There is currently conflicting data as to the effects of hypercapnia on clinical outcomes among mechanically ventilated patients in the emergency department (ED). These conflicting results may be explained by the degree of acidosis. We sought to test the hypothesis that hypercapnia is associated with increased in-hospital mortality and decreased ventilator-free days at lower pH, but associated with decreased in-hospital mortality and increased ventilator-free days at higher pH, among patients requiring mechanical ventilation in the emergency department (ED). Secondary analysis of patient level data from prior clinical trials and cohort studies that enrolled adult patients who required mechanical ventilation in the ED. Patients who had a documented blood gas while on mechanical ventilation in the ED were included in these analyses. The primary outcome was in-hospital mortality, and secondary outcome was ventilator-free days. Mixed-effects logistic, linear, and survival-time regression models were used to test if pH modified the association between partial pressure of carbon dioxide (pCO) and outcome measures. Of the 2348 subjects included, the median [interquartile range (IQR)] pCO2 was 43 (35–54) and pH was 7.31 (7.22–7.39). Overall, in-hospital mortality was 27%. We found pH modified the association between pCO and outcomes, with higher pCO associated with increased probability of in-hospital mortality when pH is below 7.00, and decreased probability of in-hospital mortality when pH is above 7.10. These results remained consistent across multiple sensitivity and subgroup analyses. A similar relationship was found with ventilator-free days. Higher pCO is associated with decreased mortality and greater ventilator-free days when pH is >7.10; however, it is associated with increased mortality and fewer ventilator-free days when the pH is below 7.00. Targeting pCO based on pH in the ED may be a potential intervention target for future clinical trials to improve clinical outcomes.

中文翻译：

---

二氧化碳/pH 相互作用的分压及其与急诊科机械通气患者死亡率的关系


目前，关于高碳酸血症对急诊科 (ED) 机械通气患者临床结果的影响，存在相互矛盾的数据。这些相互矛盾的结果可以用酸中毒的程度来解释。我们试图检验以下假设：在需要机械通气的患者中，高碳酸血症与较低 pH 值下的院内死亡率增加和无呼吸机天数减少相关，但在较高 pH 值下与院内死亡率降低和无呼吸机天数增加相关。急诊科 (ED)。对之前纳入急诊室需要机械通气的成年患者的临床试验和队列研究的患者水平数据进行二次分析。这些分析包括在急诊室接受机械通气时记录有血气的患者。主要结局是院内死亡率，次要结局是不使用呼吸机的天数。使用混合效应逻辑、线性和生存时间回归模型来测试 pH 值是否改变了二氧化碳分压 (pCO) 与结果测量之间的关联。在纳入的 2348 名受试者中，pCO2 中位数[四分位距 (IQR)] 为 43 (35–54)，pH 值为 7.31 (7.22–7.39)。总体而言，院内死亡率为 27%。我们发现 pH 值改变了 pCO 与结果之间的关联，当 pH 值低于 7.00 时，pCO 越高，院内死亡概率增加；而当 pH 值高于 7.10 时，院内死亡概率降低。这些结果在多项敏感性和亚组分析中保持一致。与无呼吸机的天数也存在类似的关系。当 pH > 7 时，较高的 pCO 与死亡率降低和无呼吸机天数增加相关。10；然而，当 pH 值低于 7.00 时，它会导致死亡率增加和不使用呼吸机的天数减少。根据急诊室 pH 值确定 pCO 可能是未来临床试验改善临床结果的潜在干预目标。