Page 306 Guide to Pain Management in Low-Resource Settings

294 Steven D. Waldman

Table 1
Th e do’s and don’ts of diagnostic nerve blocks
Do analyze the information obtained from diagnostic nerve blocks in the context of the patient’s history, physical, laboratory,
neurophysiological, and radiographic testing
Don’t over-rely on information obtained from diagnostic nerve blocks
Do view contradictory information obtained from diagnostic nerve blocks with skepticism
Don’t rely on information obtained from diagnostic nerve block as the sole justifi cation to proceed with invasive treatments
Do consider the possibility of technical limitations that limit the ability to perform an accurate diagnostic nerve block
Do consider the possibility of patient anatomical variations that may infl uence the results
Do consider the presence of incidence pain when analyzing the results of diagnostic nerve blocks
Don’t perform diagnostic blocks in patients currently not having the pain you are trying to diagnose
Do consider behavioral factors that may infl uence the results of diagnostic nerve blocks
Do consider that patients may premedicate themselves prior to diagnostic nerve blocks

with caution and only as one piece of the overall di- block, e.g., conjoined nerve roots, the Martin Gruber
agnostic workup of the patient in pain. Results of a anastomosis (a median to ulnar nerve connection), etc.
diagnostic nerve block that contradicts the clinical Since each pain experience is unique to the in-
impression that the pain management specialist has dividual patient and the clinician really has no way to
formed, as a result of the performance of a targeted quantify it, special care must be taken to be sure that
history and physical examination and consideration of everybody is on the same page regarding what pain the
available confi rmatory laboratory radiographic, neu- diagnostic block is intended to diagnose. Many patients
rophysiological, and radiographic testing, should be have more than one type of pain. A patient may have
viewed with great skepticism. Such disparate results, both radicular pain and the pain of diabetic neuropathy.
when the nerve block is used in a prognostic manner, A given diagnostic block may relieve one source of the
should never serve as the sole basis for moving ahead patient’s pain while leaving the other untouched.
with neurodestructive or invasive surgical procedures, Furthermore, if the patient is having incident
which in this situation have little or no hope of helping pain, e.g., pain when walking or sitting, the performance
to alleviate a patient’s pain. of a diagnostic block in a setting other than one that will
In addition to the above admonitions, it must provoke the incident pain is of little or no value. Th is
be recognized that the clinical utility of the diagnostic often means that the clinician must tailor the type of
nerve block can be aff ected by technical limitations. In nerve block that he or she is to perform to allow the pa-
general, the reliability of data gleaned from a diagnos- tient to be able to safely perform the activity that incites
tic nerve block is in direct proportion to the clinician’s the pain. Finally, a diagnostic nerve block should never
familiarity with the functional anatomy of the area in be performed if the patient is not having, or is unable to
which the nerve block resides and the clinician’s expe- provoke the pain that the pain management specialist is
rience in performing the block being attempted. Even trying to diagnosis as there will be nothing to quantify.
in the best of hands, some nerve blocks are technically Th e accuracy of diagnostic nerve block can be
more demanding than others, which increases the like- enhanced by assessing the duration of nerve relief rela-
lihood of a less-than-perfect result. Furthermore, the tive to the expected pharmacological duration of the
proximity of other neural structures to the nerve, gan- agent being used to block the pain. If there is discor-
glion, or plexus being blocked may lead to the inadver- dance between the duration of pain relief relative to
tent and often unrecognized block of adjacent nerves, duration of the local anesthetic or opioid being used,
invalidating the results that the clinician sees, e.g., the extreme caution should be exercised before relying
proximity of the lower cervical nerve roots, phrenic solely on the results of that diagnostic nerve block.
nerve, and brachial plexus to the stellate ganglion. It Such discordance can be due to technical shortcom-
should also be remembered that the possibility of un- ings in the performance of the block, anatomical varia-
detected anatomical abnormality always exists, which tions, and most commonly, behavioral components of
may further confuse the results of the diagnostic nerve the patient’s pain.