To the Editor We thank Fukuda et al¹ for their study analyzing the association of prehospital advanced life support (ALS) with the outcomes of out-of-hospital cardiac arrest. The authors conclude that ALS by physicians resulted in a higher 30-day survival than ALS by emergency medical service (EMS) personnel and basic life support (BLS).

However, the implications of the study may be overstated. First, given the retrospective design of the study, there are multiple confounding factors that the authors have not accounted for. These mainly include patient demographic characteristics, like age and sex; modifiable predictors of survival outcomes, like body mass index; general health status as assessed by the American Society of Anesthesiologists index; and comorbidities present, as shown in Table 1.¹ Importantly, the extent of blunt injury (assessed by the Injury Severity Score or Abbreviated Injury Scale score) and etiology of cardiac arrest were not evaluated. A major predictor of survival was time to response,² which was statistically different between the various cohorts (Tables 1 and 3).¹ When comparing between EMS and physicians, it is pertinent to match their expertise, since physicians, unlike EMS, may have differing experience and hence success in providing life support.³ Similarly, many patients who survive long enough to reach the hospital for ALS by physicians fare better because of other above-mentioned factors.

致编辑我们感谢Fukuda等人¹的研究分析了院前高级生命支持（ALS）与院外心脏骤停的结局之间的关系。作者得出的结论是，与紧急医疗服务（EMS）人员和基本生命支持（BLS）相比，由医生进行的ALS可以提高30天生存率。

但是，该研究的意义可能被夸大了。首先，考虑到研究的回顾性设计，有许多混杂因素是作者没有考虑的。这些主要包括患者的人口统计学特征，例如年龄和性别；可修改的生存结果预测指标，例如体重指数；由美国麻醉医师学会指数评估的总体健康状况；如表1所示^。1重要的是，未评估钝性损伤的程度（通过伤害严重度评分或缩写的伤害量表评分评估）和心脏骤停的病因。生存的主要预测指标是反应时间，²在不同队列之间有统计学差异（表1和3）。^1个在EMS和医生之间进行比较时，需要匹配他们的专业知识，因为与EMS不同，医生可能具有不同的经验，因此可以成功地提供生命支持。³同样，由于其他上述因素，许多存活时间足够长的患者也可以由医生到ALS医院住院治疗。