Page 357 Guide to Pain Management in Low-Resource Settings

Chapter 47

Insights from Clinical Physiology

Rolf-Detlef Treede

Insights on acute pain Practical consequences
Ask each patient about movement-evoked pain, and
Aside from alleviating suffering, one of the major
treat with eff ective, multimodal analgesics.
aims of postoperative pain management is to facili-
tate and speed up recovery, reestablish mobility, and
ultimately favor a rapid discharge. One of the funda- Insights on cancer pain
mental mechanisms in the nociceptive system is in-
terfering with these aims is called central sensitiza- One of the most painful conditions in a patient with
tion. Sensitization is a basic learning mechanism that advanced cancer is bone metastasis. Th is well-known
describes an increased neural response when stimuli clinical reality is in confl ict with traditional basic sci-
of constant intensity are simply repeated. (Its coun- ence teaching: according to standard textbooks, only
terpart, habituation, a decrease in response upon re- the periosteum is innervated, but not the bone itself.
petitive stimulation, is less prominent in the nocicep- If this were true, only large bone metastases that ex-
tive system). In central sensitization, the increased tend into the periosteum should be painful. But ex-
neural response is due to enhanced efficacy of the perience teaches otherwise: fortunately, painful bone
synaptic connections within the nociceptive system. metastases usually have not yet destroyed the com-
Central sensitization mostly enhances pain to me- pacta. Th us, when they are treated causally by radia-
chanical stimuli, whereas peripheral sensitization al- tion or chemotherapy, the stability of the bone is still
most exclusively increases heat pain sensitivity. This preserved. It is also well known that aspiration of
makes central sensitization highly relevant in the bone marrow is very painful, in spite of local anesthe-
postoperative setting. sia of the periosteum.
When sensitization occurs in the nociceptive sys- Th us, the bone’s interior structures are densely in-
tem, the patient perceives more pain in response to nervated by nociceptive aff erents, probably very similar
relatively mild stimuli such as moving around in bed to the innervation of teeth. Only recently have anato-
or coughing. As a consequence, the patient will move mists been able to demonstrate nociceptive nerve fi bres
less and breathe less deeply, in order to titrate the pain within the bone using the marker CGRP (calcitonin
down to a tolerable level. Fortunately, eff ective pain gene-related peptide), where they appear to have con-
treatment (e.g., with opioids or local anesthesia) also tacts with both the bone trabecula and the osteoclasts.
reduces central sensitization. Physiologically, there is also some recent evidence that

Guide to Pain Management in Low-Resource Settings, edited by Andreas Kopf and Nilesh B. Patel. IASP, Seattle, © 2010. No responsibility is assumed by IASP 345
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