Pain Management

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


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 pawsGrandma’s teacup

stimulation of the skin is localized, identified and evaluated before it produces a perceptual experience & response


Attention & Anxiety

typically, attention to the noxious stimulus and anxiety bothincrease pain perception

BUT note: stress induced analgesia

distraction of attention works best when the pain is steadyor rises slowly in intensity

Feelings of Control

perceived and actual control can reduce painperceived inadequate control is likely to make things worse


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 quitesimplistic, 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 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!

Descending Noxious Inhibitory Controls (DNIC)

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 spinalcord segment

Pain might be felt when the gateis open

Treatment Options for Pain

Drug Therapies

The majority of pain relievers come from one of two families

Aspirin type > mild analgesicsOpium 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 unknownhigh doses can produce liver damagepill 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 studiesthe 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.


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


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


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 Counseling no evidence that psychoanalysis is effect against paindespite 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...)


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 highnevertheless, reduces affective and sensory dimension of pain possible that women expect too muchsuccess of PCT depends largely on the individual instructor

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Pain Management