Kadkhodai Leila, Saghaei Mahmoud, Habibzadeh Mohammadreza, Alikiaii Babak, Hashemi Seyed Jalal
Department of Anesthesia, Isfahan University of Medical Sciences, Isfahan, Iran.
Anesthesiology and Critical Care Research Center, Isfahan University of Medical Sciences, Isfahan, Iran.
J Res Med Sci. 2022 May 30;27:38. doi: 10.4103/jrms.jrms_558_21. eCollection 2022.
The ratio of partial pressure of oxygen in arterial blood (PaO2) to the fraction of inspiratory oxygen concentration (FiO2) is an indicator of pulmonary shunt fraction. PaO2/FiO2 (P/F) ratio is used to classify severity of acute respiratory distress syndrome (ARDS). With the same shunt fraction, P/F ratio decreases with increases in FiO2 which may lead to errors in classifying severity of ARDS. The effect of FiO2 on P/F ratio has not been investigated in COVID-19 pneumonia. In this study, we estimated the best FiO2 for the calculation of P/F ratio in a sample of patients with ARDS due to COVID-19 pneumonia.
Blood gas and ventilatory data of 108 COVID-19 ARDS patients were analyzed in a cross-sectional observational study. Using Oxygen Status Algorithm the calculated shunt fraction served a basis for calculating P/F ratio for different FiO2. The severity of ARDS determined by P/F ratios at each FiO2s was compared with the shunt-based severity to find the optimum FiO2 for calculation of P/F ratio so the resulting classification has the best match with the reference classification.
A FiO2 of 1.0 for calculation of P/F ratio and ARDS classification showed the best match with shunt-based ARDS classification. A regression model was obtained with the PaO2, patient's original FiO2, Hemoglobin concentration, and SaO2 as the independent predictors of the P/F ratio for the FiO2 of 1.0.
This study shows a FiO2 of 1.0 as the best value for correct calculation of P/F ratio and proper classification of ARDS.
动脉血氧分压（PaO2）与吸入氧分数（FiO2）的比值是肺分流分数的一个指标。PaO2/FiO2（P/F）比值用于对急性呼吸窘迫综合征（ARDS）的严重程度进行分类。在分流分数相同的情况下，P/F比值会随着FiO2的增加而降低，这可能导致ARDS严重程度分类出现错误。FiO2对P/F比值的影响在新型冠状病毒肺炎（COVID-19肺炎）中尚未得到研究。在本研究中，我们在一组因COVID-19肺炎导致ARDS的患者样本中，估算了用于计算P/F比值的最佳FiO2。
在一项横断面观察性研究中，分析了108例COVID-19 ARDS患者的血气和通气数据。使用氧状态算法，计算出的分流分数作为计算不同FiO2下P/F比值的基础。将每个FiO2时由P/F比值确定的ARDS严重程度与基于分流的严重程度进行比较，以找到计算P/F比值的最佳FiO2，从而使所得分类与参考分类的匹配度最佳。
用于计算P/F比值和ARDS分类的FiO2为1.0时，与基于分流的ARDS分类显示出最佳匹配。以PaO2、患者初始FiO2、血红蛋白浓度和SaO2作为FiO2为1.0时P/F比值的独立预测因子，获得了一个回归模型。
本研究表明，FiO2为1.0是正确计算P/F比值和正确分类ARDS的最佳值。
