独立与相关是否矛盾？

Classification systems and risk scores can help estimate perioperative risk.The American Society of Anesthesiologists (ASA) Physical Status Classification System, for example, classifies patients into categories according to their overall health status and is independently associated with surgical outcomes. In a prospective study of 6301 patients, healthy patients (ASA class I) had a 0.1% risk of cardiac complications and mortality, whereas patients with “severe systemic disease that is a constant threat to life” (ASA class IV) had an 18% risk.Cardiovascular risk scores commonly used include the Revised Cardiac Risk Index6,26and the National Surgical Quality Improvement Program perioperative myocardial infarction and cardiac arrest risk calculator and the universal surgical risk calculator (Table).These scores provide estimates of cardiovascular risk based on perioperative factors. For example, to calculate the Revised Cardiac Risk Index (range, 0-6; 6 = worst), 1 point is assigned for each of the following: ischemic heart disease, cerebrovascular disease, heart failure, insulin-dependent diabetes, chronic kidney disease (serum creatinine level ?2.0 mg/dL), and high-risk surgery (intraperitoneal, intrathoracic, or vascular). Patients with a Revised Cardiac Risk Index of 0 have an approximate risk of 0.4% for major cardiovascular complications, whereas those with an index of 3 or greater have an approximate risk of 10%. In a pooled analysis of 24 validation studies, the Revised Cardiac Risk Index had modest risk discrimination for cardiac events in patients undergoing noncardiac surgery (receiver operating characteristic curve, 0.75) and had poorer discrimination in patients undergoing vascular surgery (receiver operating characteristic curve, 0.64).26The 21-component National Surgical Quality Improvement Program universal surgical risk calculator may provide superior predictive discrimination.

分类系统和风险评分可以帮助评估围术期风险。例如，美国麻醉医师协会（American Society of Anesthesiologists，ASA）的身体状况分类系统会根据患者的整体健康状况将患者分类，这个分类与手术结果独立相关。在一项对6301名患者进行的前瞻性研究中，健康患者（ASA I级）发生心脏并发症和死亡的风险为0.1%，而患有“持续威胁生命的严重系统性疾病”（ASA IV级）的患者风险为18%。常用的心血管风险评分包括修订后的心脏风险指数和国家外科质量改善计划围术期心肌梗死和心脏骤停风险计算法和通用手术风险计算法（表）。这些评分提供基于围术期因素上的心血管风险估计。例如，要计算修订后的心脏风险指数（范围0-6；6=最差），以下各项各1分：缺血性心脏病、脑血管病、心力衰竭、胰岛素依赖型糖尿病、慢性肾病（血清肌酐水平>2.0 mg/dL）和高危手术（腹腔、胸腔或血管内手术）。修订的心脏风险指数为0的患者患重大心血管并发症的风险约为0.4%，而指数为3或更高的患者约有10%的风险。在对24项验证性研究的pooled分析中，修订后的心脏风险指数对接受非心脏手术的患者的心脏事件有中等的风险区分（接受者操作特征曲线，0.75），而在血管手术的患者中的区分较差（接受者操作特征曲线，0.64）。由21个部分组成的国家外科质量改进计划通用手术风险计算方法可能提供更好的预测性区分。

独立与相关是否矛盾？validation studies？验证性研究