Relax about the thromboprophylax

Clin Pharmacol Ther. 2008 Sep;84(3):370-7. has an interesting article on the pharmacokinetics of enoxaparin in pregnancy. Basically, the clearance of enoxaparin greatly increases during the course of pregnancy resulting in a marked decrease in anti-Xa activity. The authors even recommend that thromboprophylaxis should be dosed to the pregnant patient's weight rather than a standard 40 mg/day.

What I find curious about this graph I trapped on my mobile phone (no online version available) is that the peak level in late pregnancy (the dark line) is the same level as the 12 hour point for non-pregnancy. Guidelines warn us off CNBs for 12 hours after 40 mg enoxaparin, but in pregnancy the anti-Xa level at the 4 hour peak is the same as when the level is presumed safe in the non-pregnant safe.

So if the parturient has recently had a standard 40 mg enoxaparin, is it reasonable to offer an epidural or spinal? If no, the poor soul will be denied the benefits of an obstetric regional analgesia/anaesthesia as well as being managed with sub-therapeutic thromboprophylaxis!

FAB for CNB

The BJA in "Advanced Access" publishes Major complications of central neuraxial block: report on the Third National Audit Project of the Royal College of Anaesthetists. In brief, its conclusions are reassuring. The absolute risk of CNB is low, but is relatively higher for perioperative use compared to obstetric use. In obstetrics, the risk of a major complication of CNB is extremely low, but curiously (and unsurprisingly!) CSE is given a higher rate compared to both spinal and epidural. In the perioperative group, spinal is given a much lower rate than both epidural and CSE. This audit sought severe complications. One wonders if less severe, but troublesome complications such as neuropathy and headache have similar comparitive rates of relative risk between the clinical groups and types of CNB.

As a practice implication, for me this report reinforces that epidural alone is the choice technique for a routine request for "an epidural" in labour, and spinal anaesthesia is the choice for routine caesarean section in an uncomplicated parturient. In the perioperative setting, this report reinforces an advantage of intrathecal opioid via a spinal needle compared to epidural catheter infusion of anaesthetic and opioid for postoperative analgesia.