title: [Relationship between the alveolar-arterial oxygen gradient and PaO₂/FiO₂-introducing PEEP into the model].
abstract: OBJECTIVE
  To determine whether the alveolar-arterial oxygen gradient (Grad[A-a]O₂) helps confirm the influence of PEEP on PaFi (PaO₂/FiO₂).
  
  
  METHODS
  Observational study; we used linear regression to perform a multivariate study to improve the PaFi formula by taking PEEP into account.
  
  
  METHODS
  Tertiary hospital.
  
  
  METHODS
  We included all patients who were admitted to the intensive care unit, regardless of pulmonary damage.
  
  
  METHODS
  We recorded personal history, clinical judgment, intensive care data, severity scores on the first day and progression. Two calculated variables: PaFi and Grad(A-a)O₂.
  
  
  RESULTS
  A total of 956 patients were included: 63.9% men; median age 68 years. On the first day, 31.8% did not have mechanical ventilation (MV), 13.1% had non-invasive MV and 55.1% had invasive MV. PaFi values: 32.9% 0-200, 32.2% 201-300, and 34.8% >300. PEEP values: 0-5 69.8%, 6-10 27.5% and >10 2.6%. We observed a correlation (Pearson) between Grad(A-a)O₂ and PaFi of -0.84 (p<0.001). On performing multiple regression (dependent variable: Grad[A-a]O₂), the following variables were included in the model: PaFi, PEEP, APACHE IV and SOFA; coefficient of determination (R²) of 0.62 without PEEP and 0.72 with PEEP. We changed the PaFi formula, referring to it as PaFip (PaFi plus PEEP): Ln (PaFi/[PEEP+12]). Correlation index between PaFip and Grad(A-a)O₂: -0.9 (p<0.001). We performed linear regression (dependent variable: Grad[A-a]O₂) and used PaFip instead of PaFi. Only PaFi remained in the model, and was discretely complemented by APACHE IV; R²=0.8.
  
  
  CONCLUSIONS
  By adding PEEP to the PaFi model (PaFip), we clearly improve the latter, as reflected by a better goodness of fit.
authors.affiliation: Unidad de Cuidados Intensivos, Complejo Hospitalario de Toledo, Toledo, España. marcel55@terra.es
authors.forename: M
authors.initials: M
authors.lastname: Sánchez Casado
authors.forename: M
authors.initials: M
authors.lastname: Quintana Díaz
authors.forename: D
authors.initials: D
authors.lastname: Palacios
authors.forename: V
authors.initials: V
authors.lastname: Hortigüela
authors.forename: C
authors.initials: C
authors.lastname: Marco Schulke
authors.forename: J
authors.initials: J
authors.lastname: García
authors.forename: A
authors.initials: A
authors.lastname: Canabal
authors.forename: M J
authors.initials: MJ
authors.lastname: Pérez Pedrero
authors.forename: A
authors.initials: A
authors.lastname: Velasco Ramos
authors.forename: M A
authors.initials: MA
authors.lastname: Arrese
mesh_terms: D018806:APACHE; D055371:Acute Lung Injury / Q000378:metabolism / Q000628:therapy; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003422:Critical Care; D016638:Critical Illness; D005260:Female; D006801:Humans; D007442:Intubation, Intratracheal; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D015999:Multivariate Analysis; D010100:Oxygen / Q000032:analysis* / Q000097:blood; D010313:Partial Pressure; D011175:Positive-Pressure Respiration; D011650:Pulmonary Alveoli / Q000737:chemistry*; D011659:Pulmonary Gas Exchange; D012121:Respiration, Artificial; D055815:Young Adult
chemical_list: D010100:Oxygen