Systemic Anticoagulant Effect of Low-Dose Subcutaneous Unfractionated Heparin as Determined Using Thrombelastography

Abstract

In an observational study using heparinase-modified thrombelastography, we investigated the percentage of elective cardiothoracic surgical patients receiving low-dose unfractionated heparin (5000 IU 12 hourly subcutaneously) who had a demonstrable systemic heparin effect. Blood samples were obtained at induction from 40 adult elective cardiothoracic surgical patients who had received 5000 IU unfractionated heparin subcutaneously within six hours. Simultaneous kaolin and heparinase-modified thrombelastographies were run on all samples. Fourteen patients (35%; 95% CI: 20 to 50%) had a demonstrable heparin effect(defined as a kaolin thrombelastography R time >25% longer than the heparinase-modified control). Their mean±SD kaolin thrombelastography R time was 13.6±5.9 minutes (normal range 4 to 8 minutes) vs. 7.1±2.0 minutes for the heparinase-modified controls. In 10 patients the thrombelastography R times were >50% longer and in four patients >100% longer, than their respective heparinase-modified controls. In a post hoc analysis, there was little correlation between the extent of the prolongation and patient age (r=0.02), weight (r=-0.31), preoperative creatinine (r=-0.17), or time since administration of heparin (r=0.14). These results indicate that about one third of patients who have received low-dose unfractionated heparin subcutaneously within six hours have a demonstrable heparin effect. The potential for this effect should be considered if central neural blockade is planned.

Use of thromboelastography to guide thromboprophylaxis after caesarean section

“…9 Although both studies used small study populations, and larger studies are needed adequately to assess the effect of thromboprophylaxis on venous thromboembolism post CS, it seems likely that UH at this dose has an insufficient anticoagulant effect for clinical use and should be abandoned. TEG can, however, detect a heparin effect, 11,12,15,17 and the current findings suggest that it can do so when anti-factor Xa assays cannot.…”

“…19 A heparin effect has been arbitrarily defined as a difference >25% between plain and heparinise R time samples. 15 Nine patients showed this effect, yet the majority remained hypercoagulable compared to baseline results. Only two samples (in patients 4 and 14 at 4 h) were hypocoagulable following heparin relative to their baseline sample, and in neither of these was the difference >25%.…”

“…A heparin effect was defined as a kaolin TEG R time > 25% longer than the heparinase-modified TEG R time. 15 Additional samples were taken at 2 and 4 h for antifactor Xa levels and Activated Partial Thromboplastin Time (APTT). A volume of 4.5 mL of blood was placed in a tube containing trisodium citrate (BD Vacutainer 9NC 0.109 M) and were centrifuged in the laboratory within 1 h at 3000 rpm for 10 min at 4°C.…”

Reference ranges for thromboelastography (TEG®) and traditional coagulation tests in term parturients undergoing caesarean section under spinal anaesthesia*

“…Conversely, Boyce et al. recently demonstrated a significantly shorter R time, shorter K time and wider alpha angle following caesarean section compared with pre‐operative values [18]. However, the greatest increase in coagulability in their study was found at 3 h. Since our postoperative samples were taken either immediately postoperatively, or 4 h following enoxaparin administration (itself given 3–4 h following surgery), we may have missed the peak hypercoagulable period.…”

“…A heparin effect has been defined as a TEG R time > 25% longer than the heparinase‐corrected control [18, 19]. Of the 33 patients who had post‐enoxaparin TEG samples, only 17 (52%) showed this effect, although 24 (73%) were hypocoagulable compared to their pre‐operative samples, with increased R times, decreased MA and decreased CI values.…”