Pain management
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Transcript of Pain management
CONTENTS
Defination of PAINTypes of painNociceptors :Locaton & TypesPathway of PainMechanisam of Action of NSAID & Opoid as
Analgesic
PAIN
Pain is an unpleasant sensory & emotional experience arising from actual or potential tissue damage.
It is often described in terms of peneterating or tissue destructive process(eg.,stabbing,burning,tearing) or of a bodily or emotional reaction(eg.,nauseating,terrifying)
Classification of pain
Pain can be classified on the base of intensity ,duration, physiology and syndrome
Intensity (mild,moderate & severe)
Duration(acute,choronic)Physiology(nociceptive,inflammatory)
Syndrome(cancer,migraine & other)
Pain Threshold – The point at which a stimulus, usually one associated with pressure or temperature, activates pain receptors and produces a sensation of pain. Individuals with low pain thresholds experience pain much sooner and faster than those with higher thresholds
Pain Tolerance – amount of pain a person is willing or able to tolerate
Allodynia :mean a painfull response to a normaly innocuous stimuls.
Hyperalgesia: is an increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves.
Neuroanatomy of Pain
The portion of the nervous systemresponsible for the sensation & perception ofthe pain is devided into three areas.
i. Afferent pathway
ii. CNSiii. Efferent pathway
Afferent portion is composed of
Nociceptors (pain receptor) Afferent nerve fiber Spinal cord network
Primary afferent nerves
Primary afferent nerve fibres that transmit electrical impulses from the tissues to the spinal cord via the ascending nerve tracts.
The cell bodies of primary sensory nerves are located in the dorsal root ganglion in the vertebral foramina
It has two branches:i. one projects centrally into the spinal cordii.other projects peripherally to innervated
tissues.
Classification of primary afferent nerves
Primary afferents are classified by their diameter,degree of myelination and conduction velocity
Basically divided into 3 classesi. The largest diameter afferent fibers A-
beta(responsd maximally to light touch or moving stimuli)
ii.The small diameter myelinated A-deltaiii.The small diameter unmyelinated C fiber
axons
NOCICEPTORS
Primary afferent nociceptors are specialized free nerve endings of primary afferent nerves (A-delta and C fibres).
They are generally the first structures to be involved in the nociceptive process and are located in various body tissues including skin, muscle, connective tissue, blood vessels and thoracic and abdominal viscera
NOCICEPTIONThe peripheral nervous system includes
primary sensory nerves specialized to detect mechanical ,thermal or chemical condition associated with potential tissue damage
The signals,when these nociceptors are activated,must be transduced & transmited to the spine & brain where signal are modified before they are ultemately understood or "felt"
Transduction
During this stage,noxious stimuli trigger the release of biochemical mediator that sensitize nociceptor.
Noxious or painfull stimulation also cause movement of ions across cell membrane,which excite nociceptor
Transmition
includes 3 segments
First segment -pain impulse travels from the peripheral nerve fiber to thr spinal cord
Second segment- transmission from the spinal cord & ascension via spinothalamic tract ,to the brain stem and thalamus
Third segment - involves transmission of signals between thalamus to the somatic sensory cortex where pain perception occur
Modulation
Often discribed as "Descending System"
occur when neurons in the thalamus and the brain stem send signal down to the
Dorsal horn of the spinal cord
Perception
Transduction,Transmission & Modulation intrect to create subjective emotional experience of pain
Anterolateral pathway
Pain & Temperature 3 neuron pathway. Its primary neurons axons enter the spinal cord and then ascend one
to two levels before synapsing in the substantia gelatinosa.
After synapsing, secondary axons decussate and ascend in the anterior lateral portion of the spinal cord as the spinothalamic tract.
This tract ascends all the way to the thalamus, where it synapses on tertiary neurons.
Tertiary neuronal axons then travel to the primary sensory cortex
NSAIDS
Nonsteroidal anti-inflammatory drugs are a class of drugs that provides analgesic (pain-killing) and antipyretic (fever-reducing) effects, and, in higher doses, anti-inflammatory effects.
The most prominent members of this group of drugs are aspirin, ibuprofen and naproxen.
Most NSAIDs act as nonselective inhibitors
of the enzyme cyclooxygenase (COX), inhibiting both the cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) isoenzymes.
COX catalyzes the formation of prostaglandins and thromboxane from arachidonic acid
PGs directly stimulate pain receptors and increase sensitivity of pain receptor to bradykinin etc to produce pain . NSAIDs relieve pain via inhibition of PGs biosynthesis.
Opioids
Opioids are act directly on the CNS to relive the pain
they produce analgesia by binging to specific G protein coupled receptors in brain & spinal cord
They open K+ channelsPrevent opening of Ca++ channels This results in hyperpolarization and
a reduction in neuronal excitability Inhibit the release of other
neurotransmitters