title: Can venous-to-arterial carbon dioxide differences reflect microcirculatory alterations in patients with septic shock?
abstract: OBJECTIVE
  Septic shock has been associated with microvascular alterations and these in turn with the development of organ dysfunction. Despite advances in video microscopic techniques, evaluation of microcirculation at the bedside is still limited. Venous-to-arterial carbon dioxide difference (Pv-aCO2) may be increased even when venous O2 saturation (SvO2) and cardiac output look normal, which could suggests microvascular derangements. We sought to evaluate whether Pv-aCO2 can reflect the adequacy of microvascular perfusion during the early stages of resuscitation of septic shock.
  
  
  METHODS
  Prospective observational study including 75 patients with septic shock in a 60-bed mixed ICU. Arterial and mixed-venous blood gases and hemodynamic variables were obtained at catheter insertion (T0) and 6 h after (T6). Using a sidestream dark-field device, we simultaneously acquired sublingual microcirculatory images for blinded semiquantitative analysis. Pv-aCO2 was defined as the difference between mixed-venous and arterial CO2 partial pressures.
  
  
  RESULTS
  Progressively lower percentages of small perfused vessels (PPV), lower functional capillary density, and higher heterogeneity of microvascular blood flow were observed at higher Pv-aCO2 values at both T0 and T6. Pv-aCO2 was significantly correlated to PPV (T0: coefficient -5.35, 95 % CI -6.41 to -4.29, p < 0.001; T6: coefficient, -3.49, 95 % CI -4.43 to -2.55, p < 0.001) and changes in Pv-aCO2 between T0 and T6 were significantly related to changes in PPV (R (2) = 0.42, p < 0.001). Absolute values and changes in Pv-aCO2 were not related to global hemodynamic variables. Good agreement between venous-to-arterial CO2 and PPV was maintained even after corrections for the Haldane effect.
  
  
  CONCLUSIONS
  During early phases of resuscitation of septic shock, Pv-aCO2 could reflect the adequacy of microvascular blood flow.
authors.affiliation: Department of Intensive Care Medicine, Fundación Valle del Lili, Universidad ICESI, Cali, Colombia. gusospin@gmail.com.|Universidad del Valle, Escuela de Ciencias Básicas, Cali, Colombia. gusospin@gmail.com.
authors.forename: Gustavo A
authors.initials: GA
authors.lastname: Ospina-Tascón
authors.affiliation: Department of Intensive Care Medicine, Fundación Valle del Lili, Universidad ICESI, Cali, Colombia.
authors.forename: Mauricio
authors.initials: M
authors.lastname: Umaña
authors.affiliation: Universidad del Valle, Escuela de Ciencias Básicas, Cali, Colombia.
authors.forename: William F
authors.initials: WF
authors.lastname: Bermúdez
authors.affiliation: Department of Intensive Care Medicine, Fundación Valle del Lili, Universidad ICESI, Cali, Colombia.
authors.forename: Diego F
authors.initials: DF
authors.lastname: Bautista-Rincón
authors.affiliation: Department of Intensive Care Medicine, Fundación Valle del Lili, Universidad ICESI, Cali, Colombia.
authors.forename: Juan D
authors.initials: JD
authors.lastname: Valencia
authors.affiliation: Department of Intensive Care Medicine, Fundación Valle del Lili, Universidad ICESI, Cali, Colombia.
authors.forename: Humberto J
authors.initials: HJ
authors.lastname: Madriñán
authors.affiliation: Departamento de Medicina Intensiva, Pontificia Universidad Católica de Chile, Santiago, Chile.
authors.forename: Glenn
authors.initials: G
authors.lastname: Hernandez
authors.affiliation: Departamento de Medicina Intensiva, Pontificia Universidad Católica de Chile, Santiago, Chile.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Bruhn
authors.affiliation: Department of Intensive Care Medicine, Fundación Valle del Lili, Universidad ICESI, Cali, Colombia.|Universidad del Valle, Escuela de Ciencias Básicas, Cali, Colombia.
authors.forename: César
authors.initials: C
authors.lastname: Arango-Dávila
authors.affiliation: Intensive Care Department, CHIREC Hospitals, Université Libre de Bruxelles, Brussels, Belgium.
authors.forename: Daniel
authors.initials: D
authors.lastname: De Backer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001158:Arteries / Q000503:physiopathology*; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000097:blood*; D003105:Colombia; D005260:Female; D006801:Humans; D008297:Male; D008833:Microcirculation / Q000502:physiology*; D008875:Middle Aged; D011446:Prospective Studies; D012772:Shock, Septic / Q000503:physiopathology*; D014680:Veins / Q000503:physiopathology*
chemical_list: D002245:Carbon Dioxide
keywords: Microcirculation; Microcirculatory blood flow; Septic shock; Venous-to-arterial carbon dioxide difference