吸入氧浓度对急性呼吸窘迫综合征诊断的影响

The influence of inspired oxygen fraction for the diagnosis of acute respiratory distress syndrome

目的 探讨吸入氧浓度（FiO2）对急性呼吸窘迫综合征（ARDS）患者氧合指数（P/F=PaO2/FiO2）的影响及其临床意义.方法 采用前瞻性研究,选择16例PEEP≥5 cmH2O（1 mmHg=0.098 kPa）时P/F为100～200 mmHg（1 mmHg=0.133 kPa）需机械通气的ARDS患者,实施肺复张（BIPAP,PH 40 cmH2O,40 s）后维持基线通气,稳定30 min后,按随机顺序设定FiO2为0.5,0.6,0.7,0.8,0.9和1.采用SPSS 13.0统计软件比较不同FiO2下患者呼吸力学、血气及血流动力学各指标的变化及其相关性.结果 随FiO2增加P/F逐渐增加,FiO2增加至0.7以上,P/F增加更加明显,FiO2分别为0.5和1.0两组进行比较,P/F的变化为24.70%±23.36%;6例（37.5%）患者FiO2为0.5时P/F＜200,而FiO2为1.0时P/F＞200;FiO2与Qs/Qt呈负相关（r=-0.390,P=0.027）,吸入氧浓度越高,分流越小,FiO2为0.5和1.0时△Qs/Qt与△P/F呈正相关（r=0.82,P=0.005）.结论 吸入氧浓度影响ARDS患者的氧合指数,从而可能影响ARDS的诊断,这与其对肺内分流的影响有关.

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.