title: End-tidal arterial CO2 partial pressure gradient in patients with severe hypercapnia undergoing noninvasive ventilation.
abstract: BACKGROUND
  Patients with severe hypercapnia represent a particularly serious condition in an emergency department (ED), requiring immediate attention. Noninvasive ventilation (NIV) is an integral part of the treatment for acute respiratory failure. The present study aimed to validate the measurement of end-tidal CO2 (EtCO2) as a noninvasive technique to evaluate the effectiveness of NIV in acute hypercapnic respiratory failure.
  
  
  METHODS
  Twenty consecutive patients admitted to the ED with severe dyspnea were enrolled in the study. NIV by means of bilevel positive airway pressure, was applied to the patients simultaneously with standard medical therapy and continued for 12 hours; the arterial blood gases and side-stream nasal/oral EtCO2 were measured at subsequent times: T0 (admission to the ED), T1h (after 1 hour), T6h (after 6 hours), and T12h (after 12 hours) during NIV treatment.
  
  
  RESULTS
  The arterial CO2 partial pressure (PaCO2)-EtCO2 gradient decreased progressively, reaching at T6h and T12h values lower than baseline (P < 0.001), while arterial pH increased during the observation period (P < 0.001). A positive correlation was found between EtCO2 and PaCO2 values (r = 0.89, P < 0.001) at the end of the observation period.
  
  
  CONCLUSIONS
  In our hypercapnic patients, the effectiveness of the NIV was evidenced by the progressive reduction of the PaCO2-EtCO2 gradient. The measurement of the CO2 gradient could be a reliable method in monitoring the effectiveness of NIV in acute hypercapnic respiratory failure in the ED.
authors.affiliation: Emergency Department, Riuniti Hospital, University of Foggia, Foggia, Italy.
authors.forename: Vito
authors.initials: V
authors.lastname: Defilippis
authors.affiliation: Department of Anaesthesiology and Intensive Care, University of Foggia, Foggia, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: D'Antini
authors.affiliation: Department of Anaesthesiology and Intensive Care, University of Foggia, Foggia, Italy.
authors.forename: Gilda
authors.initials: G
authors.lastname: Cinnella
authors.affiliation: Department of Anaesthesiology and Intensive Care, University of Foggia, Foggia, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Dambrosio
authors.affiliation: Emergency Department, San Paolo Hospital, Naples, Italy.
authors.forename: Fernando
authors.initials: F
authors.lastname: Schiraldi
authors.affiliation: Emergency Department, Riuniti Hospital, University of Foggia, Foggia, Italy.
authors.forename: Vito
authors.initials: V
authors.lastname: Procacci
keywords: acute respiratory failure; arterial end-tidal CO2 gradient; bilevel positive airway pressure; noninvasive ventilation