The influence of inspired oxygen fraction for the diagnosis of acute respiratory distress syndrome / 中华急诊医学杂志

ABSTRACT

Objective To investigate the influence of inspired oxygen fraction (FiO2) on the ratio of PaO2/FiO2(P/F) during the implementation of lung protective ventilation strategy in patients with acute respiratory distress syndrome(ARDS) in order to unravel its clinical significance. Method This was a prospective study of 16 selected patients with ARDS treated with mechanical ventilation ( MV ) to get ratio of P/F in range of 100 to 200 by PEEP≥5 cmH2O and high inspired oxygen. After lung recruitment maneuvers by BiPAP with high pressure (PH) of 40 cmH2O for40 s, the MV was maintained the basic requirement for stabilizing the patients for 30 minutes. A series of FiO2 were set at fractions of 0.5,0.6,0.7,0.8,0.9 and 1in random sequence, and the changes of respiratory mechanics, blood gas and hemodynamics under the different concentrations of FiO2 were analyzed by using SPSS version 13.0 software. Results ( 1 ) The ratio of P/F increased as FiO2 increased, and it's significant as FiO2 increased to 0.7 or above. As the fractions of FiO2 were set at 0.5 and 1. O, the ratios of P/F changed in 24.70% ± 23.36% respectively. ( 2 ) Of them,6 patients ( 37.5% ) treated with FiO2 set at 0.5 had the ratio of P/F ＜ 200, and the fraction of FiO2 was increased to 1.0, the P/F ＞ 200. (3) FiO2 and Qs/Qt were negatively correlated ( r = - 0.390, P = O. 027 ),the higher inspired oxygen fraction, the lower shunt. When the fractions of FiO2 were set at 0.5 and 1.0 ,there was a positive correlation between △Qs/Qt and △P/F( r = 0.82, P = 0.005 ). Conclusions The inspired oxygen fraction affects the ratio of P/F, which may be resulted from shunt and it may influence the diagnosis of ARDS.