约8%的急性肺栓塞局限于亚段支气管。2016和2021年美国胸科医师学会（CHEST）指南和专家小组报告建议对亚段肺栓塞出院患者中没有活动性癌症、深静脉血栓、心肺功能不全、明显症状或复发性静脉血栓栓塞危险增加的选择性患者应采用结构化监测而不使用抗凝治疗；然而，社区实践中的指南应用情况以及适合监测的门诊患者比例尚不清楚。本研究致力于描述急性亚段肺栓塞门诊患者的监测患病率，并利用修改后的CHEST标准估计适合结构化监测的患者比例。该回顾性队列研究在美国21家社区医院的Kaiser Permanente Northern California综合健康体系中进行，时间跨度为2017年1月1日至2021年12月31日。纳入的是成年门诊急性亚段肺栓塞患者。排除具有以下高风险特征的患者：需要住院治疗的并发症、非低风险的生命体征（如收缩压<90 mm Hg、脉搏≥110 bpm或周围切口皮肤脉搏血氧饱和度≤92%）、诊前抗凝药物使用或临终关怀。数据分析时间为2022年11月至2023年2月。主要结果为（1）监测的患病率和（2）使用两组标准进行监测的患病资格：通过排除具有高风险特征或右心室功能异常的患者对CHEST标准进行修改和使用更严格的标准要求年龄小于65岁且只有1个栓子的患者。计算了结构化监测的患病率，并估计了适合监测的患者比例。本研究纳入了666例急性亚段肺栓塞门诊患者中的229例低风险特征患者。他们的中位年龄为58岁（IQR，42-68岁），半数以上是男性（120人，52.4%）和自认为非西班牙裔的白人（128人，55.9%）。有6名患者（2.6%）最初未接受抗凝治疗。在低风险队列中，仅有1名患者（0.4% [95% CI，0.01%-2.4%]）接受了结构化监测，且在90天内没有后遗症。低风险组中有35名患者（占低风险组的15.3%和全队列的5.3%）适合使用修改后的CHEST标准进行监测。有15名患者（占低风险组的6.6%和全队列的2.3%）适合使用更严格的标准进行监测。在这个亚段肺栓塞低风险门诊队列研究中，少数患者适合进行结构化监测，且仅有小部分适合的患者根据CHEST指南接受了监测。如果未来的试验发现监测是安全和有效的，那么将其推广到临床实践中可能需要更多积极的宣传。

Approximately 8% of acute pulmonary emboli are confined to the subsegmental arteries. The 2016 and 2021 American College of Chest Physicians (CHEST) guidelines and expert panel reports suggest the use of structured surveillance without anticoagulation for select ambulatory patients with subsegmental pulmonary embolism who do not have active cancer, deep vein thrombosis, impaired cardiopulmonary reserve, marked symptoms, or increased risk of recurrent venous thromboembolism; however, guideline uptake in community practice is unknown, as is the proportion of outpatients eligible for surveillance.To describe the prevalence of surveillance among outpatients with acute subsegmental pulmonary embolism and to estimate the proportion of patients eligible for structured surveillance using modified CHEST criteria.This retrospective cohort study was conducted across 21 US community hospitals in the Kaiser Permanente Northern California integrated health system from January 1, 2017, to December 31, 2021. Adult outpatients with acute subsegmental pulmonary embolism were included. Patients with the following higher-risk characteristics were excluded: codiagnoses requiring hospitalization, non-low-risk vital signs (ie, systolic blood pressure <90 mm Hg, pulse ≥110 bpm, or peripheral cutaneous pulse oximetry ≤92%), prediagnosis anticoagulant use, or hospice care. Data analysis was performed from November 2022 to February 2023.The main outcomes were the (1) prevalence of surveillance and (2) eligibility for surveillance using 2 sets of criteria: the CHEST criteria modified by excluding patients with higher-risk characteristics or right ventricular dysfunction and a stricter set of criteria requiring age younger than 65 years and no more than 1 embolus. The prevalence of structured surveillance was calculated and the proportion of patients eligible for surveillance was estimated.Of the 666 outpatients with acute subsegmental pulmonary embolism included in this study, 229 with lower-risk characteristics were examined. Their median age was 58 (IQR, 42-68) years; more than half were men (120 [52.4%]) and self-identified as non-Hispanic White (128 [55.9%]). Six patients (2.6%) were initially not treated with anticoagulants. Among the lower-risk cohort, only 1 patient (0.4% [95% CI, 0.01%-2.4%]) underwent structured surveillance, without 90-day sequelae. Thirty-five patients (15.3% of the lower-risk group and 5.3% of the full cohort) were surveillance eligible using modified CHEST criteria. Fifteen patients (6.6% of the lower-risk group and 2.3% of the full cohort) were surveillance eligible using stricter criteria.In this cohort study of lower-risk outpatients with subsegmental pulmonary embolism, few were eligible for structured surveillance, and only a small proportion of eligible patients underwent surveillance despite the CHEST guideline. If forthcoming trials find surveillance safe and effective, substantial uptake into clinical practice may require more than passive diffusion.