AFFIRA NASIR4TH YEAR MBBS STUDENT

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

Pain pathways

Anterolateral or spinothalamic pathway

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

MECHAINISM OF ACTION OF NSAID

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.

MECHAINISM OF ACTION OF OPOIDS AS

ANALGESIC

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