Pain Management
Definition of Pain:
Hard to define because there is no objective measure of pain
physical, emotional, cognitive-evaluative dimensions
if purely physical, pain would not bother us so much –
evidence?
pain experience in preverbal infants and animals –
role of brain development and frontal lobe function
Red indicates more
gray matter, blue
less gray matter.
Gray matter wanes
in a back-to-front
wave as the brain
matures and neural
connections are
pruned
Types of Pain
1. transient: brief, little or no tissue damage
2. Acute/phasic: pain decreases as healing is underway
3. Chronic/tonic: pain persists beyond healing or when it no
longer serves a purpose… it becomes a
syndrome in and of itself
pain types 1-3 -> each could be mild, moderate, severe
transient pain = peripheral mechanism predominates
acute pain = spinal cord mechanism predominates
chronic pain = brain mechanisms predominate
Relationship between pain and injury
in the real word: not one to one, highly variable
in the laboratory: can find one-to-one relationship, but…
in the real world psychosocial variables come between stimulus
and response
examples of the variable link between pain and injury
1. pain without injury: migraines, low back pain
2. injury without pain: episodic analgesia, congenital analgesia
3. pain disproportionate to the injury: paper cuts, kidney stones
4. pain after all healing: gun shot wounds – causalgia
Purpose of Pain:
Congenital Analgesia: life without pain
1. warn of impending or actual injury
2. promote recovery
3. teach us what not to do
4. punishment (social invention and use)
Psychosocial Variables and the Variable Link:
Culture: hook swing ritual, trephination
no effect on sensation threshold
moderate effect on pain perception threshold
large effect on pain tolerance threshold
http://www.youtube.com/watch?v=c0kgWelgRfM&feature=related
Psychosocial Variables and the Variable Link:
Past Experience & Memories:
childhood upbringing & parental attitudes toward pain
Melzack’s terriers raised in isolation
Meaning of the Situation:
Pavlov’s dogs: left vs. right paws
Grandma’s teacup
stimulation of the skin is localized, identified and evaluated
before it produces a perceptual experience & response
Psychosocial Variables and the Variable Link:
Attention & Anxiety
typically, attention to the noxious stimulus and anxiety both
increase pain perception
BUT note: stress induced analgesia
distraction of attention works best when the pain is steady
or rises slowly in intensity
Feelings of Control
perceived and actual control can reduce pain
perceived inadequate control is likely to make things worse
Psychosocial Variables and the Variable Link:
Personality
generally anxious and “neurotic” people typically experience
more pain, as do people with an external locus of control
people who use adaptive coping strategies for stress typically
experience less pain
Mood
depression, low self-esteem, anxiety… increase pain perception
Gender
who experiences more pain, men or women?
The Biological Basis of Pain
A Model for Pain Mechanisms
burned finger --> receptors --> neural impulses --> nerves --> spinal cord --> brain
What do we know about this model?
1) Accuracy:
Though it is a useful model, it is also quite
simplistic, and in no way should the lines
and arrows trick you into thinking that pain
follows a simple pathway
2) Receptors:
These are specialized to translate physical energy (e.g. heat) into
a pattern of nerve impulses - something the brain can understand.
Specificity vs. Specialization
free nerve endings as pain receptors?
What about the earlobe?
Theory of specialization
different receptor types are specialized to respond to a
given kind of stimulation, but they may respond to other
forms (though less well). The resulting sensation is not
always the same.
3) Neural Impulses:
A pattern of neural impulses is created once the receptors are
stimulated. These impulses travel through the body along
nerves.
4) Nerves involved in pain
A-delta: medium-fast speed, small fibers
A-beta: fast, large fibers
C: slow, small fibers
It is believed that pain results from A-delta & C fiber activity, and
that A-beta fiber stimulation inhibits the A-delta & C fibers to
reduce pain (more later)
5) Spinal Cord:
Neural impulses enter the cord at the dorsal horns. Some go to the
first 2 layers of cells (called substantia gelatinosa cells, SG). Other
neural impulses go to dorsal horn cells called T cells
Pain may be triggered when activity in the T cells exceeds a
threshold. This threshold is unstable: it can be raised and lowered
by many physical and psychological factors.
Inhibitory controls exist within each spinal cord segment to lower T
cell activity
A-beta fiber stimulation
When these nerves are stimulated
(by gently rubbing the area around
the injury) SG cell activity increases
and T cell activity decreases
6) The Brain:
If activity in the cord exceeds threshold, this information
ascends along a number of different nerves to reach
different areas of the brain.
Areas of the brain important for pain perception overlap with
the areas involved in the stress response:
diencephalon (thalamus & hypothalamus)
reticular activating formation (RAF)
limbic system
cerebral cortex
Is there a pain center?
Descending Noxious Inhibitory Controls (DNIC)
Descending fibers from the PAG and RAF to the spinal cord inhibits
T cell activity.
DNIC may be enhanced via drugs, electrical stimulation of certain
brain areas, and even cognitive (cerebral cortex) activity.
Descending influences from the brain to the cord can make local
inhibitory controls (A-Beta activity) more effective.
These are several good reasons for NOT letting doctors sever the
spinal cord in chronic pain patients!
Gate Control Theory
S = small fibers A-delta & C
L = large fibers A-beta
i = inhibitory SG cells
P = T cells
There is a “gate” in each spinal
cord segment
Pain might be felt when the gate
is open
Treatment Options for Pain
Drug Therapies
The majority of pain relievers come from one of two families
Aspirin type > mild analgesics
Opium type > powerful analgesics
A. THE MILD ANALGESICS
Aspirin (nonsteroidal anti-inflammatory drugs NSAIDS)
fights pain, inflammation and fever
Rationale: inhibits prostaglandin synthesis, works directly
on the injured tissue itself (not on the central nervous system)
Acetaminophin (Tylenol)
weak inhibitor of prostaglandin synthesis so less effective
against pain caused by inflammation
site of action is unknown
high doses can produce liver damage
pill for pill, same analgesic action as Aspirin
B. THE POWERFUL ANALGESICS
opiates (i.e. narcotics)
opium first used for medicinal purposes in 1550 BC,
to calm crying children
morphine, codeine, and heroin are opiate derivatives
for all narcotics, as dose increases, so do changes in mood &
mental clouding ... unless the drug is injected directly onto the
spinal cord
rationale: site of action is the central nervous system (brain and
spinal cord)
activates DNIC (descending noxious inhibitory control)
acts within the spinal cord to inhibit T cell activity
Addiction: “Nonsense” according to Melzack and some others. Only
“sick” people who take narcotics for their psychodelic
effects become addicted. Those taking it for pain do not.
morphine self-administration studies
the people vs. Larry Flynt
Tolerance:
At first, patients need increasing doses to get the
same pain relieving effect, but this soon stabilizes.
Afterwards, the dose changes only if their condition
changes. If their condition worsens, the dose will
have to be increased. If it gets better, the dose is
decreased without any complaints from the patient.
Withdrawal: If patient was taking the drug for pain relief, s/he can be
tapered off the drug in 1-2 days with very minor side
effects.
Synthetic vs. Endogenous Opioids
Our bodies are equipped with their own pain killers. We call
these “endogenous opiates”. Specifically, these are
enkephalins, dynorphins, and endorphins.
Drugs, like morphine, reduce pain by mimicking the
endogenous opiates.
C. PSYCHOTROPIC DRUGS
Chronic pain can lead to depression and vs. Antidepressants work by a)
decreasing the depression, and b) by increasing the effectiveness of
DNIC. Antidepressants can decrease pain even in people who are not
depressed.
D. COMBINATION ANALGESICS
Mild analgesics work directly on the injured tissue itself; powerful
analgesics work on the CNS. By combining small doses of each type of
drug, you get greater pain relief than by using either drug alone in large
doses. Hence, the rationale for giving aspirin and codeine tablets.
F. INHALANT ANALGESICS
If given in small doses produces excellent pain relief with no loss of
consciousness. Also...very safe when administered by a trained
professionals.
SENSORY MODULATION OF PAIN
Neurosurgical Approaches to Pain Control
e.g. cutting the nerves that run from the periphery (the site of the injury) to
the spinal cord, or destroying the nerves just before they enter the cord.
less input to the spinal cord = the spinal cord will respond by increasing
its activity and pain… for 2 reasons:
1) to try and compensate for the lack of input (homeostatic mechanism)
2) the local inhibitory controls (A- Beta fiber stimulation) can no longer be
activated. As spinal cord activity increases, so does the chance that
the gate will be “opened”.
In sum, the neurosurgical approaches are disappointing. Pain usually
returns worse than before. Neurosurgical approaches should only be
attempted as a last resort, and only in people who have a terminal illness
and will die soon anyway.
Temporary local anaesthesia
e.g. “freezing” of the nerves in the mouth to fill a cavity. The drug
influences the nerves in such a way that they are unable to fire.
The nerves can only be anaesthetized for a certain period of time,
however, before they will incur damage.
HYPERSTIMULATION ANALGESIA or COUNTER-IRRITATION
fighting pain with pain
Massage and Manipulation
These procedures increase sensory input to the cord and often
produce pain in and of themselves. Why they work, and sometimes
not work, is not clear.
Heat Therapy
Most effective for low-moderate levels of pain associated with
deep tissue damage. May help reduce pain through:
1) increasing blood flow to the injured area > brings nutrients and
chemicals for repair & sweeps away breakdown products of
injury
2) stimulating small fibers which trigger
DNIC (distant noxious inhibitory control)
to “close the gate”
Electrical Stimulation (TENS)
stimulates the large A-Beta fibers which activate local inhibitory controls in
the spinal cord to close the gate.
raises the threshold of spinal cord T cells, such that it takes more to
stimulate them
safe, easy, and relatively free of side effects
better than placebo for chronic pain
pain relief often outlasts the period of stimulation
duration of pain relief increases with successive
stimulation
PSYCHOLOGICAL INTERVENTIONS
Relaxation
more effective than placebo, easy to teach, effective for severe
chronic pain
Biofeedback
does not appear to add anything above relaxation training alone
useful for distraction of attention, relaxation, suggestion, sense
of control, and may enhance other psychological approaches to
the control of pain.
PSYCHOLOGICAL INTERVENTIONS
Hypnosis
placebo and hypnosis are the oldest forms of pain therapy
appears to be somewhat effective for experimentally induced pain
not true for naturally-occurring chronic pain
hypnosis decreases in effectiveness over time - not suitable for
chronic pain
when it does work for chronic pain, it may not be better than a
placebo effect
PSYCHOLOGICAL INTERVENTIONS
Cognitive Coping Skills
using imagery which is incompatible with pain
think of the experience as purely sensory, or think of it as trivial or unreal
acknowledge the pain, but in a different context (e.g. fighting off aliens)
focus on external objects e.g. counting tiles
mental arithmetic, composing a limerick
focus on the pain in a detached, academic manner
studies suggest may not be better than placebo, but control groups
not taught any strategy probably used their own anyway. Even patients
taught these strategies may not have used them, in preference for their
own
PSYCHOLOGICAL INTERVENTIONS
Operant Conditioning Techniques
pain consists of pain behaviors which are being reinforced
remove all reinforcement and pain behaviors will disappear
Usually involves hospitalization, lengthy process, & very
disappointing even if it does work
1) just because they complain less doesn’t mean they are in less pain
2) no well controlled studies to determine its effectiveness
3) very expensive
PSYCHOLOGICAL INTERVENTIONS
Psychological Counseling
no evidence that psychoanalysis is effect against pain
despite the fact that pain results from many psychological
disturbances
Multiple Convergent Therapy
the effects of two therapies are additive
RATIONALE: each therapy may be targeting a
different mechanism
(e.g. one might target DNIC, the other A-Beta fiber
stimulation etc...)
PSYCHOLOGICAL INTERVENTIONS
Prepared Childbirth Training
does reduce pain by reducing anxiety and
giving women a feeling of control
but results are disappointing >
pain levels are still very high
nevertheless, reduces affective
and sensory dimension of pain
possible that women expect too much
success of PCT depends largely on the individual instructor