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Subcutaneous Water Blocks for Back Pain in Labor
(Originally posted 21 September 1998 on About Anesthesiology)
INTRODUCTION
This week we will discuss the use of sterile water blocks for
management of back pain in labor. I have received a number of
questions about this lately, and there seems to be little about
it available on the internet (at least that I could find) - so
I thought I would write a brief summary about it here.
BACK LABOR DEFINED
Back pain is often a difficult problem to treat during labor
- especially for the patient who receives analgesia of some type
other than an epidural. Back pain during labor is commonly called
"back labor" and is usually due to occiput posterior
positioning (OP) of the baby. This means that the baby is facing
the wrong direction - this makes descent difficult, can prolong
labor and places more pressure on the nerves supplying sensation
to the back. Other than some positioning
suggestions there are not many other suggestions for non-pharmaceutical
treatment. Water blocks seem to offer this alternative.
Approximately 30% of women will have this sort of constant
low back pain during labor - the nerve roots at T11 and T12 level
are irritated - they are the same nerves that supply the back
and therefore the pain is referred to that area. The technique
works up to 93% of the time (depending on what study you read) and the relief can last
as long as 90 minutes. It can be repeated if necessary.
PROPOSED MECHANISMS
Some of you are probably thinking that this is akin to voodoo medicine. Knowing a mechanism for the effect is often helpful when it seems the effect is greater than expected. In this case, the mechanism is thought to be an interruption of the dermatomal pathway - by creating a small amount of pain from the injection
over the same dermatomal
level (T11-T12), the pain is blocked at the spinal cord level.
Some have suggested a mechanism similar to acupuncture - although
the validity of this is not clear. What is clear is that it is indeed very effective.
PERFORMING THE INJECTIONS
The injections involve four seperate subcutaneous injections
of 0.1 - 0.5 cc of sterile water using a small needle at the posterior
superior iliac spines and 2 to 4 centimeters below these two initial
injections. The injection itself is initially painful (like a
bee sting) and is best done during a contraction so that it is
less noticeable. The technique works best for the first stage
of labor and seems to work more reliably when done early (some
say before the pain pathway is well established and easier to
interrupt).
This technique technically can be done by the obstetrician,
a family practitioner, even an experienced nurse. If used as a
sole technique, it does not need the presence of an anesthesiologist
- however, I think that anesthesia providers should learn and
remember this technique as an option or adjunct to the more traditional
techniques of spinal, epidural, etc. Who knows - it might come in handy someday!
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