physiology of pain in labour

8/13/2019 Physiology of Pain in Labour

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PHYSIOLOGY OF PAIN IN

LABOUR

K.W. Gondwe, 2009


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Objectives

Define pain

Describe of types of pain in labour

Explain the gate theory and its relationshipto labour pains

Explain non-pharmacological and

pharmacological management of pain inlabour


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PAIN

Pain is whatever the person says it is.

Pain's an unpleasant sensation which may be

associated with actual or potential tissue

damage and which may have physical andemotional components

Pain is very subjective and the degree varies in

Different women

Same woman in successive labours

Same woman at different time in the same labour


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PAIN

Pain is describe by individual as being

Throbbing

Slicing

Burning Crushing

Squeezing

Cutting Pounding

Pricking e.t.c


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PAIN THRESHOLD AND TRANSMISSION

Pain threshold refers to the lowest level at

which the brain perceives pain.

Nociceptors are free nerve endings that

generate pain impulses

Nociception refers to causative factors for

pain impulses i.e. somatic or visceral


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TYPES OF PAIN IN LABOUR

There are two different kinds of labour

Somatic pain: related to pressure on and

stretching of the birth canal as descent occurs

Visceral pain: generally is experienced during

active dilatation and is related to cervical

stretching and uterine contraction intensity


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VISCERAL PAIN

This pain is transmitted slowly throughunmyelinated fibers and is felt as dull, diffuse,persistent or aching sensation

Pain sensation transmitted thorough myelinatednerve fibers travel more rapidly and areperceived as localised sensations.

During first stage nerve impulses enter the

sympathetic chain at L1 to L5 then travel to theposterior roots of the X, XI, XII thoracic nervesup the spinal cord to the thalamus


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They may also be referred to the

dermatomes of the same nerves and pain

is felt in the skin, thighs, lower back andhips as well as hot spots of generalized

aching.

Some pain is pressure induced, some maybe caused by fatigue and hypoxia of

uterine muscles

During labour areas of referred painchange location and if prolonged uterine

fatigue may increase pain sensation


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SOMATIC PAIN

Usually begins during the transition phasebecause descent is speeded

Pressure of the fetus on the cervical,

vaginal and perineal tissues is intense;first felt as need to bear down and thissensation may become overpowering

These pain sensation travel through thepudendal nerves through the dorsal rootsof the II, III, IV sacral nerves


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Pain is felt as contractions intensity rises

15 to 20mmHg above the resting tonus

(above 25mmHg pressure on monitor

strips).


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GATE-CONTROL THEORY

This is important for understanding theapproaches used in pain management. Itwas developed by Ron Melzack and

Patrick Wall in 1962. Gate control theory asserts that activation

of nerves which do not transmit painsignals, called nonnociceptive fibers, caninterfere with signals from pain fibers,thereby inhibiting pain.


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Afferent pain-receptive nerves bringsignals to the brain and comprise at least

two kinds of fibers a fast, relatively thick, myelinated "A" fiber

(delta fibers) that carries messages quicklywith intense pain,

and a small, unmyelinated, slow "C" fiberthatcarries the longer-term throbbing and chronicpain.

Large-diameter A fibers arenonnociceptive (do not transmit painstimuli) and inhibit the effects of firing by

Aand C fibers.
http://en.wikipedia.org/wiki/Myelinhttp://en.wikipedia.org/wiki/A_delta_fiberhttp://en.wikipedia.org/wiki/A_delta_fiberhttp://en.wikipedia.org/wiki/C_fiberhttp://en.wikipedia.org/wiki/C_fiberhttp://en.wikipedia.org/wiki/C_fiberhttp://en.wikipedia.org/wiki/C_fiberhttp://en.wikipedia.org/wiki/A_delta_fiberhttp://en.wikipedia.org/wiki/A_delta_fiberhttp://en.wikipedia.org/wiki/A_delta_fiberhttp://en.wikipedia.org/wiki/Myelin


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The peripheral nervous system has

centers at which pain stimuli can be

regulated. Some areas in the dorsal hornof the spinal cord that are involved in

receiving pain stimuli from A and C

fibers, called laminae, also receive inputfromAfibers.

The nonnociceptive fibers indirectly inhibit

the effects of the pain fibers, by 'closing a

gate' to the transmission of their stimuli. In

other parts of the laminae, pain fibers also

inhibit the effects of nonnociceptive fibers,

thus 'opening the gate'.


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depending on the relative rates of firing of C and

A fibers, the firing of the nonnociceptive fiber

may inhibit the firing of the projection neuronand the transmission of pain stimuli

The pain seems to be lessened when the area is

rubbed because activation of nonnociceptive

fibers inhibits the firing of nociceptive ones in thelaminae. For example in transcutaneous

electrical stimulation (TENS), nonnociceptive

fibers are selectively stimulated with electrodes

in order to produce this effect and thereby

lessen pain.


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One area of the brain involved in reduction

of pain sensation is the periaqueductal

gray matter that surrounds the thirdventricle and the cerebral aqueduct of

the ventricular system. Stimulation of this

area produces analgesia (but not totalnumbing) by activating descending

pathways that directly and indirectly inhibit

nociceptors in the laminae of the spinal

cord.It also activates opioid receptor-

containing parts of the spinal cord.


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FACTORS AFFECTING PAIN PERCEPTION

Worry and anxiety

Insecurity Fear

Ignorance

Fatigue

Intense heat or cold Poor general physical condition

Malnutrition and starvation

Infection

Continuous pain or severe pain experiencedover an extended period (hypertonic contractionor in prolonged labour


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Culture

Parity

Education

Marital stability

Childbirth preparation Past experiences

Race

Unplanned or planned pregnancy


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NON-PHARMACOLOGICAL PAIN MANAGEMENT

Touch: most women respond positively to touch.

Effleurage refers to light rhythmic stroking over thewomans abdomen in rhythm with breathing during

contractions and aids in relaxing muscles

Counter pressure against the sacrum

Backrub over the sacral area and buttocks every twohours or less

Foot massage

Acupressure for additional endorphin response and

relief of painful sensation


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Warm bath or shower for relaxation

Breathing techniques

Dilatation less than 3cm: woman feels for onset ofcontraction and takes a deep breath through thenose and out through pursed lips. She should focuson slow chest breathing (6 to 9 per minute). When

contraction is over she takes a final deep breath inand blows the contraction away through pursedlips. She may focus on an object or close her eyes

Dilatation 4 to 7cm: change to shallower, lighter

breaths (no more than 16/min). Ask her to slowlyraise her abdomen when breathing in (this movesthe abdomen away from the contracting uterus


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Cervical dilatation 8 to 10:women has difficultiesconcentrating on breathing. Ask the woman to breath3 times and then puff (as if blowing out a candle) out

to blow away the contraction (breath, breath, breath,puff)

NB. avoid hyperventilation which can result in alkalosis,discourage early pushing

Do not leave the woman alone. A support

person: husband or close relation may be used.Talk with support person and give themreassurance, nourishment, rest elimination.Remember they need to be comfortable for themto provide adequate support.

Minimize adverse environmental stimuli: controlglaring lights, decrease traffic flow and noise inbirth setting


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Remind mother that to select the best position in

which she feels comfortable. Encourage walking

in early labour. The mother can also stand, leanagainst the wall or over a chair or support

person, sit on a chair.

Provide privacy and space with adequate room

temperature and ventilation

Talk of contractions and not pains

Relax and get as near to the womans level as

possible. Sit by the bedside. Do not tower overher


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Adjust the labour bed to provide comfortable

position i.e. semi fowlers. The woman should

never be flat on her back. Use pillows to supportall dependent parts.

Use comfort measures such as cold cloths, ice

chip, backrubs, baths or shower Chat with the woman in-between contractions.

Do not distract her during a contraction. WAIT.

Assure the mother that she is doing well with

kind voice

Remind mother to urinate frequently


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Encourage rest in between contractions

Keep her bedding clean, dry without

wrinkles or kinking During actual birth trust and work with the

woman. The goal is pelvic floor release

and relaxation it is not an athletic contest.Encourage series of quick breaths holding

for five seconds while pushing with

grunting sounds or expiratoryvocalizations. Give her verbal support i.e.

beautiful, go with it, you are doing fine.


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PHARMACOLOGICAL MANAGEMENT

Pharmacological pain management

includes use of

Analgesia: brings loss of pain sensation by

raising pain threshold for pain perception.Analgesics are the agent used and they

relieve pain without causing unconsciousness

Anesthesia: use of agents to bring loss ofsensation


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Local infiltration anesthesia: used withepisiotomy i.e. 1% lidocaine, chloroprocaine.Epinephrine can be added to the solution tocontrol bleeding

Pudendal block: useful in second stage andadministered 20 to 30 minutes before perinealanesthesia is needed, but may result into lossof the bearing down reflex.

Spinal anesthesia: local anesthetic used forC/S.

Epidural block: relieves pain of uterinecontractions and delivery both vaginal andabdominal by injecting anesthetic in theepidural (peridural) space


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Paracervical block: relieves pain from cervical

dilatation and distension of LUS

Inhalation analgesia

General analgesia


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When to give narcotics in labour Maternal assessment

Mother should be willing Vital signs should be stable

Fetal assessment

FHR between 120 and 160 and reactive

Fetus is term

Meconium staining not present

Labour assessment

Contraction pattern well established Cervix less than 6cm (4-5 in prims and 3-4 in multips)

Fetal presenting part engaged

Progressive descent of presenting part with no complication


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YEBO

physiology of pain in labour

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