Preoperative Hematologic Concerns (Anesthesia Text)


Anticoagulation Therapy

Venous Thromboembolism

Graded compression elastic stockings reduce risk by 44% [Agu et al. Br J Surg 86: 992, 1999]. Low-dose heparin reduces risk 68-76%, and LMWH vs. unfractionated seem to have the same preventive effect in the general surgery population, although they may have different rates of bleeding complications [Geerts et. al. Chest 126: 338S, 2004]. A randomized, controlled trial of 40 mg enoxaparin vs. UFH 5000 U q12h in 1762 stroke patients (PREVAIL study) showed that enoxaparin reduced the risk of venous thromboembolism by 43% as compared with UFH (10% vs 18%; p = 0.0001), and while the frequency of any haemorrhage was similar (1% vs 1%; p = 0.23), the rate of major extracranial bleeding was higher with enoxaparin than with unfractionated heparin (7 [1%] vs 0; p=0.015) [Sherman et. al. Lancet 369: 1347, 2007]. A criticism of this study is that it did not use 5000 U q3.

Risk Stratification for VTE[edit]

(from [Douketis et. al. Chest. 133(6S): 299S, 2008])


High Any mitral, cage/disk aortic, stroke within 6 mo.
Med Bi-leaflet aortic valve prosthesis and one of: AF, stroke/TIA, HTN, DM, CHF, > 75
Low Bi-leaflet aortic valve w/o a-fib and no risk factors for stroke


High CHAD2 > 4, stroke/TIA within 3 mo., rheumatic dz
Med CHADS2 3-4
Low CHADS2 0-2

CHADS2 Score: CHF [1] HTN [1] ≥ 75 [1] DM [1] Stroke/TIA [2]

CHADS2 Annual Risk of CVA: 0 (1.9%) 1 (2.8%) 2 (4.0%) 3 (5.9%) 4 (8.5%) 5 (12.5%) 6 (18.2%)


High VTE < 3 mo., pC, pS, AT, antiphospholipid Ab, multiple abnormalities
Med Leiden, heterozygous fII, recurrent VTE, active Ca
Low Single VTE > 12 mo. ago, no other RFs

Recommendations re: VTE prevention

High Risk: “we recommend… bridging w/therapeutic LMWH (Grade 1C)… suggest SQ LMWH over IV UFH (Grade 2C)… last dose 24h before surgery”
Med Risk: same as for high risk but evidence is Grade 2C
Low Risk: “we recommend… low dose SQ LMWH (Grade 2C)”

Antiplatelet Therapy

(from [Douketis et. al. Chest. 133(6S): 299S, 2008])

  • Note: according to ACCP, there are no comprehensive risk stratification schemes for antiplatelet therapy. The following is offered only as a guide

Risk Stratification for Anti-Platelet Therapy

Risk Indication for Anti-Platelet Therapy
High Recent stent placement (definitely), MI within 3 months (probably)
Low Primary prevention of stroke or MI

Non-Cardiac Surgery

Non-Cardiac Surgery: there are no RCT or prospective cohort studies to serve as a guide. ACCP recommends that “for patients who are at high risk, we suggest continuing ASA up to and beyond the time of surgery (Grade 2C)… for patients who are not at high risk of cardiac events… interruption of antiplatelet drugs (Grade 1C) [7-10 days for ASA/Plavix]”

Cardiac Surgery

Cardiac Surgery: “for CABG, we recommend continuing ASA up and to beyond the time of CABG (Grade 1C)… we recommend interrupting Plavix for at least 5 days, and preferably 10 days prior to surgery (Grade 1C)… for PCI, we suggest continuing ASA up to and beyond the time of the procedure; if Plavix is interrupted prior to PCI, we suggest resuming after PCI with a loading dose of 300-600 mg (Grade 2C)

Carotid Surgery

Carotid Surgery: a RCT of 75 mg ASA started preoperatively and continued 6 mos. in 232 CEA patients reduced strokes at 6 mo. (11 total vs. 2) with no change in bleeding [Linblad et al. Stroke 24: 1125, 1993]. A second RCT of 2849 patients showed that ASA started pre-surgery and continued for 3 months reduced stroke/MI/death at 30 days (81-327 mg/day was optimal) [Taylor et al. Lancet 353: 2179, 1999]. “Although clopidogrel has defined indications for stroke prevention, it is not clear how to manage this medication at the time of surgery” [Szeder et al. The Neurologist 14: 30, 2008].