Clots, clocks and clexane

"So what about the clot that's forming now?" grumped the obstetrician after the elective caesarean section upon the 110 kg 40 year old multipara with legs that just looked they were waiting to clot. I had written the enoxaparin dose for 8 pm, 10 hours later, at a time when I thought was nicely convenient for patient and nurse.

It has been apparently observed that DVTs form during surgery itself, although I have not been able to find the published studies. For this reason there has been enthusiasm in non ob-gyn surgery, particularly in North America for LMWH to commence preoperatively. It is in orthopaedic lower limb joint replacement surgery that DVT is most endemic and thus the most fertile area for study. There are no trials involving cesarean sections. There have been several reviews (e.g.Raskib and Hish in Chest Dec 2003)contemplating the timing of anticoagulant prophylaxis (mostly fondaparinux) and it seems that preoperative dosing does not only improve the DVT rate but also increases the risk of significant surgical bleeding. (Different authoritative guidelines warn against LMWHs between 2 to 12 hours after neuraxial anaesthesia.) This lack of effect and presence of side-effect of anticoagulant prophylaxis persists until 6 hours postoperatively at which time there is a reduction in DVT risk without increased bleeding. Beyond 12 hours the benefit might begin to wane. There seems to be a lack of strict timing in the study protocols for these anticoagulants which make finer comparisons of timing impossible. Whether the 10 hour interval after my case created a greater DVT risk than a 6 hour interval is not clear. Perhaps for the patient with accumulating risk factors, timing should be more based on clinical demands rather than social convenience and be closer to the 6 hours than the 12 hours. Certainly the sun should not cross the horizon more than once before the initial dose of prophylactic anticoagulant.