Xem mẫu
- 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, Interval Comments
mg
NONNARCOTIC ANALGESICS: USUAL DOSES AND INTERVALS
Acetylsalicylic 650 q4h Enteric-coated
acid PO preparations available
Acetaminophen 650 q4h Side effects
PO uncommon
Ibuprofen 400 q 4–6 h Available without
PO prescription
Naproxen 250– q 12 h Delayed effects
500 PO may be due to long half-
life
Fenoprofen 200 q 4–6 h Contraindicated
- PO in renal disease
Indomethacin 25–50 q8h Gastrointestinal
PO side effects common
Ketorolac 15–60 q 4–6 h Available for
IM/IV parenteral use
Celecoxib 100– q 12–24 Useful for
200 PO h arthritis
Valdecoxib 10–20 q12–24 Removed from
PO h U.S. market in 2005
Generic Name Parenteral PO Comments
Dose, mg Dose, mg
NARCOTIC ANALGESICS: USUAL DOSES AND INTERVALS
Codeine 30–60 q 4 h 30– Nausea
- 60 q 4 h common
Oxycodone — 5– Usually
10 q 4–6 h available with
acetaminophen or
aspirin
Morphine 10 q 4 h 60 q
4h
Morphine — 30– Oral slow-
sustained release 200 bid to release preparation
tid
Hydromorphone 1–2 q 4 h 2–4 Shorter acting
q4h than morphine
sulfate
Levorphanol 2 q 6–8 h 4 q Longer acting
6–8 h than morphine
sulfate; absorbed
- well PO
Methadone 10 q 6–8 h 20 q Delayed
6–8 h sedation due to long
half-life
Meperidine 75–100 q 300 Poorly
3–4 h q4h absorbed PO;
normeperidine a
toxic metabolite
Butorphanol — 1–2 Intranasal
q4h spray
Fentanyl 25–100 — 72 h
µg/h Transdermal patch
Tramadol — 50– Mixed
100 q 4–6 opioid/adrenergic
h action
- Ge Uptake S An O C R
neric Blockade edativ ticholiner rthostat ardiac ve. ange,
Name e gic ic Arrhy Dose mg/d
Potenc Potency Hypote thmia ,
-HT E y nsion mg/
d
ANTIDEPRESSANTSa
D H Mo M L 7
oxepin + igh derate oderate ess 00 5–400
A H Hi M Y 2
mitriptyl +++ + igh ghest oderate es 50 5–300
ine
I M Mo H Y 7
miprami +++ + oderate derate igh es 00 5–400
ne
N M Mo L Y 4
- ortriptyli ++ + oderate derate ow es 00 0–150
ne
D L Lo L Y 5
esiprami ++ +++ ow w ow es 50 0–300
ne
V L No N N 7
enlafaxi ++ + ow ne one o 50 5–400
ne
D L No N N 3
uloxetin ++ ++ ow ne one o 0 0–60
e
Generic P Inte Generi P Inte
Name O Dose, rval c Name O Dose, rval
mg mg
ANTICONVULSANTS AND ANTIARRHYTHMICSa
- Phenytoi 3 daily Clonaz 1 q 6
n 00 /qhs epam h
Carbama 2 q6h Gabap 6 q 8
zepine 00–300 entinb 00–1200 h
Oxcarbaz 3 bid Pregab 1 bid
ine 00 alin 50–600
nguon tai.lieu . vn
