What is preemptive analgesia?
Can it reliably be performed in this patient?
Preemptive analgesia is a technique via which
an anal-gesic modality is introduced prior to the painful procedure so that the
patient will have less pain in the postoperative period. This idea is based on
the theory of “central nervous system wind-up”, whereby if the spinal cord
receives a con-stant barrage of painful stimuli it becomes hyperexcitable and
thus more prone to evoke a pain response, even to less painful stimuli.
Different modalities have been investi-gated, such as the use of preoperative
NSAIDs to provide peripheral analgesia, the use of local anesthetic peripheral
nerve or neuraxial block to prevent transmission of painful impulses into the
spinal cord, as well as the use of high doses of systemic narcotics, to blunt
cortical perception.
Unfortunately, a reliable way to achieve
preemptive analgesia in association with major abdominal surgery has not been
achieved. A few small studies have shown efficacy with the use of neuraxial
opioids, but no large study has been able to confirm this. In a recent study
(Aida et al., 1999) epidural catheters were placed preoperatively in their
respective areas (cervical placement for upper limb surgery, low thoracic
placement for abdominal surgery, lumbar placement for lower limb surgery, etc.)
and an appropriate anesthetic level with local anesthetics was achieved
pre-incision. A preemptive analgesic effect was noted in the limb and
mastectomy patients but not in the laparotomy patients. The authors concluded
that to per-form preemptive analgesia properly, one must completely block all
afferent input into the spinal cord, and that as some input is provided via the
vagus nerve which was not blocked with the epidural, preemptive analgesia could
not be reliably achieved.
Many questions remain to be answered with
respect to preemptive analgesia. The first and foremost is, does it clin-ically
exist, and if so, by what modality can it be achieved? Perhaps a single
procedure, such as the administration of a properly placed epidural with local
anesthetic prior to the surgical stimulation, can provide pre-emptive
analge-sia. Most likely, we will discover that both central and peripheral modalities
will need to be utilized. Another question is whether a single procedure prior
to the initial stimulus will be sufficient for preemptive analgesia, or whether
it will be necessary to continue this technique dur-ing the entire procedure,
as well as into the postoperative period.
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