Lecture 5: Pain Flashcards
What is pain?
An unpleasant sensory and emotional experience associated with actual or potential tissue damage.
Pain is whatever the experiencing person says it is.
Is pain directly proportional to amount of tissue injury?
Not always
Why is pain underrated?
It is highly subjective
What does pain cause?
Amplifies the body’s stress response to traumatic injury (through SNS and glucocorticoids)
Causes endocrine and metabolic abnormalities
Impedes a patient’s recovery from trauma and surgery
What is acute pain?
lasts less than 6 months, subsides once the healing process is accomplished.
What is chronic pain?
involves complex processes and pathology.
Usually involves altered anatomy and neural pathways.
It is constant and prolonged, lasting longer than 6 months, and sometimes, for life.
Why treat pain?
Tissue damage has the potential to elicit mechanisms that can create disabling, refractory, chronic situations that may prolong and even
outlast the period of healing.
If you don’t treat the initial pain, it may lead to chronic pain
What is pain theory?
Severe, unrelieved acute pain results in abnormally enhanced physiological responses that lead to pronounced and progressively increasing pathophysiology
Increased pathophysiology -> increased morbidity and mortality
Harmful effects of pain
Cardiovascular and respiratory systems are significantly affected
Adrenergic stimulation
Hypercoagulation
Increased heart rate, cardiac output and myocardial oxygen consumption
Decreased pulmonary vital capacity, alveolar ventilation, functional residual capacity
Arterial hypoxemia
Supression of immune functions -> wound infections and sepsis
What happens to person’s social life during chronic pain syndrome
Pain becomes focus of life
Relationships become altered
Causes of chronic pain syndrome
Can be the result of acute, unrelieved pain (multiple trauma, phantom limb pain after amputation, repeated back surgeries)
Sometimes set,s from near-muscular disorders (fibromyalgia, rheumatoid arthritis, multiple sclerosis)
Pain pathways (receptors, stimulation, neurons, processes)
Specialized receptors = free nerve endings
Stimulation: Mechanical damage, extreme temperature, chemical irritation
2 types of neurons: A-delta and C
Four processes: transduction, transmission, modulation, perception
Four processes to pain
Transduction: Local biochemical changes in nerve endings that generate a signal
Transmission: Movement of that signal from the site of pain to the spinal cord and brain
Perception: Synthesis and analysis in the brain
Modulation: Endogenous systems in place that can inhibit pain at any point along the pathway
Which receptors send pain signals?
All receptors can
What are nocireceptors?
Involved in transduction of pain
Free nerve endings
Capacity to distinguish between noxious and innocuous stimuli
What happens when person is exposed to mechanical, thermal or chemical stimuli
Involved in transduction
Tissue damage occurs
Substances are released by the damaged tissue which facilitates the movement of pain impulse to the spinal cord.
Substances released during transduction? What do they cause?
Released from traumatized tissue
Bradykinin
serotonin
substance P
histamine prostaglandin
Cell depolarization by sodium influx
What drugs act on transduction process of pain?
Non-steroidal anti-inflammatories (ex: ibuprofen) - minimize the effects of substances released during transduction, especially prostaglandins.
Corticosteroids (ex: dexamethasone) - used for cancer pain, interferes with the production of prostaglandins.
Transmission process of pain
Initial damage/stimulation -> nerve -> spinal cord -> brain stem -> thalamus -> central structures of brain -> pain is processed
What is required to continue pain impulse from spinal cord to brain? What drugs targeted this step?
Transmission
Neurotransmitters
Opioids (narcotics) are analgesics, block release of neurotransmitters
Two different types of peripheral that transmit pain signals from pain receptors to spinal cord
Transmission
A delta: “fast pain”, protective pain
C-fibers: “slow pain” nerve fibres, learning and behavioural modification
Fast pain vs slow pain
See table
Where does perception of pain occur?
Somatosensory cortex, cingulate cortex - sensory discrimination, emotional response (fear, anxiety, panic, subjective)
Reticular formation (increased arousal, emotional response, somatic and autonomic motor reflexes)
Therapeutic strategies that target perception of pain
Behavioural strategies
Therapy
Brain can accommodate a
limited number of signals, so distraction, imagery and relaxation signals may get through the gate, leaving limited signals (such as pain) to be transmitted to the higher structures.
How do higher vertebrates handle pain vs primitive vertebrates
Higher vertebrates: have anatomical components for perception of pain
Primitive vertebrates (Fish, reptiles, amphibians): avoidance or escape behaviour, poorly developed cerebral cortex
Where does modulation process occur?
Descending tract (brain -> spinal cord)
Changing or inhibiting pain impulses
What occurs during modulation
Descending fibres release substances (endogenous opioids or endorphins) which have capability of inhibiting transmission of pain
Why are anti-depressants used to treat cancer pain?
Antidepressants interfere with reuptake of serotonin and norepinephrine, which increases their availability to inhibit noxious stimuli
What activates descending pain modulation system?
STRESS!
fear
hunger
thirst
fatigue
prolonged motor activity
hypnosis
Pain processes and possible medications
Perception: parenteral opioids, a2 agonists, general anaesthetics
Transmission: Local anaesthetics
Modulation: spinal opioids, a2 agonists, NMDA receptor antagonists, Ach esterases, NSAIDS, CCK antagonists, NO inhibitors, potassium channel openers
Transduction: NSAIDS, Antihistamines, Membrane stabilizing agents, local anesthetic cream, opioids, bradykinin and serotonin antagonists
See figure
Categories of pain
Nociceptic: injury, trauma, infection
Neuropathic: damage or dysfunction of the peripheral or central nervous system
Visceral: Arising from internal organ (MI, appendicitis, bowel obstruction)
Nociceptive vs neuropathic pain
See figure
What does neuropathic pain feel like
Fire
Electricity
Typically in feet, legs and hands
Types of neuropathic pain
Hyperalgesia: intense pain in response to mildly painful stimulus (pinprick)
Allodynia: pain in response to completely innocuous stimulus (touch)
What can neuropathic pain be caused by?
injury (amputation and subsequent phantom limb pain)
scar tissue from surgery (back surgery high risk)
nerve entrapment (carpal tunnel)
damaged nerves (diabetic neuropathy)
