Table 1.
Preoperative Characteristics of the Derivation Population (NSQIP Registry 2011–2013) and Validation Population (NSQIP Registry 2014–2015)
| Variable | Definition | Derivation Population, % | Validation Population, % |
|---|---|---|---|
| Age, y | 18–70 | 44.7 | 46.6 |
| 71–80 | 37.3 | 37.5 | |
| >80 | 18.1 | 16.0 | |
| Sex | Men | 60.9 | 61.8 |
| Women | 39.1 | 38.2 | |
| Race or ethnicity | White | 86.6 | 79.8 |
| Black | 4.4 | 4.3 | |
| Hispanic | 2.4 | 3.2 | |
| Asian | 1.9 | 1.8 | |
| Unknown | 4.7 | 10.9 | |
| Preoperative functional status | Independent | 96.5 | 97.3 |
| Dependent | 3.3 | 2.5 | |
| Missing | 0.2 | 0.2 | |
| Smoking | … | 26.6 | 27.0 |
| Hypertension | … | 85.2 | 82.0 |
| COPD | … | 10.0 | 10.1 |
| CHF | … | 1.4 | 1.5 |
| Dyspnea | … | 13.9 | 12.0 |
| Diabetes mellitus | None | 71.1 | 69.0 |
| Noninsulin | 18.2 | 19.0 | |
| Insulin | 10.8 | 12.1 | |
| Bleeding disorder | … | 20.8 | 20.0 |
| Body habitus | Normal weight | 28.3 | 25.7 |
| Overweight | 38.2 | 38.0 | |
| Class I obesity | 21.6 | 22.2 | |
| Class II/III obesity | 11.0 | 11.8 | |
| Missing | 0.9 | 2.3 | |
| Weight loss | … | 0.5 | 0.4 |
| Preoperative sodium, mEq/L | >135 | 86.1 | 85.5 |
| ≤135 | 10.1 | 10.2 | |
| Missing | 3.8 | 4.4 | |
| Preoperative GFR, mL/min per 1.73 m2 | ≥40 | 86.2 | 87.3 |
| <40 | 10.6 | 9.1 | |
| Missing | 3.2 | 3.6 | |
| Preoperative white blood cell count, cells/μL | 4000–12 000 | 90.1 | 89.0 |
| >12 000 | 3.7 | 4.1 | |
| <4000 | 1.8 | 2.1 | |
| Missing | 4.4 | 4.9 | |
| Preoperative hematocrit, % | >36 | 73.8 | 74.2 |
| ≤36 | 23.0 | 21.6 | |
| Missing | 3.2 | 4.2 | |
| Preoperative platelet count, platelets/μL | ≥150 000 | 85.2 | 85.3 |
| <150 000 | 10.3 | 9.9 | |
| Missing | 4.5 | 4.9 | |
| Preoperative PTT, s | <50 | 56.7 | 52.9 |
| 50–80 | 3.7 | 3.5 | |
| >80 | 1.3 | 1.0 | |
| Missing | 38.3 | 42.6 | |
| Preoperative INR | >1.4 | 71.5 | 66.7 |
| ≤1.4 | 3.5 | 3.0 | |
| Missing | 25.0 | 30.3 | |
| Symptomatic status | Asymptomatic | 56.9 | 54.5 |
| Amaurosis fugax | 7.1 | 7.4 | |
| TIA | 15.7 | 16.4 | |
| Stroke | 18.4 | 20.0 | |
| Missing | 1.9 | 1.8 | |
| Preoperative modified Rankin Scale score | 0–1 | 7.5 | 8.7 |
| 2–5 | 7.8 | 7.6 | |
| Not recorded | 3.1 | 3.7 | |
| Presentation other than stroke | 81.6 | 80.0 | |
| High‐risk physiological characteristics | No | 93.3 | 94.0 |
| Yes | 4.9 | 4.7 | |
| Missing | 1.9 | 1.3 | |
| High‐risk anatomical characteristics | No | 86.3 | 87.8 |
| Yes | 11.9 | 10.8 | |
| Missing | 1.9 | 1.4 | |
| Preoperative antiplatelet agents | No | 11.2 | 10.0 |
| Yes | 88.2 | 89.7 | |
| Missing | 0.6 | 0.3 | |
| Preoperative statin | No | 19.8 | 18.4 |
| Yes | 79.6 | 81.3 | |
| Missing | 0.6 | 0.3 | |
| Preoperative β blocker | No | 43.5 | 45.9 |
| Yes | 55.6 | 53.5 | |
| Missing | 0.9 | 0.6 | |
| Ipsilateral carotid artery stenosis | Mild (<50%) | 1.2 | 1.1 |
| Moderate (50%–79%) | 28.4 | 30.8 | |
| Severe (80%–99%) or occlusion | 68.8 | 66.1 | |
| Not obtained | 1.8 | 2.0 | |
| Contralateral carotid artery stenosis | Mild (<50%) | 49.9 | 51.8 |
| Moderate (50%–79%) | 27.2 | 26.9 | |
| Severe (80%–99%) or occlusion | 10.5 | 10.4 | |
| Not obtained | 12.4 | 10.9 | |
| Admission type | Home | 93.3 | 92.7 |
| Transfer | 6.7 | 7.3 | |
| Emergent operation | … | 2.5 | 2.8 |
| ASA class | I–II | 7.4 | 5.4 |
| III | 76.0 | 74.1 | |
| IV–V | 16.5 | 20.3 | |
| Missing | 0.1 | 0.2 | |
| Revision endarterectomy | … | 0.8 | 0.5 |
Glomerular filtration rate was calculated using the Modification of Diet in Renal Disease equation. Missing data for laboratory values include patients in whom such testing was not obtained. ASA physical classification designation IV is a severe systemic disease with constant threat to life and includes, but is not limited to, recent (<3 months) myocardial infarction or cardiac stent placement, severe valve dysfunction, sepsis, and renal dysfunction. ASA class V designation is a moribund patient not expected to survive without the operation. Modified Rankin Scale score of 2 to 5 indicates at least slight disability and is only recorded among patients who presented with a stroke. ASA indicates American Society of Anesthesiologists; CHF, congestive heart failure; COPD, chronic obstructive pulmonary disease; GFR, glomerular filtration rate; INR, international normalized ratio; NSQIP, National Surgical Quality Improvement Program; PTT, partial thromboplastin time; TIA, transient ischemic attack.