Hospital Clínico Universitario
Correspondence to: Juan V. Llau, MD, Department of Anesthesiology and Post-Surgical Intensive Care, Hospital Clinico Universitario, Av Blasco Ibáñez 17, Valencia, Spain 46006; e-mail: email@example.com
To the Editor:
I read with interest the recent article by Aguilar and Goldhaber
(May 1999)1 on the subject of low-molecular-weight
heparins (LMWHs). LMWHs are widely employed in the perioperative period
for the prophylaxis of deep venous thrombosis (DVT) and are considered
to be safe and effective.
However, the decision to use LMWHs may not be made without some
trepidation. When deciding to perform neuraxial blockade on a
patient who is already receiving an LMWH, the anesthesiologist may
believe that the benefits of regional anesthesia for this specific
patient are greater than the risk of developing intraspinal bleeding,
even assuming that the patient has had an alteration in hemostasis.
So, what should be done to minimize the very low risk of
developing neurologic injury while maintaining the antithrombotic
effectiveness of LMWHs? I would like to propose a checklist (Table 1
) and to summarize some recommendations to improve the safety of
neuraxial anesthesia in patients who have received or will
receive thromboprophylaxis with LMWHs2–7:
1. Postsurgical administration of LMWH. Except
in some specific patients (very high-risk patients or in those having
surgery for a hip fracture), it is possible to perform
thromboprophylaxis with LMWH starting 10 to 12 h after surgery
without a loss of effectiveness. This would be the best choice for
improving the safety of neuraxial anesthesia.
2. Preoperative LMWH. If LMWH has to be administered
before surgery, spinal anesthesia should be delayed at least 10 to
12 h after the last LMWH dose, with the next dose being given 2 to
4 h after that initial dose.
3. LMWH dosing. It has to be the minimal effective
dose. Sometimes an LMWH dose can be adjusted for body weight to avoid
overdosing. Furthermore, it is of primary importance to know the
differences in drug regimens between Europe and the United States: the
current American dosing practice is to administer 50% more than is
called for by the current European practice (eg, enoxaparin,
30 mg twice daily vs 40 mg once daily, respectively).
4. Continuous catheter technique. There is no problem
in using it if the LMWH is started postoperatively or at least 12
h before. It is not safe to place a catheter for postoperative
analgesia when LMWH has been administered < 10 to 12 h before.
However, frequent monitoring for signs of neurologic impairment is
needed in all cases. The removal of this catheter has to be delayed
until 10 to 12 h after the last dose of LMWH (ideally, 24 h).
5. Remaining questions. If the decision is made to
perform neuraxial anesthesia despite the prior administration of LMWH,
the following procedures are recommended: • Do not
use the continuous-catheter technique. A single-dose spinal anesthesia
may be the safest regional anesthesia
technique. • Use small-gauge needles. •
Use short-acting anesthetics. • Use the midline
approach. • Observe the patient closely in the early
postoperative period for any sign of cord compression, and if signs are
noticed, obtain immediate radiographic confirmation and treat the
patient without delay.
In conclusion, the decision to perform regional
anesthesia in patients receiving LMWH for prophylaxis of DVT can be
made safely in selected patients. Some anesthesia and
thromboprophylaxis guidelines should be followed to minimize the risk
of spinal bleeding. However, the final decision should be made by the
clinician after estimating the benefits and risks of the simultaneous
use of LMWH and regional anesthesia.
Yes = central nerve block is safe; No = need to
estimate benefits and risks to perform central nerve block.
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