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Medicina Intensiva

versión impresa ISSN 0210-5691


SANCHEZ CASADO, M. et al. Relationship between the alveolar-arterial oxygen gradientand PaO2/FiO2-introducing peep into the model. Med. Intensiva [online]. 2012, vol.36, n.5, pp.329-334. ISSN 0210-5691.

Objectives To determine whether the alveolar-arterial oxygen gradient (Grad[A-a]O2) helps confirm the influence of PEEP on PaFi (PaO2/FiO2). Design: Observational study; we used linear regression to perform a multivariate study to improve the PaFi formula by taking PEEP into account. Setting: Tertiary hospital. Patients: We included all patients who were admitted to the intensive care unit, regardless of pulmonary damage. Variables: 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.

Palabras clave : Alveolar-arterial oxygen gradient; PaFi; PaO2/FiO2; Lung damage.

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