An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.
Nociception is the physiological process by which information about tissue damage is communicated to the CNS
Pain perception consists of four processes:
· Is the conversion of a mechanical, thermal or chemical stimulus into a neuronal action potential.
· It occurs at the level of peripheral nerves, in particular the free nerve endings or nociceptor.
· Noxious stimulus causes cell damage with the release of numerous chemicals into the area surrounding these nociceptors.
Transduction Substances includes:
· Substance P
· Hydrogen ions
These substances activate nociceptors and lead to generation of action potential.
Activation results in an action potential, which is carried from the nociceptors to the spinal cord via myelinated A-delta fibers and unmyelinated, slowly conducting C fibers.
Transmission is the movement of pain impulses from the site of transduction to the brain
Action potential continues from-
Site of injury to spinal cord
Dorsal Horn processing
Spinal cord to brain stem to thalamus
Thalamus to cerebral cortex for processing
· Conscious experience of pain
· Perception occurs when pain is recognized, defined and responded to by the individual experiencing pain.
· Pain perception involves several brain structures.
· Modulation involves the activation of descending pathways that exert inhibitory or facilitatory effects on the transmission of pain.
· Depending on the type and degree of modulation, pain is perceived.
· Modulation of pain signals can occur at the level of periphery, spinal cord, brainstem and cerebral cortex.
· Descending modulatory fibers release chemicals – serotonin, norepinephrine, GABA, endogenous opioids that inhibit pain transmission.
Types of pain
· Neuropathic pain
· Acute & chronic pain
· Nociceptive pain is caused by damage to somatic or visceral tissue.
· Somatic pain: It is characterized as deep, aching or throbbing that is well localized, arises from bone, joint, muscle, skin or connective tissue.
· Visceral pain: which may result from stimuli such as tumor involvement or obstruction, arises from internal organs such as the intestine & bladder.
· Neuropathic pain is caused by damage to peripheral nerves or CNS
· Common causes are trauma, inflammation, DM, tumors, toxins and neurological disorders
· Pain is typically described as numbing, burning, shooting, stabbing or electrical in nature.
· Neuropathic pain can be sudden, intense, short lived or lingering
Difference between acute & chronic pain
Gradual or sudden
< 3 months
> 3 months
Mild to severe
Mild to severe
Cause of pain
May not be known
Course of pain
Goes away as recovery occurs
Typically pain does not go away
Goals of treatment
Pain control to the extent possible
· Pattern of pain: onset and Duration
· Area of pain: Precise location, Radiating
· ‘Intensity of pain; use pain scale – no pain to worse pain.
· Nature of pain: burning, shooting, stabbing, sharp, aching, throbbing and cramping.
· Salicylates: E.g.- Aspirin
· NSAIDS: Ibuprofen, Diclofenac, COX-2 inhibitors (cyclooxygenase).
Adjuvent drugs for pain
· Corticosteroids – for inflammation
· Antidepressants (Imipramine) – Neuropathic pain
· Antiepileptic drugs (Tegretol) – Neuropathic pain
· Muscle relaxant (Baclofen) – Neuropathic pain and muscle spasm.
· Alpha 2 Adrenergic agonist (Clonidin) – Neuropathic pain, given intrathecally.
· Anesthetics (Lidocaine 2.5%)
· Rectal – Suppository
· Transdermal – Applied on non- hairy skin.
· Parenteral – IV, 1M
· Intra spinal – Involves insertion of a catheter into the subarachnoid space (Intra thecal) or epidural space (epidural).
· Patient controlled analgesia
· Intervention therapy: Therapeutic nerve block – local anesthetics administered to reduce pain.
· Transcutaneous electrical nerve stimulation (TENS)
· Percutaneous electrical nerve stimulation (PENS)
· Acupuncture, exercise
· Heat therapy
· Cold therapy