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January 1998
Safety steps for epidural injection of local anesthetics: Review of the
literature and recommendations.
Mulroy MF, Norris MC, Liu SS; Anesth Analg1997; 85:1346-1356.
No abstract available
Few would argue with the notion that establishment of good habits based on
sound science should occur during clinical training and be renewed
periodically. The current issue of Anesthesia and Analgesia contains a
review article from a department and an individual long renowned for an
association with regional anesthesia. Dr. Michael Mulroy and his
colleagues at Virginia Mason Medical Center have provided a timely review
of the issues and science behind safe administration of epidural anesthesia.
The authors describe the risks associated with subdural and subarachnoid
injection of local anesthetics and the tests recommended to minimize those
risks. They conclude that with careful attention to testing
(aspiration, administration of an initial dose of 3 ml of local anesthetic
and incremental dosing) the incidence of serious side effects from these
two complications is low. Systemic toxic reactions after
inadvertent intravenous administration are apparently becoming less
frequent, but they remain the most significant hazard of epidural blockade.
One unfortunate limitation of this article is that it does not devote more
space to safety issues in epidural injection of local anesthetics in
infants and children. The last decade or two has seen an explosion
of popularity of epidural (both lumbar and caudal) anesthesia in pediatric
patients. Venous air embolism and the limitations of b-agonists in test
dosing for halothane- or isoflurane-anesthetized patients remain
significant clinical problems.
Two recent case reports (Schwartz N, Eisenkraft JB. Probable venous air
embolism during epidural placement in an infant. Anesth Analg.
76(5):1136-8,1993 and Guinard JP, Borboen M. Probable venous air embolism
during caudal anesthesia in a child. Anesth Analg. 76(5):1134-5,1993) and
an accompanying editorial (Sethna NF, Berde CB. Venous air embolism during
identification of the epidural space in
children. Anesth Analg. 76(5):925-7,1993) describe the first problem. Some
authorities have recommended injecting air to identify inadvertent
subcutaneous needle placement during a caudal approach to the epidural
space; others suggest that air be used to facilitate the loss of resistance
technique for identification of the epidural space or inadvertent
intravascular tip placement (in parturients). Injection of
as little as 2.5 ml of air into the circulation of a small patient has
caused signs of significant venous air embolism, thus using saline for loss
of resistance tests is a safer approach.
There are a number of reasons why pediatric patients are at greater risk
than adults for unintentional intravascular injection of local anesthetics.
1. Epidural catheters are usually placed while children are under general
anesthesia. Halothane and isoflurane attenuate the tachycardic response to
epinephrine in test doses. Pretreatment with atropine
improves the response, but still leaves a significant number of false
negative responses (Desparmet J, et.al, Anesthesiology 72:249-51, 1990).
2. The needles and catheters used in children are large relative to the
size of the epidural space.
3. Catheters are often threaded long distances.
4. The softness of the surrounding bones makes intraosseus injection more
likely; injection into the bone has the same effect as intravascular
injection.
5. A 3 ml bolus that serves as a test dose in an adult can be the entire
dose for an infant.
For these reasons, particular care should be paid to the principles of
atropine pretreatment, using a size appropriate, epinephrine-containing
test dose (usually 1/10th of the anesthetizing dose) and slow
incremental injection (with careful ECG monitoring) of the total dose.
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