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| Pain
Classification |
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Nociceptive Pain
arises from the stimulation of specific pain receptors.
These receptors can respond to heat, cold, vibration,
stretch and chemical stimuli released from damaged
cells.
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Non Nociceptive
Pain arises from within the
peripheral and central nervous system. Specific
receptors do not exist here, with pain being generated
by nerve cell dysfunction.
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Somatic Pain |
- Source - tissues such as skin, muscle, joints, bones,
and ligaments - often known as musculo-skeletal
pain.
- Receptors activated
- specific
receptors (nociceptors) for heat, cold, vibration,
stretch (muscles), inflammation (e.g. cuts and sprains
which cause tissue disruption), and oxygen starvation
(ischemic muscle cramps).
- Characteristics
- often sharp and well localised,
and can often be reproduced by touching or moving the
area or tissue involved.
- Useful Medications
/ may respond to combinations
of Acetaminophen,
Weak Opioids OR Strong Opioids, and NSAIDs (see Analgesic Flow Chart).
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Visceral Pain |
- Source - internal organs
of the main body cavities. There are three main cavities
- thorax (heart and lungs), abdomen (liver, kidneys,
spleen and bowels), pelvis (bladder, womb, and
ovaries).
- Receptors activated -
specific receptors (nociceptors) for stretch,
inflammation, and oxygen starvation (ischaemia).
- Characteristics - often
poorly localised, and may feel like a vague deep
ache, sometimes being cramping or colicky in nature. It
frequently produces referred pain to the back, with
pelvic pain referring pain to the lower back, abdominal
pain referring pain to the mid-back, and thoracic pain
referring pain to the upper back.
- Useful medications /
usually very responsive to Weak Opioids and Strong Opioids.
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Nerve Pain |
- Source - from within the
nervous system itself. The pain may originate from the
peripheral nervous system (the nerves between the tissues
and the spinal cord), or from the central nervous system
(the nerves between the spinal cord and the brain).
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Causes - may be due to any
one of the following processes
- Nerve Degeneration -
multiple sclerosis, stroke, brain haemorrhage, oxygen
starvation
- Nerve Pressure -
pinched nerve
- Nerve Inflammation -
torn or slipped disc
- Nerve Infection -
shingles and other viral infections
- Receptors activated -
the nervous system does not have specific receptors for
pain (non nocicpetive). Instead, when a nerve becomes
injured by one of the processes named above, it becomes
electrically unstable, firing off signals in a completely
inappropriate, random, and disordered fashion.
- Characteristics - These
signals are then interpreted by the brain as pain, and
can be associated with signs of nerve malfunction such as
hypersensitivity (touch, vibration, hot and cold),
tingling, numbness, and weakness. There is often referred
pain to an area where that nerve would normally supply
e.g. sciatica from a slipped disc irritating the L5
spinal nerve produces pain down the leg to the outside
shin and big toe i.e. the normal territory in the leg
supplied by the L5 spinal nerve. Nerve pain is often
described as lancinating, shooting, burning, and
hypersensitive.
- Useful Medications /
only partially sensitive to acetaminophen, NSAIDs,
opioids. More sensitive to Anti/depressants, Anti/convulsants, Anti/arrhythmics, and NMDA Antagonists. Topical Capsaicin, may be helpful.
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Sympathetic
Pain |
- Source - due to possible
over-activity sympathetic nervous system, and central /
peripheral nervous system mechanisms. The sympathetic
nervous system controls blood flow to tissues such as
skin and muscle, sweating by the skin, and the speed and
responsiveness of the peripheral nervous system.
- Causes - occurs more
commonly after fractures and soft tissue injuries of the
arms and legs, and these injuries may lead to Complex
Regional Pain Syndrome. CRPS was previously known as
Reflex Sympathetic Dystrophy.
- Receptors activated -
like nerve pain there are no specific pain receptors (non
nociceptive). The same nerve processes as mentioned above
may operate in CRPS.
- Characteristics -
presents as extreme hypersensitivity in the skin around
the injury and also peripherally in the limb, and is
associated with abnormalities of sweating and temperature
control in the area. The limb is usually so painful, that
the sufferer refuses to use it, causing secondary
problems after a period of time with muscle wasting,
joint contractures, and osteoporosis of the bones. It is
possible that the syndrome is initiated by trauma to
small peripheral nerves close to the injury.
- Useful medications /
many of the features of sympathetic pain are similar to
those of nerve pain, and therefore nerve pain medications
may be useful (Anti/depressants, Anti/convulsants, and Anti/arrhythmics). Drugs which lower blood
pressure by causing vasodilatation (nifedipine) may also
be useful when used in combination. Treatment should
include appropriate multi/modal medications, sympathetic
nerve blocks, and intensive rehabilitation combining
occupational and physical therapy.
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