Chapter 012. Pain: Pathophysiology and Management (Part 5) pps

Pain: Pathophysiology and Management Part 5 Sympathetically Maintained Pain Patients with peripheral nerve injury can develop a severe burning pain causalgia in the region innervated

Chapter 012 Pain:

Pathophysiology and Management

(Part 5)

Sympathetically Maintained Pain

Patients with peripheral nerve injury can develop a severe burning pain (causalgia) in the region innervated by the nerve The pain typically begins after a delay of hours to days or even weeks The pain is accompanied by swelling of the extremity, periarticular osteoporosis, and arthritic changes in the distal joints The pain is dramatically and immediately relieved by blocking the sympathetic innervation of the affected extremity Damaged primary afferent nociceptors acquire adrenergic sensitivity and can be activated by stimulation of the

sympathetic outflow A similar syndrome called reflex sympathetic dystrophy can

be produced without obvious nerve damage by a variety of injuries, including fractures of bone, soft tissue trauma, myocardial infarction, and stroke (Chap

370) Although the pathophysiology of this condition is poorly understood, the pain and the signs of inflammation are rapidly relieved by blocking the sympathetic nervous system This implies that sympathetic activity can activate undamaged nociceptors when inflammation is present Signs of sympathetic hyperactivity should be sought in patients with posttraumatic pain and inflammation and no other obvious explanation

Acute Pain: Treatment

The ideal treatment for any pain is to remove the cause; thus, diagnosis should always precede treatment planning Sometimes treating the underlying condition does not immediately relieve pain Furthermore, some conditions are so painful that rapid and effective analgesia is essential (e.g., the postoperative state, burns, trauma, cancer, sickle cell crisis) Analgesic medications are a first line of treatment in these cases, and all practitioners should be familiar with their use

Aspirin, Acetaminophen, and Nonsteroidal Anti-Inflammatory Agents (NSAIDs)

These drugs are considered together because they are used for similar problems and may have a similar mechanism of action (Table 12-1) All these compounds inhibit cyclooxygenase (COX), and, except for acetaminophen, all have anti-inflammatory actions, especially at higher dosages They are particularly effective for mild to moderate headache and for pain of musculoskeletal origin

Table 12-1 Drugs for Relief of Pain

Generic Name Dose,

mg

Interval Comments

NONNARCOTIC ANALGESICS: USUAL DOSES AND INTERVALS

Acetylsalicylic

acid

650

PO

preparations available

PO

uncommon

PO

prescription

500 PO

may be due to long half-life

PO in renal disease

PO

side effects common

IM/IV

parenteral use

200 PO

q 12–24

h

arthritis

PO

q12–24

h

U.S market in 2005

Generic Name Parenteral

Dose, mg

PO Dose, mg

Comments

NARCOTIC ANALGESICS: USUAL DOSES AND INTERVALS

60 q 4 h common

10 q 4–6 h

Usually

aspirin

4 h

Morphine

sustained release

200 bid to tid

slow-release preparation

q 4 h

Shorter acting

sulfate

6–8 h

Longer acting

well PO

6–8 h

Delayed sedation due to long half-life

3–4 h

300

q 4 h

Poorly

toxic metabolite

q 4 h

Intranasal spray

µg/h

Transdermal patch

100 q 4–6

h

Mixed opioid/adrenergic action

Uptake Blockade

Ge

neric

Name

-HT E

S edativ

e Potenc

y

An ticholiner gic

Potency

O rthostat

ic Hypote nsion

C ardiac Arrhy thmia

ve

Dose , mg/

d

R ange, mg/d

D

H igh

Mo derate

M oderate

L

7 5–400

A

mitriptyl

ine

H igh

Hi ghest

M oderate

Y

2 5–300

I

miprami

ne

M oderate

Mo derate

H igh

Y

7 5–400

ne

D

esiprami

ne

L

ow

Lo

w

L

ow

Y

5 0–300

V

enlafaxi

ne

L

ow

No

ne

N one

N

7 5–400

D

uloxetin

e

L

ow

No

ne

N one

N

3 0–60

Generic

Name

P

O Dose,

mg

Inte rval

Generi

c Name

P

O Dose,

mg

Inte rval

n

3

00

daily /qhs

Clonaz epam

h

Carbama

zepine

2 00–300

entinb

6 00–1200

q 8

h

Oxcarbaz

ine

3

00

alin

1 50–600

bid