To The Editor:
I found the recent Symposium entitled "Recent Advances in Venous
Thromboembolic Prophylaxis During and After Total Hip Arthroplasty" (82-A:
252-270, Feb. 2000), by Salvati et al., very informative. Their
technique is innovative and their discussion, intelligent and convincing. I
do, however, feel that in the section entitled "The Role of Anesthesia,"
the authors were incorrect in saying that "it is unsafe to administer epidural
anesthesia to a patient who has received low-molecular-weight heparin
preoperatively or to use low-molecular-weight heparin postoperatively
before removal of an epidural catheter. Low-molecular-weight heparin
is suitable for use in patients receiving general anesthesia, provided
that it is administered twelve hours after the operation."
When one examines the case reports on epidural hematoma from
1993 through 1998 as presented by Horlocker and Wedel2, it is clear
that at least some of the epidural hematomas occurred from misuse
of the drug. Specifically, considering that the peak activity of
the drug is three to four hours after administration and that the
half-life is 3.5 hours, any neuraxial intervention (spinal or epidural)
within twelve hours (less than three half-lives) is contraindicated.
To say that these drugs are contraindicated preoperatively if regional
anesthesia is anticipated is wrong. What if the patient received
the drug three days or three weeks prior to surgery? At the Hospital
for Joint Diseases, we have routinely treated hip-fracture patients
preoperatively with Lovenox (enoxaparin) and safely administered
spinal anesthetics twelve hours later. We have used this approach
on hundreds of patients and have not observed a single epidural
hematoma. In addition, the majority of total joint arthroplasties
at our institution are performed with the patient under spinal anesthesia,
and low-molecular-weight heparin is administered postoperatively
as prophylaxis against deep-vein thrombosis. Considering our volume
of cases, this amounts to thousands of patients, again, without
a single epidural hematoma. According to published guidelines, low-molecular-weight
heparins are not contraindicated in patients with epidural catheters
in place. One must simply recognize that withdrawing an epidural
catheter is also a traumatic event, wait twelve hours after the
previous dose before withdrawing the catheter, and wait an additional
two hours before redosing. When one examines the aforementioned
case reports on epidural hematoma, it becomes clear that epidural
catheters were placed or removed well short of the safe twelve-hour
window and sometimes right at the peak activity of the drug. The
obvious conclusion is that the anesthesiologists involved did not
know that their patients had received this drug.
In May 1998, at the urging of the Food and Drug Administration,
the American Society of Regional Anesthesia convened a panel to
evaluate the use of low-molecular-weight heparins and to formulate
guidelines for their safe use with neuraxial anesthesia. A consensus
statement was published in December 1998, to which I would refer
the reader2.
I believe, as does the American College of Chest Physicians and
the American Society of Regional Anesthesia, that the use of low-molecular-weight
heparins is a safe and efficacious means of venous thromboembolic
prophylaxis. Further, these drugs can be used safely in the context
of regional anesthesia as long as the published guidelines are followed.
Statements to the contrary are simply untrue and serve only to create
more confusion, which many in the fields of anesthesia and orthopaedics
have spent the past two years trying to eliminate.
Dominick Cannavo, M.D.
Department of Anesthesiology
Hospital for Joint Diseases Orthopaedic Institute
New York University Medical Center
301 East 17th Street
New York, N.Y. 10003
E. A. Salvati, V. D. Pellegrini, Jr., N. E. Sharrock,
P. A. Lotke,
D. W. Murray, H. Potter, and G. H. Westrich reply:
Dr. Cannavo raises a very important unresolved issue in anesthetic
practice - namely, how can one safely use conduction anesthetics
in conjunction with low-molecular-weight heparin? This is extremely
important due to the rare but potentially tragic consequences of
epidural hematoma. Epidural hematomas are distinctly rare in patients
managed with aspirin or Coumadin (warfarin), but a significant number
were described after the introduction of low-molecular-weight heparin.
Some occurred after spinal anesthesia, but most were noted in association
with the use of epidural catheters. Cases were more frequent when
higher doses of low-molecular-weight heparin were utilized.
The use of spinal anesthesia according to the guidelines described
by Dr. Cannavo is probably safe, as his experience would suggest.
However, placing an epidural catheter entails more trauma than placing
a spinal needle. Our concern relates to two issues. The first issue
relates to dosage. If higher doses, such as forty milligrams twice
a day, caused a significant number of epidural hematomas, how certain
can one be that a dose of forty milligrams once a day will completely eliminate
the risk? Adjusting the dose according to weight may be another
option to reduce risk. The second issue relates to the time when
the epidural catheter is removed. The recommendation is to withdraw
the catheter twelve hours after the administration of low-molecular-weight heparin.
The problem is that catheters become dislodged spontaneously in
up to 10 percent of cases1.
It is likely that, with judicious management, low-molecular-weight
heparin can be used effectively with spinal anesthesia. However,
due to difficulties with epidural catheters and unpredictable patient
responsiveness to low-molecular-weight heparin, epidural anesthesia
and analgesia should be approached with considerable caution, if
at all, when patients are receiving low-molecular-weight heparin.
Eduardo A. Salvati, M.D.
Vincent D. Pellegrini, Jr., M.D.
Nigel E. Sharrock, M.B., Ch.B.
Paul A. Lotke, M.D.
David W. Murray, F.R.C.S.
Hollis Potter, M.D.
Geoffrey H. Westrich, M.D.
Corresponding author: Nigel E. Sharrock, M.B., Ch.B.
Department of Anesthesiology
The Hospital for Special Surgery
535 East 70th Street
New York, N.Y. 10021