title: Improving the validity of peripheral venous blood gas analysis as an estimate of arterial blood gas by correcting the venous values with SvO₂.
abstract: BACKGROUND
  Peripheral venous blood gas (pVBG) analysis in replacement of arterial blood gas (ABG) is limited by the unpredictable differences between arterial and venous values, especially for PCO2 and pH (ΔPCO2 and ΔpH).
  
  
  OBJECTIVE
  We hypothesized that, using the theoretical relationship linking SvO2 and blood flow, we could diminish the effect of local circulatory conditions on ΔPCO2 and ΔpH and thereby increase pVBG validity.
  
  
  METHODS
  This was a prospective cross-sectional study performed in emergency patients requiring a blood gas analysis in which ABG and pVBG were performed simultaneously. The data of 50 randomly selected patients (model group) were used for developing two equations to correct PvCO2 and pHv according to the peripheral SvO2 (SpvO2) level. The formulas derived were PvCO2cor = PvCO2 - 0.30 × (75 - SpvO2), and pHvcor = pHv + 0.001 × (75 - SpvO2). The validity of the corrected values was then tested on the remaining population (validation group).
  
  
  RESULTS
  There were 281 patients included in the study, mainly for dyspnea. ΔPCO2 and ΔpH were strongly correlated with SpvO2 (r(2) = 0.62 and r(2) = 0.53, respectively, p < 0.001). Using the data of the model group, we developed equations that we applied on the validation group. We found that the corrected values were more valid than the raw values for detecting a PaCO2 > 45 mm Hg (AUC ROC = 0.96 ± 0.01 vs. 0.89 ± 0.02, p < 0.001), a PaCO2 < 35 mm Hg (AUC = 0.95 ± 0.02 vs. 0.84 ± 0.03, p < 0.001), a pHa < 7.35 (AUC = 0.97 ± 0.01 vs. 0.95 ± 0.02, p < 0.05), or a pHa > 7.45 (AUC = 0.91 ± 0.02 vs. 0.81 ± 0.04, p < 0.001).
  
  
  CONCLUSIONS
  The variability of ΔPCO2 and ΔpH is significantly lowered when the venous values are corrected according to the SpvO2 value, and pVBG is therefore more accurate and valid for detecting an arterial abnormality.
authors.affiliation: Emergency Department, Hôpital Saint-Roch, Nice, France.
authors.forename: Fabien
authors.initials: F
authors.lastname: Lemoël
authors.forename: Sandra
authors.initials: S
authors.lastname: Govciyan
authors.forename: Mouna
authors.initials: M
authors.lastname: El Omri
authors.forename: Charles-Hugo
authors.initials: CH
authors.lastname: Marquette
authors.forename: Jacques
authors.initials: J
authors.lastname: Levraut
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001784:Blood Gas Analysis / Q000592:standards*; D002245:Carbon Dioxide / Q000097:blood*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D011446:Prospective Studies; D012372:ROC Curve; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen