El índice de oxigenación es un mejor indicador del intercambio gaseoso que la relación PaO2: FiO2 en pacientes adultos sometidos a ventilación mecánica / Oxygenation index is a better indicator of gaseous interchange than PaO2/FiO2 ratio in adult patients receiving mechanical ventilation

ABSTRACT

Oxygenation Index (Oxlx = MAP x 100 / Pa/FiO2) has been widely used to assess gas exchange in pediatric patients. We evaluated Oxlx and PaO2:FiO2 ratio (Pa/FiO2) in adults patients under Mechanical Ventilation (MV). Seventy-two patients (39 M, 33 F, 53 ± 21 yo, APACHE II 17 ± 7) required MV for 4 ± 3 days (1-18), of which 17 died (24 per cent). Arterial blood gases along FiO2, PEEP and mean airway pressure (MAP), to calculate Pa/FiO2 and Oxlx, and static toraco-pulmonar Compliance (Cst) were measured on a daily basis. Compliance had a good correlation with Oxlx (r = -0.7, p = 0.0001) and Pa/FiO2 (r = 0.5, p = 0.0001). Correlation between Cst and Oxlx improved (r = 0.8, p = 0.0001) when considering only Acute Respiratory Failure patients (ARF, n = 37). Mortality in ARF patients was related to a greater MAP, lower Cst and a worst Oxlx but not Pa/FiO2. Patients who fulfilled ARDS criteria had the worst Pa/FiO2, Oxlx and Cst values. In contrast, no relationship could be observed between Cst and gas exchange markers in neurologic patients (n = 22), or between these parameters and mortality. Oxygenation Index seems to be a better marker of gas exchange than Pa/FiO2 in adults patients under MV. It had a better relationship with the impairment in pulmonary function and mortality in ARF patients.