients treated in our emergency department (ED) during 9 months. Arterial blood gas values and concomitant EtCO2 levels were recorded. Regression was used to determine the strength of correlation among all trauma patients and subgroups based on injury severity (Abbreviated Injury Score and Injury Severity Score) and physiologic markers of perfusion status (lactate, shock index, and arterial base deficit).
  
  
  RESULTS
  During 9 months, 180 patients were evaluated. The EtCO2 Paco2 correlation was poor at R2 = 0.277. Patients ventilated in the recommended EtCO2 (range, 35 to 40) were likely to be under ventilated (Pa(CO2) > 40 mm Hg) 80% of the time, and severely under ventilated (Pa(CO2) > 50 mm Hg) 30% of the time. Correlation was best for patients with isolated traumatic brain injury and worst for those with evidence of poor tissue perfusion.
  
  
  CONCLUSIONS
  EtCO2 has low correlation with Pa(CO2), and therefore should not be used to guide ventilation in intubated trauma patients in the ED. Better strategies for guiding prehospital and ED ventilation are needed.
authors.affiliation: Department of Trauma Surgery, Harborview Medical Center, Seattle, Washington 98104, USA. keirw@u.washington.edu
authors.forename: Keir J
authors.initials: KJ
authors.lastname: Warner
authors.forename: Joseph
authors.initials: J
authors.lastname: Cuschieri
authors.forename: Brandon
authors.initials: B
authors.lastname: Garland
authors.forename: David
authors.initials: D
authors.lastname: Carlbom
authors.forename: David
authors.initials: D
authors.lastname: Baker
authors.forename: Michael K
authors.initials: MK
authors.lastname: Copass
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Jurkovich
authors.forename: Eileen M
authors.initials: EM
authors.lastname: Bulger
mesh_terms: D019296:Capnography / Q000379:methods*; D005260:Female; D015600:Glasgow Coma Scale; D006801:Humans; D015601:Injury Severity Score; D016014:Linear Models; D008297:Male; D008991:Monitoring, Physiologic; D011446:Prospective Studies; D012121:Respiration, Artificial; D014947:Wounds and Injuries / Q000378:metabolism*